Wind Tunnel Testing of a Passive Gust Load Alleviation Spoiler

Gust load alleviation systems have the potential to significantly reduce airframe mass by reducing peak wing root bending moments. However, existing systems are active in that they rely on sensors and actuators to function, which adds weight and complexity. This work demonstrates a passively actuated load alleviation spoiler concept. This spoiler utilises a nonlinear structure to gather and store strain energy from the wingbox, which is then rapidly released via a structural instability to deploy a leading edge tab. The deployment of this tab locally stalls the wing, thus reducing its lift coefficient (C_L). Wind tunnel testing is used to investigate the performance of the device. It is found that the spoiler is capable of deploying and reducing C_L within a few convective time units across a range of flow speeds and angles of attack. Fluid loads have been observed to have a small but measurable adverse impact on the desired response of the spoiler. A reduced degree-of-freedom model is used to explain this phenomenon, and to explore strategies for minimising it. To our knowledge, this is the first time that a purely strain-actuated gust load alleviating control surface has been demonstrated experimentally.