Airliner upset — improving our understanding through sub-scale flight testing

What is it about?

When an airplane exits its normal operational flight regime, it is exposed to highly nonlinear and unsteady aerodynamics. This is especially troublesome for airliners which have their tailplane mounted to the top of the fin (T-tail), since they are prone to enter an unrecoverable stalled state, the so-called deep stall. With this research, for the first time, flight tests under upset conditions were conducted with a sub-scale, remotely-piloted generic T-tail airliner. Its geometry and weight is accurately scaled with respect to full-size aircraft to enable realistic simulations of upset conditions. The vehicle has been built specifically for this task and includes many unique design features, such as a robust carbon fiber composite structure, internal control linkages, a ballistic recovery system, extensive flight test instrumentation, and a computerized flight control system with advanced stability augmentation. These features allowed the model to be safely flown into extreme upset conditions, including deep stalls, collecting hundreds of data points. The results were compared to a high-fidelity aerodynamic model, which has been obtained during previous wind tunnel tests. Although some stability characteristics were correctly predicted by this model, significant improvements in the critical stall behavior were made with the flight test data.

Featured Image

Photo by Donna White on Unsplash

Photo by Donna White on Unsplash

Why is it important?

Accidents due to upsets are responsible for the most fatalities in commercial aviation, but the behavior of an aircraft outside of its normal flight envelope is still not fully understood. Upsets impose a high risk to an aircraft and its crew, which makes gathering data through full-scale flight testing impossible in most cases. Although aerodynamic models can be obtained through other methods, such as wind tunnel tests and computational fluid dynamics (CFD), these have to be validated with real-world data. In this work, this was achieved with a sub-scale test vehicle and the resulting enhanced aerodynamic representation can be used to improve pilot training, develop advanced fly-by-wire systems, and guide future aircraft designs.

Perspectives