aviationbangladesh.files.wordpress.com€¦ · Web viewAir is a mixture of gases, 78% nitrogen and...

Unit: 66 Theory of flight

Assignment 1: The ISA and Subsonic Airflow over Aerofoil Sections.

P1

a. What is International Standard Atmosphere? Define the parameters and their standard atmospheric values at sea level according to ISA.

Answer:

In 1920s the International Standard Atmosphere (ISA) is being developed and later on 1952 it’s being modified and introduced by International Civil Aviation Organization. It is a model where the atmospheric fixed information is given such as the pressure, temperature, and viscosity. The value changes as the altitude increases.

Atmospheric parameters and their standard atmospheric values at sea level according to ‘ISA’ are:

At sea level (msl), pressure = 1013.25 hPa

temperature = T0 15.0 degC

density = p0 1.225 kg/m3

speed of sound = a0 340.294 m/sec

acceleration of gravity = g0 9.80665 m/sec2

Figure: International standard atmosphere chart

BySifat Mohammad Rafsun Juny

1

https://www.facebook.com/Rafsunjuny

Unit: 66 Theory of flight b. Describe about the properties and behavior of air.

Answer:

Air is a mixture of gases, 78% nitrogen and 21% oxygen with traces of water vapor, carbon dioxide, argon, and various other components.

Figure: Air properties

Behaviors of air:

As the altitude increases the behaviour of air changes, the pressure, density, viscosity, temperature etc all r related to each other.

Atmospheric pressure and temperature:

The pressure of the atmosphere varies with time and location. Due to the changing atmospheric pressure, a standard reference was developed. The standard atmosphere at sea level is a surface temperature of 59 °F or 15 °C and a surface pressure of 29.92 in. Hg or 1013.2 mill bars.


2



Figure: Standard sea level pressure

A standard temperature lapse rate is one in which the temperature decreases at the rate of approximately 3.5 °F or 2 °C per thousand feet up to 36,000 feet. Above this point, the temperature is considered constant up to 80,000 feet. A standard pressure lapse rate is one in which pressure decreases at a rate of approximately 1 in. Hg per 1,000 feet of altitude gain to 10,000 feet.

The diagram below show the change in atmosphere in graphical order


3


Unit: 66 Theory of flight c. What is the purpose of using ISA chart?

Answer:

International Standard Atmosphere is used for aircraft. as the climate changes and the weather is not same everywhere, so a standard formats is used for a better performance of the aircraft.

The international atmosphere gives as stander measurement of weather given below:

At mean sea level (msl), the pressure = 1013.25 hPa and temperature = 15.0 degC

From msl to 11 km, a decrease in temperature (or lapse rate) of 6.5 degC/km

From 11 km to 20 km, the temperature is held to be isothermal (not changing) at a value of - 56.5 degC

From 20 km to 32 km, an increase in temperature of about 1 degC/km.

P2

a. Explain about dynamic and kinematic viscosity of air.

Answer:

Viscosity:

The resistance of a fluid to move through it. A “thin” fluid have a low viscosity and “thick” fluid have high viscosity. This is also known as fluid resistance, fluid friction, and internal friction.

Dynamic viscosity:

Dynamic viscosity is also known as absolute viscosity or coefficient of absolute viscosity. It is the resistance of liquid flow from one point to another at a given speed. The value depends on the temperature of the gas. The shear stress ratio of the velocity gradient is the technical form of dynamic viscosity and it is defined as Newtonian Fluid.

Kinematic viscosity:

Kinematic viscosity measures the resistance to flow the liquid in the presence of gravity and the ratio of a fluid's absolute viscosity is divided by the fluid’s density.


4


Unit: 66 Theory of flight b. Write down the difference between laminar and turbulent flow.

Answer:

Laminar flow:

Laminar flows are parallel flow it is characterized by layers, or laminas, of air moving at the same velocity. Laminar flow are smooth and do not interact. No air molecules are exchanged between the laminas air flow and the flow is not in a straight line.

Turbulent flow:

In turbulent flow, the flow lines are not organized, distributed in ever changing eddies. Air molecules of differing speeds bump into one another and their speeds are constantly changing.

Figure: laminar flow and turbulent flow.

P3

a. How does subsonic airplanes airfoil get lift?

Answer:

Airfoils are the Cross section area of a wing or propeller. They are shaped in such a way that they can produce maximum lift through fluid. A subsonic aircraft has maximum which is Mach 1 or less than Mach 1, which is less than the speed of sound sometimes.


5


Unit: 66 Theory of flight Subsonic flight airfoils have a rounded leading edge, followed by a sharp trailing edge; often with asymmetric camber. The lift on an airfoil is primarily the result of its angle of attack and shape. When oriented at a suitable angle, the airfoil deflects the oncoming air, creating a force on the airfoil in the direction opposite to the deflection.

b. Define all the terminology of a basic aerofoil.

Answer:

Aerofoil: An aerofoil is the cross-section area of a wing.

Figure: cross section area of an aerofoil.

Angle of attack (AOA):

It is the angle between the chord line and the relative wind. This will vary, depending on the longitudinal attitude of the aircraft with the respect of the relative airflow.

Leading edge and trailing edge:

These are the points on the center of curvature of the leading and tailing part of the aerofoil section that intersect the chord line.

Camber (upper and lower):

This is the term used for the upper and lower curved surface of the aerofoil. The mean camber line is the line draw halfway between the upper and lower cambers.

Chord line:


6


Unit: 66 Theory of flight It’s a line draw from the center connecting the leading edge and the trailing edge. It is the longitudinal dimension of an aerofoil.

Assignment 2: Flight Forces, Maneuvers Loads and Flight Envelopes.

P4

a. Write down the Bernoulli and Venture principles and their relationship to the generation of lift and the factors that affect lift generation over aircraft.

Answer:Bernoulli's principle:

In fluid dynamics, Bernoulli's principle states that for an in viscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy

where:

is the fluid flow speed at a point on a streamline,

is the acceleration due to gravity,

is the elevation of the point above a reference plane, with the positive z-direction pointing upward – so in the direction opposite to the gravitational acceleration,

is the pressure at the chosen point, and

P is the density of the fluid at all points in the fluid.

EQUTION :


7



Venture principal:

The Venture effect is a jet effect; as with a funnel the velocity of the fluid increases as the cross sectional area decreases, with the static pressure correspondingly decreasing. When a fluid such as water flows through a tube that narrows to a smaller diameter, the partial restriction causes a higher pressure at the inlet than that at the narrow end. This pressure difference causes the fluid to accelerate toward the low pressure narrow section, in which it thus maintains a higher speed. The Venture meter uses the direct relationship between pressure difference and fluid speeds to determine the volumetric flow rate.

Figure: venture tube.

The air across the top of a conventional airfoil experiences constricted flow lines and increased air speed relative to the wing.


8


Unit: 66 Theory of flight This causes a decrease in pressure on the top according to the Bernoulli equation and provides a lift force.

Figure: Aerofoil in motion.

While an airplane wing is one of the most popular examples of the Bernoulli Effect, the Bernoulli lift is actually a small part of the lift force which allows the aircraft to fly. The main lift comes from the fact that the wing is angled slightly upward so that air striking the underside of the wing is forced downward. The Newton's 3rd law reaction force upward on the wing provides the lift. Increasing the angle of attack can increase the lift, but it also increases drag so that you have to provide more thrust with the aircraft engines.

P5

a. Describe various kinds of drags.

Answer:

Drag is the force that opposes forward motion through the atmosphere and is parallel to the direction of the airflow. Drag must be overcome by thrust in order to achieve forward motion.

There are two main type of drag

1) Induced drag


9


Unit: 66 Theory of flight 2) Parasite drag

Induced drag:

Induced drag is the drag created by the vortices tip of an aircraft's wing. Induced drag is the drag due to lift. Induced drag increases in directly proportion to increases in the angle of attack. The circular motion creates a change in the angle of attack near the wing tip which causes an increase in drag. The greater the angle of attack up to the critical angle (where a stall takes place), the greater the amount of lift developed and the greater the induced drag.

Parasite Drag:

Parasite drag is comprised of all the forces that work to slow the plane down. There are 3 types of parasite drag: form drag, interference drag, and skin drag.

Figure: induce drag and parasite drag relation.

1. Form Drag

Form drag is the portion of parasite drag generated by the aircraft due to its structure and airflow around it. For example, engine cowlings, antennas etc.

2. Interference Drag

Interference drag comes from the intersection of air streams that creates eddy currents, turbulence, or restricts smooth airflow. For example, the intersection of the wing and the fuselage joint with the wing has significant


10


Unit: 66 Theory of flight interference drag. It is also highest when two surfaces meet at perpendicular angles.

3. Skin Friction Drag

Skin friction drag is formed due to the moving air around the surface of an aircraft. No matter how apparently smooth a surface appears, has a rough, ragged surface when viewed under a microscope. The actual speed at which the air molecules move depends upon the shape of the wing, the stickiness of the air through which the wing or airfoil is moving.

b. Write down the factors affecting for lift and drag forces for a propeller driven airplane.

Answer:

The affects and the amount of lift and drag a wing creates and the factors affecting lift and drag forces are:

The shape and size of the wing. The angle at which it meets the oncoming air. The speed at which it moves through the air and, Even the density of the air.

P6

a. Describe the basic four forces of flight.

Answer:

There are four major forces acting on an airplane. they are

LIFT

WEIGHT

THRUST

DRAG

While in steady-state flight, the attitude, direction, and speed of the

airplane will remain constant until one or more of the basic forces changes

in magnitude.


11


Unit: 66 Theory of flight Lift:

Lift opposes the downward force of weight, is produced by the dynamic

effect of the air acting on the wing, and acts perpendicular to the flight path

through wind and wing span.

As the angle of attack increases, lift increases. When the aircraft reaches

the maximum angle of attack, lift begins to diminish rapidly. This is the

stalling angle of attack, or burble point.

Weight:

Weight is the combined load of the airplane itself, the crew, the fuel, and

the cargo or baggage. Weight pulls the airplane downward because of

gravity. It acts opposite of lift, and vertically downward through the

aircraft’s center of gravity.

Thrust:

Thrust is the forward force produced by the engine. It overcomes the force

of drag. It acts parallel to the longitudinal axis. The thrust must be exerted

and be greater than drag to move an aircraft forward. The aircraft will

continue to move and gain speed until thrust and drag are equal.

In order to maintain a constant airspeed, thrust and drag must remain

equal, just as lift and weight must be equal to maintain a constant altitude.

Drag:

Drag is a rearward, retarding force, and is caused by disruption of airflow

by the wing, fuselage, and other protruding objects. Drag opposes thrust,

and acts rear-ward parallel to the relative wind. When the four forces are

equal, an aircraft is in a level flight. The plane goes up if the forces of lift

and thrust are more than gravitational force and drag .And if gravity and


12


Unit: 66 Theory of flight drag is more than lift and thrust, the aircraft goes downward. Four forces

are opposite to each other. Lift works opposite of weight and perpendicular

to relative wind. Thrust works opposite of drag.

When the weight is decreased while the lift is constant, the airplane will

rise and when then lift decrease while the weight is constant the aircraft

fall

Lift > Weight - Aircraft Rises

Weight > Lift - Aircraft Falls

When the thrust increasing while the drag is constant this will cause

accelerates the airplane. And increasing the drag at a constant thrust will

cause the airplane to slow down

Thrust > Drag - Aircraft Accelerates

Drag > Thrust - Aircraft Slows.

Figure: the effect of four force

P7


13


Unit: 66 Theory of flight Describe and write down the procedure of following flight modes for C 150/ C152/C 172/ ATR 72 airplane. And explain the forces resposible for turns.

Answer: The proceduer pf C152.

a) Steady level flight:

Figure: Steady level flight

Lower the nose of the airplane with reference to the horizon to acquire a steady and level attitude.

Firstly, we have to hang around for the airspeed which is settled at the required cruise speed for steady and level flight.

At about 5kts prior to the required cruise speed, have to start reducing power slowly via the throttle lever.

We should keep reducing power till the required airspeed is attained.

Now we must bring to a close reducing power when the ASI pointer stabilizes itself on the required cruise speed.

Then we need double check the ASI, VSI and the Altimeter to ensure that the ASI indicates the exact cruise speed, the VSI reads zero and that the altimeter depicts the intended altitude for flight (plus, minus corrections).

And finally have to trim to maintain the current flight attitude.


14



b) Climb:

Figure: climbing

Wing Flaps: Angle should be 0°- 1 0°. Throttle: We should fully open the throttle. Mixture: RICH (above 3000 RPM). Feet, LEAN to obtain maximum Elevator Control: LIFT NOSE WHEEL (at 55 KIAS). Climb Speed: Climb speed 70-80 KIAS. Wing Flaps: Have to retract the wings flaps.

c) Descend:

Figure: descending

Airspeed: 65-75 KIAS (flaps UP). Wing Flaps: As Desired (0°- 1 0° below 1 1 0 KIAS, below 85

KIAS). 1 0°-30°


15


Unit: 66 Theory of flight Airspeed: 60-70 KIAS (flaps Down). Touchdown: Main wheels first. Landing Roll: Lower nose wheel gently. Braking : Minimum required

d) 180 o Climbing Turn:

Have to perform two 90º clearing turns. 100 KIAS (2200 RPM) maintain altitude and have to clean

configuration flow. Should be required to Choose a reference point off wing, then

must establish / maintain 30° bank Full Throttle : We should ncrease pitch to attain approx. 10-12˚

pitch up at 90° point 1st 90° of turn, Bank = constant 30˚, Pitch = increasing to 10-12˚ pitch up.

90˚ point : We must maintain pitch and reduce bank angle to attain level flight at 180˚ point. 2nd 90° of turn, Pitch = constant 10-12˚ pitch up, Bank = decreasing to level flight

180˚ point : wings level has to minimum controllable airspeed and Accelerate while maintaining level flight

Finally we should cruise checklist.

e) Stall recovery:

Figure: stall.

Decreasing elevator back pressure, level wings with coordinated ailerons and rudder. Then we apply full power.

When control of the aircraft is re-established and airspeed begins to increase, smoothly fly the airplane to attain VY speed.


16


Unit: 66 Theory of flight Should not try to establish the best rate of climb attitude too

abruptly, as a secondary stall may occur.

Assignment 3: Stability and Control

P8

a. Describe the factors that influence the dynamic stability of a single engine light airplane.

Answer:

Stability is the tendency of an airplane in flight to remain in straight, level, upright flight and to return to this attitude, if displaced, without corrective action by the pilot.

Dynamic stability is the overall tendency of an airplane to return to its original position.

When an object moves through a fluid. The variation of velocity produces a variation of pressure on the surface of the object these is called center of pressure .Integrating the pressure times the surface area around the body determines the aerodynamic force on the object. This single force to act through the average location of the pressure on the surface of the object the average location of the pressure variation is center of gravity.

Determining the center of pressure and center of gravity is very important. It will provide enough stability to an aircraft.

Dynamic and static stability: A single engine propeller driven aircraft is influenced by CG positions. It depends on location of the wing with respect to the CG.

If CG is front side of the aircraft, the air craft is positively stabile If CG is in the backside of the aircraft then the air craft is negative

stability. If CG is in the middle of the aircraft then the aircraft is in a neutral

position.

b. Write down about one aircraft specification which is statically stable. And describe the factors responsible for its static stability.


17


Unit: 66 Theory of flight Answer:

Cessna 152>Cessna 152 is statically stable. Static stability depends on:

Location of CG - Front Location of the horizontal tail surface - Convertible horizontal

stabilizer Location of the wing with respect to the CG - High wing.

Figure: Static stability

Static Stability:

Static stability refers to the initial tendency, or direction of movement, back to equilibrium. In aviation, it refers to the aircraft’s initial response when disturbed from a given AOA, slip, or bank. There are 3 types of static stability.

Positive static stability:

The initial tendency of the aircraft to return to the original state of equilibrium after being disturbed.

Neutral static stability:


18


Unit: 66 Theory of flight The initial tendency of the aircraft to remain in a new condition after its equilibrium has been disturbed.

Negative static stability:

The initial tendency of the aircraft to continue away from the original state of equilibrium after being disturbed

c. Write down about one aircraft specification which is dynamically unstable. And describe the factors responsible for it’s dynamically instability.

Answer:

ATR 72 is dynamically unstable. Dynamic stability depends on:

Location of CG - Aft Location of the horizontal tail surface - T-Tail horizontal stabilizer Location of the wing with respect to the CG - High wing

Dynamic Stability:

Dynamic stability refers to the aircraft response over time when disturbed from a given AOA, slip, or bank. This type of stability also has three subtypes.

Positive dynamic stability: Over time, the motion of the displaced object decreases in amplitude and, because it is positive, the object displaced returns toward the equilibrium state.

Neutral dynamic stability:Once displaced, the displaced object neither decreases nor increases in amplitude. A worn automobile shock absorber exhibits this tendency.

Negative dynamic stability:


19


Unit: 66 Theory of flight Over time, the motion of the displaced object increases and becomes more divergent.

P9

What’s the purpose of using SWEEPBACK and DIHEDRAL Wings?

Answer:

SWEEPBACK:

The use of sweepback softens the force divergence.

When an aircraft changes its position from neutral with a small roll to the left and then will also roll in a process called yaw, to the left. For the span’s effectiveness the down going leading edge will be greater than that of the up going, which produces a positively stable moment. Sweepback wing includes an increase in critical Mach number and sweepback delays onset compressibility effects.

Figure: sweepback wings.

DIHEDRAL:

The wings on either side of the aircraft join the fuselage to form a slight V or angle is dihedral.

Dihedral wing usually makes an aircraft more stable and if the aircraft is fitted with dihedral wings the lower wing will be at a higher angle of attack


20


Unit: 66 Theory of flight than the upper wing which results change in lift will roll, the aircraft back to its former equilibrium position and a sideslip force is introduced.

Figure: Dihedral wing

P10

Describe the primary and secondary control surfaces of C152/ C172/ ATR 72 Aircraft.


21


Unit: 66 Theory of flight Answer:

Primary control of C152

Aileron:

Ailerons control roll about the longitudinal axis. The ailerons are attached to the outboard trailing edge of each wing and move in the opposite direction from each other. Ailerons are connected by cables, bell cranks, pulleys, or push-pull tubes to each other and to the control wheel.

Figure: Aileron

Elevator:

The elevator controls pitch about the lateral axis. Like the ailerons on small airplanes, the elevator is connected to the control column in the cockpit by a series of mechanical linkages. Aft movement of the control column deflects the trailing edge of the elevator surface up.

The up-elevator position decreases the camber of the elevator and creates a downward aerodynamic force, which is greater than the normal tail-down force that exists in straight-and-level flight. The overall effect causes the tail of the airplane to move down and the nose to pitch up. The pitching moment occurs about the center of gravity (CG).


22



Figure: Elevator and rudder are shown

Rudder:

The rudder controls movement of the airplane about its vertical axis. This motion is called yaw. Like the other primary control surfaces, the rudder is a movable surface hinged to a fixed surface, in this case, to the vertical stabilizer, or fin. Moving the left or right rudder pedal controls the rudder. When the rudder is deflected into the airflow, a horizontal force is exerted in the opposite direction.

By pushing the left pedal, the rudder moves left. This alters the airflow around the vertical stabilizer/rudder, and creates a sideward lift that moves the tail to the right and yaws the nose of the airplane to the left. Rudder effectiveness increases with speed, so large deflections at low speeds and small deflections at high speeds may be required to provide the desired reaction. In propeller-driven aircraft, any slipstream flowing over the rudder increases its effectiveness.

Secondary control surface of C152

FLAPS:

These surfaces, which are attached to the trailing edge of the wing, increase both lift and induced drag for any given angle of attack. Flaps allow a compromise between high cruising speed and low landing speed, because they may be extended when needed, and retracted into the wing’s structure when not needed. There are four common types of flaps: plain, split, slotted, and Fowler flaps.


23



Figure: Type of flaps

Trim tabs:

The most common installation on small airplanes is a single trim tab attached to the trailing edge of the elevator. Trim tabs are manually operated by a small, vertically mounted control wheel. The cockpit control includes a tab position indicator. Placing the trim control in the full nose-down position moves the tab to its full up position. With the tab up and into the airstream, the airflow over the horizontal tail surface tends to force the trailing edge of the elevator down.

And results in a nose-down pitch change. the trim tab to the full nose-up position, the tab moves to its full-down position. In this case, the air flowing under the horizontal tail surface hits the tab and tends to force the trailing edge of the elevator up, reducing the elevator’s angle of attack. This causes a tail-down movement of the airplane and a nose-up pitch change.


24



Figure: Trim taps

Assignment 4: High Speed Flight

P 11

a. Describe about critical Mach number.

Answer:

The Mach number (m) refers to the speed at which an aircraft is traveling in relation to the speed of sound. The critical Mach number (Mcr) of an aircraft is the lowest Mach number, at which the airflow over some point of the aircraft reaches the speed of sound. Both the speed of the aircraft and the speed of sound are true speeds. Mach number can be defined as:

M= True air speed/local speed of sound.


25



b. What are the phenomenons will be found of an aircraft if it’s flying in supersonic flight?

Answer:

Flight above mach 1.20 is smooth. Increase in airspeed as it flows over the form of an aircraft pushing its way near Mach 1 speed of sound. Air pressure and temperature both drops when air speed increases and then there is rapid changes in the density which can be enough to bend light like lens. Slightly change in primary and secondary control the aircraft position will be effected hugely.

P12

What is Shock wave? How does it form? Describe the effect of Shock wave on a supersonic flight.

Answer:

A shock wave is a very thin region in which there is a sudden decrease of velocity and increase in the pressure, temperature, and density of the air passing through it.

There are two types of shock waves of interest involved with flight:

Normal shock:

Normal shock waves are perpendicular to the direction of flight and are seen primarily on the surface of transonic wings or in pipes. They are caused by an abrupt change in density and pressure.

Oblique shock:

Oblique shock waves are formed at an angle with respect to the oncoming air and occur when supersonic air must be turned. Because a supersonic airplane is traveling so fast, the air has no chance to move out of the way as it does in subsonic speeds. Therefore, the moment the air hits the leading edge of the wing it must turn. The air turns almost instantaneously and forms the oblique shock wave.


26


Unit: 66 Theory of flight In supersonic flight a shock wave occurs when air must suddenly change speed or direction. Supersonic aircraft are designed to avoid producing normal shock waves, since the greater the change in density across a shock wave the greater the energy loss and the greater the drag. This is accomplished by making the nose and wing leading edge sharp.

Figure: shock wave

P13

What is CP? Why the centre of pressure moves forward when an aircraft flies from transonic to supersonic speed

Answer:

CP stands for center of pressure. The center of pressure is defined as the location on the airfoil where the pitch moment is zero and the center of pressure location produce equivalent force and moment on the body as the original pressure field and pressure fields occur in both static and dynamic fluid methods.


27



Figure: aircraft C.P and G.P position

When the centre pressure moves forward an aircraft flies from transonic to supersonic because, the center of pressure moves forward on an airfoil as an aircraft speeds up and pilots have to re trim with the more nose down trim any time when the speed is increased.

P 14

a. Give a short description of following terminology :

Answer:

i) Subsonic.

Subsonic conditions occur for Mach numbers less than one, M < 1 . For the lowest subsonic conditions, compressibility can be ignored. For aircraft speeds which are very much less than the speed of sound, the aircraft is said to be subsonic.

ii) Transonic:

As the speed of the object approaches the speed of sound, the flight Mach number is nearly equal to one, M = 1, and the flow is said to be transonic. At some places on the object, the local speed exceeds the speed of sound. Compressibility effects are most important in transonic flows and lead to the early belief in a sound barrier. Flight faster than sound was thought to be impossible. In fact, the sound barrier was only an increase in the drag near sonic conditions because of compressibility effects. Because of the high drag associated with compressibility effects, aircraft do not cruise near Mach 1.

iii) Supersonic:


28


Unit: 66 Theory of flight Supersonic conditions occur for Mach numbers greater than one, 1 < M < 3. Compressibility effects are important for supersonic aircraft, and shock waves are generated by the surface of the object. For high supersonic speeds, 3 < M < 5, aerodynamic heating also becomes very important for aircraft design.

iv) Hypersonic:

For speeds greater than five times the speed of sound, M > 5, the flow is said to be hypersonic. At these speeds, some of the energy of the object now goes into exciting the chemical bonds which hold together the nitrogen and oxygen molecules of the air. At hypersonic speeds, the chemistry of the air must be considered when determining forces on the object. The Space Shuttle re-enters the atmosphere at high hypersonic speeds, M ~ 25. Under these conditions, the heated air becomes ionized plasma of gas and the spacecraft must be insulated from the high temperatures.

b. Why there is a loss of control effectiveness when an aircraft flies in the transonic range from Subsonic?

Answer:

In transonic and supersonic flights the ranges of the aircraft normally operates in a speed of Mach 0.7 - 0.90 Mach. Critical mach number is the boundary between transonic and subsonic flight which is totally dependent up to the design of wing and airfoil.

When shock waves form on an aircraft, airflow separates and aircraft control difficulties occurs. Shock waves and airflow separation takes place above critical Mach number. A jet aircraft typically is most efficient when cruising at or near its critical Mach number. At speeds 5–10 percent above the critical Mach number, compressibility effects starts. Drag begins to rise sharply and with trim and stability changes, and a loss in control effectiveness.

c. What is the purpose of using trim tab?

Answer:

Trim tab is attached to the trailing edge of the elevator, airplanes have trim tabs on all three control surfaces which can be adjustable from the plane


29


Unit: 66 Theory of flight inside; some have two and some have one trim tab. The purpose of using trim tab is to make the full nose down position moves the trim tab to its full up position. With the trim tab up in the airstream, the airflow over horizontal tail surface tends to force the trailing edge of the elevator down. By doing this the tail of the airplane will move up, and the nose will move down.

The tabs are usually controlled by a wheel which is often situated on the floor between the two front seats. Some aircraft have the trim controlled by a small rocker switch on the control column. The aircraft should be trimmed after every change in attitude or power setting. It takes a little practice to trim an aircraft, but in the end it is done unconsciously.

Figure: Trim tabs

Reference:

1. http://home.anadolu.edu.tr/~mcavcar/common/ISAweb.pdf 2. http://www.grc.nasa.gov/WWW/Wright/airplane/airprop.html 3. https://www.grc.nasa.gov/WWW/k-12/airplane/bern.html

4. http://www.grc.nasa.gov/WWW/k-12/airplane/smotion.html

5. Understabding flight by david.F anderson and scott eberhardt6. Aircraft basic science by kroes rardon7. Fundamental of flight by richard s. shevell


30


http://www.grc.nasa.gov/WWW/k-12/airplane/smotion.html

https://www.grc.nasa.gov/WWW/k-12/airplane/bern.html

http://www.grc.nasa.gov/WWW/Wright/airplane/airprop.html

http://home.anadolu.edu.tr/~mcavcar/common/ISAweb.pdf

Unit: 66 Theory of flight 8. Google image


31


aviationbangladesh.files.wordpress.com€¦ · Web viewAir is a mixture of gases, 78% nitrogen and...

Documents

Transcript of aviationbangladesh.files.wordpress.com€¦ · Web viewAir is a mixture of gases, 78% nitrogen and...