1、SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and enginee ring sciences. The use of this report is entirelyvoluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefr
2、om, is the sole responsibility of the user.”SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invit es your written comments and suggestions.Copyright 1998 Society of Automotive Engineers, Inc.All rights reserved. Printed in U.
3、S.A.QUESTIONS REGARDING THIS DOCUMENT: (724) 772-8510 FAX: (724) 776-0243TO PLACE A DOCUMENT ORDER: (724) 776-4970 FAX: (724) 776-0790SAE WEB ADDRESS: http:/www.sae.org400 Commonwealth Drive, Warrendale, PA 15096-0001AEROS PACE RECOMMENDED PRACTICESubmitted for recognition as an American National St
4、andardARP1702 RE V. AIssued 1982-04Revised 1998-09Defining and Measuring Factors AffectingHelicopter Turbine Engine Power AvailableINTRODUCTIONThe very nature of the engine installation on most helicopters inevitably results in some loss of power when comparing the installed performance of the engin
5、e with the specification level for an engine run on a test bench. This loss of installed power is clearly detrimental to the overall performance of the aircraft and it is in the aircraft manufacturers interest to minimize it. The aircraft flight manual is based on the engine manufacturers performanc
6、e specification for an uninstalled engine and the airframe manufacturers allowance for the installation power losses. Therefore, careful and accurate determination of the installation effects is essential to ensure safe operation of the aircraft.The engine manufacturer, having set the specification
7、performance level, will add operating margins to allow for the effects of in-service deterioration and to ensure satisfactory installed lives. In addition the known effects of such things as bleed extraction and anti-icing selection will be declared so that the aircraft manufacturer can make appropr
8、iate allowance for these penalties. An in-service power checking procedure will be defined which takes account of installation power losses when assessing the measured performance of the engine in the aircraft against the minimum uninstalled specification level. Any underestimate of the aircraft ins
9、tallation power losses will make the installed performance of the engine appear worse than it truly is and so can lead to premature rejections for low power. It is, therefore, also in the engine manufacturers interest to ensure that installation losses are accurately measured.The determination of th
10、e installation power losses and the flight manual validation for a particular aircraft/engine combination is the responsibility of the aircraft manufacturer. However, accurate measurement of installation effects is not easy and will only be achieved through careful cooperation between aircraft and e
11、ngine manufacturers. While the individual concerns of the two parties may differ they share the common goal of accurately determining installation power losses and wherever possible ensuring that these are minimized.SAE ARP1702 Revision A- 2 -1. SCOPE: This SAE Aerospace Recommended Practice (ARP) i
12、dentifies and defines a method of measuring those factors affecting installed power available for helicopter power plants. These factors are installation losses, accessory power extraction, and operation effects. Accurate determination of these factors is vital in the calculation of helicopter perfo
13、rmance as described in the flight manual. It is intended that the methods herein prescribe and define each factor as well as an approach to measuring said factor. Only standard installations of turboshaft engines in helicopters are considered. Special arrangements leading to high installation losses
14、, such as the fitting of an infrared suppressor may require individual techniques for the determination and definition of engine installation losses.2. APPLICABLE DOCUMENTS: The following publications form a part of this document to the extent specified herein. The latest issue of SAE publications s
15、hall apply. The applicable issue of other publications shall be the issue in effect on the date of the purchase order. In the event of conflict between the text of this document and references cited herein, the text of this document takes precedence. Nothing in this document, however, supersedes app
16、licable laws and regulations unless a specific exemption has been obtained.2.1 SAE Publications: Available from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001.ARP1217 Instrumentation Requirements for Turboshaft Engine Performance MeasurementsAIR1419 Inlet Total Pressure Distortion Considerat
17、ions for Gas Turbine EnginesARP1420 Gas Turbine Engine Inlet Flow Distortion GuidelinesAIR1678 Uncertainty of In-Flight Thrust DeterminationARP4056 Helicopter Turbine Engine Exhaust Design2.2 Other Publications: AEDC-TR-73-5 Handbook: Uncertainty in Gas Turbine Measurements3. DEFINITIONS: Factors af
18、fecting power available at the engine output shaft are listed as follows:3.1 Installation Losses: a. Air intake total pressure lossb. Air intake total temperature risec. Exhaust gas back pressured. Air intake total pressure and temperature distortionSAE ARP1702 Revision A- 3 -3.2 Accessory Power Ext
19、raction: 3.2.1 Gas Generator and/or Power Turbine Accessory Power Extraction: a. Accessory pad power, blowers, pumps, compressor, etc.3.2.2 Compressor Bleed Air Extraction: a. Anti-icing, environmental control, etc.3.3 Operational Effects: a. Power turbine output shaft speed off optimum effectsb. En
20、gine thermal stabilizationc. Altitude, airspeed and ambient temperature conditionsd. Crosswind/tailwind conditions4. DISCUSSION: 4.1 Engine air inlet total pressure loss is best defined as that loss incurred by the air flowing from the atmosphere to the engine/aircraft inlet interface plane. It is n
21、ormally attributable to friction, turbulence, diffusion and bend losses. Its effect on net power output is manifested by a reduction in engine air mass flow and pressure available at the power turbine. In forward flight the degree of free stream total pressure or “ram” recovery achieved by the aircr
22、aft intake must also be considered.A good rule of thumb for all turbines stipulates intake pressure loss expressed as a percentage of the total pressure available multiplied by two, is an approximation of the power loss (i.e., 1% delta Pti = 2% power). Each engine manufacturer, in the model specific
23、ation or performance computer model (customer deck), gives the best estimate performance loss which is calculated by inputting the appropriate pressure loss.4.2 The air inlet temperature rise is that increase in compressor intake air temperature above free stream stagnation temperature. This increas
24、e can be the result of exhaust gas ingestion, anti-icing air discharge from the intake, leaks in the inlet ducting allowing hot zone air to be ingested and/or heat transfer through the intake ducting. This can be a significant loss since 1 C (2 F) represents approximately a 1/2 to 1% power loss when
25、 operating at limit turbine temperature. Good duct design and location can usually prevent temperature rise from exceeding 2 C (4 F) in the hover condition with head wind. However, for small helicopters where the engine inlet flow is used for cooling the main rotor gearbox, higher levels of temperat
26、ure rise will inevitably be suffered.4.3 Exhaust gas back pressure power loss is due to the increased back pressure in excess of that imposed by the engine manufacturers diffuser (datum) tailpipe resulting from additional bends, a different effective exit area and/or the incorporation of an exhaust
27、ejector. A good rule of thumb for all turbine engines is 1% increase in total exhaust back pressure loss results in approximately 1% power loss.SAE ARP1702 Revision A- 4 -4.4 Air intake total pressure and total temperature distortion can affect compressor performance and surge margin. The effect can
28、 be estimated but is generally measured from an engine test which simulates radial and circumferential inlet distortion of total pressure and temperature. Installed pressure and temperature distortion is measured during flight testing of the aircraft with instrumentation specified by the engine manu
29、facturer. Levels of distortion are calculated by procedures defined by the engine manufacturer. AIR1419 and ARP1420 should be consulted for a wider appreciation of inlet distortion effects. It should be noted that excessive inlet distortion could have mechanical as well as performance implications f
30、or the engine compressor. The engine manufacturers installation documentation should be consulted for any limitations.Inlet pressure distortion will tend to reduce engine mass flow for a given gas generator speed. Since power is directly related to mass flow for a given engine speed or temperature,
31、it follows that such an effect will reduce power available for a given value of either parameter. If a significant level of inlet pressure distortion is present this will manifest itself as a loss of power on both a temperature and speed base.Inlet temperature distortion will cause the engine compre
32、ssor to operate at values of corrected speed (XN/ a20T) which can vary in both a circumferential and radial sense. Since both compressor mass flow and efficiency are functions of corrected speed it is possible for inlet temperature distortion to adversely affect both these parameters. Reductions in
33、mass flow and efficiency will both result in a loss of engine power available.Inlet temperature distortion can result in an erroneous inlet temperature measurement (either high or low) due to the limited measurement locations. This may cause the control to set off optimum conditions of stator vanes
34、or other control schedules, or may unnecessarily limit the output power.It is possible, in extreme cases, for inlet distortion to affect the outlet temperature profile of the engine combustion system. Since gas temperature is measured at a limited number of positions, it is possible for this change
35、in profile to result in an apparent change of measured temperature. Such an effect can lead to an apparent power penalty by raising the mean measured gas temperature at a given running condition. Such an effect is not readily discernible and if suspected may require the assessment of individual ther
36、mocouple readings or the use of a special multi-point harness.4.5 Mechanical power can be extracted from several sources such as the gas generator rotor or power turbine drive train. Power extracted from the compressor rotor generally incurs a larger penalty than that taken from the power turbine. P
37、ower extracted from the compressor rotor changes the thermodynamic match of the compressor and gas generator turbine which requires an increase in fuel flow to maintain output power (necessary to maintain the required rotor speed) and a corresponding increase in engine reference temperature. Engines
38、 that are rated on gas generator speed will exhibit a gain in power when mechanical offtake is applied to the gas generator shaft providing this does not cause the engine temperature to increase to the limiting value. For engines rated on gas generator speed the offtake power should wherever possibl
39、e be set to zero when determining the installed power available. It should be noted that some engine performance specifications already include the effects of mechanical offtakes and care must always be taken in the accounting of these effects.SAE ARP1702 Revision A- 5 -4.6 Bleed air extraction powe
40、r effects occur when compressor air is utilized for cabin heating, air conditioning, engine inlet anti-icing, etc. It becomes an unrecoverable power loss only when operating at the power ratings turbine inlet temperature limit. At part power conditions of constant torque and output speed the loss is
41、 manifested as increases of gas producer speed, turbine inlet temperature and fuel flow, of which the latter two suffer the most significant effect. On most engines, bleed air extraction is quite costly and the relationship between bleed flow and power loss will be dependant on the location of the b
42、leed tapping. To give an indication of the penalty which is associated with bleed extraction, 1% bleed flow taken from compressor delivery can cost 2 to 3% power at limit turbine temperature. Because of the cost in power available, systems not essential for flight, such as environmental control syst
43、ems and heating systems that rely on engine bleed air, are shut down during the high power requirements of take-off and landing. The engine manufacturer will be required to supply data showing the effect of bleed extraction on engine performance for all flight conditions. This data is usually obtain
44、ed from the engine performance computer model (customer deck).4.7 Off Optimum Power Turbine Speed Power Effects: This power loss is the result of operating the power turbine at some speed other than that at which maximum internal engine efficiency is achieved. It is calculated by using the engine ma
45、nufacturers performance computer model for the specific speed at which the helicopter rotor system is operated. It should be noted that reducing power turbine speed will mean that less power can be delivered for a given aircraft torque limitation.4.8 Engine Thermal Stabilization: Following any chang
46、e in operating condition the temperatures of the various engine components will respond at different rates depending on their position relative to the gas stream, their material properties and mass. These differing thermal responses will result in differing rates of expansion or contraction leading
47、to variations in clearances and gas path steps. These variations can lead to very significant effects on component performance and hence on the overall performance of the engine. Compressor and turbine tip clearances and air seal clearances can be particularly significant in this context.During an a
48、cceleration from a low power condition to the take-off rating it is possible that, whereas the appropriate rating limit will be achieved almost immediately, the power output will take a significant time to reach the full level as clearances settle to their steady state values. Such transient power l
49、osses must be considered when establishing the helicopter flight manual performance.SAE ARP1702 Revision A- 6 -5. INSTALLATION LOSSES IN RELATION TO IN-SERVICE ENGINE POWER CHECKING: The helicopter flight manual is based on the engine manufacturers performance specification after subtracting the measured installation losses to determine the net power available. The engine in-service power checking procedure is also based on the specification level of performance with the same allowance being made for installation losses. This consistency of approach is essential to maintain
