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


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


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


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


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


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


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


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


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


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


Smart Control System

Ambientdisturbance

Information fromnavigation sys.

Commandsfrom pilot

AirborneComputer

Helicopter flight dynamic model

Actuators

Sensors

Helicopter

直升机飞行力学 Helicopter dynamics chapter 2

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