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The emerging ultra high bypass ratio ADP engines, with nozzle pressure ratios significantly lower, and bypass ratios significantly higher, than those of the current turbofan engines, may present new in-flight thrust determination challenges that are not specifically covered in AIR1703. This document addresses candidate methods and the additional challenges to the thrust determination for these ADP engines. These novel challenges result in part from the fact that some large ADP engines exceed present altitude test facility capabilities. The traditional methods of nozzle coefficient extrapolation may not be most satisfactory because of the increased error due to the ADP higher ratio of gross to net thrust, and because of the increased sensitivity of in-flight thrust uncertainty at the lower fan nozzle pressure ratio.

In-Flight Thrust Determination, SAE AIR1703 reviews the major aspects of processes that may be used for the determination of in-flight thrust (IFT). 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 (Reference 1.11), 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. Application to a specific in-flight thrust determination program will require the use of many important assumptions not fully developed in this document, and these assumptions must be evaluated during the conduct of the program.

In-Flight Thrust Determination, SAE AIR1703 reviews the major aspects of processes that may be used for the determination of in-flight thrust (IFT). 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 (Reference 1.11), 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. Application to a specific in-flight thrust determination program will require the use of many important assumptions not fully developed in this document, and these assumptions must be evaluated during the conduct of the program.

Propulsion measurements and thrust methods presented in the current published versions of AIR1703 and AIR5450 place a primary focus on the engine reactionary force (thrust) acting to propel an aircraft in the forward direction. In contrast, this document addresses the use of the engine reactionary force in the opposite direction (reverse thrust) to supplement aircraft deceleration. This document’s application spans commercial and military transport turbofan engine applications for various engine and reverse thrust configurations. The discussion and examples primarily focus on separate flow exhaust turbofan engines. Piston and turboprop variable-pitch propeller blade applications are not covered. Although reverse thrust has been utilized for in-flight deceleration, primarily for short takeoff and landing aircraft and military fighter applications, this application of reverse thrust is only covered in a cursory manner.