Drone Aerodynamics: MUAS Rotor-Rotor Interaction Effects

Multi-rotor Unmanned Aircraft Systems (MUAS), also known as “drones”, are an emerging technology that have been applied to a growing number of civil and defence applications. MUAS use several closely-spaced fixed-pitch rotors to provide thrust and attitude control, with some configurations using sixteen or more rotors. The dynamic and aerodynamic models used to develop these systems typically consider each rotor to be operating in isolation, and do not account for aerodynamic interference effects in hover and forward flight conditions.

Smoke flow visualisation of quadrotor wakes

Studies of manned helicopters have identified that aerodynamic interactions between closely spaced rotors can have negative impacts on stability and performance, however, the impacts of these interactions on small-scale rotorcraft operating at low Reynolds numbers are not well understood. To further develop this research, experimental methods were used in this research project to study the influence of rotor-rotor aerodynamic interactions on individual rotor performance and overall propulsion system efficiency for MUAS. The research focused on hover and steady level flight conditions for quadrotor configurations.

“Adjustaquad” flying test rig demonstrating changes to longitudinal rotor separation.

Experimental flow analysis methods including Particle Image Velocimetry (PIV) and multi-hole pressure probes were used to identify primary flow mechanisms responsible for changes in rotor performance. Empirical models were developed from these measurements that can be used to optimize the efficiency of MUAS designs for different applications and improve control system aerodynamic models. It is hoped that this research could lead to MUAS designs that are optimised for specific flight profiles, such as long-range package delivery or racing.

 

Sam Prudden