In electric helicopters, yaw control (the swing of the tail end) is achieved by varying either the rudder pitch or its speed. The first method depends on a complicated belt and servo mechanism, whilst the second uses a simple variable speed motor connected to a fixed pitch rotor.
The belt-driven tail rotor is generally considered the superior of the two. However, motor-driven tails are improving all the time.
In both cases, a gyro is often used to improve performance, by negating outside influences such as crosswinds. Considered essential for outdoors flying, the gyro is a piezo-electric device installed between the receiver and the tail rotor. Its job is to detect unwanted vibrations or movement, and adjust the tail rotor speed accordingly so it matches the torque strength of the main rotor.
A standard Piezo gyro only responds to conditions at that exact moment, and does not take into account the overall direction the pilot wishes to fly. Pilots performing intricate 3D manoeuvres in breezy conditions often find themselves “battling” the gyro, although the gyro sensitivity can be altered to suit flying conditions.
Therefore, Heading Hold Gyros are often used in RC Electric Helicopters. These are more advanced, and require the pilot to input data detailing the direction he wants to go. The HHG performs complex calculations to keep the helicopter to that heading, which is memorised until the next input is made. Again the sensitivity is fully adjustable, depending on the type of flying being done, and the prevailing weather conditions.
Are Heading Hold Gyros a better choice for Electric Helicopters? Bearing in mind the control they give, the answer has to be yes. However, they are complicated to get to grips with, and outside the scope of most novice pilots. Even up to intermediate level, standard piezo gyros work just fine.