User manual

DodoSim 206 FSX User Manual

Page 43

your maximum permitted speed (VNE) in order to avoid loosing control due to Retreating Blade

Stall.)

3.4.1.12 Effect of Wind on Horizontal Stabiliser

The horizontal stabiliser is the small “wing” situated midway along the tail boom. Its purpose is to

provide stability in the pitch axis during forward flight.

Because the horizontal stabiliser is pitched downward slightly with respect to the airframe, when

hovering in tail winds the wind can “get under it”, pushing it up and therefore the nose down. The

pilot may need to apply aft cyclic input to counter this behaviour.

3.4.1.13 Loss of Tail Rotor Efficiency

The tail “anti-torque” rotor is designed to counter torque-induced yaw and maintain a constant

heading. If the airflow through the rotor is disturbed in any way then the rotor’s efficiency can be

negatively effected and consequentially its ability to hold a steady heading is reduced.

When flying at airspeeds lower than approximately 30 knots, there are three main factors that can

effect tail rotor efficiency, depending on wind azimuth:

3.4.1.13.1 Main Rotor Vortex Interference

Much like the swirling vortices seen expanding from an airliner’s wingtips on touchdown, spinning

helicopter rotor blades produce tip vortices. When the wind is coming from between approximately

285° and 315° of the helicopter’s nose, the swirling vortices can be blown into the tail rotor which

requires “clean”, undisturbed air to work at maximum efficiency.

The effect of the main rotor vortices on the tail rotor is to effectively increase the tail rotor blades’

angle of attack and thrust generated. To compensate and maintain a heading or yaw turn rate the

pilot will find it necessary to reduce anti-torque input, (less left pedal.) However, during a turn to

the right, as the tail moves out of the main rotor vortices, the requirement for anti-torque pedal input

will once again rise or an uncommanded yaw to the right can quickly develop.

3.4.1.13.2 Tail Rotor Vortex Ring State

Winds from the left, between relative 210° and 240° may provoke tail rotor Vortex Ring State,

where the thrust generated is non-uniform and the pilot may have to constantly adjust the anti-

torque pedal input to compensate and maintain a steady heading.

Relative wind

Main rotor vortex