NOVEL PROPULSION CONCEPTS FOR MULTIROLE UNMANNED AIR VEHICLES

摘要

A study has been carried out to investigate the impact of differing engine types (turbofans and turboprops) on the performance of unmanned air vehicles configured to carry out the following roles: wide area surveillance (WAS) and tactical reconnaissance/attack (TRA). A vehicle optimized for the WAS role featured a high aspect ratio wing and twin pod mounted turboprops. In contrast, the TRA role favoured a low aspect ratio wing and an 'embedded' low bypass ratio turbofan. The endurance of a twin turboprop powered WAS aircraft could be substantially improved by shutting down one of the engines during loiter. A single 'multi-role' aircraft was defined with a medium aspect ratio wing and an 'embedded' turbofan, aimed at performing both roles.. This resulted in a substantial reduction in the endurance whilst performing the WAS role, compared with the optimized solution. An alternative concept is discussed which has detachable wings to allow a change in configuration for the differing roles. To compliment this concept, a novel re-configurable propulsion system is proposed called the "Flexi-prop". This features an 'embedded' low BPR turbofan, used during the TRA. Whilst for the WAS role an additional propeller unit(s) is added driven by a shaft from the turbofan LP spool. In this way, many of the benefits of both a turbofan and a turboprop are achieved. In the future, it may be possible to replace the mechanical drive system of the "Flexi-prop" with an electrical drive. This would confer advantages of improved reliability and operational flexibility. However, at present the electrical systems would be prohibitively heavy.