The determination of in-flight thrust can be a complex process. Success depends upon careful planning and meticulous attention to detail throughout the test program. It is important that the participants involved (engine and airframe manufacturers, military service, government agency, etc.) agree at the outset on the definitions and the methods to be used for demonstration. Provision for flexibility and redundant methods is important to provide for unforseen difficulties with a particular method.

There are no industry or government standards for determining in-flight thrust or associated uncertainty at present. The purpose of this AIR is to present information and guidance on the selection of methodologies to predict and assess propulsion system thrust during flight development programs of conventional aircraft employing turbofan or turbojet engines. Methodologies beyond those presented are required in order to evaluate configurations such as vectored thrust or V/STOL aircraft. The document is intended to be used as a technical guide, not as a standard or legal document. A companion document, SAE AIR 1678, presents procedures for the estimation of uncertainty of in-flight thrust determination. Both documents describe comprehensive procedures and tasks for implementing the methodologies. Each program would select those tasks that are appropriate to meet its particular objectives.

This report reviews the major aspects of processes that may be used for the determination of in-flight thrust. It includes discussions of basic definitions, analytical and ground-test methods to predict installed thrust of a given propulsion system, and methods to gather data and calculate thrust of the propulsion system during the flight development program of the aircraft. Much of the treatment is necessarily brief due to space limitations. This document and the British Ministry/Industry Drag Analysis Panel (MIDAP) Guide, which SAE Committee E-33 used as a starting point, can be used to understand the processes and limitations involved in the determination of in-flight thrust.(1.1)(Footnote *) Application to a specific in-flight thrust determination program will require the use of many important assumptions not fully developed herein, and these assumptions must be evaluated during the conduct of the program.

Footnote * - References are listed in Section 9.