Infotech@Aerospace 26 - 29 September 2005, Arlington, Virginia
Conceptual Design of UAV Airframes Using a Generic Geometry Service
Andr´s S´bester∗, Andy J. Keane† a o James Scanlan‡ Neil W. Bressloﬀ§ , University of Southampton, Southampton, Hampshire, SO17 1BJ, UK
With the increased freedom in layout selection possible when designing an Unmanned Air Vehicle (UAV) concept(compared, for example, to the relatively constrained and mature world of commercial airliner design), comes the signiﬁcant challenge of building a geometry engine that will provide the variety of airframe models demanded by the highly global nature of the design search. In order to enable multidisciplinary trade-oﬀ studies, both an external surface and an internal structure are required – we usea single, generic model to supply these, in the form of a parametric geometry residing in a commercial CAD tool. In addition to discussing the challenges of oﬀering a truly ﬂexible geometry service, we also delve into the UAV-speciﬁc issues of the initial sizing of the model. A wealth of statistical data provides one of the traditional handholds for this step in manned aircraft conceptual design –we discuss the applicability of such statistical approaches to their unmanned counterparts.
HE techniques of aircraft conceptual design have come a long way over the ﬁrst century of ﬂight. The design algorithms advocated by modern textbooks1–3 are distillations of a vast
body of collective engineering experience and are underpinned by a wealth of design, manufactureand ﬂight data. However, the knowledge base that lies at their foundation, though very broad, is inevitably biased towards the aircraft categories that form the bulk of today’s commercial and military ﬂeets and the workﬂows of these design processes are also better suited to certain applications than to others. One of the roads less well traveled is the design of unmanned air systems and this isour main motivation here. Although Unmanned Air Vehicles (UAVs) go back almost as far as aviation itself, they only account for a fairly small proportion of the combined design eﬀort of the aircraft industry over the past decades and this is reﬂected to some extent in our current ability to conduct eﬀective UAV conceptual design studies. The ﬁrst UAV-speciﬁc challenge of conceptual design – themore limited availability of historical data – can have a signiﬁcant impact on the initial steps of most current design algorithms. Tradition∗ Research
Fellow, Computational Engineering and Design Group, AIAA Member. of Computational Engineering, Chair of Computational Engineering and Design Group. ‡ Professor of Engineering Design, Computational Engineering and Design Group. § Senior ResearchFellow, Computational Engineering and Design Group.
1 American Institute of Aeronautics and Astronautics
Copyright © 2005 by the Authors. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.
ally, these preliminary sizing techniques have a strong statistical bent and, inevitably, the data that they are based on is mostly related to mannedaircraft. Although correction factors can go some way towards mitigating this (Raymer3 recommends using 0.5 − 0.7 crew members in weight calculations to account for the systems that replace the human pilot), inaccuracies can still arise. For example, it is not obvious how much weight penalty is accrued by designing an airframe to accommodate a pressurized cockpit, doors, crew escape systems, airconditioning systems, active and passive safety elements, landing gears (which some UAVs do not have), etc. Another diﬃculty lies in the vast design space UAV designers tend to have at their disposal. Consider, for example, the category of High Altitude Long Endurance (HALE) UAVs. The Northrop Grumman RQ-4A Global Hawk, the Aurora Flight Sciences Theseus and the Scaled Composites Proteus,...
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