Hogeschool van Amsterdam Domein Techniek … van Amsterdam Domein Techniek Project Team 2A1Z...

Hogeschool van Amsterdam Domein Techniek Project Team 2A1Z

0 Project: Modification flight controls 2008/2009


Project: Modification flight controls 2008/2009

Preface Since the first flight of the Wright brothers back in 1903 much has changed in airplane design. Today’s airplanes are more efficient, can fly much further and carry more passengers than the early planes. They have also become much safer these days, and can in some cases carry up to 853 passengers. Technology came a long way for this to be possible and the techniques used to control the plane’s flight have developed significant. The Wright flyer had only a rudder and an elevator. The elevator was in front of the wings making it an instable airplane. The roll movement was also limited because it had to be generated by the rudder. Nowadays the elevator is often positioned behind the centre of gravity so that the plane becomes more stable in flight. Today there are more control surfaces like ailerons spoilers flaps and slats. Since the use of wind tunnels, engineers and scientists got a better under-standing in the effects of an airfoils shape. Small airplanes are still using the cables and pulley’s be-cause it is a cheap and simple system. The passenger jets on the other hand use hydraulics to control their flight because the forces simply become too big for a pilot to handle. Most of the passenger jets still use a hydraulic system with a mechanical back-up. But since computer technology really devel-oped in the 1980’s it is possible to create a flight control system that uses wires to transport the pilot’s input to the control surfaces. The system saves weight and the pilot’s input get’s smoothed so that the flight will become more stable and therefore more pleasant for the passenger. Airlines can choose to buy new airplanes equipped with the fly-by-wire system or it can modify its own planes with fly-by-wire systems to safe costs. Will it be profitable?



Introduction Project team 2A1Z, employees from Amstel Leeuwenburg Airlines (ALA), has the assignment to inves-tigate the possibilities of a modification in the flight controls system of the Boeing 737. The Boeing 737 has a conventional flight controls system and ALA wants to know if it is profitable to install a fly-by-wire system. The result of this project is a report, which is based on the Wentzel (2008) method. The time for this project is seven weeks and the report consists of maximum 40 pages. The report consists of three chapters, regarding the design process. The knowledge about how flight controls work is necessary to invest a possible modification. The basic theory about flight controls is based on the Cessna 172. The theory includes wing aspects, aerody-namics and forces on the airplane. The flight controls of the Cessna 172 are divided into primary- and secondary flight controls. (1) To know if the modification is profitable, the conventional and the fly-by-wire system need to be com-pared. This is based on the Boeing 737 and the Airbus A320, with both benefits and drawbacks. The laws and requirements have to be taken into account to define the options for a possible modification. This comparison results in a decision whether to modify the Boeing 737 with a fly-by-wire system or not. (2) To install the fly-by-wire system, several parts have to be modified. The design aspects include safety, maintenance, costs and benefits, backup and flight deck display. These aspects are important for the final recommendation to ALA. (3) The main sources for this project are: Anderson (2008 for the introduction to flight and several main-tenance manuals of the Boeing 737 and Airbus A320. Next to the three chapters, the report consists of a bibliography, list of appendices and an abbreviation list.



Index

Summary ........................................... ........................................................................ 1

1. Definition Flight Controls ........................ .......................................................... 2 1.1 Theory ............................................... .................................................................................... 2

1.1.1 Wings ........................................................................................................................ 2 1.1.2 Aerodynamic Aspects ............................................................................................... 4 1.1.3 Forces Around the Airplane ...................................................................................... 6

1.2 Flight Controls ........................................ ............................................................................. 7 1.2.1 Primary Flight Controls ............................................................................................. 7 1.2.2 Secondary Flight Controls ...................................................................................... 11

1.3 Laws and Requirements .................................. ................................................................. 14 1.3.1 Laws ........................................................................................................................ 14 1.3.2 Client requirements ................................................................................................. 15

1.4 Comparison Small and Large Airplanes ....................... .................................................. 15 1.5 Functionality research ................................ ...................................................................... 17

2. Flight Controls on the Boeing 737 and Airbus A320 . .................................... 18 2.1 Flight Controls Boeing 737 ................................ ............................................................... 18

2.1.1 Primary Flight Controls ........................................................................................... 18 2.1.2 Secondary Flight Controls Boeing 737 ................................................................... 20 2.1.3 Backup Systems ..................................................................................................... 22

2.2 Flight Controls Airbus A320 .............................. ............................................................... 23 2.2.1 Primary Flight Controls ........................................................................................... 23 2.2.2 Secondary Flight Controls ...................................................................................... 25 2.2.3 Backup Systems ..................................................................................................... 26

2.3 Benefits and Drawbacks .............................. ..................................................................... 27 2.3.1 Boeing 737 .............................................................................................................. 27 2.3.2 Airbus A320 ............................................................................................................ 28

2.4 Conclusion ........................................... .............................................................................. 28

3. Modification Boeing 737 ........................... ....................................................... 29 3.1 Fly-By-Wire Installation ............................. ........................................................................ 29

3.1.1 Modification flight controls ...................................................................................... 29 3.1.2 Flight Deck Display ................................................................................................. 31

3.2 Design Aspects ...................................... ............................................................................ 32 3.2.1 Safety ...................................................................................................................... 32 3.2.2 Maintenance ........................................................................................................... 33 3.2.3 Backup .................................................................................................................... 33

3.3 Costs and Benefits .................................... ........................................................................ 33 3.3.1 Design Starting Costs ............................................................................................. 33 3.3.2 Installation, material and test costs ........................................................................ 35 3.3.3 Benefits ................................................................................................................... 36

3.4 Conclusion and recommendation ............................... .................................................... 37 3.4.1 Conclusion .............................................................................................................. 37 3.4.2 Recommendation .................................................................................................... 38

Bibliography ...................................... ...................................................................... 39

List of appendices ................................ .................................................................. 41



Summary

The purpose of this project ‘Modification flight controls’ is to research the consequences when a con-ventional Boeing 737 flight control system is modified to a fly-by-wire system such as in the Airbus A320. The project analysis consists among others of the research of the benefits and drawbacks of a conventional flight control system compared to a fly-by-wire control system. Before the two flight control systems can be compared, the working, forces on the wings and flight controls are researched. The comparison for both flight control systems are found on a simple Cessna 172. The flight controls on this small Cessna have a lot of comparison to the Boeing 737 and Airbus A320. The flight controls are divided into the primary and secondary flight controls. Both the simple flight controls on the Cessna plus the advanced controls on the Boeing 737 as the A320 are explained in: position working and numbers. When the flight controls are designed they need to apply to a few different laws and regulations. When designing, the regulations and the requirements of the client must be researched on law possibility before these regulations are installed. With all of the control and law researches completed, the differences on the small and large airplanes can be researched. Here the size and the forces which work on the airplane are the main exit points for the comparison. With the laws, flight controls and differences explored, the basic flight control system can be divided up in different kinds of functions. These functions together make up the working from input to output of the flight control. With all the research that has been done a conclusion can be drawn. Now the theory has been completed, there is the part of finding out how the flight controls on the Boe-ing 737 and A320 work with the help of their aide systems which have the obligated back-up systems. The Boeing 737 and A320 are first compared for the differences in flight control systems and surfaces. The major thing that stands out is the difference in flight control system. Now the difference is found, the Boeing 737 is first up to give its secrets of how the conventional flight controls work. Hydraulic pumps are the aid for this flight control system .The primary and secondary flight controls are constant with those found in chapter one, the backup system is somewhat interest-ing. The A320 also uses a hydraulic system but, the system uses another setup than the Boeing 737. But the rest of the primary and secondary flight controls work via the same principle, only the input is dif-ferent from the conventional system. The backup of the Airbus also differs from the Boeing 737. Both systems have been dug out there is the discussion of which has more benefits? To answer this question the two systems are faced with their benefits and drawbacks. Finally the conclusion can be drawn which system is more benefit full. Now the flight control systems have been research, adding more information to the pile of knowledge. A system is chosen to be installed into the fleet of the Boeing 737s. An installation plan is made with the aid of a functionality research of the A320 flight control system. The new aspects and costs for the new integrated features are divided into four different categories ranging from the safety to costs and benefits. Now a large quantity of knowledge has been obtained, a definite conclusion and recommendation can be given to the Airliner.



1. Definition Flight Controls

To understand the working of flight controls it is necessary to have some knowledge of the wing in general, the aero dynamical aspects and the forces which are working around the airplane (1.1). Flight controls are divided into two groups. The elevator, rudder and ailerons are the primary flight controls. The trailing edge devices, LE devices, spoilers and trim are the secondary flight controls (1.2). All of these flight controls must be compliant to the law and must meet the demands of the client. There are different laws for light airplanes and heavy airplanes (1.3). One of the big differences between a small and large airplane is the amount of force on the control surfaces is (1.4). Before the flight control system can be modified every function between the steering commands, the movement of the flight control surface and feedback will be researched (1.5).

1.1 Theory Most flight controls surfaces are located on the wings of an airplane. Therefore some basic knowledge of wings is explained (1.1.1). Wings provide the lift forces of an airplane. Lift gained by the difference in pressure over a wing, this is one of the aerodynamic aspect (1.1.2). Lift is one of the four forces experienced by the airplane. The other forces are: drag, weight and thrust (1.1.3).

1.1.1 Wings Due to the lack of knowledge in boundary layer theory before the 1920’s, the creation of wings was a matter of trying and hoping the right combination of pressures was found. When knowledge of the pressures around a wing and transition layer improved a period came where airfoil production could be made systematically. With the creation of the National Advisory Committee of Aeronautics (NACA), there were some major spurts in wind tunnel designs. In the period from 1930 till 1940 they created calculation methods for the calculations of pressure separation on a wing. These methods were devel-oped based on wind tunnel test results. Now they could calculate and make the kind of airfoil shape they needed. To understand these different kinds of airfoil shapes a little nomenclature of an airfoil is needed (A). With this knowledge the different kinds of cambered airfoils for example a positive or neg-ative, can be explained on the hand of design and purposes with graphical drawings (B). There are also different kinds of wing shapes but almost all modern high speed airplanes have swept back wings (C). To understand more about flight controls a nomenclature of the wing with its control surfaces is needed (D). A Airfoil Nomenclature An airfoil (figure 1.1) (1) is a cross-cut section of the wing. One of the reference lines is the mean camber line (2). This line is at the middle point of the imaginary circles (3) between the upper and low-er airfoil surfaces. The edge which is rounded and facing forward during flight is the leading edge (4). The radius of an imaginary circle at this point is the leading edge radius (5). The other end of the air-foil, the trailing edge (6) is the most rearward point and is quite narrow and tapered. Between these extremities another reference line is drawn. This is the chord line (7) and is a straight line. The maxi-mum height between the mean camber line and the chord line is the camber (8). The camber of an airfoil determines the aero dynamical aspects of the wing. The airstream is often displayed as an ar-row with a letter v, this stands for velocity (9). This airstream velocity is the velocity of the airstream far up stream of the airfoil. The angle between the chord line and the airstream is the angle of attack (α).



1. Airfoil 2. Mean camber line 3. Imaginary circles 4. Leading edge 5. Leading edge radius 6. Trailing edge 7. Chord line 8. Camber 9. Velocity

Figure 1.1 Airfoil nomenclature B Different Kinds of Airfoils An ideal airfoil should at least meet the following requirements: a low drag coefficient (��) for the nor-mal cruise flight, a high lift coefficient (��) for a low landing speed and a high proportion of the �� /�� values. But these requirements are in conflict with each other because a high �� value automatically comes with a high �� value. That is why compromises have to be made with the design of an airfoil to optimize the specific characteristic features. A positive cambered airfoil (figure 1.2a) can be cambered positive in different ways. It depends where the biggest positive camber takes place in percent of the chord line. Notice the upper surface is more curved then the lower surface. This is why they call it a positive cambered airfoil. The �� and �� can be drawn in a graphic with different angles of attack. Notice the first characteristic feature of a positive cambered airfoil (figure 1.2b); the airfoil has a positive �� at a 0° α. Even if the airfoil has a slightly negative α it still produces lift. In the first part of the drawing the �� varies linearly with the α, then at a certain α the �� reaches its maximum value. The lowest airspeed, where the lift and gravity forces are still in balance, can be found where the �� has reached its maximum. As α in-creases beyond this value the �� drops. This happens at the critical angle of attack. When the α in-creases after this point the lift is gone and this is referred as the stall point. The airflow around the airfoil is at its best with a slightly negative α. That is why the lowest �� value is found at a negative α (figure 1.2c). This is the second characteristic feature of a positive cambered airfoil. The maximum airspeed can be reached when the �� value is at its minimum. When the �� and �� values are drawn in one graphical drawing it is named the wing characteristics (figure 1.2d).

a b c d Figure 1.2 Positive cambered airfoil

A symmetric cambered airfoil, where the lower and upper surfaces are now mirrored at the chord, only creates a lift force when it has a positive α. A negative cambered airfoil creates a down force at an α of 0°. This airfoil only creates lift when it has a lar ge angle of attack. (appendix II) C Sweptback Wings During World War II people discovered how they could postpone the beginning of compressibility symptoms by changing the plan form of the wing. By sweeping the wings backwards, the ‘new’ airflow



velocity over the airfoil becomes less because the normal airflow velocity over the airfoil is a resultant of this ‘new’ airflow velocity and a velocity perpendicular to the airfoil. The purpose of bringing down these speeds is to lower the critical Mach number. This is necessary to avoid unwanted pressure forces. Although this will increase the induced drag forces it is used for almost every modern high speed airplane. D Wing Control Surfaces Nomenclature Where large airplanes such as a Boeing 737 have several extra control surfaces in comparison to smaller airplanes such as the Cessna 172, they both have the same basic flight controls. To under-stand more about the later explained control surfaces a simple nomenclature about control surfaces on the wing will follow (figure 1.3). The smaller airplanes only have ailerons (1) on the tip of the wings. Large airplanes have these too, but now they’re only for low speed maneuvering. This is because large airplanes have high speed or inboard ailerons (2) as well. The Krueger flaps (3) and the slats (4) are located on the leading edge. On the trailing edge there are the three slotted flaps, inboard (5) the nearest to the fuselage and outboard (6) in the middle of the wing. There spoilers are located on top of the wing (7). The spoilers the nearest to the fuselage are the airbrakes (8).

1. Low speed ailerons 2. High speed ailerons 3. Krueger flaps 4. Slats 5. Inboard three slotted flaps 6. Outboard three slotted flaps 7. Spoilers 8. Airbrakes

Figure 1.3 General wing control surfaces nomenclature

1.1.2 Aerodynamic Aspects The aerodynamic aspects of an airplane are very important in understanding how flight controls work. The wings of the airplane produce lift (A) as they move through the air. Depending on the surrounding factors, different kinds of boundary layers can be found (B). The influence of the angle of attack on the effects of lift can be plotted in a �� -α graphic (C). With flight controls the lift on some of the surfaces can be adjusted so that the plane starts to rotate around a certain axis. A Lift Lift is the force created by the wings of an airplane and it can counter the force of gravity so that an airplane can stay in the air. There is a formula to calculate the amount of lift that could be produced by an airfoil (formula 1).

This formula can be converted in to the �� configuration (formula 2).

The lift coefficient shows the lift characteristics of the wing.

Lift Formula 1

� � � · · �� L = lift

q = dynamic pressure S = wing area ��= lift coefficient

L in N q in Pa S in m2 �� is dimensionless

Lift coefficient Formula 2

��

q · S

��= lift coefficient L = lift q = dynamic pressure S = surface

�� is dimensionless L in N q in Pa S in m2



The amount of lift that can be produced by a wing depends on multiple factors. Such as the density of the air, the velocity of the airflow over the surface of the wing, the airfoil, the angle of attack and the dimensions of the wing surface. The continuity equation (formula 3) tells us that if an amount of air flows into a tube, the same amount of air will come out on the other side in a steady airflow. So if the inlet is larger than the outlet, the air has to move faster through the outlet because the same amount of air will have to pass through in the same amount of time.

The continuity equation only applies for an ideal gas. This same situation occurs around an airfoil. Because the wings camber line is positively curved, the top of the wing will push the air away more so that the effect of a narrow tube appears between the imaginary streamlines. The streamlines will compact, creating a narrow tube in which the air will travel faster. The airflow underneath the wing stays relatively unchanged. If the air flows faster the pressure will decrease. And it is this difference in pressure that creates lift. The pressure underneath the wing wants to equalize the lower pressure above the wing pushing the wing up. The speed of the airflow can be calculated by using Bernoulli’s equation (formula 4).

Bernoulli’s equation only applies for an ideal gas. B Boundary layer As air flows over the surface of the wing it starts of as a laminar boundary layer. This means that the streamlines are smooth and regular, and that the air particles move smoothly along a streamline. As the air travels further over the surface, the air close to the surface slows down. The boundary layer loses its energy and starts to grow in height. When it reaches the critical Reynolds number of about 530000 it will turn into a turbulent boundary layer. This normally happens around the thickest point of the wing. The Reynolds number is dimensionless, and can be calculated (formula 5).

By calculating the Reynolds number the kind of boundary layer can be predicted. If a laminar boundary layer (1) turns into a turbulent boundary layer the streamlines break up and the air particles move in an irregular and un-orderly fashion. The transition region (2) normally lies around the thickest point of the airfoil. Behind it are the turbulent boundary layer (3) and the laminar sub layer (4) (figure 1.4).

1. Laminar boundary layer 2. Transition region. 3. Turbulent boundary

layer 4. Laminar sub layer

Figure 1.4 Boundary layer

Continuity equation Formula 3

�1 · �1 · �1 � �2 · �2 �2 P = pressure

A = Area v = velocity

P in Pa A in m2 v in m/s

Bernoulli’s equation Formula 4

�� 1

2 · � · ��

� � �� 1

2 · � · ��

� P = pressure ρ = density of the air v = velocity

P in Pa ρ in kg/m3 v in m/s

Reynolds number Formula 5

��

� · � ·�

�

Re = the Reynolds number ρ = density of the air v = velocity × = a point along the cord line µ = viscosity

Re is dimensionless

ρ in kg/m3 v in m/s × in m µ in Pa/s



A turbulent boundary layer offers more shear stress than a laminar one. If the velocity of the airstream around an object increases the laminar boundary layer will separate from the object at its thickest point and it will create a slipstream behind it. A turbulent boundary layer contains more energy and will fol-low the airfoil of an object longer, decreasing its slipstream and there for decreasing its drag (figure 1.5).

1. Streamlines in a slow airflow 2. Streamlines in slightly faster

airflow 3. Streamlines in a fast airflow

Figure 1.5 Slipstream around an object at different speeds.

C Variation of Lift coefficient and angle of attack graphic If an airplane slows down, it will have to increase its angle of attack to maintain the same altitude. There is a point where the angle of attack becomes too big and the airflow can no longer follow the wings airfoil. This is called flow separation. If the angle of attack increases the point of separation will move forward towards the leading edge of the wing. The wing will produce less and less lift, it will stall. The variation of �� and the α can be seen in a �� -α graphic (figure 1.6). If the angle of attack increas-es so will the �� until the critical angle of attack is reached and the �� will decrease rapidly. The wing will no longer produce lift.

1. Normal situation. 2. Maximum lift. 3. Stalled

Figure 1.6 ��-α graphic

1.1.3 Forces Around the Airplane During flight, there are many forces which are working on the airplane. (figure 1.7). Every force has to have an opposite force to make them combined a neutral force. The four basic forces that are most common are the gravity (A), the lift (B), the thrust (C) and the drag (D). These four forces will be ex-plained separately.

1. Lift 2. Drag 3. Weight 4. Thrust

Figure 1.7 Forces around the airplane



A Weight Everywhere on earth there is gravity (appendix III). The reason that all the objects on earth will not float in the air, is because of the gravity that keeps all objects on the surface of the earth. Instead of speaking of gravity, it is common to speak of weight. The reason for that is that the weight of the air-plane is one of the forces that is working on an airplane during flight, instead of the gravity. The gravity is a result of the mass of the airplane. As a result of the mass of the airplanes and other objects that are flying in the air, they are pulled down to the earth surface by the gravity. The scientist Isaac New-ton became very famous with his formula about the gravity on earth. His formula was; F= m × g, which means that the more mass an object has, the more power it is being pulled down to the surface of the earth.

This is the formula all airplanes are using to measure of the gravity force. During flight, the center of gravity changes due to decreasing weight of the airplane, because fuel is burned. B Lift Lift is the most important force that is works on the airplane. Without the lift airplanes will not be able to fly. The reason for this is that the airplane is already pulled down to the surface of the earth by the mass of the airplane. The result of this mass, the force of gravity, needs to have an opposite force to neutralize the two forces. Without the force of lift, the airplane drops down, because it only has the downward force of the gravity. Most of the lift is generated by the wings of the airplane keeping the airplane airborne. Wings need a medium to create lift. C Thrust Thrust is a force that needs energy to produce propulsion. Without thrust it is impossible to keep an airplane in the air. Thrust is the force that keeps the airplane moving forward. This force is generated by the engines of the airplane. Because the force is generated by the engines, the airplane cannot fly without enough fuel to keep the engines running. The fact that the force is driven by engines makes it a mechanical force. The magnitude of the thrust depends on the amount of fuel that the engines used and the density of the air. D Drag Drag is the aerodynamic force that opposes an aircraft’s motion through the air. It is generated by the air the airplane is going through. Without the air, the airplane experiences no drag at all. This drag, caused by the air, has to do with the velocity, the density and the direction of the air compared to the airplane. With movement comes drag. If there is no movement, whether it is the airplane, or the air, there is no drag. When the airplane moves south and the air direction moves north, the airplane expe-riences drag from the air, because of the difference in direction. The amount of drag depends on the velocity of both. The higher the velocity of the air, the more drag the airplane experiences. The higher the density of the air, the more drag the airplane experiences. Next to the velocity, the density and the direction of the air, the body of the airplane also has influence on the amount of drag. The smoother the airplane is, the less amount of drag the airplane experiences.

1.2 Flight Controls The flight control can be divided in two groups, the primary flight controls and the secondary flight controls. The primary flight controls (1.2.1) provide the pilots control about the three axis of the air-plane. The secondary flight controls (1.2.2) are there to support the primary flight controls. The sec-ondary flight controls improve take off and landing characteristics.

1.2.1 Primary Flight Controls The primary flight controls provides control about the three axis of the airplane. The elevator pitches the airplane up and down (A). The rudder controls the yaw of the airplane (B) and the aileron controls the bank and roll of the airplane (C).

Gravity Formula 5

� � � � � P = pressure

ρ = density of the air V = velocity

P in Pa ρ in kg/m3 V in m/s



A Elevator The elevator system provides primary control of the airplane about its lateral axis. This movement is referred to as pitch. With use of the elevator the angle of attack of the airplane can be changed. The elevator is connected to the trailing edge of the horizontal stabilizer. Movement of the elevator is ac-complished by moving the control column, when the pilot pulls the control column back the elevator will move up and the lift on the elevator will decrease. The nose of the airplane will go up. To descent the pilot moves the control column forwards. The elevator will move down this will increase the lift and the nose will move down. Movement of the elevator (figure 1.8) in the Cessna 172 is done mechanically. The elevator is con-nected to the horizontal stabilizer by hinges. The control columns in the cockpit are connected to each other and to the elevator by cables, push-pull tubes and bell cranks. When the pilot moves the control column (1), the push pull rod (2), which connects the forward bell crank (A) with the control column moves the forward up-cable (3) and the forward down-cable (4). The cables are guide through the airplane by pulleys (B). The end of the aft up-cable is connected to the top (5) of the after bell crank and the aft down-cable is connected to the bottom (6) of the aft bell crank (C). A tube (7) is used to connect the aft bell crank with the elevator (8). The after and the forward cables are connected to each other by turnbuckles (9) with this turnbuckle the tension in the cables can be changed.

1. Control column 2. Push pull rod 3. Forward up-cable 4. Forward down-cable 5. Aft up-cable 6. Aft down-cable 7. Tube 8. Elevator 9. Turnbuckle

A. Forward bell crank B. Pulley C. Aft bell crank

Figure 1.8 Elevator control system

B Rudder The rudder system provides control of the airplane about its vertical axis. Movement around the vertic-al axis is referred to as yaw. The Rudder is connected to trailing edge of the vertical stabilizer. Control of the rudder is accomplished by the rudder pedals (appendix IV). When one pedal moves forward the other one comes backwards. When the left pedal is pushed in the rudder moves to the left, the lift force on the left side of the vertical stabilizer will increase and the nose of the airplane will move to the left. If the pedal on the right side is pushed forward the lift force on the right side will increase and the nose of the airplane will move right. Changing the position of the rudder (figure 1.9) on the Cessna 172 is done mechanically. The rudder is connected to the vertical stabilizer by hinges. The Cessna 172 has two sets of rudder pedals (1), the left pedals are connected to each other the right ones are connected as well. When the right pedal is moved forward the right cable (2) will move forward and the left cable (3) moves backwards. Because the left cable is attached to the left pedal, the left pedal moves backwards as well. The cables are guided through the airplane by pulleys (A). The right cable is connected to the right side (4) of the bell crank (B) and the left cable is connected to the left side (5). Due to the fact that the rudder and the bell crank are attached to each other the rudder (6) will move with it. The maximum travel of the rudder is limited by the rudder stop (7).



1. Rudder pedals 2. Right cable 3. Left cable 4. Right side 5. Left side 6. Rudder 7. Rudder stop

A. Pulley B. Bell crank

Figure 1.9 Rudder control system The use of the rudder has one side effect. When the pilot wants to yaw to the left, the lift force on the right side of the vertical stabilizer will increase and the nose will go to the left. To yaw to the left the right wing must have a greater speed then the left wing, therefore the right wing will generate more lift. The pilot will have to use the ailerons to compensate for this effect. C Ailerons The pilot uses the control column to move the ailerons. This mechanical system (figure 1.10) uses cables and pulleys. At the control wheel (1) a pulley (2) is installed in vertical position. This cable (3) goes down and heads a next pulley. This pulley is connected with cables in horizontal position. This cable is coupled to push-pull rod (4). The push-pull rod is connected with both ailerons (5).

1. Control wheel 2. Pulley 3. Cable 4. Push-pull rod 5. Aileron

Figure 1.10 Aileron mechanism To provide a roll about the longitudinal axis the ailerons move in opposite direction (figure 1.11). The maximum deflection of the ailerons is about 30 degrees with regard to the horizontal position. When the control column is pulled to the left to provide a roll to the left side, the right aileron will move down-wards (1). The left aileron moves in opposite direction, so this one will rise (2). Because the right aile-ron moved downwards, the right wing will get more camber and a bigger angle of attack. At the left side the wing will get less camber and a smaller angle of attack. The total lift at the right wing increas-es and at the left wing the total lift will decrease. Because the left wing has less lift, the wing will go down and the airplane rolls about its longitudinal axis (3).



Figure 1.11 Aileron operations Ѐ A side effect when using the ailerons is adverse yaw (figure 1.12a). When the airplane rolls to the left, the left aileron will rise and the right ailerons moves downwards. As a result of the difference in lift the right wing will move up. The right wing will get more drag and the drag at the left wing will decrease. As a result of that difference the airplane will also move around the top axis. The airplane will move right around the top axis. This is called adverse yaw. To prevent the adverse yaw the rudder can be used to compensated for this effect. There are also different designs of ailerons that do not have this side effect. Placing differential ailerons (figure 1.12b) is one of the possibilities to prevent adverse yaw. Using ordinary ailerons, the aileron in downwards position has most drag. Using differential ailerons, the aileron in downwards position is less deflected with regard to the aileron in upwards position. The drag will increase at the risen aileron. This prevents the adverse yaw. Another possibility to prevent adverse yaw is to place frise ailerons (figure 1.12c). The aileron in up-wards position a part of the aileron sticks out at the bottom. This will cause more drag. As a result of that the adverse yaw will be prevented.

Figure 1.12a Adverse Yaw

Figure 1.12b Differential aileron

Figure 1.12c Frise Aileron

A Cessna 172 has two ailerons, one at each wing. These ailerons are placed at the tip of the wing at the trailing edge side. The ailerons are placed like this to get great moment. At some airplanes four ailerons are installed, each wing has an outboard aileron and an inboard aileron. The inboard ailerons are smaller than the outboard ailerons. In the wing a lock out mechanism is installed that will lock the outboard ailerons in the neutral position at higher airspeeds. At a high speed the moment of forces will get too big. At high airspeed only the inboard ailerons will be functioning. When outboard ailerons are still functioning at high speed they could cause a torsion effect. For example, the ailerons in upwards position gets too much forces and the angle of attack increases. Instead of the wing going down, the wing goes up. This aileron reversal is caused because the wing is too small at the tip and the forces at that point are too large. For that reason the outboard aileron locks of at higher speeds.

1. Right aileron goes downwards, right wing goes up 2. Left wing goes upwards, left wing goes down 3. Roll to the left side



1.2.2 Secondary Flight Controls Secondary flight controls have influence on the performance of the airplane. The secondary flight con-trols consist of trailing and leading devices. The spoilers and trim system influence the amount of lift or drag. The trailing edge devices stimulate the performance of the airplane by increasing the camber (A). The leading edge devices also stimulate the performance of the airplane (B). The Spoilers in-crease the drag to reduce the speed (C). A trim tab is used to ease the force applied by the pilot on the control surfaces and help maintaining stability (D). A Trailing Edge Devices Trailing Edge (TE) devices, also named as flaps, are located on the back of the wing and increase camber, drag and decrease stall speed. TE flaps are used during take-off and landing because of the low forward speed. The chance of low speed stall is reduced. Besides the decreasing of the stall speed, the airplane with extended TE flaps will increase the critical angle of attack. The lift coefficient for a specific angle of attack has a value which is based on the characteristics of the airfoil (figure 1.13). The first line represents the ��variable without flaps and slats (1). When the critical angle of attack is almost reached, the line changes to a curve until all the lift is lost. By selecting the flaps the lift coefficient increases (2). When the slats are extended only, the critical angle of attack is increased (3). The flaps and slats both extended, results in a higher lift coefficient and an increased critical angle of attack (4).

Figure 1.13 �� – α graphic

1. Normal ��– α wing 2. Flaps extended 3. Slats extended 4. Flaps + slats extended

There are several types of TE flaps (appendix V):

1. Plain flap 2. Split flap 3. Slotted flap 4. Fowler flap

Ad1 Plain flap The plain flap is the simplest flap. The flap can deflect down which increases the camber. Ad2 Split flap The split flap consists of a hinged section at the lower surface of the wing. The flap can deflect down which increases the camber. The upper and lower surfaces are separate, the lower surface operates like a plain flap, but the upper surface stays in position. Ad3 Slotted flap The slotted flap has the same principle as the plain flap, except the fact that there is a gap between the wing surface and the extended slotted flap. This gap has the same effect as a venturi. The air flows from the lower surface to the upper surface and adds energy to the boundary layer. This pre-vents separation of the airflow.



Ad4 Fowler flap The fowler flap (figure 1.14) is used on the most commercial jet airplane. The flap increases the camber, like all other flaps, but the fowler flap also increases the wing area. The wing surface (1) is increased with an extended fowler flap. This causes a significant change in lift. The fowler flap is used on the Cessna 172.

Figure 1.14 Fowler flap

1. Wing surface 2. Extended fowler flap

B Leading Edge Devices Leading Edge (LE) devices are high lift devices. Some increase lift by extending wing surface during take-off, landing and low speed flights. The LE slats allow some of the high air pressure from beneath the wing, to float trough a slot to the upper surface of the wing. The airplane with extended LE slats can thereby fly at a greater angle of attack and lower airspeeds. Because of the larger frontal surface, there flows more air over the upper surface of the wing, which creates more lift. Besides the increase of lift, the cord line increases length and the nose drops down. There are several types of LE devices (appendix VI):

1. Fixed slot 2. Krueger flap 3. Slat

Ad1 Fixed slot The fixed slot flap cannot extend, it is a permanent device on the airplane. The slot allows the airflow to add more energy to the upper surface. The gap works like a venturi, just like the slotted flap. Ad2 Krueger flap The Krueger flap can extend with two parts at two different angles on the surface under the wing and increases camber and also the wing area. This flap is only located on the wing surface on the root of the wing. The Krueger flap is used because the wing is thicker at the root then at the tip Ad3 Slat The slat is located on the front of the wing and works exactly the same as the slotted flap. This slat is often used on airplane in combination with the Krueger flap. The slat is then located on the remaining wing surface. C Spoilers Spoilers are secondary flight controls that can be found on high speed airplanes. Spoilers are devices that disturb the airflow over the wing and “spoil it” hence the name spoilers. They increase drag, re-duce lift and slow the airplane down. An airplane has two types of spoilers (figure 1.15): the flight spoi-lers (1) and the ground spoilers (2). These devices are located on the top side of the wing near the TE devices on the wing.



1. flight spoiler (air brake) 2. Ground spoiler

Figure 1.15 Spoilers and their position on the wing In the air, spoilers can be used for multiple tasks. They can be used to: slow the airplane down, to make an airplane descend and to assist when one of the spoilers on one of the wings is deployed it can help make a roll moment on the airframe; roll assist. The air spoilers are also referred to as air-brakes. These devices are located on the middle section of the wing near the TE of the wing. When the airplane needs to be slowed down, both air spoilers on both wings are deployed to a specific an-gle, because if deployed too far out the airplane could stall. The effect that takes place when the spoi-lers are deployed is that the boundary layer on the top of the wing is disrupted decreasing the lift and increasing drag due to the more turbulent behavior of the disrupted boundary layer. When the airplane needs to descend the same action is done only the spoilers can be deployed further out. When used as roll assist, than the spoiler on one of the wings is deployed out to create a moment difference on the wings making the airplane roll. For example if the airplane wants to bank to the left, the spoilers on the left wing will be deployed. This is done when flying at high speeds and minimal deflection of the inboard ailerons is not enough to roll the airplane over to another position. When the airplane touches down for landing both inner and outer spoilers are deployed to slow the airplane down. The ground spoilers are operated by the pilot via a lever that when pulled, hydraulic pressure is ap-plied on the spoilers to make them deflect and slow the airplane down. The ground spoilers are the inner spoilers these are used during landing and on the ground when an emergency stop is required. Another name for these spoilers is lift dumpers due to their ability to increase drag and slow the air-plane down, they disrupt the flow of air on top of the wing what results in decreasing lift on the wing. When these spoilers are deployed the full weight of the airplane comes on the wheels while braking and slowing the airplane down. D Trim Airplanes of all sizes have tabs installed on the trailing edge of some primary flight controls. These tabs can be moved up and down and can be set to a specific angle by the pilot. This tab is called the trim tab (figure 1.16). The trim tab is used to ease the force applied by the pilot on the control surfaces and help maintaining stability. When the trim tab angle is set correct the airplane can fly “hands-off’’, this means it will maintain its heading and position without any input of the pilot. The varying angle of the trim tab changes the momentum force on the control surface, if this force is equal to zero than the trim point is reached and de airplane can fly “hands-off”.

1. Aileron, rudder or elevator 2. Trim tab

Figure 1.16 aileron, rudder or elevator with trim tab



1.3 Laws and Requirements To ensure the safety of an airplane, there are laws concerning the different aspects of flight controls (1.3.1). The client also has set some requirements that need to be taken in consideration for the flight control system (1.3.2).

1.3.1 Laws The laws are separated in two categories, the light airplanes which weigh less than 5700 kilogram (A) and the heavy airplanes which weigh more than 5700 kilogram (B). A Light airplanes The Certification Specifications created by the European Aviation Safety Agency (EASA) concerning small airplanes can be found in CS-23 (appendix VII). The laws can be divided in:

1. General flight control laws 2. Elevator laws 3. Rudder laws 4. Aileron laws

ad1 General flight control laws Flight controls which are placed in the designated fire zones or areas around it, must be made out of fireproof material or be shielded so that they can withstand the effects of fire. Each element of any flight control system must be designed or distinctively marked to minimize the chance of a faulty as-sembly and a possible failure of the system. Every flight control system and it supportive structure must be designed to cope with 125% of the calculated hinge moment of the control surfaces. ad2 Elevator laws The maximum pilot force which is needed to achieve the maximum deflection of the elevator can be calculated (formula 6). Maximum pilot force control wheel

Formula 6

�� ! " 10 $

F= Maximum pilot force W= Weight of the airplane

F in N W in kg

This formula is used for a steering column controlled airplane. For a stick control the maximum pilot force can be calculated (formula 7). Maximum pilot force control stick

Formula 7

�� ! " 14 $

F= Maximum pilot force W= Weight of the airplane

F in N W in kg

If the Fmax is smaller than 89 N, than 89 N must be used. The elevator must be designed to withstand 125% of computed hinge movements. If the data is not calculated, but acquired from a real flight, the elevator may be designed using a 100% factor. ad3 Rudder laws In case of an engine loss, it is possible to maintain control over the airplane with that engine still not operative, the rudder pedal force needed to maintain control must not be in excess of 667 Newton. During this maneuver, the plane must not go in a dangerous attitude. A 125% factor on calculated hinge movements must be used to design the rudder. The factor may be 100% if the data is obtained during a real flight.



ad4 Aileron laws A 125% factor on computed hinge movement must be used to design the aileron. The pilot force limit may not exceed 298 N in case of a stick control and 222 Nm in case of a wheel control. The minimum pilot force is for the stick control is 178 N and for the wheel control to is 178 Nm. B Heavy airplanes The certification specifications created by the EASA concerning heavy airplanes can be found in CS-25 (appendix VIII). The laws are divided in:

1. General flight control laws 2. Elevator laws 3. Rudder laws 4. Aileron laws

ad1 General flight control laws The flight controls placed in marked fire zones and areas around it, must be shielded or designed in such a way that they can resist the effects of fire and extreme heat. Every single part of each flight control system must be distinctively marked or designed to reduce the possibility of an incorrect assembly and a failing system. The longitudinal, lateral, directional and drag control system and its supportive structure must be designed for loads corresponding to 125% of the computed hinge moments of the moveable control surface. ad2 Elevator laws The maximum pilot force may not exceed 1112 N if it is a stick control and 1335 N if it is a wheel con-trol. The minimal thickness of the elevator system cables is 3.2 mm. ad3 Rudder laws It must be possible, with the wings level, to yaw into the operational engine and to make a relatively sudden chance in heading of about fifteen degrees in a safe way. The rudder forces required to keep control of the plane at the minimal control airspeed (VMC) may not be more than 667 N. The maximum pilot force may not exceed 1335 N. 3.2 mm is the minimal thickness of the cables used in the rudder control system. ad4 Aileron laws The pilot force limit must not be over 445 N if it is a stick controlled system and 356 Nm if it is a wheel controlled system. The minimum pilot force is 178 N in case of a stick control and 178 Nm in case of a wheel control. The cables used in the aileron control system may not be thinner than 3.2 mm.

1.3.2 Client Requirements The client has certain requirements considering the different kinds of flight control system:

• The client requires a research-team to investigate the differences between two flight control systems, the Fly-By-Wire system found in the Airbus A320 and the conventional flight controls as found in the Boeing 737.

• The client wants the research-team to find out if it is advisable to accommodate the latest Boeing 737 with a flight control system, similar to the Fly-By-Wire system created by Airbus

1.4 Comparison Small and Large Airplanes The biggest difference between a small, for example a Cessna 172 and a large airplane, for example a Boeing 737 is of course the size. At a large airplane everything is bigger than a Cessna 172; nose, body, wings and the whole empennage. Because everything is larger these airplanes needs larger and more aerodynamic control surfaces to control the airplane. These large airplanes often fly faster than the smaller airplanes. This in combination with the larger aerodynamic control surfaces results in higher aero dynamical forces. That is why a more powerful mechanical control system for the larger airplanes is needed.



For the small airplanes human power is enough to make the control surfaces move. The control sur-face for a small airplane consists of the ailerons, rudder and elevator. These surfaces are directly linked by cables, wheels and springs and are moved mechanically by the power of the pilot. A charac-teristic of this in small airplanes used mechanism is that it’s reversible. This means that the force needed to move the aero dynamical surfaces is directly felt by the pilot. When time extends the force needed to make the control surfaces move will get relatively seen too much for him. That’s why a re-duction of forces for the pilot is made by adding pulleys or servo tabs into this system for small air-planes. Midsized and larger airplanes also got other devices to control the airplane. These devices are the secondary flight controls and consist among others of the flaps, slots, slats and spoilers. Because the increase of the force on the control surfaces is getting bigger at larger airplanes pulleys and servo tabs do no longer suffice the required control force. This leads to the use of a hydraulic powered flight con-trol system. This system is an early mechanical system with addition of a hydraulic part. The steering commands of the pilot are mechanically transported to the hydraulic system. This hydraulic system moves the control surfaces with the required force. This system is irreversible because the pilot cannot feel the forces which are needed to move the surfaces. For this reason artificial feel devices are im-plemented to provide the feeling force of controlling the airplane. Small Airplane (for example Cessna 172) Large Airplane (for example Boeing 737)

• Control surfaces: ailerons, rudder, ele-

vator and flaps; • Control surfaces are moved direct with

human strength; • Steering commands are transported

mechanically by cables, wheels and springs. Later by cables, pulleys and servo tabs;

• Control system is reversible.

• Control surfaces: ailerons, rudder, eleva-

tor and flaps + high speed ailerons, Krueger flaps, slats, inboard three slotted flaps, outboard three slotted flaps and spoilers;

• Control surfaces are indirectly moved with the use of a hydraulic control sys-tem;

• Steering commands are transported me-chanically by cables and servo tabs;

• Control system is irreversible.



Input

Convert

Correct

Transport

Amplify

Execute

Feedback

1.5 Functionality Research To make an airplane move around its axes, there are certain actions required to make this happen. These actions or functions can be split in to seven different functions, these are: input, convert, cor-rect, transport, amplify, execute and feedback. These steps are individual phases that shall be hig-hlighted and shown one by one in the diagram figure.

1. Input 2. Convert 3. Correct 4. Transport 5. Amplify 6. Execute 7. Feedback

Ad 1 Input To make the airplane change attitude or heading the pilot needs to bring in a single via the primary or secondary flight controls. Ad 2 Convert This input signal from the pilot needs to be converted to a specific signal for further transportation of the input signal. Ad 3 Correct The input signal needs to be corrected from any loss of input signal to main-tain an accurate signal for amplification.

Ad 4 Transport The corrected signal can now be transported to the specific flight control sur-face.

Ad 5 Amplify The signal needs to be amplified before moving the flight control surface. Ad 6 Execute Now the pilot input can be executed after the amplification and move the flight control surface to the desired position. Ad 7 Feedback After the control surface has moved the results are seen and felt directly, the feedback. With this feedback the pilot can decide what the next input shall be and start this all over again.



2. Flight Controls on the Boeing 737 and Airbus A32 0

The flight controls on different types of airplanes are not all the same. Depending on the size, shape and the purposes of the airplane, the control surfaces vary in size and numbers. The location of the control surfaces also varies between different types of airplanes. The system that makes the control surfaces move is different for the Boeing 737 (2.1) as for the Airbus A320 (2.2). The primary flight controls are roughly the same on both planes because they have the same purpose, but there is a difference in the system behind them. The secondary flight controls of both planes differ from each other because of the planes properties such as weight, airfoil, overall shape of the wings and the land-ing and takeoff speed. Because both systems are different in one or more ways both have their own benefits and drawbacks (2.3). As a result, a conclusion can be drawn (2.4).

2.1 Flight Controls Boeing 737 The flight control system of the Boeing 737 uses a conventional flight control system, as found on the Cessna 172. The only difference is that the input of the pilot is enforced by an hydraulic system. The flight controls can be divided in primary flight controls (2.1.1) and secondary flight controls (2.1.2). To ensure airplane safety there are different backup flight control systems (2.1.3).

2.1.1 Primary Flight Controls The primary flight control system of the Boeing 737 (appendix IX) is a conventional flight control sys-tem like the one on a Cessna 172, except for the fact that the input of the pilot is enforced by a hy-draulic system (A). The hydraulic systems that are used are system A and system B. Either one of these systems are capable of powering all the primary flight controls; the ailerons (B), the elevator (C) and the rudder (D). A Hydraulic system There are two normal hydraulic systems (appendix X) on the Boeing 737, system A and system B. There is also a stand-by system. System A and B are the systems that are used during normal opera-tions. Each system contains a reservoir, two pumps and the tubes that transport the hydraulic pres-sure. Both systems have a reservoir; the hydraulic reservoirs are pre pressurized by bleed air at 50 psi to ensure there is a enough fluid flow to the pumps. It also prevents foaming and helps to prevent cavi-tation. System A powers the primary flight controls, which consist of four flight spoilers; two on each wing, and the four ground spoilers. System B powers the primary flight controls and the four flight spoi-lers, the TE flaps, the LE devices. To pressurize the systems to 3000 psi, two pumps are installed for each system. There is one engine driven pump and one alternating current (AC) motor driven pump. The engine driven pump of system A is connected to the accessory gear box of engine 1, and system B to engine 2. The engine driven pump can supply four times more hydraulic fluid than the AC driven pump. A power transfer unit is installed to supply additional hydraulic fluid which is needed to operate the leading edge flaps and slats if the engine driven pump of system B is lost. Hydraulic power from system A is used to power a hydraulic motor-driven pump used to pressurize system B. The stand-by hydraulic system is a backup if systems A and/or B are lost. This system consists of a single electric motor driven pump that can be used to control the rudder, thrust reversers, standby yaw damper and to extend the LE devices. The hydraulic reservoirs (figure 2.1) of the two systems are not the same. If there is a leak in the en-gine driven pump section (1) of system A there is a standpipe (2) to prevent total hydraulic fluid loss. But if there is a leak in the electric driven pump section (3) there will be a total hydraulic fluid loss. System B only has one standpipe, a leak in either one of the pump sections will lead to a total loss in power. However the quantity of fluid in the standpipe is enough for power transfer unit operations. The hydraulic pressure is transferred to the power control units (PCU) by hydraulic tubes. These units con-trol the control surface movements.



The simplest PCU (figure 2.2) consists of a selector valve (1) that is mechanically moved by the input of the pilot. By moving the selector valve the pressure (2) and the return tube (3) can be transported to one of the sides of the actuator (4), and the actuator moves in or out.

1. Selector valve 2. Pressure line 3. Return line 4. Actuator

Figure 2.2 Power control unit B Ailerons The ailerons system (appendix XI) of the Boeing 737 has two ailerons, one on each wing. When one of the control wheels is rotated the ailerons move differentially to provide lateral control. The control wheel of the Captain is connected to the aileron feel and centering unit. The control wheel of the first officer is connected to the spoiler mixer. The two control wheels are connected to each other by a cable drive system; this allows control of the ailerons by either control wheel. The input of the control wheel travels through the feel and centering mechanism to the input lever on the PCUs that move the aileron control surfaces. The aileron feel and centering mechanism gives the pilots a feedback of the forces and aerodynamic load of the control surfaces. It also puts the control column in its neutral posi-tion. The PCUs move the ailerons, and uses hydraulic pressure of systems A and B. If both hydraulic systems would fail the ailerons can be mechanically positioned. The forces on the control wheel are higher due to the aerodynamic loads. C Elevator The elevator system (appendix XII) on the Boeing 737 consists of two elevators that are intercon-nected by a torque tube. The elevator provides control of the airplane about its pitch axis. The elevator on the Boeing 737 is connected to the TE of the horizontal stabilizer and responds to the input from the control column which is a forward or backward movement. The control columns are intercon-nected. The input of both control columns travel separately to the PCUs and to the elevator feel com-puter. The elevator power control packages are powered by hydraulic systems A and B, and move the control surface. The elevator feel and centering computer simulates the aerodynamic force on the elevator to the control column using the airspeed, which is measured using two pitot tubes, one on each side of the fuselage. D Rudder For control about the vertical axis there is a rudder system (appendix XIII) installed on the Boeing 737. The rudder pedals are mechanically connected to the rudder feel and centering unit. The output of this

1. Engine driven pump 2. Standpipe 3. AC motor driven pump 4. Bleed air pressure

Figure 2.1 Hydraulic reservoir A



unit is the input of the main and the standby PCU of the rudder. The feel and centering unit is used to center the control column and to add an artificial feel to the control column. The main PCU has two actuators; one is powered by system A and the other by system B. In the main rudder PCU there is a Force Flight Monitor (FFM) installed that detects if there is a difference in pressure between the actua-tor from system A and/or B, the FFM will automatically turn on the standby hydraulic pump to pressur-ize the standby power control pack. At speeds above 135 knots, the hydraulic pressure of the hydrau-lic systems is reduced in the main PCU by approximately 25%. The reduced pressure is necessary to limit the rudder deflection, because the forces on the rudder would be too great.

2.1.2 Secondary Flight Controls Boeing 737 The secondary flight controls improve the lift and handling properties of the airplane. The secondary flight controls consist of; TE and LE devices, spoilers and a trim system. TE devices stimulate the performance of the Boeing 737, because they increase camber, drag and decrease stall speed (A). The LE devices help the Boeing 737 to fly at slower airspeeds and greater angle of attack, especially during take-off and landing (B). The spoilers help the airplane roll (C). The trim assists the pilot during the flight and makes it easier to control the airplane (D). A Trailing Edge Devices The TE flaps (figure 2.3) increase the wing area and the wing camber. This increases lift to help im-prove the takeoff and landing performance of the airplane. The Boeing 737 has two double-slotted flaps (1) on each wing extend during takeoff (2) to increase lift. This permits a lower vrotation speed for the airplane during takeoff. During cruise (3), the TE flaps are fully retracted. During landing (4), the TE flaps are fully extended to increase lift and increase drag to permit slower speeds at touchdown.

Figure 2.3 Trailing edge devices

1. TE flaps 2. During take-off 3. During cruise 4. During landing

The TE flaps are controlled by the flap lever, this lever gives the command to the hydraulic system that moves the flaps. The flap lever moves a cable system that supplies a mechanical input to a flap con-trol valve in the flap control unit. The hydraulic system B supplies the pressure, through the bypass valve, to the power drive unit (PDU) and is controlled by the flap control valve. The PDU activates the flap drive system to move the TE flaps and supplies a mechanical feedback to the flap control valve. If the TE flaps do not stay in alignment, the bypass valve prevents hydraulic power to the flap PDU and the TE flaps stop moving. B Leading Edge Devices The LE devices (figure 2.4) consist of two Krueger flaps (1) and four slats (2) on the LE of each wing. During cruise, these surfaces fully retract (3). These surfaces extend (4) during takeoff to increase lift, which results in slower speeds for airplane rotation. During landing, the LE devices (5) fully extend (6) to increase lift and help to prevent stall.



Figure 2.4 Leading edge devices

1. Krueger flaps 2. LE slats 3. Up 4. Extend 5. LE devices 6. Full extend

The flap control unit consists of the TE and LE flap control valve. The TE flap system sends inputs to the LE flap and slat control valve. As the TE flaps move, feedback from the TE flap system moves the LE flap and slat control valve. The LE flap and slat control valve receives hydraulic system B pressure from the LE cruise depressurization valve. The depressurization valve depressurizes the LE flap and slat actuators during cruise. The LE flap and slat control valve sends hydraulic power through the auto slat control valve to the LE flap and slat actuators. If the LE slats are in the extended position and the airplane gets near stall conditions, the auto slat control valve is activated and sends hydraulic power to the LE slat actuators to fully extend the LE slats. C Spoilers The spoilers help the ailerons control airplane roll about the longitudinal axis. They also supply speed brake control to reduce lift and increase drag during landing and refused takeoffs. The Boeing 737 has six spoilers on each wing. One spoiler inboard of each engine strut and five spoilers outboard of each engine strut. The spoilers can be divided into two groups:

1. Flight spoilers 2. Ground spoilers

ad1 Flight spoilers On every wing there are four flight spoilers. The inboard spoilers are powered by hydraulic system A and the outboard spoilers are powered by system B. The flight spoilers are used to decelerate the airplane and increase the rate of descend. During roll control, the flight spoilers assist airplane roll movement. The flight spoilers are manually controlled by the control wheels. The control wheel gives mechanical input trough the feel and centering unit to the aileron power control units . When the con-trol wheel moves, a control valve in each flight spoiler actuator permits hydraulic power to move the actuators. Each actuator moves a flight spoiler. The flight spoilers and the ailerons are connected with the spoiler mixer. The spoiler mixer creates an optimal roll, because the ailerons and the flight spoilers move simultaneous. ad 2 Ground spoilers The flight crew uses the speed brake lever to manually move the ground spoilers (appendix XIV). The auto speed brake actuator automatically controls them. The ground spoilers only move when the air-plane is on the ground. The speed brake lever supplies mechanical inputs through the spoiler mixer and ratio changer to the ground spoiler actuators. The spoiler mixer mechanically moves the ground spoiler control valve. The ground spoiler control valve sends hydraulic system A pressure to the ground spoiler interlock valve. The ground spoiler interlock valve sends hydraulic power to the ground spoiler actuators, which move all the ground spoilers. There is one actuator for each outboard ground spoiler and two actuators for each inboard ground spoiler. The speed brake lever (figure 2.5) has different positions. The down position represents the situation that all spoilers are down and the up position when all the spoilers are up. When the lever is in the armed position, the spoilers are automatically deployed on touchdown. The flight position is used to decelerate the airplane during flight.



Figure 2.5 Speed brake lever

D Trim The trim optimizes the flight controls. There are different flight controls which have a trim:

1. Aileron trim 2. Rudder trim 3. Elevator trim

ad1 Aileron trim The aileron trim is controlled by two trim switches. When these switches are selected, the aileron feel and centering unit (FCU) determents what the current position of the ailerons is and what the position should be. The trim helps to maintain the desired position and therefore there is no need to constantly give an input to the ailerons. The amount of trim can be controlled manually with the trim wheel. The aileron trim system is powered by electricity. The aileron trim sends an electrical signal to the aileron FCU, which changes the neutral position of the trim wheel. On the trim wheel, there is a scale which moves the trim wheel simultaneously with the aileron trim. ad2 Rudder trim The rudder trim is used for trimming away unwanted rudder pedal forces. Most frequently, the rudder is operated automatically by the yaw damper, which helps preventing Dutch roll and other unwanted movements. The yaw damper keeps the airplane stable around the vertical axis. The pilots manually command a yaw input with the rudder pedals. When engaged, the yaw damper automatically makes small yaw corrections. When the pilot controls the rudder trim, a signal goes from the control to the rudder trim actuator. This moves the feel and centering unit, which creates an input to the rudder PCUs. ad3 Stabilizer trim When the airplane needs to maintain altitude, the pitch has to be changed to keep enough lift. To re-lease the pilot from constant input to change the pitch, a trim system is necessary. The stabilizer trim can be controlled in two different ways. When the trim switch is used, the system is controlled by elec-tricity. Another way to control the stabilizer trim, is with the stabilizer trim wheel. This is a manually controlled system and is only used when the electric trim reached its maximum. When the electric system is on its maximum, the stabilizer trim cannot be further controlled with the electric system. The autopilot controls the stabilizer trim automatically using the digital flight control system.

2.1.3 Backup Systems The backup system of the flight controls of the Boeing 737 are separated in the backup systems of the pitch (A), roll (B), yaw movement (C) and the backup system for the secondary flight controls (D). A Pitch Backup The elevators are normally powered by the hydraulic systems A and B. In case of a failure, in either one of these systems, for example; a loss in pressure, the other system is sufficient enough to power the elevator. If both hydraulic systems fail, mechanical control can also be used to power the elevator. The horizontal stabilizer is normally powered electrically, but in case of a failure in the electrical sys-tem, it is possible to position the horizontal stabilizer by rotating the stabilizer trim wheel.



B Roll Backup The captain’s control wheel is connected by cables to the aileron PCU and the first officer’s control wheel is connected by cables to the spoiler PCU. The two control wheels are interconnected with each other. If, for example, the control wheel of the captain blocks, the captain and first officer can separate the two control wheels. In this way, the first officer can control the roll of the airplane by using the spoi-lers. The ailerons are powered by hydraulic system A and B, but in case of a failure of this hydraulic sys-tem, the remaining hydraulic system alone can power the ailerons. In case of complete loss of the hydraulic systems the ailerons can be controlled mechanically. C Yaw Backup The rudder is normally powered by the hydraulic systems A and B, but for backup there is a standby PCU powered by a standby hydraulic system. If the FFM in the main PCU detects a difference in pres-sure between both hydraulic systems, the FFM will automatically switch on the standby hydraulic pump to pressurize the standby power control pack. The yaw damper uses the hydraulic system B. If the hydraulic system loses its pressure, the yaw damper becomes inactive, until the standby hydraulic system is used to control the yaw damper. D Secondary Flight Controls Backup System The secondary flight controls are powered by hydraulic system A or B, but if both systems lose pres-sure, it is possible to control the TE-flaps electrically. Under certain conditions the LE-flaps are po-wered automatically by the power transfer unit. They can also be operated by the standby hydraulic system.

2.2 Flight Controls Airbus A320 The flight control system of the Airbus A320 uses a fly-by-wire flight control system (appendix XV). The flight controls can be divided in primary flight controls (2.2.1) and secondary flight controls (2.2.2). To ensure airplane safety there are different backup flight control systems (2.2.3).

2.2.1 Primary Flight Controls The Airbus A320 uses a fly-by-wire system to control the flight controls. The primary flight controls make the airplane able to move around three different axes. When using the elevators (A) the airplane is able to move around its lateral axis. To move around the top axis the rudder (B) is used and when using the aileron (C) a move around the longitudinal axis is provided. A Elevators To provide a movement around the lateral axis (figure 2.6) two side sticks (1) are installed in the cock-pit. During a flight in normal conditions an elevator aileron computer (ELAC) (2) gets signals when moving the side stick. An A320 has two ELACs. In normal operation ELAC 2 receives signals to con-trol the elevators and the horizontal stabilizer. The output of the ELAC is the input for a hydraulic jack. The A320 has three hydraulic systems (appendix XVI): the green (3), yellow (4) and blue system (5). Every system has its own reservoir with hydraulic fluid. During normal operations the yellow and green jacks are driven, which power the elevators. Three electric motors (6) are installed and motor number 1 drives the trimmable horizontal stabilizer (THS) (7). Electric motor number 2 and 3 are used for backup.



Figure 2.6 Elevator control system

B Rudder To yaw the airplane (figure 2.7) rudder pedals (1) are used. The output of the pedals is the input for the ELAC (2). The ELAC computes the data; turn coordination and yaw damping and transmits it to the flight augmentation computer (FAC) (3). This FAC is used for electrical control of the rudder. To power the rudder, three hydraulic jacks (4) are installed. In normal operation the green system drives all the jacks. With the output of the FAC the hydraulic jacks power the rudder. To trim the rudder two electric motors (5) are installed. FAC1 is connected with motor number 1. The other motor is used for backup.

Figure 2.7 Rudder control system

C Ailerons To control a roll (figure 2.8), one aileron and four spoilers are installed on each wing. Two ELACs (1) are installed. When moving the side stick the ELAC receives signals. In normal operation ELAC 1 controls the ailerons. Each aileron has two hydraulic jacks (2), a blue and a green one. By moving the side stick (3) the ELAC gets an input. The ELAC drives these hydraulic jacks which power the aile-rons.

1. Side stick 2. ELAC 1-2 3. Green system 4. Yellow system 5. Blue system 6. Electric mo-tors 7. THS

7

6

5

4

3

2

1

1. Rudder pedals 2. ELACs 3. FACs 4. Hydraulic jacks 5. Electric motors

4

5 3

2

1



Figure 2.8 Aileron control system D Lay out The Electronic Centralized Aircraft Monitor (ECAM) is a display (figure 2.9) that gives information about the flight controls. On this display the position of the flight controls is shown. The rudder (1) is placed below the display in the middle. When the rudder symbol is in vertical position, the rudder is set to zero. When using the left rudder pedal the rudder symbol turns to the left. The position of the eleva-tors (2) are displayed at the right and left side of the rudder. When the elevators are deflected down, the green triangles move downwards. The triangles move upwards when the elevators are in upwards position. The ailerons (3) are displayed above the elevators. In this case the right aileron is in upwards position and the left aileron is in downwards position. The spoilers (4) are displayed above the aile-rons. In the figure the right spoiler is extended.

2.2.2 Secondary Flight Controls The secondary flight controls on the Airbus A320 consist of the: leading- and trailing edge devices (A), spoilers (B), trimmable horizontal stabilizer (C) and the rudder trim (D). These controls are grouped and located at the pedestal (appendix XVII).

Figure 2.9 Lay out

1. Rudder 2. Elevators in neutral position 3. Ailerons 4. Spoilers, right one extended

4

3

2

1

2

1. ELACs 2. Hydraulic jacks (green and blue) 3. Side stick 1

3



A Leading- and Trailing Edge Devices The LE devices on the airbus A320 are slats and the TE flaps on the Airbus A320 are single slotted flaps. The airplane has five slats and two flaps on every wing. These slats are operated by the pilot or autopilot via a lever. This lever has four set points and controls the leading- and the TE flaps. The pilot input on the lever is converted to an electrical signal which is received by the slats flaps computer control (SFCC). This computer calculates the amount of deflection and speed is necessary. This new signal than is send from the SFCC to the corresponding hydraulic lines, the hydraulic lines yellow and green for the flaps and blue and green for the slats. These hydraulic lines power the hy-draulic jacks that operate the flap screw spindles which set the flaps and slats in there requested posi-tions. B Spoilers The spoilers on the Airbus A320 are located near the TE devices. There are five spoilers on each wing. These spoilers are controlled by the pilot via a lever. The spoilers are grouped for various parts of flight. Counted from inboard to outboard, numbers one through five are used as ground spoilers. The number of spoilers used for actions and movements are controlled via the spoiler elevator com-puter (SEC). Via this computer the spoilers are activated according to the phase of the flight. On the ground all five spoilers on one wing are activated. During a roll only the spoilers two through five are activated on the wing which needs a downward momentum. For reducing speed in the air only spoilers two through four are used. The deployed spoilers give a feedback to the pilot and the computer. The pilot notices that the speed is decreasing or in a turn he notices he is banking. The computer checks for faults and if the “safe speeds” are not exceeded. C Trimmable Horizontal Stabilizer The THS, on the Airbus A320, is the horizontal stabilizer which can deflect upward or downward to trim the airplane horizontally. There are two trim wheels in the cockpit, located on the sides of the throttle levers, one for each pilot. The input signal from the pilot is electrically transported to the hy-draulic systems: green, yellow and blue. A hydraulic signal is send to the jacks which move the THS. D Rudder Trim The rudder trim on the airbus A320 is located in the vertical tail stabilizer. This device trims the air-plane in the yaw directions and is controlled via a turn knob in the cockpit. The pilot input is converted to an electrical signal, which is received by the FAC. There are two signals send to the hydraulic lines yellow, green and blue. One signal feeds the yellow and green lines for the yaw dampening. The yaw damper damps the uncontrolled side movements of the rudder, which keeps the rudder in place. The second signal is send to the rudder trim. This trims the airplane in the yaw directions, which keeps the airplane stabilized without much pilot input.

2.2.3 Backup Systems The backup system for the flight controls of the Airbus A320 permits the pilot to keep control of the airplane during a system failure. The pilot maintains control over pitch (A), roll (B) and yaw (C) move-ments. If there is a failure in the secondary flight controls (D), they will no longer work but will go into neutral position. There is also a backup for the electric power (E). A Pitch Backup If one of the elevators does not work properly, the deflection of the other one is limited to avoid too much asymmetrical force on the tail section. Each elevator has two hydraulic servo jacks installed. One is active and the other one is in damping mode. If the active one fails it will automatically switch to damping mode and the one that was in damping mode will become active. In case of a total electric control failure both jacks will retract into a neutral position so that both elevators will go into neutral position. When both computers ELAC and SEC do not work anymore the pilot can still control the pitch of the plane by using the mechanical trim of the THS. When there is a failure in the system, and the ELAC 2 is not working anymore, the system switches over to ELAC 1. The blue hydraulic jacks are



driven. And these drive the THS by using electric motor 2. If both ELACs have a failure the system switches to one of the SEC. In this case electric motor 2 or 3 drives the THS. B Roll Backup Each aileron has two servo jacks installed just like the elevator. If one jack fails their functions will reverse. If both ELAC 1 and ELAC 2 fail the SEC takes over and roll can still be achieved by control-ling the spoilers. Every roll spoiler is powered by only one servo jack, if failure occurs the jacks will fully retract. C Yaw Backup If the rudder pedals disconnect from the artificial feel unit the centering spring will make sure that the input signal for the hydraulic jacks is neutral. If the green jack fails the system switches to the yellow jack. The rudder can be trimmed by an electrical motor. When this system fails motor number 2 and FAC 2 get activated. In case of a total electrical failure the rudder can still be operated by the rudder pedals, this is the mechanical backup. D Secondary Flight Control Backup Each upper wing surface is powered by one servo jack. If a failure occurs in one of the jacks it will fully retract so that it is in its neutral position. If a spoiler has failed on one wing the symmetrical one on the other wing will retract too. If the hydraulic supply fails the spoilers will stay in their current deflection unless they get pushed down by aerodynamic forces. If the flaps are disconnected or locked, they can no longer be operated to prevent further damage. The slats have an alpha/speed lock so that they can’t be retracted at low speeds or high angles of attack. E Electrical Backup If the electric power fails, an emergency supply of power is ensured by the essential bus supplied from an emergency generator driven by the blue hydraulic circuit. In emergency conditions the blue hydrau-lic system gets pressurized by the ram air turbine (RAT).

2.3 Benefits and Drawbacks Since the 1960’s the Boeing 737 is one of the most successful commercial airplanes in the world. For almost forty years it has been more than a reliable airplane. In these years technology improved enormously as well as the technology in flight controls. Newer produced airplanes such as the Airbus A320 with their fly-by-wire flight control system joined the airplane industry and turned out to be a real competitor for the Boeing 737. The Boeing 737s conventional system is reliable for years but has drawbacks as well (2.3.1). The Airbus A320 has lots of benefits but also some drawbacks despite its modern fly-by-wire system (2.3.2).

2.3.1 Boeing 737 The Boeing 737 still uses a mechanical system instead of a modern fly-by-wire system, therefore it has its benefits (A) and drawbacks (B). A Benefits Instead of using a fly-by-wire system, the Boeing 737 uses a mechanical hydraulic system to steer the airplane. The hydraulic system powers up almost every steering system and is relatively cheap to install. Besides that, the system is very reliable, that is because it uses two compartments which both can power up the different systems they are supplying. During normal procedures both systems work, but when one of the compartments loses pressure and/or is not working properly, the other system is capable to fill in. In case, both compartments are down, there is still another mechanical system which can be used. Besides that, some systems have the opportunity to use an electric system, when the hydraulic system fails. Because of the amount and variety of the backup systems, the Boeing 737 is a reliable airplane. Be-sides that the Boeing 737 has a control wheel, which gives the pilot an artificial feedback from the control surfaces. During a roll the control wheel has the same amount of degrees as the airplane.



B Drawbacks The Boeing737 is not using a fly-by-wire system yet, instead it is using mechanical systems. Therefore the airplane is very heavy. Next to that, because the mechanical systems are constantly moving, the system needs a lot of maintenance. This will result in higher costs. Because the Boeing 737 needs a lot of maintenance, the airplane has not got a big life expectancy.

2.3.2 Airbus A320 The Airbus A320 is the first commercial airplane produced on a large scale, were flight control signals are transported by wires. This relatively new technology has its benefits (A) and its drawbacks (B). A Benefits The steering commands supplied by moving the side stick will no longer be transported mechanically by cranks and pulleys but by wires with electrical signals. This results in a decrease of overall weight of the flight control system. The signals are transported electrically and therefore no mechanical parts are needed which can break or need heavy maintenance. The computers used in this system, can be replaced quickly when broken. This leads to a decrease of aircraft on ground (AOG) time during maintenance. Because the side stick is not connected mechani-cally to the flight controls the forces on the control surfaces are not passed on to the pilot. This will decrease the pilot his effort, to control the airplane. The several flight control computers in this system monitor the position of the flight control surfaces and check these with the steering commands. That is why this system can prevent the airplane against stalling and other over controlled airplane commands. There is a continue feedback which makes this type of flight control systems very safe. B Drawbacks The costs of this modern flight control technology will be relatively high because of the use of different flight control computers. While one of the benefits is the decrease of the pilot his effort, to control the airplane at the same time it is a drawback as well. The forces the pilot wants to feel, to control the airplane are no longer there with this type of flight control system. When all the hydraulic systems fail, there is a backup mechanically cable system installed. This sys-tem is attached to the rudder pedals and the trim wheel. Because of the fact that the backup system is mechanical, the airplane gets heavier.

2.4 Conclusion Having gained information about the way the different systems in the Boeing 737 and the Airbus A320 work and having examined the benefits and drawbacks of these systems, the following conclusion can be drawn:

• The Boeing 737 has the benefit over the Airbus A320 in terms of purchase costs. The 737 is a very safe airplane because of its multiple backup systems. The drawbacks of the 737 are mainly the weight and the high maintenance costs. Because the system used in the 737 is mechanical, it is very heavy and the moving parts need a lot of maintenance.

• The Airbus A320 has the benefit that the electrical system is relatively light compared to the mechanical system. Furthermore, the electrical system can prevent stalling and other over-stressing airplane commands, which makes the A320 a very safe airplane. Another benefit of the A320 is the fact that the maintenance costs are relatively low, because of the electrical system, which does not need a lot of maintenance. Because the electrical system does not need a lot of maintenance, the AOG is decreased. The main drawback of this system is the high purchase costs.

This means that the system in the Airbus A320 is a better system and might be a good alternative system to equip the Boeing 737 with, instead of the conventional system which is now used in the Boeing 737.



3. Modification Boeing 737

Now that the conventional and the fly-by-wire system has been researched, there is concluded that the fly-by-wire system has more benefits than the conventional system. This new flight control system needs to be installed (3.1) in the current Boeing 737 fleet. There are design aspects (3.2) that prove safety, maintenance and backup. In order to see if the installation of the new fly-by-wire system is profitable the costs and benefits are calculated (3.3). Finally an overall conclusion and recommenda-tion (3.4) of the modification can be made.

3.1 Fly-By-Wire Installation For the installation of the fly-by-wire system (appendix XVIII) different parts of the system have to be removed or replaced (3.1.1). A display is needed to show the information about the flight controls (3.1.2).

3.1.1 Modification Flight Controls For the installation of a fly-by-wire system, some parts of the Boeing 737 system have to be removed. The hydraulic system will be modified to coop with a ram air turbine (RAT) (A). In the flight control systems (B) of the Boeing 737 several computers have to be installed. A Hydraulic system On an A320 all the hydraulic systems are connected to standby systems. The Boeing 737 has a me-chanical system, a system that works with steel cables, which is used when the hydraulic system fails. The A320 does not have such a mechanical system. In case of a pressure loss a fly-by-wire system has not got the possibility to send the flight controls by steel cables and pulley’s. That is why every hydraulic system is connected to a standby system. An electrically driven pump pressurizes the hy-draulic standby systems. Also the flight computers are driven electrically. A problem occurs when there is a loss of electricity and hydraulic pressure. In that case the systems cannot be powered. Therefore a ram air turbine (RAT) will be installed. This RAT obtains hydraulic pressure, but without electricity the flight controls still cannot be moved. That’s why an emergency generator is installed between the RAT and the flight controls. The hydraulic pressure will generate electric energy, so the flight controls can still be moved. In the Boeing 737 a standby system is used in case of hydraulic failure. For the new system the standby system is linked to the RAT and when deployed, the standby system will hydraulically power the primary flight controls. Every system has its own standby system driven by an electric pump. The PCU does normally have a mechanical or electric input, but due to the transformation of the flight con-trol system the PCU’s need to be modified for a digital input. The PCU’s receive a digital input, they can be controlled by the flight computers. B Flight controls systems Every flight control in Boeing 737 has to be changed to a fly-by-wire system. New computers and software programs are installed for the:

1. Primary flight controls 2. Secondary flight controls

ad1 Primary flight controls The two conventional steering columns stay in place. Every flight control system changes in a different way:

• Elevator; To use the elevator an input is given to the steering column. Normally this input is transported mechanically in the Boeing 737. The steel cables are replaced for wires and the input is transported to a feel computer. This computer registers the movements of the control column and transforms them into electrical/digital signals. This output is the input for the ele-vator aileron computer (ELAC). This ELAC calculates and corrects this electric signal. Two ELACs will be installed. Because ELACs control the rate of deflection and its correction, a feel and centering unit is no longer needed. The output of the ELAC will be transported via an



ARINC data bus. A hydraulic system amplifies the signal from the ARINC data bus. Two hy-draulic actuators need to be modified to receive the digital signal input. The mechanism that will move the control surfaces will not be removed. Usually a Boeing 737 only has got a standby PCU for the rudder. Because the mechanical system is replaced, the elevator needs to be connected to a newly installed standby PCU, which is connected to the standby system.

• Aileron; In the conventional aileron controls system the PCU’s are mechanically controlled by cables. In the new aileron controls system an electric signal is created by the movement of the steering column. This electric signal is transported by wires to a feel computer, which will reg-ister the movement of the steering column. This signal is the input for the ELACs. The ELACs are connected to SECs. A feel and centering unit is no longer necessary, for the same reason as for the elevator. The electric signal is transported from the ELAC through the wings by an ARINC data bus. New PCUs will be installed at each aileron, and will receive a digital input from the ELACs. This will activate the PCU and pressurize the aileron so that the aileron can be controlled. A standby PCU has to be installed and connected to the ailerons to receive hy-draulic pressure from the standby system.

• Rudder; The conventional rudder control system which makes use of a mechanical connec-tion between the rudder pedals and the rudder itself. This connection is made by steel cables. When using the rudder in the new fly-by-wire system the input that is given by the rudder ped-als is an electric signal. This input is transported to the feel computer and the ELACs. These are connected to the flight augmentation computers (FACs); also two FACs will be installed. This electrical signal will be transported through an ARINC data bus to modified PCUs, two PCUs are installed. One main that is pressurized by systems A and B, and a standby PCU which is powered by the standby system.

Electrical wires are used instead of steel cables. A feel computer is required to get a digital signal after moving the steering column. Flight control computers, ELACs, SECs and FACs, will be in-stalled to correct and calculate the signals. Because of the flight computers the feel and centering units are no longer needed, these will be removed. ARINC data busses are installed to transport the output of the flight computers to the flight controls. As a result of removing the mechanical sys-tem, the PCUs have to be connected to all the flight controls.

ad 2 Secondary flight controls To modify a fly-by-wire system on the Boeing 737 the secondary flight controls also need to be changed.

• Slats and LE flaps; To use the slats and leading edge flaps in the conventional system a me-chanical input is given to the PCU’s by moving the lever. In the new system this mechanical connection is replaced by an electric connection. A position sensor is installed on the flap con-trol lever to transmit the position of the lever. This electric signal will be transported to a slat flap control computer (SFCC), which will calculate the deflection. The output of the SFCC will be transported through an ARINC data bus. This data bus divides the signals to all the slats and LE flaps.

• TE flaps; To control the TE flaps an input is given through the flap control lever to the flap power drive unit (PDU). In the conventional system the input is a mechanical movement which is transported by steel cables. In the new fly-by-wire system this mechanical movement is re-placed by an electric signal. This electric signal is the input for the feel computer and the SFCC. The cables and rods will be replaced by the wires. The output of the SFCC will be transported to the PDU, this PDU drives the TE flaps.

• Spoilers; The control of the spoilers in the conventional system is done by a mechanical con-nection between the speed brake lever, the spoiler mixer and the spoiler PCU’s. In the new fly-by-wire system it is not necessary to replace the lever but the mechanical system behind the lever has to be removed. A feel computer will be installed, which will send the input of the speed brake lever which is an electric signal to a SEC. The SECs are connected to ELACs which make the spoilers work together with the ailerons. The electric output signal from the ELAC will be transported through an ARINC data bus to the PCU, which control the spoilers.

This means that for the secondary flight controls, the mechanical systems have to be removed. The steering column is connected to a feel computer. Instead of the cables used in the mechanical system,



wires are used, which are connected to computers such as: SFCCs, SECs and ELACs. From these computers the signals are transported to the installed ARINC data bus.

3.1.2 Flight Deck Display In the new Boeing 737, with the fly-by-wire system installed, all important systems are a part of the EICAS-system. Two of the systems are the flight control surfaces (A), as well as the hydraulic system (B). A Flight control surfaces With the flight control surfaces there is the possibility to see all the flight control surfaces separately and which flight control is doing what. On the upper part of the screen (figure 3.1), the speed brakes are illustrated (1). The position and status of the speed brakes can be checked with it. The Left and the Right ailerons are illustrated on the left and right side of the speed brakes (2). The green indexes are figuring the movement of the ailerons. The elevators are more to the middle of the screen and are figured out with the same principles as with the ailerons (3). Right in the middle of the screen, the Pitch Trim is illustrated, whereby the amount of degrees is illustrated (4). In the bottom of the screen, the rudder is displayed (5). It has been illustrated with a green index like the rudder, displayed on a scale to watch the direction of the rudder.

1. Speed brakes 2. Ailerons 3. Elevators 4. Pitch trim 5. Rudder

Figure 3.1 Display of the flight control surfaces B Hydraulic system Next to the flight control surfaces, there is also the hydraulics displayed on the screen (figure 3.2). Hereby the amount of pressure in the three compartments of the hydraulic system (1) and the amount of energy coming from the AC-busses (2) are illustrated. In this picture it is shown that all the three hydraulic compartments are dealing with the same amount of pressure and the generators are in the same situation. Another info that comes in handy and which is illustrated in the same screen is the amount of fuel and the temperature in the hydraulic system.



1. Hydraulic pressure 2. AC busses

Figure 3.2 Display of the hydraulic systems

3.2 Design Aspects With the new flight control system installed on the Boeing 737 come new beneficial aspects. There are new safety measurements installed (3.2.1), new maintenance procedures have been developed for the new system (3.2.2.). New backup systems need to be installed (3.2.3).

3.2.1 Safety By converting the Boeing 737’s flight control system into a fly-by-wire system, it will become safer. The conventional system only provides a warning tone and a vibration warning when the plane is entering a dangerous position. The fly-by-wire system not only gives a warning, it also gives a correction to prevent the airplane from getting into a dangerous position. By using a fly-by-wire system it becomes almost impossible to put the airplane in a dangerous position because the computers limit the move-ments of the plane so there is not too much stress on the airframe (A). Therefore the maximum load factor will not be surpassed. The movements of the plane become more stable because computers process the signal. This system also reduces the workload of the pilot. In event of a failure in one of the flight controls, the E/WD page shows the type of failure (B). The F/CTL page shows a schematic view of the flight control system and the location of the failure, it also shows which systems are active (C). A Normal law The pilot’s input into the computer can be seen as a rate of demand. The normal law that the comput-ers follow, exists out of 3 phases. The first one is the ground phase when the plane is on the ground, the second one is the flight phase which starts as soon as the plane leaves the ground. The third phase is the flare phase, this is during the landing and it gives the pilot an artificial feel of the move-ments of the airplane. The computers make sure that every movement is steady and controlled. If the steering column is moved all the way to the left the computers will calculate according to the planes speed what the maximum deflection of the ailerons will be. The computers also get a feedback from the control surfaces so that they can process the pilots demand accurately. This means that even if the control column is all the way to the left the ailerons deflection can be adjusted by the computer. The computers also make sure that the banking of the plane will not exceed 67˚. If, for example, the speed is low and the angle of attack is high, the computers help with the secondary flight controls. For example if the pilot is not able to retract the LE slats this is called high angle of attack protection. Turn co-ordination and dutchroll damping are also done by the computers so that the pilot does not have to use the rudder pedals when entering a turn. A protection is installed for high speed.



B E/WD page An E/WD page can be seen in the cockpit and it shows the pilots if there are any failures and it also provides the pilot with a checklist to solve the problem. This means the pilot does not have to use an operation manual when a failure occurs. In this way the pilot can operate quickly and more efficient. C F/CTL page An F/CTL page is located underneath the E/WD screen so that the information about the failure that occurred can be found quickly and accurate.

3.2.2 Maintenance Maintenance procedures on the modified Boeing 737 will change with the installation of the fly-by-wire system. The day-to-day maintenance that consists of a preflight check will not significantly change. The only advantage of the fly-by-wire system will be, that if there is a system failure, the relevant com-puter can be replaced. This due to the fact that the fly-by-wire computers are Line Replaceable Units (LRU). With larger maintenance checks like the D-check, the new system will reduce maintenance time on the flight control systems. This because the mechanical parts that move and therefore wear out are reduced. The new fly-by-wire computers do not need much maintenance because they are equipped with Built In Test Equipment (BITE). The BITE enables a system or computer to test itself, so if there is an error in a system it will be quickly detected by the BITE system therefore saving mainten-ance time.

3.2.3 Backup The systems on the Boeing 737 are powered up by multiple different power systems (appendix XVIII). These different systems are needed in case there is a loss of pressure in the hydraulic system. An electric driven pump powers up all the electric systems, like the flight computers. In case of a pressure loss in the hydraulic system, the electric driven pump will also power up the systems which were con-nected to the hydraulic system. In the worst case, when the hydraulic system as well as the electric driven pump is not functioning properly, there is also a Ram Air Turbine available. The RAT powers up the generator which is connected between the RAT and the flight controls. The RAT drives the genera-tor with its hydraulic energy and the generator converts it into the electricity that is needed to power up the flight controls.

3.3 Costs and Benefits A modification of a fleet from an airliner does not come without a price. Therefore all the costs that need to be made for the modification per airplane are estimated and calculated per category: the de-sign starting costs (3.3.1) and the installation, material and test costs (3.3.2). In case of very expensive projects the benefits are interesting, because these indicate if the project has enough benefits to main-tain the profits (3.3.3). All costs in the paragraph are estimates because precise costs could not be obtained.

3.3.1 Design Starting Costs Before the actual design can be purchased and installed in the airplane, there are some pre modifica-tion costs attached to the operation; the designers need to be paid, the flight crews and ground me-chanics need to be re-educated on the new design, the training simulator needs to be modified to the new cockpit lay-out and handling characteristics and the design needs to be tested and certified via the official aviation authorities. All the design starting costs only have to be paid once and these will not be paid for every modified airplane. There are three different kind of design starting costs:

1. Development costs 2. Training costs 3. Certification costs

ad1 Development Costs The design of the new flight control system is done by the research department of ALA. The estimated costs for used employees and recourses have been calculated (table 1).



Table 1 Costs Number of

employees Total hours

p/p Hour wage Extra information Total costs

Development design

8 1120 p/p €50,- 52.000,- for materials, rent office, etc.

€500.000,-

Total: €500.000,- The design team consists of eight people, with an hour wage of €50,-. The team worked 1120 hours per person on the project and have used €52.000,- for materials, office space, and other expenses. This brings the design development costs at €500.000,-. This is a onetime calculated cost. ad2 Training Costs Due to a change in cockpit and maintenance, both the flight crew and ground mechanics need to be re-educated on the design and handling characteristics. There are 36 pilots and 36 ground mechanics who are qualified to maintain and operate the airplane. The flight crew trains in six groups of six pilots for a period of five days. The reason is to keep enough pilots on the deployment planning for the usa-ble airplanes while one of the airplanes is in the hanger. The flight simulator needs to be modified to complement the new cockpit design features. The ground mechanics train in three groups of twelve persons for a period of four days. This is done to have enough people available in the hanger for the modification and regular repair works. The costs for training the flight crew and ground mechanics are listed (table 2). Table 2 Costs Number of em-

ployees Total hours

p/p Training per hour Total costs

Training Pilots 6 x 6 240 €250,- €60.000,- Training Maintenance crew 3 x 12 98 €250,- €24.000,- Modifying Flight simulator 1 x €200.000,- Total: €284.000,-

The training costs are consistent for both the flight crew as the ground mechanics and is rated at €250,- per hour. Both the flight crew as the ground mechanic crew consists of 36 people, which are in total 72 people that need to be trained. The six flight crew training teams and the three ground crew training teams use estimated 40 and 32 hours per group with an total training estimate of €84.000,-. The modification of the flight simulator is estimated at €200.000,-. Due to the fact that there are new procedures and extra computers are installed to fly the airplane, brings the training costs to a total estimate of €284.000,-. ad3 Certification Costs The design needs to be certified before the modified airplane are legally allowed to fly. The certifica-tion is done by the European Aviation Safety Administration (EASA) and the Dutch ministry of trans-portation and waterways aviation department. Without the approval of these organizations the mod-ified airplanes are not allowed to fly in the Netherlands or any other European country. The costs for these certifications are listed (table 3). Table 3 Costs Quantity Cost per design Extra info Total costs Certifying 1 x €250.000,- €250.000,- Total: €250.000,-

The certification costs for the design is estimated at € 250.000,-.



The total starting costs for the design are the following costs (table 4): Table 4 Costs Quantity Total costs Development design 1 x €500.000,- Training 1 x €84.000,- Certificating the design 1 x €250.000,- Modify the Simulator 1 x €200.000,- Total: €1.034.000,-

With the estimated starting cost for the project that is calculated, the design modification and the bene-fits can now be researched and calculated for a total price for the airliner.

3.3.2 Installation, Material and Test Costs The development costs are onetime costs. The costs of the modification and the materials are costs that are needed at every airplane. The modification is being done during the D-check to keep the AOG costs low. Because it is not possible to finish the modification completely during the D-check an extra five days will be needed to finish the modification. These five extra days translates into extra costs for hangar rent and for the lease of the airplane, to replace airplane which is modified. The costs for the installation process that is performed by three shifts that consists of twelve ground mechanics for a additional five days needs to be added (table 5). Table 5 Costs Quantity Time Price Total costs Install 3 × 12 pers. 180 hours €100,- p/hour €18.000,- Hangar rent 1 5 days €20.000,- p/day €100.000,- Lease airplane 1 5 days €100.000,- p/day €500.000,- Total: €618.000,-

The new fly-by-wire system will need new parts to replace the old parts from the conventional system. The old mechanical parts will be replaced by computers. ARINC data bus cables will be installed to replace the steel cables. The overhead panel has to be modified to make room for the computer switches. Because the PCU’s receive the input mechanically modification packages has to be installed so the PCU’s can receive an electric signal (table 6). Table 6 Material cost Quantity Price Total costs ELAC 2 €20.000,- €40.000,- FAD 2 €20.000,- €40.000,- FCDC 2 €20.000,- €40.000,- SEC 3 €20.000,- €60.000,- SFCC 2 €20.000,- €40.000,- Overhead panel 1 €500,- €500,- ARINC cables 460m €10,- p/m €4.600,- D/A Converter 6 €300,- €1.800,- A/D Converter 6 €300,- €1.800,- Modification packages PCU’s

34 €200,- €6.800,-

PCU 5 €50.000,- €250.000,- RAT 1 €150.000,- €150.000,- Feel computer 2 €10.000,- €20.000,- Total: €655.500,-

A test flight at the end of the modification is needed to test if all the primary and secondary flight con-trols and there backup systems work properly (table 7). Table 7 Test flight cost Quantity Price Total costs Test flight 1 €100.000,- €100.000,- Total: €100.000,-



The total costs are per airplane and without the design starting costs (table 8). Table 8 Cost Quantity Total costs Install, hangar and airplane lease 1 €618.000,- Materials 1 €655.500,- Test flight 1 €100.000,- Total: €1.373.500,-

The total project costs are the start costs with an addition of the modification costs. The sum of these costs is: €7.901.500,-.

3.3.3 Benefits The conventional flight control system needs to have a relative small maintenance check eight times a year. This small check is the A check. The aircraft on ground (AOG) time is one full day. The C check is a bigger check and takes place once every year. The AOG for the C check is a full week. Once every 5 year the airplane must be fully stripped. This is the D check. The AOG for the D check is 30 days. The total costs for these checks are calculated with AOG costs which are €48.800,- per day. This is included loan costs and airplane hangar rent. Loan costs are calculated for three shifts of twelve em-ployees with loan costs defined at €100,- an hour, working eight hours per shift. The rent for an air-plane hangar is €20.000,- per day. The total maintenance costs per year with this conventional system will be €1.024.800,- (table 9). Table 9 Costs Times per year AOG AOG costs p/d Total costs A check 8 x 1 day €48.800,- €390.400,- C check 1 x 7 days €48.800,- €341.600,- D check 0.2 x 30 days €48.800,- €292.800,- Total: €1.024.800,-

When the Boeing 737 is modified with a new control system it will lead into a decrease of the AOG time needed for maintenance reasons. The A check does not change but the AOG for the C and D check will decrease because of the replacements of mechanical parts into wires it is easier to main-tenance this new system. The C check last half a day shorter and the D check even last two days shorter than the AOG of the convention system. The total maintenance costs per year with this new modified system will be €980.880, - (table 10). Table 10 Costs Times per year AOG AOG costs p/d Total costs A check 8 x 1 day €48.800,- €390.400,- C check 1 x 6,5 days €48.800,- €317.200,- D check 0.2 x 28 €48.800,- €273.280,- Total: €980.880,-

The modified Boeing 737 weights 200kg less than the conventional system due to the replacements of mechanical parts, cranks and steel cables. In this calculation model the price paid by the airline per kilogram is set to €5,-. This is based on the price which passengers have to pay per kilogram. The price which is asked by the airlines for overweighed luggage varies around €35,-. Assuming a modified airplane makes 3 flights per day and has 20 days AOG time per year will result into 1034 flights per year per airplane. A decrease of 200 kg in weight per airplane will lead into a decrease of weight costs of €5.170.000,- per year for five Boeing 737s. (table 11). Table 11 Costs saves Flights per year Weight save costs p / kg Total save Due to weight decrease

1034 200 kg €5, - €1.034.000, -

x 5 airplanes Total: €5.170.000, -



The total project costs are calculated with the start costs and the modification costs. The sum of these costs is: €7.901.500,-. This amount is the total investment for the five Boeing 737 modifications (figure 3.3).

Figure 3.3 Costs comparison for the Boeing 737 flight control system

The conventional system does not have start costs that is why the difference at the start is almost eight million euro. Although the AOG costs for the modified system are less than the conventional system AOG costs the first 60 years this will not lead into a benefit (formula 1).

3.4 Conclusion and Recommendation By using the information from the flight control investigation a conclusion can be drawn about the mod-ification of the fly-by-wire system in the Boeing 737 (3.3.1). In this conclusion it will become clear if it is profitable to install this fly-by-wire system. By using this conclusion a recommendation or a dissuasion can be given (3.3.2).

3.4.1 Conclusion Having gained information about flight controls, a fly-by-wire system is investigated. The fly-by-wire system is compared to the conventional system of a Boeing 737. Beside this information the laws and requirements have been taken in account. After the benefits and drawback investigation the fly-by-wire system turned out to be a very safe sys-tem. The A320 has a system that prevents stalling or overstressing the airplane. A fly-by-wire system weights less than the conventional system on the Boeing 737, with the result that less fuel is required. The amount of maintenance required has reduced slightly. The moving parts of the Boeing 737 need more maintenance than the electric system in the A320. The costs of the installation and the checks that are required are relatively high, but for the conven-tional system the maintenance costs are higher. The starting costs are almost eight million euro. Mon-ey is saved because the airplane has less weight and needs less maintenance.

0

5

10

15

20

25

30

35

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

Cu

mu

lati

ve

co

sts

in m

illi

on

s E

uro

s

Time in years

Costs comparison for five airplanes

Conventional

Modified

Breakeven point calculation Formula 1

� & ' · �()�*+. -– /

� ' · �() 0*1.

S = start costs y = years AOG mod. = AOG costs modified system AOG con. = AOG costs conventional system w = weight costs saves modified system

S in Euro y in years AOG per year w in Euro



3.4.2 Recommendation The fly-by-wire system is very safe and has less weight than the system in the Boeing 737. Less main-tenance is needed for the fly-by-wire system. When a comparison is made between the costs of the conventional system and the fly-by-wire system, the fly-by-wire system has no benefits at all. This is not enough money to recommend the system. The expected service span of a Boeing 737 is estimated around 15 years. Our breakeven point is reached after 60 years. Therefore the modification is too expensive and not profitable. The fly-by-wire system is dissuaded. Despite the fact that it is a very safe and light system, the system is not profitable because of the costs.



Bibliography

Airbus company A320 Flight Crew Operating Manual Revision 34 Revision date: October 27 2001 Anderson, John D., jr. introduction to Flight 5th edition New York, 2005 Davis, D.P. Civil Aviation Authority, United Kingdom Handling the Big Jets 3rd edition London, 1988 Graaf, I.de Vliegtuigaërodynamica theorieboek 1 4th edition Bleskensgraaf, 2003 Graaf, I.de Vliegtuigaërodynamica theorieboek 2 1st edition Bleskensgraaf, 1999 Kermode, A.C. Mechanics of Flight 8th edition London, 1979 Langedijk, C.J.A. Vliegtuigen voor B1 en B3, deel A Amsterdam, 1991 Hogeschool van Amsterdam Mosbach, B. Theorie voor privévliegers 10th edition Wassenaar, 1996 Shevell, Richard S. Fundamentals of flight 2nd edition Prentice-Hall, 1983 Underdown, R.B. Ground studies for pilots Navigation General and Instruments (Vol.3) 5th edition Oxford, 1993 Uitgeverij Jeweka b.v. Vliegtuigaerodynamica, constructies en systemen voor vliegtuigonderhoud Deel 1 en 2 A. Kouseband R. De Moor



J. Stoffelen Januari 2007 Wentzel, Tilly Het projectgroepsverslag Amsterdam, 2008 Hogeschool van Amsterdam Domein Techniek US Department of transportation Federal Aviation Administration Pilot's Handbook of Aeronautical Knowledge Flight standards Service 2003 US Department of transportation Federal Aviation Administration Airplane Flying Handbook Flight standards Service 2004 Aircraft Operations Manual [AOM] Boeing 737 (KLM en Boeing) Basic Operations Manual [BOM] KLM Boeing 737( -700, -800, -900) Operations Manual Boeing 737 (-600, -700, -800) maintanance manual (AMM) Flight crew Reference Guide [FRG] KLM Service manual Cessna 172 1977 Airbus A320 operation manual Websites: www.B737.org.uk http://www.grc.nasa.gov/WWW/K-12/airplane/alr.html www.dutchops.com www.smartcockpit.com



List of appendices

I. Abbreviation List 1 II. Airfoils 2 III. Grafity formula 3 IV. Rudder Pedals 4 V. Trailing Edge Devices 5 VI. Leading Edge Devices 6 VII. CS-23 7 VIII. CS-25 8 IX. Primary Flight Controls Boeing 737 9 X. Hydraulic System Boeing 737 10 XI. Aileron Control System Boeing 737 11 XII. Elevator Control System Boeing 737 12 XIII. Rudder Control System Boeing 737 13 XIV. Ground Spoiler System 14 XV. Fly-by-wire flight control system 15 XVI. Secondary Flight Controls Airbus A320 17 XVII. Pedalstal 18 XVIII. Location fly-by-wire parts 19 XIX. General flight control architecture 20 XX. Informatie groepsleden 21 XXI. Planning 22 XXII. Procesgroepsverslag 23



I. Abbreviation List

Short term:

Full word: Explanation: Found on page:

α Alpha; angle of attack The angle between the chord line and the air-stream

2, 3, 4, 6

AC Alternate Current Flow of electric charge periodically reverses direc-tion

18

AOG Aircraft On Ground Time the aircraft is not flying due to maintenance 28, 33, 34, 35

BITE Build In Test Equip-ment

Enables a system to test itself 31

�� Drag coefficient Used to denote the dimensionless statistic of drag 3 �� Lift coefficient Used to denote the dimensionless statistic of lift 3, 4, 6 CS Certification Specifica-

tions Law for aero planes 14, 15

EASA European Aviation Safety Agency

Agency of the European Union in the field of avia-tion safety

14, 32

ECAM Electronic Centralized Aircraft Monitor

Monitor which gives information about position of flight controls

25

ELAC Elevator Aileron Com-puter

Device which measures signals from side stick (input) and computes it for output

23, 24, 26, 27, 29, 30, 33

FAC Flight Augmentation Computer

Device used for electrical control of the rudder 24, 26, 27, 30, 33

FCU Feel Centering Unit Determines current position of flight control sur-face

22, 30

FFM Force Flight Monitor Detects difference in pressures between actuators 20, 23 LE Leading Edge Edge of the wing facing forward during flight 2, 12, 20, 21,

23, 26 LRU Line Replaceable Unit A complex component of an airplane that is de-

signed to be replaced quickly at the organizational level.

31

NACA National Advisory Committee of Aero-nautics

A U.S. federal agency founded in 1915 to under-take, promote and institutionalize aeronautical research

2

PCU Power Control Unit Unit which powers the control movement of the flight control surfaces

18, 19, 20, 23, 29, 30, 33

PDU Power Drive Unit Activates the flap drive system and supplies me-chanical feedback to the flight control valve

20, 30

RAT Ram Air Turbine Turbine which obtains hydraulic pressure 27, 29, 33, 35

SEC Spoiler Elevator Com-puter

Computer which activates the spoilers according to the phase of flight

26, 27, 30, 33

SFCC Slat and Flap Control Computer

Computer which calculates the amount of deflec-tion

26, 30, 33

TE Trailing Edge Edge of the wing facing backwards during flight 2, 11, 20, 21, 23, 26

THS Trimmable Horizontal Stabilizer

Horizontal stabilizer which can deflect up or downwards to trim the airplane horizontally

23, 26



II. Airfoils

A symmetric cambered airfoil (figure 1.1a) only gets lift forces when it has a positive α. The lower and upper surface is now mirrored at the chord. One of the noticeable characteristics of a symmetric cam-bered airfoil; the �2 line comes from the source of the diagram (figure 1.1b). This is because an α at 0° has �2 of zero as well. Also the lowest value of �3 is at an α of 0° (figure 1.1c). Now the maximum air-speed can be reached when the airfoil is at an α of 0°. The wing characteristic follows when �2 and �3 gets combined (figure 1.1d).

a

b c d Appendix figure 1.1 Symmetric cambered airfoil

A negative cambered airfoil (figure 1.2a) creates a down force at an α of 0°. This airfoil only creates lift when it’s in a big positive α. Notice the negative �2 value at a 0° α (figure 1.2b). The minimum �3 val-ue is at a positive α (figure 1.2c). When the �2 and �3 gets combined the wing characteristic is found (figure 1.2d). Negative cambered airfoils are used as horizontal stabilizer for the balance of gravity forces. In modern wings a part of the wing can be cambered negative this part is often at the root of the wing near the fuselage.

a b c d Appendix figure 1.2 Negative Cambered Airfoil



III. Gravity formula

Gravity The gravity is a result of the mass of the airplane. As a result of the mass of the airplane and other objects that are flying in the air, they are pulled down to the earth surface by the gravity. The scientist Isaac Newton became very famous with his formula about his idea of the gravitation. One of his lines of gravitation was; “The law says that the gravitational force between two objects is inversely (oppo-sitely) proportional to the distance between the two objects squared (Multiplied by itself)”. For instance when you have two objects whose distance is being doubled, the gravitational force between them is cut to one fourth of their originally gravitational force. Gravity Formula 1 � � m1 � m2/+2

F= Gravitational Force m= masses of the objects d= distance between the two objects squared

F in N m in kg d in m

This means that the higher the airplane is flying, the less gravitational force the airplane experiences. Drag Isaac Newton has multiple famous formulas designed. Next to the formula about gravitation the formu-la he designed for drag is also very famous. Drag Formula 2 6 � 7 � 82 � � � �+

D= drag K= pressure factor V=velocity squared A= wing area Cd=dragfactor

D in N K in Pa V in m/s2

A in m2

Cd in N



IV. Rudder Pedals

The rudder is controlled by the rudder pedals (figure 1.3). There are two sets of pedals, one for the left seated pilot (1) and one for the right seated pilot (2). When the right pedal is pushed forward, the right cable (3) moves forward and moves the left cable (4) backwards, and because the left pedal is con-nected to the left cable, the left pedal moves backwards. The return spring (5) is used to bring the rudder pedals back in the neutral position. The rudder pedals are also used as brake pedals, to use the brakes the tip of the pedals has to be push down instead of forward. This motion controls the brake cylinder (6). Figure 1.3 Rudder pedals

1. Left seated pilot pedals 2. Right seated pilot pedals 3. Right cable 4. Left cable 5. Return spring 6. Brake cylinder



V. Trailing Edge Devices

These are figures of different kind of flaps that are generally used on airplanes. There is the plain flap, The split flap and the slotted flap.

Figure 1.4 Plain flap

Figure 1.5 Split flap

Figure 1.6 Slotted flap



VI. Leading Edge Devices

These figures of the leading edge devices that are found in combination or alone on the leading edge of airplanes

Figure 1.7 Fixed slot

Figure 1.8 Krueger flap

Figure 1.9 Slat



VII. CS-23

This is the part of the Certification Specification-23 concerning flight controls on small airplanes. CS 23.395 Control system loads (a) Each flight control system and its supporting structure must be designed for loads correspond-ing to at least 125% of the computed hinge mo-ments of the movable control surface in the condi-tions prescribed in CS 23.391 to 23.459. In addi-tion, the following apply: (b) A 125% factor on computed hinge movements must be used to design elevator, aileron and rud-der systems. However, a factor as low as 1·0 may be used if hinge moments are based on accurate flight test data, the exact reduction depending upon the accuracy and reliability of the data. CS 23.865 Fire protection of flight controls, engine mounts and other flight structure (See AMC 23.865) Flight controls, engine mounts, and other flight structure located in designated fire zones, or in adjacent areas that would be subjected to the effects of fire in the designated fire zones, must be constructed of fireproof material or be shielded so that they are capable of withstanding the ef-fects of a fire. Engine vibration isolators must incorporate suitable features to ensure that the engine is retained if the non fire proof portions of the isolators deteriorate from the effects of a fire. CS 23.155 Elevator control force in manoeu-vres (a) The elevator control force needed to achieve the positive limit manoeuvring load factor may not be less than – (1) For wheel controls, W/10N (where W is the maximum weight in kg) (W/100 lbf (where W is the maximum weight in lb)) or 89 N (20 lbf), whi-chever is greater, except that it need not be greater than 222 N (50 lbf); or (2) For stick controls, W/14N (where W is the maximum weight in kg) (W/140 lbf (where W is the maximum weight in lb)) or 66·8 N (15 lbf), whichever is greater, except that it need not be greater than 156 N (35 lbf). CS 23.149 Minimum control speed (e) At VMC, the rudder pedal force required to maintain control must not exceed 667 N (150 lbf) and it must not be necessary to reduce power of the operative engine . During the manoeuvre the aeroplane must not assume any dangerous atti-tude and it must be possible to prevent a heading change of more than 20°.



VIII. CS-25

This is the used part of the certification specification-25 concerning the flight controls on large air-planes. CS 25.865 Fire protection of flight controls, engine mounts, and other flight structure Essential flight controls, engine mounts, and other flight structures located in designated fire zones or in adjacent areas which would be subjected to the effects of fire in the fire zone must be con-structed of fireproof material or shielded so that they are capable of withstanding the effects of fire. CS 25.671 General (b) Each element of each flight control system must be designed, or distinctively and permanent-ly marked, to minimise the probability of incorrect assembly that could result in the malfunctioning of the system. (See AMC 25.671 (b).) CS 25.395 Control system (a) Longitudinal, lateral, directional and drag con-trol systems and their supporting structures must be designed for loads corresponding to 125% of the computed hinge moments of the movable control surface in the conditions prescribed in CS 25.39 CS 25.689 Cable systems (a) Each cable, cable fitting, turnbuckle, splice, and pulley must be approved. In addition – (1) No cable smaller than 3.2 mm (0·125 inch) diameter may be used in the aileron, elevator, or rudder systems; and CS 25.149 Minimum control speed (See AMC 25.149) (d) The rudder forces required to maintain control at VMC may not exceed 667 N (150 lbf) nor may it be necessary to reduce power or thrust of the operative engines. During recovery, the aero-plane may not assume any dangerous attitude or require exceptional piloting skill, alertness, or strength to prevent a heading change of more than 20º.



IX. Primary Flight Controls Boeing 737

This illustration shows the flight control positions, both the primary- as the secondary flight controls on the Boeing 737



X. Hydraulic System Boeing 737

This is the hydraulic system diagram of the Boeing 737. Shown are the systems fed by system A, system B and standby system.



XI. Aileron Control System Boeing 737

The working of the aileron controls on the Boeing 737 is shown in this illustration. Noticeable is that the aileron transfer also uses a spoiler mixer for banking. Which can be manually activated via the spoiler system A,B switches on the overhead panel.



XII. Elevator Control System Boeing 737

The working of the elevator controls on the Boeing 737



XIII. Rudder Control System Boeing 737

The working of the rudder control as well as the yaw damper on the Boeing 737



XIV. Ground Spoiler System

The working of the ground spoiler system on the Boeing 737



XV. Fly-by-wire flight control system

The Fly-By-Wire system is a type of control system that uses computers to move the control surfaces. The development of this system was done by the NASA for the flight controls of their space shuttle program (A). Now the system is broadly used by civilian as military airplanes (B). Airbus uses its FBW systems with extra safety programs installed to ensure airplane safety in normal and abnormal use (C). A Development of the fly-by-wire flight control system The fly-by-wire control system was developed in the 1970s by the NASA flight research center for their space shuttle program. The Airplane that served as a test bed, used an Flight control computer from the Apollo spacecraft, which was modified to comp with: atmospheric flight and wings. The principle of the system was than installed in the test space shuttle “Enterprise”. Among the tests an important feature of the fly-by-wire system was developed and tested to overcome Pilot Induced Oscillation. This means that the pilot corrects the aircraft in opposite directions in a short amount of time, to cover up and correct the previous movement. With both the frequencies of the pilots input and the aircraft movement, the aircraft creates a oscillation movement. The FBW FCS was tested on this behavior and was reprogrammed to overcome this error of movement and input. This is also incorporated in the flight control system of the space shuttle. The program ended in 1985 and was the major start point of the modern Fly-By-Wire system. This system that is now incorporated in numerous aircraft around the world. With the introduction of this system, more complex and unstable aircraft could be developed without overstressing the pilot with controlling and correcting the aircraft. B The Fly-By-Wire system The fly-by-wire system has a functionality diagram of how the controls move.

First there is the side stick (1) with which the pilot gives an input (2). This signal is sent to the flight control computer (3) needed for the movement to happen. The autopilot (4) sends an independent signal to the flight control computer when autopilot is engaged. The computer sends a signal to the needed actuators (5) which make the flight control move (6). The output of the flight control (7) gives an feedback (8) tot the computer, which in turn gives a pilot feedback on position and movement of the airplane. The Fly-By-Wire system is broadly used today by both the military and civilian world. This system is broadly used because: in the military world, wires are less vulnerable of damage due to combat than hydraulic lines and steel cables. It makes the used aircraft more reliable and makes them lighter to use. Giving them the ability to carry more fuel, cargo or combat ordnance. In the civilian world it is broadly used to ease pilot work load, compensate for pilot error and lighten the airplanes in weight, giving them more range or they can carry more fuel ,passengers or cargo. Also the ability to fly with les stable designed airplanes makes this a highly benefitual system for high performance aircraft. The fly-by-wire system these days consists of multiple computer systems that control various controls on the aircraft, but not all. For example the airbus flight computer hierarchy. All the primary and sec-ondary flight controls are divided over 11 control computers. In case of a computer failure another



takes over. This does not mean it takes over al the controls but for example the half of the controls go to one computer, the other half goes to the second computer. The computers used in the Airbus for flight control are the: SEC, ELAC, FAC, SFCC. There are two ELACs which control the elevator and stabilizer, three SECs which control the spoilers and standby elevator and stabilizer control, two FACs which control the rudder and two SFCC which control the slats and flaps. In fighter aircraft there could be two or three flight computers which control and stabilize the aircraft what makes trim tabs obsolete on these aircraft. C Airbus fly-by-wire system The airbus fly-by-wire system differs from the standard fly-by-wire systems because it has integrated laws, better known as system restrictions. This means that the pilot cannot overstress, over steer or do something stupid to jeopardize the safety of the passengers, cargo and the airframe. With this system the chance to hit stall is reduced to a minimum because the computer does not for example pitch up the aircraft nose higher than 15 degrees, because if that would happen the airplane would stall. There are bank restrictions too. If a pilot holds its stick fully deflected to left or right, the airplane would not exceed a bank angle of 67 degrees, also the use of the rudder pedals is almost not needed anymore, since the airplane makes controlled coordinated turns without pedal input requirements. Because if this angle would be surpassed, the airplane could lose lift and crash. Also installed are speed and stalls seed restrictions. These make sure that an aircraft could not over speed or stall at certain speeds. With the help of these systems the airbus system is more safer than an ordinary fly-by-wire system. But this system can be turned off in case of system breakdowns. Some of the safety laws are disen-gaged what makes it possible to over roll the airplane, or to pitch up at to high angles making the air-craft stall, or to over speed the aircraft or stall it. But the chances of this to happen when law is disen-gaged is high unlikely because behind the controls there is still a certified and skilled pilot who can control the airplane even without the use of flight computers. When this happens, this is a highly unlikely situation but it can occur. Then there is a backup backup system which is controlled via steel cables and rods. The little required power is received by a Ram Air Turbine and helps the pilot to control the rudder and THS. The pilot controls these surfaces via the rudder pedals and the horizontal trim wheels. This backup of the backup system makes it possible to control and land the airplane even when main power and hydraulics are offline. With the use of these systems the airbus airplanes are safe and reliable to fly and with the help of these systems the airbus A320 family was certified for transportation in and around Europe.



XVI. Airbus Secondary flight control computer/hydra ulic lines



XVII. Pedestal

1. spoilers 2. flaps 3. hor.trim 4. rud trim 5. rud trim angle and direction.



XVIII. Location fly-by-wire parts

Avionics bay with: 1. two ELAC’s 2. two FAD’s 3. two FCDC’s 4. two SFCC’s 5. three SEC’s

Flight deck with: • two control columns • two feel computers • rudder pedals • flap handle • speed brake • modified overhead panel

Left and right wing with each: • main aileron PCU • two Krueger flap PCU’s • four slat PCU’s • six spoiler PCU’s • standby aileron PCU

MLG wheel well with: • Flap PDU

Vertical stabilizer with: • main rudder PCU • standby rudder PCU

Empennage with: • two elevator PCU’s • standby elevator PCU

Ram Air Turbine

Black color represents normal operations Red color represents backup

Mechanical backup THS



XIX. General flight control architecture

Hogeschool van Amsterdam Domei

Project: Modification flight controls

XX. Informatie groepsleden

Terence Bottse Gershwinstraat 281323 RR [email protected]@hva.nl _________________________________ Anouk ElsendoornZandkreek 613823 JK [email protected]@hva.nl Vincent MooijKamille 14 8252 CA [email protected]@hva.nl __________________________________ Maxine de VriesUiterweg 2351431 AG Aalsmeer0297-3609020644648963maxine_is_lief@[email protected]

Hogeschool van AmsterdamDomein Techniek


Informatie groepsleden

Terence Bottse

Gershwinstraat 28 1323 RR Almere 0614043270

[email protected]@hva.nl

_________________________________

Anouk Elsendoorn Zandkreek 61 3823 JK Amersfoort

21428967 [email protected]@hva.nl

Vincent Mooij

Dronten 47191816


__________________________________

Maxine de Vries Uiterweg 235 1431 AG Aalsmeer

360902 0644648963 [email protected]@hva.nl

Hogeschool van AmsterdamTechniek



[email protected]

_________________________________

[email protected] [email protected]

[email protected]

__________________________________


Hogeschool van Amsterdam



_________________________________

__________________________________

2008/2009


Robbert Coller Leverkruid 91964 KL [email protected]@hva.nl ________________________ Remco van HeumeBos en Lommerweg 214 III1055 EJ, [email protected]@hva.nl ____________________________________ Rick van den MuckhofKoppertweg 305962 AL [email protected]@hva.nl ____________________________________ Sander WestraKarel Doormanplantsoen 22121XA [email protected]@hva

Robbert Coller Leverkruid 9 1964 KL Heemskerk06-11920203 [email protected]@hva.nl ________________________ Remco van HeumeBos en Lommerweg 214 III1055 EJ, Amsterdam0641776629 [email protected]@hva.nl ____________________________________ Rick van den MuckhofKoppertweg 305962 AL Melderslo06-59632276 [email protected]@hva.nl ____________________________________ Sander WestraKarel Doormanplantsoen 22121XA Bennebroek06-51756987 [email protected]@hva

Robbert Coller

1964 KL Heemskerk


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Remco van Heume n Bos en Lommerweg 214 III1055 EJ, Amsterdam


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Rick van den Muckhof Koppertweg 30 5962 AL Melderslo


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Sander Westra Karel Doormanplantsoen 22121XA Bennebroek


Project Team 2A1Z

________________________

Bos en Lommerweg 214 III


____________________________________


____________________________________

Karel Doormanplantsoen 2

[email protected]

Project Team 2A1Z

21

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XXI. Planning

Project taken Uitvoerder(s)

week nr --->> 1 2 3 4 5 6 7 8

1. Defenition of flight controls

1.1 Theory

1.1.1 Wings vincent

1.1.2 Aerodynamics Sander

1.1.3 Forces around the airframe Rick

1.2 Flight controls

1.2.1 Primary flight controls Anouk;Robbert

1.2.2 Secondary flight controls Terence;maxine

1.3 Laws and regulations Remco

1.3.1 Legal laws

1.3.2 Client regulations

1.4 difference small vs large airplane vincent

1.5 Functionality research Terence

1.6 conclusion Remco

2. Flight controls on the B737 and

A320

2.1 Boeing 737

2.1.1 Hydraulics Robbert

2.1.2 Primary flight controls Robbert

2.1.3 Sencundary flight controls Maxine

2.1.4 Bakc up Remco

2.2 Airbus A320

2.2.1 Primary flight controls Anouk

2.2.2 secundary flight controls Terence

2.2.3 back up Rick

2.3 difference A320 B737 Sander

2.4 Benefits vs drawbacks vincent

2.5 Conclusion Remco

3. modification program

3.1 FBW instalation Anouk

3.2 Design Aspects

3.2.1 Safety Rick;Maxine

3.2.2 Maintanance Robbert

3.2.4 Back-up remco;Sander

3.3 Costs and benefits

Te-

rence;Robbert;Vincent

3.4 conclusion and reccomendation Anouk;groep

3.4.1 conclusion

3.4.2 recomendation



XXII. Proces groepsverslag

Met dit procesverslag kijken we terug op het verloop van het project, zowel het goede als de slechte momenten. Het begon heel erg strak en met een goede inzet van de groep, met de kennis van het vorige project nog in het hoofd werden de vergaderingen krachtig gehouden en het werk direct strak verdeeld over de groep. Frenchez werd dan minder effectief gebruikt als informatie bron als hij zelf had gehoopt, maar toch waren zijn bijgeschreven opmerkingen meestal wel een teken dat het de goede kant op ging. De vergaderingen waren aan het begin vol bezocht, maar later werd dit van een paar groepsle-den infrequent en begon de aanwezigheid van de groep in te krimpen. Gelukkig heeft dit niet tot ver-wijderingen of uitval van de groep tot gevolg gehad. Er zijn een paar punten gegeven aan twee men-sen, maar de groep bleef doorwerken. De gemaakte notulen waren snel te vinden op BSCW, de een wat beter als de ander maar soms ook heel erg vaag. De voorzitters waren bijna allemaal wel bekwaam in hun vak en de notulisten net zo, maar soms zou iemand anders wel ff de taak van een van de twee moeten overnemen voor duidelijkere instructies en notulen. Het project verliep bijna geheel volgens planning en na ieder hoofdstuk was er een goed nakijk mo-ment voordat frenchez het werk kreeg te zien. Het werk afgeleverd door de groep was over het alge-meen goed van kwaliteit en direct in een lay-out voor een gemakkelijke samenvoeging van het project aan het eind. Het project is afgekomen voor tijd en is met geen enkele lange schooldag en veel plezier gemaakt. Dit verslag kan nu op 24 maart worden ingeleverd bij de project docent door de nog steeds voltallige groep van acht man sterk. 2A1Z Werkoverzicht Terence Robbert Anouk Remco Vincent Rick Maxine Sander 1.2.2 1.2.1 1.2.1 1.3 1.1.1 1.1.3 1.2.2 1.1.2 1.5 2.1.1/2.1.2 2.2.1 2.1.3 1.4 2.2.3 2.1.2 2.3 2.2.2 3.3 3.1 3.2.1 3.3 3.2 3.2 3.2.5 3.3 3.2.2 3.4 summary Lay-out summary Lay-out

Hogeschool van Amsterdam Domein Techniek … van Amsterdam Domein Techniek Project Team 2A1Z...

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