User manual

DodoSim 206 FSX User Manual

Page 37

Note that due to the aerodynamic nature of the fuselage and vertical stabiliser, (the “tail fin”), the

effects of torque-induced yaw diminish as airspeed increases, to the point where little or no left

pedal input is required above forward speeds of about 40 knots.

Torque-induced yaw is only present when the engine is physically driving the rotor system, (since if

there is no “action”, then there can be no “equal and opposite reaction.”) For example: If the

transmission is de-coupled from the rotor through the one-way “sprag” clutch due to either an

engine failure or intentional reduction of the engine throttle, then torque-induced yaw is not present

and the pilot need not account for it with pedal inputs. In forward flight, this may result in a yaw to

the left if engine power is reduced as there is little or no torque for the vertical stabiliser to act

against, in which case right pedal may be required to maintain a constant heading.

3.4.1.2 Dissymmetry of Lift

As a helicopter moves through the air, lift is generated as the rotor rotates. Due to the difference in

relative airspeed, the advancing blade generates more lift than the retreating blade. This creates a

tendency for the helicopter to try and roll in the direction of the retreating blade. (The left when

viewed from above for a helicopter with a counter-clockwise main rotating rotor.)

To counter this tendency, the pilot is required to input increasing amounts of opposing right cyclic

stick as airspeed increases. Note however that Dissymmetry of Lift is applicable to any direction of

flight, though it is unlikely that a pilot would gain enough speed in any but forward flight for it to

become noticeable. (The advancing blade is therefore always the blade moving towards the

direction of travel and opposing cyclic input must be made towards it.)

3.4.1.3 Collective / Pitch Coupling

Application of collective pitch control induces a pitching movement of the helicopter’s fuselage. As

collective pitch is increased or decreased, the pitching movement increases and decreases in

magnitude respectively. The pilot is required to apply fore and aft cyclic input in order to maintain a

constant aircraft pitch attitude.

Advancing blade

Retreating

blade

Rotor direction

Direction of travel