Distributed propulsion and future aerospace technologies

Abstract

This thesis describes an Engineering Doctorate project in Distributed Propulsion carried out from 2004 to 2007 at Cranfield University. Distributed propulsion is a propulsion system arrangement that consists in spreading the engine thrust along the aircraft span. This can be accomplished by distributing a series of driven fans or the engines themselves. The aim of this project is to determine the feasibility of distributed propulsion for civil aviation in the medium term (with small gas turbines) and long term (with driven fans) from a technical and economic perspective. The effect of distributed propulsion was assessed by creating a long-range subsonic airliner baseline with conventional technology for the small gas turbines study, and an equivalent blended wing body baseline for the driven fans study. Different distributed propulsion effects were modelled and integrated together to produce optimised baselines with different technological parameters. The feasibility of small gas turbine distributed propulsion was found to be limited by the excessive fuel consumption associated with small gas turbines. Although advanced heat exchanger technology could improve their performance, the resulting cost advantage might not be large enough to justify the development costs. The feasibility of distributed driven fans depends on the availability of superconductive elements, as electrical power transmission seems to be the only promising transmission method in the long run. If superconductive elements are applied, distributed driven fans could afford fuel burn reductions of more than 50% relative to current technology. As both distributed propulsion concepts rely on small propulsive units, their enabling technologies coincide with those required to develop future unmanned aerial vehicles. UAVs therefore represent the most appropriate technological avenue to develop technologies with the potential to become distributed propulsion enablers. Future work should therefore concentrate on improving engine performance and cost for unmanned aerial vehicles.