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Goals and Constraints

At the most basic level, a UAV aims to carry a payload over a specified distance or for a specified length of time, often at some desired cruise speed and height. The payload may be a simple dumb mass or may be active in some way, requiring power supplies or the ability, in the widest sense, to “see” its environment and perhaps communicate with the ground or other aircraft. It is also commonly the case that the precise payload and mission details will vary

Small Unmanned Fixed-wing Aircraft Design: A Practical Approach, First Edition. Andrew J. Keane, Andras Sobester and James P. Scanlan.

©2017 John Wiley & Sons Ltd. Published 2017 by John Wiley & Sons Ltd.

Explosion of information content as design progresses

Figure 8.1 Explosion of information content as design progresses.

over the life of the design and even the life of an individual airframe. Thus designers are also keenly interested in the impact of payload and mission changes on aircraft performance. It is often useful to carry out concept evaluation using a range of missions and payloads so as to ensure that a suitably flexible design emerges. These can then be considered using a raft of multiobjective decision-making aids so as to identify the concepts worthy of more detailed and time-consuming assessment. We have, for example, used event-based simulation tools to assess maritime search aircraft in realistic scenarios. It must be remembered though, that all vehicle design leads to multiple goals and that whatever aids are used, the eventual trade-off choices between performance across these goals will have to be taken by the designer, usually in collaboration with the eventual end users. It is also important to note that many goals are expressed in the form of constraints: for example, the maximum speed must be at least 40 m/s, or the service interval must be at least 100 h of flight. The most commonly encountered user goals in UAV design (in no particular order) are as follows:

  • • maximum speed
  • • maximum operational ceiling
  • • maximum range
  • • maximum endurance
  • • maximum service interval
  • • maximum payload mass
  • • minimum purchase and service costs.

To optimize one or more of these goals, the designer will probably work with more technical quantities, such as wing and overall airframe lift to drag ratios, stall speeds, wing aspect ratio and loading, and so on.

 
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