直升机飞行力学 Helicopter dynamics chapter 2
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Transcript of 直升机飞行力学 Helicopter dynamics chapter 2
Helicopter Flight Dynamics
Chapter 2: Helicopter Flight Controllers
Topics
1. External forces acting on helicopter
2. Control manners of helicopter
3. Control systems and their mechanical
characteristic
4. The Development of helicopter controllers
External Forces Acting on Helicopter
V
V
Aerodynamic Forces of Main Rotor
GxM
GzM
GxMGxM
GzMGzMThrust: T
Hind force: H
Side force: S
Anti-torque: Mk
Hub moments: MGx, MGz
V
V
Aerodynamic Forces of Tail Rotor
Thrust: TT
Anti-torque: MkT
V
V
Aerodynamic Forces of Fuselage
Drag: Qf
Lift: Yf
Side Force: Sf
Roll Moment: Mxf
Yaw Moment: Myf
Pitch Moment: Mzf
Aerodynamic Forces of Horizontal Tail
V
V
Drag: Dh
Lift: Yh
Aerodynamic Forces of Vertical Tail
V
V
Drag: Dv
Lift: Yv
Helicopter Control Manners
• Control manners of helicopter with main rotor and tail rotor
• Control manners of twin rotors helicopter• Control manners of tilt-rotor aircraft• Other control manners
Helicopter Types
Control of Fixed-wing Aircraft
aileron
rudder
elevator
aileron
Control of Fixed-wing Aircraft
Degree of Freedoms
Cockpit Control Unit
Aerodynamic Surfaces
Control Forces
Direct Control
Forward Throttle Thrust T
Pitch Stick Elevator MZ
Roll Stick Aileron MX
Yaw Paddle Rudder MY
Indirect Control
Altitude Stick + Throttle F
Sideward Stick + Paddle S
Control of Helicopter
Main Rotor Tail RotorEnginesControl System
Control of Helicopter with Main & Tail Rotors
Degree of Freedoms
MotionsCockpit
Control UnitAerodynamic
SurfacesControl Forces
Vertical Altitude Collective stick Rotor T
LongitudinalPitching, Forward & backward
Stick Rotor H, MGz
LateralRolling, sidestep
Stick Rotor S, MGx
Yaw Heading Rudder Tail rotor TT
Main rotor is the lift surface to produce the lift of helicopter. On the other hand, it is the control surface to produce the forces or moments of heaving, pitching and rolling. Furthermore, it is the propeller to make
helicopter to fly in any directions.
Comparison of Control Between helicopter and Fixed-wing Aircraft
Degree of Freedoms
Cockpit Control Unit
Aerodynamic Surfaces
Control Forces
Helicopter
Direct Control
Altitude Collective Rotor T
Pitch Stick Rotor H, MGz
Roll Stick Rotor S, MGx
Yaw Rudder Tail rotor TT
Indirect Control
Forward Collective + stick H
SidewardCollective + stick + Rudder
S
Fixed_wing
Aircraft
Direct Control
Forward Throttle Thrust T
Pitch Stick Elevator MZ
Roll Stick Aileron MX
Yaw Paddle Rudder MY
Indirect Control
Altitude Stick + Throttle F
Sideward Stick + Paddle S
Control Manners of Twin Rotors Helicopter
Configuration
Tandem rotorsControl
Side by side rotorsSingle rotor Co-axis rotors
Vert.
Lon.
Lat.
Yaw
Anti-Torque
Balance
Control Tandem Helicopter
Control of Tilt-rotor Aircraft
Pitch
Thrust
Roll
Side Force
Yaw
Helicopter Mode Fixed-wing Mode
Control of Tilt-rotor Aircraft
Helicopter Airplane
• Thrust /power level controls Collective pitch and throttles
• Acts as altitude control
• Thrust /power level controls blade pitch and engine throttles
• Acts as altitude control
Thrust/power Control
Control of Tilt-rotor Aircraft
Helicopter Airplane
Forward longitudinalcyclic pitch
elevator
• Proprotor discs tilt forward• Aircraft assumes nose-down altitude• Airspeed increases
• Elevator deflects downward• Aircraft assumes nose-down altitude• Altitude decreases• Airspeed increases
Forward Stick Control
Control of Tilt-rotor Aircraft
Helicopter Airplane
elevator
Backward longitudinalcyclic pitch
• Proprotor discs tilt backward• Aircraft assumes nose-up altitude• Airspeed decreases
• Elevator deflects upward• Aircraft assumes nose-up altitude• Altitude increases• Airspeed decreases
Backward Stick Control
Control of Tilt-rotor Aircraft
Helicopter Airplane
differential collective pitchand lateral cyclic pitch
flaperon
• Right proprotor increase collective pitch• Left proprotor decrease collective pitch• Proprotor discs tilt to left • Aircraft rolls to left
• Right flaperon deflects downward• Left flaperon deflects downward• Aircraft rolls to left
Left Stick Control
Control of Tilt-rotor Aircraft
Helicopter Airplanedifferential collective pitch
and lateral cyclic pitch flaperon
• Left proprotor increase collective pitch• Right proprotor decrease collective pitch• Proprotor discs tilt to right • Aircraft rolls to right
• Left flaperon deflects downward• Right flaperon deflects downward• Aircraft rolls to right
Right Stick Control
Control of Tilt-rotor Aircraft
Helicopter
Airplane
Differential longitudinal cyclic Rudder
• Left proprotor disk tilts forward• Right proprotor disk tilts backward• Aircraft yaws to left
• Rudder deflect to left• Aircraft yaws to left
Left Pedal Control
Control of Tilt-rotor Aircraft
HelicopterAirplane
Differential longitudinal cyclic Rudder
• Left proprotor disk tilts backward• Right proprotor disk tilts forward• Aircraft yaws to right
• Rudder deflect to right• Aircraft yaws to right
Right Pedal Control
Direct Control Manner
In the early time, The small helicopter was controlled by directly rotating the rotor shaft.
Advantages: structure simple
Disadvantages: too large control forces and difficult to control precisely
Status: Still be used now by Gyroplane
Control by Hiller Bar
1. Two Heller bars forms the control rotor (teetering rotor)
2. The control rotor is connected directly to swashplate.
3. The flap motion of bar adjust the blade cyclic pitching angles of main rotor.
4. Advantages:
1) Small control forces and air loads.
2) Large aerodynamic damping, good stability (stable hover)
5. Disadvantage: delay of response
6. Status: Used by most of model helicopter
Hiller Bar
Control by Servoflap
1. There is a flap at the blade trail edge.
2. Pilot controls the deflection angle of servoflap.
3. The blade pitching angle is achieved with the blade torsional deflection
4. Servofalp has been successfully used on the Kaman helicopter
Controller and Mechanical Features
• Swashplate
• Typical Controller of Helicopter
• Mechanical Feature of Controller • Other Controller
Swashplate
Blade
Pitch Link
Rotating Swashplate
Non-rotating Swashplate
Shaft
Helicopter Typical Controller
Mechanical Feature of Controller
• Gradient of Stick Force
• Breakout Forces
• Limited Control Forces
• Cockpit Control Free Play
The movement and load ranges of cockpit controllers shall be suitable to the pilot physiological characteristics. The mechanical features directly affect the control precision and pilot workloads.
Gradient of Stick Force
1. The relationship between stick force and displacement should be monotonous, continuous, primarily linear and symmetry to center point.
2. The magnitude of stick forces gradient shall be suitable to control the helicopter precisely. The adjust system for trimming stick force is needed.
Forward Force
Backward Force
Backward Position
Forward Position
Ideal Stick force vs. displacement
ForwardForce
BackwardForce
Breakout Force
Trim
Free Play
Frictionband
ForwardPosition
BackwardPosition
real Stick force vs. displacement
Breakout Forces
1. Breakout forces, including friction, preload, etc., refer to the cockpit control force required to start movement of the control surface in flight.
2. In some cases, the engineers intently increase the friction to prevent from the slippage of stick position so that the pilot can remove his hands from the stick for a short time to do something.
ForwardForce
BackwardForce
Breakout Force
Trim
Free Play
Frictionband
ForwardPosition
BackwardPosition
Cockpit Control Free Play
1. The free play is that any motion of the cockpit control does not move the appropriate moment - or force - producing device in flight.
2. The free play is caused by clearance.3. In design, the engineers will do their best to keep the free play as
small as possible.
ForwardForce
BackwardForce
Breakout Force
Trim
Free Play
Frictionband
ForwardPosition
BackwardPosition
Limited Control Forces
1. Too large limited control forces will make the pilot tired and difficult to control the helicopter precisely.
2. Unless otherwise specified in particular requirements, the maximum control forces required shall not exceed the given value.
3. The value of limited control forces is given by the specification of flight qualities.
The Development of Controller
Fly-by-IronThis controller was very common in the early time. It is still used in the small helicopters.Advantages: simple, direct and reliableDisadvantages: large stick force, dithering of stick, free play and friction hurting the flight qualities
Fly-by-OilCombination of fly-by-iron and hydraulic system, stick control the hydraulic actuator which move the swashplate.Advantages: large control power, no stick dithering, easy working with SCASDisadvantages: complicated structure, heavy, need of backup for safety
The Development of Controller
Stick inputs commands into computer with redundant technology. The computer controls the actuators (electric or hydraulic)Advantages: small, light, good flight qualities (insured by computer software), high reliability (redundant, self check)Disadvantages: electromagnetic effects (such as thunder)
Fly-by-Wire
The Development of Controller
Fly-by-LightSignals is carried by optical fiber, the others is the same as fly-by-wire. There is no electromagnetic effects. It is still under the development.Sidestick ControllerDeveloped for fly-by-wire or fly-by-light. It located on the right side of pilot. The command signals are forces.Advantages: small size, big cockpit room. One hand and foot of pilot are free.Status: Installed on RAH-66 helicopter
The Development of Controller
Smart Control System
Ambientdisturbance
Information fromnavigation sys.
Commandsfrom pilot
AirborneComputer
Helicopter flight dynamic model
Actuators
Sensors
Helicopter