1、_6$(7HFKQLFDO6WDQGDUGV%RDUG5XOHVSURYLGHWKDW7KLVUHSRUWLVSX EOLVKHGE6$(WRDGYDQFHWKHVWDWHRIWHFKQLFDODQGHQJL neering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any paUWLFXODUXVHLQFOXGLQJDQSDWHQWLQIULQJHPHQWDULVLQJWKHUHIURPLVWKHVRO HUHVSRQVLELOLWRIWK
2、HXVHUSAE reviews each technical report at least every five years at which time it may be revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments and suggestions.Copyright 2017 SAE InternationalAll rights reserved. No part of this publication may be reproduced, stored in a re
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4、rServicesae.orgSAE WEB ADDRESS: http:/www.sae.orgSAE values your input. To provide feedback on thisTechnical Report, please visithttp:/standards.sae.org/AIR4951AEROSPACEINFORMATION REPORTAIR4951Issued 2011-06Reaffirmed 2017-02Test Cell Thrust MeasurementRATIONALEAIR4951 has been reaffirmed to comply
5、 with the SAE five-year review policy.1. SCOPEThrust measurement systems come in many sizes and shapes, with varying degrees of complexity, accuracy and cost. For the purposes of this information report, the discussions of thrust measurement will be limited to axial thrust in single-axis test system
6、s. 1.1 Purpose There are several purposes served by this information report: a. To provide guidelines for the specification of thrust measurement systems.b. To address the major factors which can influence thrust measurement uncertainty.c. To consider the operational characteristics and the effects
7、on system performance.2. REFERENCESThe following publications form a part of this document to the extent specified herein. The latest issue of SAE publications shall apply. The applicable issue of the other publications shall be the issue in effect on the date of the purchase order. In the event of
8、conflict between the text of this document and references cited herein, the text of this document takes precedence. Nothing in this document, however, supersedes applicable laws and regulations unless a specific exemption has been obtained. 2.1 Applicable Documents 2.1.1 ASME Publications Available
9、from American Society of Mechanical Engineers, 22 Law Drive, P.O. Box 2900, Fairfield, NJ 07007-2900, Tel: 973-882-1170, www.asme.org.ASME 86-WA-DE-3 Evaluating and Testing of Turbofan Jet Engines, miller, T.M., 1986 ASME PTC 19.1-2006 Test Uncertainty 2.1.2 ISO Publications Available from Internati
10、onal Organization for Standardization, 1, rue de Varembe, Case postale 56, CH-1211 Geneva 20, Switzerland, Tel: +41-22-749-01-11, www.iso.org.ISO/IEC Guide 98-1-2009 Uncertainty of measurement - Part 1: Introduction to the expression of uncertainty in measurementISO/IEC Guide 98-3:2008 Uncertainty o
11、f measurement - Part 3: Guide to the expression of uncertainty in measurement (GUM:1995) 2.1.3 Other Publications Covert, E.: “Thrust and Drag: Its Prediction and Verification“, Volume 98, Progress in Astronautics and Aeronautics, American Institute of Aeronautics and Astronautics, 1985. Ashwood, P.
12、F. et al.: “Operation and Performance Measurements on Engines in Sea Level Test Facilities“, AGARD Lecture Series No. 132 (AGARD-LS-132), Advisory Group for Aerospace Research and Development, North Atlantic Treaty Organization, Neuilly-sur-Seine, France, 1984. Stroud, J.F.: “Propulsion System Testi
13、ng Requirements for a Commercial Transport“, AGARD CP-293, 1981. Roberts, J.H., et al.: “Engine Thrust Measurement Uncertainty“, AIAA 85-1404, 1985. MacWhorter, R.F.: “F404-GE-400 NARF Engine Test Cell Mount System Vibration Test“, General Electric Component Development Laboratory, TN4759, 1981. 2.2
14、 Definitions ANGULAR LOAD, CONCENTRIC: A load applied concentric with the primary axis at the point of application and at some angle with respect to the primary axis. ANGULAR LOAD, ECCENTRIC: A load applied eccentric with the primary axis at the point of application and at some angle with respect to
15、 the primary axis. AXIAL LOAD: A load applied along or parallel to and concentric with the primary axis. CALIBRATION: The comparison of thrust frame output to a standard load. A calibration curve is obtained by performing a calibration at a number of increasing and decreasing load points. COMBINED E
16、RROR: The maximum deviation of output from a straight line drawn between the no-load and rated load outputs expressed as a percentage of the rated output and measured on both increasing and decreasing loads. COMPENSATION: The use of supplementary devices, materials, or processes to minimize known so
17、urces of error. CREEP: The change in load cell output occurring with time while under a constant load condition and with all environmental conditions remaining constant. Usually measured at the rated load and expressed as a percentage of the rated load over a specific period of time. DEFLECTION: The
18、 change in length along the primary axis of the load cells between no-load and rated load conditions. ERROR FACTORS: Systematic and random differences between the measured and true value of the parameter being measured, the combination of which comprise the measurement uncertainty.EXCITATION, ELECTR
19、ICAL: The voltage or current applied to the terminals of the load cell. SAE INTERNATIONAL AIR4951 2 OF 18FLEXURE: A plate or cylinder incorporating two areas of reduced thickness (webs) which act as pivots. Each pivot allows a rotation or pivoting action as the result of elastic deformation in the a
20、reas of reduced thickness. GROUND FRAME: The part of the thrust frame structure which is rigidly attached to the building feature such as the roof or a foundation. It is also referred to as the fixed frame. HYSTERESIS: The maximum difference between output readings for the same applied load, one rea
21、ding being obtained by increasing the load from zero, and the other by decreasing the load from the rated load. It is usually measured at 50% of the rated load and expressed as a percentage of the rated load. LIVE FRAME: The part of the thrust frame structure which is suspended from the ground frame
22、 by the flexures. It is also referred to as the floating frame. LOAD: The force applied to the load cell. LOAD CELL: A device which produces an electrical signal proportional to the force applied to it. MEASUREMENT UNCERTAINTY: The difference between the measured value of a physical quantity and the
23、 true value of the same physical quantity.NON-LINEARITY: The maximum deviation of the calibration curve from a straight line drawn between the no-load, and rated load outputs, expressed as a percentage of the rated load, and measured on increasing load only. OVERLOAD RATING, SAFE: The maximum load,
24、in percent of rated capacity, which can be safely applied without producing a permanent shift in the performance characteristics beyond those specified. PRIMARY AXIS: The axis along which the load cell is designed to be loaded; normally its geographic centerline. RATED LOAD: The maximum thrust the t
25、hrust frame is designed to measure. Also referred to as rated capacity. REPEATABILITY: The maximum difference between individual thrust frame output readings for repeated loadings under identical load and environmental conditions. RESOLUTION: The smallest change in load input which results in a dete
26、ctable change in output. SENSITIVITY: The ratio of the change in output to the change in mechanical input. SHUNT CALIBRATION: The electrical simulation of load cell output by known shunt resistors between appropriate points within the circuitry. SIDE LOAD: Any load acting perpendicular to the primar
27、y axis at the point of the load application. TEMPERATURE RANGE COMPENSATED: The range of temperature within which the load cell is compensated to maintain rated output and zero balance within specific limits. TEMPERATURE COEFFICIENT: The change in load cell output per unit change in temperature at a
28、 constant load condition and with all other environmental conditions remaining constant. Usually specified as effect on sensitivity in % of reading /T and effect on zero in % of rated output/T.THRUST STAND: Test cell fixture used to support and interface with the engine adapter. Consists of ground a
29、nd live frames and contains the thrust measurement and in-frame calibration system components. Sometimes referred to thrust frame or test stand.ZERO BALANCE: The output signal of the load cell with rated excitation and with no-load applied, usually expressed in percent of rated output. ZERO SHIFT: A
30、 change in the no-load output. SAE INTERNATIONAL AIR4951 3 OF 183. THEORY OF THRUST MEASUREMENT The basic challenge of thrust measurement in a test cell thrust stand is that the engine develops its thrust on the engine centerline. It is not feasible to mount thrust measurement equipment on centerlin
31、e either in front of the engine under test, where it would disturb the engine intake air, or behind it, where it would be in the hot and high-velocity exhaust stream. The practical solution is to provide a thrust stand, which consists of a pair of rigid frames that are designed to support and constr
32、ain the engine under test in such a way that it is possible to measure the thrust of the engine without placing any obstacles in the engine air paths. The thrust stand has a fixed element, which is attached to the ground or to some part of an enclosing building (a test cell), and a moving element (s
33、ometimes called the live or floating frame), which carries the engine under test. The moving element of the thrust stand is supported from the fixed element by some means which will carry the weight of the moving element and the engine under test, yet will move as freely as possible in response to t
34、he engines thrust. The thrust produced by the engine is transmitted, through a force measuring device, from the moving element of the thrust stand to its fixed element, and thence to the ground or to the building which houses the thrust stand. A typical overhead thrust stand configuration for gas tu
35、rbine engine testing is shown in Figure 1. FIGURE 1 THRUST FRAME CONFIGURATION The mechanical design of the thrust stand may require that the engine thrust be measured with a single load cell in tension, a single load cell in compression, a pair of load cells in compression or a pair of load cells i
36、n tension. When utilizing a pair of load cells, the load cell outputs are summed to obtain the applied load. Some systems that accommodate a wide range of engine thrusts incorporate “stacked” load cells that consist of axially connected low and high range load cells. When utilizing a stacked load ce
37、ll arrangement care must be taken not to overload the lower range load cell, which is usually accomplished by mechanical stops internal to the load cell, and to consider in the uncertainty analysis the side load applied to the high range load cell by the attached and overhung low range load cell. SA
38、E INTERNATIONAL AIR4951 4 OF 18Preload may applied to the thrust stand floating frame to reduce certain error factors of thrust measurement uncertainty or to provide reverse thrust measurement capability. Typically, preload is mechanically or hydraulically applied, independently measured and subtrac
39、ted from the measured thrust. Preload can be applied as either a constant force in the forward thrust direction or as a force equally applied to opposing load cells, resulting in minimal floating frame deflection at no applied thrust. The applied preload may compensate for zero offsets due to the ma
40、ss and center of gravity of different engine/adapter combinations. With opposing load cells, the subtraction can reduce the effect of load cell temperature changes, especially if the measurement and preload load cell temperature coefficients are closely matched. In systems with a constant preload th
41、e preload value is usually set to 10% 15% of the measurement range. In a system with opposing load cells the preload is typically set to a value equal to 55% to 60% of the thrust measurement range, which will ensure the preload does not unload at maximum thrust.Figure 2 is a basic schematic (free-bo
42、dy) representation of the moving element of a thrust stand and the forces which act on it.TransferStandardLoadCellHydraulicCalibrationRamPortMeasurementLoadCellStarboardMeasurementLoadCellForwardThrustGroundFrameLiveFrameFlexuresbetweenliveandgroundframesFIGURE 2 - DIAGRAM OF MOVING ELEMENT The engi
43、ne thrust and the thrust measuring system produce a substantial couple (torque) which, in this case, causes an upward force at the front of the thrust stand and a downward force at its rear. With good design these are almost purely vertical forces. Thrust stand designers exert great care to minimize
44、 any horizontal (axial) components of force which are transmitted by the apparatus which supports the moving element of the thrust stand. In this way the force measured by the load cell(s) is very nearly equal to the actual thrust of the engine under test. The cosine law relationship between the eng
45、ine (and therefore thrust) centerline and the horizontal component of thrust means that small angular displacements of the engine will have minimal effect on the measured thrust. 3.1 Thrust Measurement Uncertainty As with all other engine operating parameters which are to be observed during an engin
46、e performance test, each engine manufacturer specifies the allowable uncertainty with which thrust must be measured. Typical OEM specifications require thrust measurement system accuracy in the range of 0.10% to 0.35% of reading at maximum takeoff thrust.Basic test cell thrust measurement is only on
47、e element of the overall uncertainty that is applicable in establishing the gross thrust of an engine in an indoor test cell. For indoor ground-level testing of jet engines, the aerodynamic forces in an indoor test cell influences the thrust produced by the engine. The “true“ gross thrust may be der
48、ived from the measured thrust if the aerodynamic conditions inside the test cell are established. The “test cell effect“ may also be quantified using correlation factors determined from comparison of test data taken from indoor facilities, and reference outdoor, or “free-air“ test stands.SAE INTERNATIONAL AIR4951 5 OF 184. APPLICATIONS As with any measurement system, the type of thrust system used varies with the appl
