Wing Optimisation for Tractor Propeller Configurations

Abstract

Even though propellers are the oldest form of propulsion, they are still a popular choice for unmanned aerial vehicles (UAVs) and passenger aircraft in certain market segments. If the propellers are mounted on the wing, strong propeller-wing interactions alter the aerodynamic efficiency of the aircraft. Using low-order numerical models, it is shown in literature that the wing chord and twist distribution can be changed to maximise this efficiency. These results are only theoretical. This thesis, therefore, aims to validate and apply a numerical model for optimisation of the wing design taking propeller-wing interactions into account.

A vortex lattice method (VLM) was adapted to include the effects of propeller-induced velocities. Comparing the results of the adapted VLM with existing experimental data already validates the numerical model for predicting the lift distribution. To validate it for changes in lift distribution due to wing design changes, a wind-tunnel experiment is set up. Two wings are tested in a tractor propeller configuration. The only difference between the wings is in the twist distribution. To find the lift distribution, the circulation is evaluated in the flow around a wing at several stations along the wingspan. Particle-image velocimetry was used to obtain this flow field. Indeed, the lift distributions measured on both wings are matched by predictions from the adapted VLM, which proofs the numerical model is suitable for qualitative optimisation studies.

For the wing and operating conditions used for the wind-tunnel experiment, an optimisation study is performed using the adapted VLM. It shows the drag can be reduced with 34% by adopting the optimal chord and twist distribution. Even though the operating conditions are not representative for full-scale aircraft or UAVs, it does show there is a great potential for taking propeller-wing interactions into account for the design of the wing.