Flight Test Evaluation of Elevator Stick Force Gradients on General Aviation Aircraft
Faust, Isaac Lee
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The objective of this research is to establish a suitable method of changing elevator stick force gradients on a Piper Warrior II. After finding a range of stick force gradients, the gradients will later be evaluated to get handling qualities ratings. A stick force gradient is the change in stick force as the airspeed deviates from trim condition. An aircraft’s yoke force gives pilots haptic feedback which improves their situational awareness without the need to assess instrument readings. A high stick force gradient will give the pilots a lot of feedback but will require more physical exertion to fly the airplane. A low stick force gradient will make the aircraft easy to maneuver but will reduce the amount of response to the pilot. This research tested six varying stick force gradients in a climb, cruise, and approach configuration in an experimental Piper Warrior II. The project adjusts the stick force gradients by varying the elevator trim tab linkage length. It was estimated a shorter linkage would decrease the stick force gradient, while a longer one would increase the gradient. The research determines how the aircraft gradients change with the changing trim tab length and establishes a safe range of lengths for future testing. A future project will take a sample of pilots to fly the gradients and rate the handling qualities utilizing the Cooper-Harper scale. The stick force gradient was definitively altered utilizing varying stabilator trim linkage lengths. Although, on average, a longer linkage provided a higher stick force gradient, there was no consistent pattern between linkage length and stick force gradient. Changing the linkage length is a safe but not effective method to get a consistent range of stick force gradients for a pilot sample to rate handling qualities.