Helicopter Flight DynamicsChapter 2: Helicopter Flight Controllers

TopicsExternal forces acting on helicopterControl manners of helicopterControl systems and their mechanical characteristicThe Development of helicopter controllers

External Forces Acting on Helicopter

Aerodynamic Forces of Main RotorThrust: THind force: HSide force: SAnti-torque: MkHub moments: MGx, MGz

Aerodynamic Forces of Tail RotorThrust: TTAnti-torque: MkT

Aerodynamic Forces of FuselageDrag: QfLift: YfSide Force: SfRoll Moment: MxfYaw Moment: MyfPitch Moment: Mzf

Aerodynamic Forces of Horizontal Tail Drag: DhLift: Yh

Aerodynamic Forces of Vertical Tail Drag: DvLift: Yv

Helicopter Control MannersControl manners of helicopter with main rotor and tail rotorControl manners of twin rotors helicopterControl manners of tilt-rotor aircraftOther control manners

Helicopter Types

Control of Fixed-wing Aircraftaileronrudderelevatoraileron

Control of Fixed-wing Aircraft

Degree of FreedomsCockpit Control UnitAerodynamic SurfacesControl ForcesDirect ControlForwardThrottleThrust TPitchStickElevator MZRollStickAileronMXYawPaddleRudderMYIndirect ControlAltitudeStick + ThrottleFSideward Stick + PaddleS

Control of HelicopterMain RotorTail RotorEnginesControl System

Control of Helicopter with Main & Tail RotorsMain 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.

Degree of FreedomsMotionsCockpit Control UnitAerodynamic SurfacesControl ForcesVerticalAltitudeCollective stickRotor TLongitudinalPitching, Forward & backwardStickRotor H, MGzLateralRolling, sidestepStickRotor S, MGxYawHeading RudderTail rotorTT

Comparison of Control Between helicopter and Fixed-wing Aircraft

Degree of FreedomsCockpit Control UnitAerodynamic SurfacesControl ForcesHelicopterDirect ControlAltitudeCollectiveRotor TPitchStickRotor H, MGzRollStickRotor S, MGxYawRudderTail rotorTTIndirect ControlForwardCollective + stickHSidewardCollective + stick + RudderSFixed_wingAircraftDirect ControlForwardThrottleThrust TPitchStickElevator MZRollStickAileronMXYawPaddleRudderMYIndirect ControlAltitudeStick + ThrottleFSideward Stick + PaddleS

Control Manners of Twin Rotors Helicopter

Control Tandem Helicopter

Control of Tilt-rotor Aircraft

Control of Tilt-rotor AircraftHelicopterAirplaneThrust /power level controls Collective pitch and throttlesActs as altitude controlThrust /power level controls blade pitch and engine throttlesActs as altitude controlThrust/power Control

Control of Tilt-rotor Aircraft

Control of Tilt-rotor Aircraft

Control of Tilt-rotor Aircraft

Control of Tilt-rotor Aircraft

Control of Tilt-rotor Aircraft

Control of Tilt-rotor Aircraft

Direct Control Manner In the early time, The small helicopter was controlled by directly rotating the rotor shaft. Advantages: structure simpleDisadvantages: too large control forces and difficult to control preciselyStatus: Still be used now by Gyroplane

Control by Hiller BarTwo Heller bars forms the control rotor (teetering rotor)The control rotor is connected directly to swashplate.The flap motion of bar adjust the blade cyclic pitching angles of main rotor.Advantages: Small control forces and air loads.Large aerodynamic damping, good stability (stable hover)Disadvantage: delay of responseStatus: Used by most of model helicopter

Control by ServoflapThere is a flap at the blade trail edge. Pilot controls the deflection angle of servoflap.The blade pitching angle is achieved with the blade torsional deflectionServofalp has been successfully used on the Kaman helicopter

Controller and Mechanical FeaturesSwashplateTypical Controller of HelicopterMechanical Feature of Controller Other Controller

Swashplate

Helicopter Typical Controller

Mechanical Feature of ControllerGradient of Stick ForceBreakout ForcesLimited Control ForcesCockpit Control Free PlayThe 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 ForceThe relationship between stick force and displacement should be monotonous, continuous, primarily linear and symmetry to center point.The magnitude of stick forces gradient shall be suitable to control the helicopter precisely. The adjust system for trimming stick force is needed. Ideal Stick force vs. displacementreal Stick force vs. displacement

Breakout ForcesBreakout forces, including friction, preload, etc., refer to the cockpit control force required to start movement of the control surface in flight.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.

Cockpit Control Free PlayThe free play is that any motion of the cockpit control does not move the appropriate moment - or force - producing device in flight.The free play is caused by clearance.In design, the engineers will do their best to keep the free play as small as possible.

Limited Control ForcesToo large limited control forces will make the pilot tired and difficult to control the helicopter precisely.Unless otherwise specified in particular requirements, the maximum control forces required shall not exceed the given value.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 qualitiesFly-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