Stall/spin flight testing with a subscale aerobatic aircraft

The effects of configuration changes on the stall/spin characteristics of a single-engine subscale airplane are presented. A 35%-scale, 2.7-m (105-in) wingspan Extra 260 electric aircraft, the UIUC Aero Testbed, was used for this research. A series of flight tests were conduced with the instrumented aircraft, and over 20 different stall/spin maneuvers with varying control surface inputs, combinations, and deflections were studied. Select maneuvers were then tested with three different ventral fins, and the effects on the steady-state spin and recovery were analyzed. The data acquired by the onboard inertial measurement unit (IMU) showed which control inputs would produce a slower or more-easily recoverable stall/spin and which ventral fins were the most effective in improving the stall/spin and/or the recovery from the high bank and high yaw rates of the spin. It was observed that an increase in the motor power setting above the windmilling RPM of the propeller had an adverse effect on the spin recovery, and this adverse effect was worsened when the ailerons were deflected in an anti-spin manner. Additionally, it was observed that the installation of ventral fins removed the ability of the aircraft to spin with anti-spin deflected ailerons. For the testbed aircraft studied, a neutral-aileron spin mode occurred at approximtaely a pitch of -55 deg, a vertical velocity of -15 m/s, a roll rate of 235 deg/s, and a spin parameter magnitude of 0.20. The addition of pro-spin ailerons on average lowered the nose 5 deg, increased the vertical velocity in the negative direction by 66%, increased the roll rate by 50%, and halved the magnitude of the spin parameter, while the addition of anti-spin ailerons on average raised the nose 10 deg, reduced the roll rate by 20%, had no significant effect on the vertical velocity, and increased the magnitude of the spin parameter by 50%. These data will be used to investigate and model the complex aerodynamics experienced by the airplane in a stall/spin situation, and the results of the process of modeling the aerodynamics should be useful in the preliminary design stages of a general aviation aircraft to provide a better design-for-spin.