Variable-span wing development for improved flight performance

Abstract

This paper describes the development and testing of a variable-span wing (VSW) concept. An aerodynamic shape optimisation code, which uses a viscous two-dimensional panel method formulation coupled with a non-linear vortex lattice algorithm and a sequential quadratic programming optimisation routine, is used to solve a drag minimisation problem to determine the optimal values of wing span for various speeds of the vehicle’s flight envelope while subject to geometric constraints. Structural design is performed using the finite element method for static analysis where the particular interface between wing parts is conveniently modelled. A full-scale prototype is built for ground testing the wing/actuator system. The wing is built in composite materials and an electro-mechanical actuation mechanism is developed using an aluminium rack and pinion system driven by two servomotors. Bench tests, performed to evaluate wing under load, showed that the system is capable of performing the required extension/retraction cycles and is suitable to be installed on a UAV airframe fully instrumented for evaluating the VSW concept prototype in flight. The data collected from the performed flights showed full functionality of the VSW and its aerodynamic improvements over a conventional fixed wing for the higher speed end of the flight envelope.