Design of a swept-wing High-Altitude Long-Endurance Unmanned Air Vehicle (HALE UAV)

Abstract

High-altitude aircraft flying in the stratosphere (around 17-30 km altitude) can provide a useful platform for sensors to support a range of military and civilian surveillance tasks. The main topic of the thesis concerns the analysis of solar powered unmanned aerial vehicles designed for extended flight operations at high altitudes. An aft-swept flying wing configuration has been adopted for high altitude applications. Specific topics that were considered focussed on the development of a conceptual design tool and a multi-disciplinary optimisation tool able to converge on the layout for a solar powered HALE UAV. A true aft-swept flying wing is perhaps the most aerodynamically efficient aircraft configuration but, to date, has not been investigated in any detail for possible application to high-altitude UAVs. Such a configuration would require a moderate amount of wing sweep in order to generate the necessary stability in flight and to provide adequate control power for manoeuvring purposes. All systems and elements can now be placed inside the wing without compromising the weight distribution. This avoids the need for drag inducing mass balancing pods and/or reflexed trailing edge associated with unswept (straight) flying wings. Such features can either increase structural weight and/or overall drag whilst reducing the maximum lift that can be achieved. However, the design, in common with the other more conventional aircraft, represents a substantial challenge due to the simultaneous addressing of numerous inter-related engineering disciplines required for a fairly comprehensive analysis. The innovative aspect of this study was dedicated to the conceptual and preliminary design of a high altitude long endurance solar powered aft-swept flying wing and study in detail the design challenges along with the general problems associated with flying at high altitudes. Moreover, these aims were achieved by the author developing new design tools. The conceptual design tool was created to include all the aircraft elements and the expected power losses in addition to representing the drag estimation of the wing section rather than using a general expression as only a function of Reynolds number regardless the aerofoil performance. The preliminary design tool, also written by the author, represented by the composite structure model and the quasi 3D aerodynamic solver combined in a multidisciplinary optimisation framework, proved its capability in determining the aircraft geometry, its weight and its aerodynamic and structural performance capabilities