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This document defines and illustrates the process for determination of uncertainty of turbofan and turbojet engine in-flight thrust and other measured in-flight performance parameters. The reasons for requiring this information, as specified in the E-33 Charter, are: determination of high confidence aircraft drag; problem rectification if performance is low; interpolation of measured thrust and aircraft drag over a range of flight conditions by validation and development of high confidence analytical methods; establishment of a baseline for future engine modifications. This document describes systematic and random measurement uncertainties and methods for propagating the uncertainties to the more complicated parameter, in-flight thrust. Methods for combining the uncertainties to obtain given confidence levels are also addressed. Although the primary focus of the document is in-flight thrust, the statistical methods described are applicable to any measurement process.

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.

This report covers engine tests performed in Altitude Test Facilities (ATFs) with the primary purpose of determining steady state thrust at simulated altitude flight conditions as part of the in-flight thrust determination process. As such it is complementary to AIR1703 and AIR5450, published by the SAE E-33 Technical Committee. The gross thrust determined using such tests may be used to generate other thrust-related parameters that are frequently applied in the assessment of propulsion system performance. For example: net thrust, specific thrust, and exhaust nozzle coefficients. The report provides a general description of ATFs including all the major features. These are: Test cell air supply system. This controls the inlet pressure and includes flow straightening, humidity and temperature conditioning. Air inlet duct and slip joint. Note that the report only covers the case where the inlet duct is connected to the engine, not free jet testing.

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.

The report shows how the methodology of measurement uncertainty can usefully be applied to test programs in order to optimize resources and save money. In doing so, it stresses the importance of integrating the generation of the Defined Measurement Process into more conventional project management techniques to create a Test Plan that allows accurate estimation of resources and trouble-free execution of the actual test. Finally, the report describes the need for post-test review and the importance of recycling lessons learned for the next project.

This report covers engine tests performed in Altitude Test Facilities (ATFs) with the primary purpose of determining steady state thrust at simulated altitude flight conditions as part of the in-flight thrust determination process. As such it is complementary to AIR1703 and AIR5450, published by the SAE E-33 Technical Committee. The gross thrust determined using such tests may be used to generate other thrust-related parameters that are frequently applied in the assessment of propulsion system performance. For example: net thrust, specific thrust, and exhaust nozzle coefficients. The report provides a general description of ATFs including all the major features. These are: Test cell air supply system. This controls the inlet pressure and includes flow straightening, humidity and temperature conditioning. Air inlet duct and slip joint. Note that the report only covers the case where the inlet duct is connected to the engine, not free jet testing.

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.

AIR 4065, "Propeller/Propfan In-Flight Thrust Determination" addresses steady state propeller thrust as applied to aircraft which are usually powered by gas turbine engines. It includes theory, examples and methods which have been used. Specifically two methods are discussed, the "J" or traditional J,Cp,Ct, η method including the SBAC variation and a new method we call the "Theta" method which is dependent on knowing blade angle, power/torque and flight Mach number. Implementation guidelines are offered as well as overall approaches to flight testing. Appendices include expansions on theory and testing as well as examples.

The purpose and intent of Subcommittee E-33E’s effort, the reporting objectives, and the limitations inherent in the reported findings and recommendations are reviewed since these factors are the basis of the information contained in this document. SAE E-33E Subcommittee was formed to assess the level of industry experience that exists in the area of thrust determination during aircraft time-variant operating conditions. A prime objective was to provide a center for gathering expertise and to be a forum for the exchange of ideas and viewpoints. The committee recognized that a practice for the rigorous treatment of time-dependent thrust did not exist and that several critical aspects of its accounting would need to be investigated.

This document defines and illustrates the process for determination of uncertainty of turbofan and turbojet engine in-flight thrust and other measured in-flight performance parameters. The reasons for requiring this information, as specified in the E-33 Charter, are: - determination of high confidence aircraft drag - problem rectification if performance is low - interpolation of measured thrust and aircraft drag over a range of flight conditions by validation and development of high confidence analytical methods - establishment of a baseline for future engine modifications This document describes systematic and random measurement uncertainties and methods for propagating the uncertainties to the more complicated parameter, in-flight thrust. Methods for combining the uncertainties to obtain given confidence levels are also addressed. Although the primary focus of the document is in-flight thrust, the statistical methods described are applicable to any measurement process.

The purpose and intent of Subcommittee E-33E’s effort, the reporting objectives, and the limitations inherent in the reported findings and recommendations are reviewed since these factors are the basis of the information contained in this document. SAE E-33E Subcommittee was formed to assess the level of industry experience that exists in the area of thrust determination during aircraft time-variant operating conditions. A prime objective was to provide a center for gathering expertise and to be a forum for the exchange of ideas and viewpoints. The committee recognized that a practice for the rigorous treatment of time-dependent thrust did not exist and that several critical aspects of its accounting would need to be investigated.