PERFORMANCE AND CONTROL OF VARIABLE GEOMETRY AIRCRAFT INLETS

The aircraft inlet today is considered an integral part of all air breathing propulsion systems. The significance of inlets in high speed aircraft propulsion systems is well illustrated by citing their contribution to compression in a turbo-jet engine installation. At Mach number 2.0 the compression ratio of the induction system is approximately equal to the compression ratio of an axial compressor in a typical high compression turbo-jet engine installation.

The principles of inlet design are presented in this paper with special emphasis on the problems of matching inlets to turbo-jet engines. The requirements of matching over a large speed range lead to considerations of variable geometry in inlet design. Performance penalties incurred with fixed geometry are demonstrated and analysed. Wind tunnel performance characteristics and a description of a specific design which incorporates both variable throat and capture area is presented to illustrate some capabilities of variable geometry design.

Finally, a review is made of some approaches to the problem of controlling inlets in high speed flight. Both closed-loop and scheduled controls are considered.