Limited life engines for UAVs

Abstract

The ever expanding range of applications for unmanned air vehicles covers a wide variety of powerplant requirements. While many vehicles are high value assets and demand similar powerplant attributes to a conventional manned aircraft, there is an emerging requirement for powerplants which are designed to a limited life philosophy. This covers a range of applications: at the simplest level there are vehicles where the mission definition dictates that attrition rates will be high, for example low level reconnaissance, targeting or battle damage assessment, and the entire vehicle may only be expected to make a short number of missions. On the other hand there are applications where it may be more cost effective to remove the need for engine maintenance and to treat the powerplant as a disposable limited life unit.

In general, the industry trend is towards the reduction of life cycle costs, and a significant emphasis is placed upon continuing to increase aero-engine component lives though novel design and improved manufacturing techniques. A limited life application calls for a different approach, as it may be that the powerplant has a life requirement of anywhere between 50 and 250 hours. This allows scope to explore areas of design and manufacture which would not be suitable for a ‘conventional’ engine and can lead to large reductions in engine cost.

This paper seeks to identify the primary cost drivers for a small UAV powerplant in the 10kN thrust class, and to establish the relationships between cost, life and performance at both a whole engine and an individual component level. It also explores the feasibility of using new or unconventional designs and manufacturing methods, and presents a selection of examples.