Aircraft Engineering and Aerospace Technology

Purpose – High autogyro accident rates prompted experimental investigation of this type of aircraft's low-speed pitch characteristics. Pitch control is typically derived from main rotor tip-path-plane adjustment. Thus, autogyro designers often omit horizontal tails and pitch control surfaces. The purpose of this paper is to enable autogyro low-speed pitch control by intentionally placing elevators in the propeller wake.

Design/methodology/approach – Wind tunnel tests were conducted on a 1:10 scale teetering rotor autogyro model. The model included a horizontal tail with elevators placed in the propeller wake. Straight-and-level flight conditions were estimated via a scaling scheme based on the main rotor diameter. At minimum flight speed, the pitching moment induced by 30° elevator deflection was measured. This process was repeated for a range of elevator positions behind the centre of the pitching rotation.

Findings – When placed in an autogyro propeller wake, deflected elevators induce significant pitching moments. If the elevator is shadowed from free stream flow by the autogyro cowling, the pitching moment remains unchanged regardless of the distance between elevators and centre of pitch rotation. However, if the elevator is immersed in the freestream, the pitching moment increases via deflection of both propeller wake and freestream flow.

Research limitations/implications – Kinematic similarity ensures ratios between propeller wake, wind speed, and main rotor flows are representative of full scale. Without flow visualization, main-rotor-diameter-based scaling does not ensure kinematic similarity. Results are therefore qualitative.

Practical implications – Elevators mounted in autogyro propeller wake are worthy of inclusion on all autogyros for pitch control at low speed.

Originality/value – Improved low-speed pitch control arising from elevators mounted in autogyro propeller wake could potentially reduce accidents.