Nonlinear Flutter Test of a Very Flexible Wing

A nonlinear flutter wind tunnel test of a very flexible wing model has been conducted at the FD-09 Wind Tunnel of China Academy of Aerospace Aerodynamics (CAAA) to acquire experimental data suitable to correlate with and validate nonlinear aeroelastic analysis methods. Nonlinear aeroelastic analysis methods are necessary to accurately predict the aeroelastic response and critical velocity of high altitude long endurance (HALE) aircrafts, such as Helios or Zephyr. However, very little test data is available for validating such methods up to date. A 1.5 meter-long 0.05 meter-width flexible straight wing model was designed, whose aspect ratio is 30. The model was vertically downwards mounted on the rotating mechanism of the wind tunnel for adjusting root angle of attack (AOA). The model was fully instrumented to collect structural response data, such as strain and acceleration response data. Two different test cases were performed, with root AOA was 1° and 2°, respectively. During the test process, a low speed instability region was discovered and limit cycle oscillation (LCO) behavior was observed. As increasing in the flow speed, the aeroelastic response of the flexible wing model experienced the damping vibration, simple harmonic LCO and periodic LCO phase, but no divergent behavior occurred. A maximum deflection of the wing tip was about 30% of the model length.