Overview

The objective of propulsion systems analysis is to determine the best propulsion system for some application. Because an engine generally takes longer to design and develop than an aircraft, the needs that will be associated with future aircraft systems must be anticipated by the engine manufacturer well in advance of the commitment to the design of a new aircraft. Thus, "preliminary design" of engines to meet the needs of new aircraft (and in some cases to make possible the design of new families of aircraft) is an essential part of engine design. Components must be designed and developed on the basis of preliminary engine designs before an engine manufacturer can commit to a final engine design, and long before an aircraft system is committed to design and development.

In the preliminary design phase the criteria for optimization of the engine will usually be stated in rather general terms; for example, it may be desired to determine the "best" engine for a next-generation commercial transport to serve medium-range hub-and-spoke routes, with a capacity of about 150 passengers. In this case, "best" would mean the engine that would lead to the most profitable aircraft while meeting environmental constraints. But the best engine design depends on the aircraft design, so the engine manufacturer must include in his engine studies all those aircraft possibilities most likely to be optimum. For a high-performance military fighter, "best" might at one time have been defined as minimum takeoff gross weight to carry a given load of...