Sling Load asked:
Nick,
In another post you mentioned the 20 degree cant on the CH-53 and the HH-60 assisting with increased lift and cog. In these aircraft, is tail rotor roll compensated in the rotor shaft, or does the cant assist with this effect? It appears the tail rotor is mounted at approximately the same height as the rotor head. Would this be the reason why they are mounted that way?
Nick sez:
The canted tail rotor really has no extra roll effect due to its cant, the affect is purely in pitch, since left pedal makes the nose tuck a little, and right pedal the opposite. With a canted tail rotor, we mix the cyclic with some yaw so left pedal puts a little aft cyclic.
All high tail rotors give some roll effect, due to the lateral force they produce acting on the center of gravity (not the rotor head as you have guessed). The right thrusting force of the tail rotor would cause a right roll of the airframe in a hover, but it is countered by the right translation this force causes, and the concurrent need to put in left roll to stop translating. The translating left roll is the dominant factor. All American helicopters hover left skid/wheel low, but if the tail rotor is low, near the vertical CG, the effects don't cancel and the roll attitude is more pronounced. As a rule of thumb, the typical high tail rotor helo hovers about 3 to 4 degrees left wheel low, and a low tail rotor helo hovers about 5 to 6 degrees left wheel low.