Control and performance of small custer channel wing unmanned aircraft

Abstract

The demand for unmanned missions in places with limited runway length motivates the study of the Custer channel wing at the University of Southampton. Persisting stability issues of the existing Southampton Custer UAV were identified in slow flight, making it unsuitable for short landings. In this project, the Custer UAV flight dynamics is modelled to study the stability and dynamic effects associated with V/STOL operation. The aerodynamics model valid for standard airplanes is augmented for the high angle of attack operational range. Extensions are proposed to include the momentum of the spinning rotors, propeller slipstream, general thrust direction and channel wing lift augmentation effects. Based on model observations, a suitable control strategy for attitude stabilization using gain-scheduling has been developed and tested succesfully. The attitude dynamics was further investigated in flight tests running a system-identification program for validation of the model. Disagreement in the control effectiveness was found and attributed primarily to the structural effects that were not included in the model. The controller gains maximizing the performance with respect to the gain margins were determined by analyzing the system identification data. Satisfactory flying qualities are now attainable in slow flight using the developed stability augmentation system, allowing for V/STOL operation. Further improvements to the damping characteristics are suggested using the identified model and measured data. The Custer UAV slow flight and V/STOL performance has been measured with the help of the developed controller and evaluated in comparison to conventional take-off and landing. Favorable stall characteristics and a 2/3 runway length reduction are observed when using the channel-wings. With an accurate definition of the Custer UAV V/STOL abilities, categorization among other V/STOL concepts is conducted. Experimental comparison of the channel wing to a similar high-lift wing propeller arrangement in the form of a standard wing pusher propeller configuration shows the superior slow flight performance of the channel wing concept. This is at a cost of 7 % cruise and 9 % max speed reduction due to the extra drag from the channels. The flight test and static test experiments have been linked to the developed flight dynamics model for validation, and the errors in the modelled coefficients are pointed out where applicable. An instruction manual for operation of the installed control system, as well as a structural analysis of the channel wing are attached in separate reports to highlight some of the engineering challenges associated with the experimental work conducted in this project.

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Identifiers

ORCID for Juraj Mihalik: orcid.org/0000-0002-3810-197X

ORCID for Andy Keane: orcid.org/0000-0001-7993-1569

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