Control Friction

Part 4

By Greg Gremminger

For an unstable - airframe that responds to disturbances in the wrong, or destabilizing direction - it is extremely important that the pilot and/or the control system does not allow those airframe motions to couple into the rotor. If they do so, the rotor - lifting element - will cause that initiating disturbance to be increased - "positive feedback". Most gyroplanes will couple some amount of airframe motion into the rotor from control friction and most certainly from the trim spring / offset gimble arrangement on the rotor head. This means, that for an unstable airframe, the pilot must COMMAND precisely timed compensating inputs into the rotor so that the rotor does not "feed" the errant reactions of the airframe and cause the whole gyroplane system to diverge in either pitch or pitch oscillations.

A gyroplane airframe that is stable and responds in the proper direction to wind turbulence or g load disturbances cannot, by itself alone, cause the flight path of the whole gyroplane to move or pitch in a correcting direction. For a gyroplane, whose stable airframe responds in the stabilizing or dampening direction to a disturbance, the whole system is stabilized when that "negative feedback" response is coupled to the rotor. Contrary to the unstable airframe situation, it is highly desirable that the stable airframe motions be coupled into the rotor. This coupling can be simply that the cyclic stick is held "fixed" by the pilot or by control friction. The trim spring / offset gimble system also provides additional coupling of airframe motions into the cyclic control of the rotor. In other words, when the airframe motions of a stable airframe are coupled to the rotor, the whole gyroplane is self-stabilizing, without pilot action.

This stabilizing action is actually greatly increased if the pilot firmly holds the cyclic stick "fixed". This is likely what the less experienced pilot, in a tense situation, might be expected to do. However, good pilot technique, in any aircraft, is to loosely hold the stick without restricting it, while applying pressure to the stick for pilot "commanded" inputs. This is normally taught in order that the aircraft be allowed to stabilize itself with its own inherent self-stabilizing actions. In a gyroplane with an unstable airframe, this is much more important so that the pilot doesn't force the destabilizing airframe motions into the rotor.

Traditional gyro thinking dictates that cyclic controls should be friction free. This thinking has evolved because that is important on the traditionally unstable gyro airframes to avoid coupling destabilizing airframe motions into the rotor. Alternatively, Magni has taken advantage of the highly stable Magni gyroplane airframe by the actual addition of some cyclic control friction to assure that the stabilizing reactions of the airframe ARE coupled to the rotor, even with pilot's loose hold on the stick. The amount of friction is enough to couple airframe motions into the rotor without pilot concern or input. The amount of friction is not so great so as to possibly cause pilot over-control. The result is that the Magni gyroplane is strongly self-stabilizing without pilot input, and pilot cyclic inputs are applied intuitively and linearly to control the "commanded" flight path maneuver only. The result is a comfortable balance or "harmony" of the pilot with the gyroplane that, even in rough air, feels much like a very nimble airplane in smooth air.