A Fully Passive Pop-up Leading Edge Spoiler for Gust Load Alleviation

Extreme gust events and their resulting air frame loads often drive the structural design of an aircraft; hence, reducing the stresses induced by such events allows for a reduction in overall mass. As such, numerous gust load alleviation systems have been proposed. However, a key drawback of many systems is that they are 'active’, meaning they rely on sensors to detect gusts, and on actuators to move control surfaces in order to reduce lift and thus wing loading. These ancillary systems add complexity and cost (at the point of manufacture as well as over the aircraft lifetime), but also add weight to the air frame. To address this challenge, we are developing a `fully passive' load alleviating spoiler, which deploys automatically in response to the deformation of the wing during gust loading. The strain in the skin of the deformed wing is the only input for the deployment of this spoiler, which requires no sensors, actuators or other control systems. This device must remain fully stowed until a triggering strain is reached, after which it must deploy as rapidly as possible. We achieve this desired response by deliberately incorporating buckling and structural instability into the design of the spoiler. Such phenomena have traditionally been viewed as a failure mechanism, but here we exploit them to achieve the novel behaviour required of this device. The rapid deployment of the spoiler is achieved through a build-up of strain energy in the device during wing compression, which is then rapidly released at a critical wing deformation through a structural instability. The design concept consists of a leading edge tab, which deploys automatically in response to a critical input strain. The design concept has been successfully demonstrated by an analytical model, finite element analyses, and simple physical prototypes, with experimental validation of a small-scale demonstrator using wind tunnel tests currently under way.