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 1997 Society of Automotive Engineers, Inc.All rights reserved. Printed in U.
3、S.A.QUESTIONS REGARDING THIS DOCUMENT: (412) 772-8510 FAX: (412) 776-0243TO PLACE A DOCUMENT ORDER: (412) 776-4970 FAX: (412) 776-0790400 Commonwealth Drive, Warrendale, PA 15096-0001AEROS PACE INFORM ATION REPORTSubmitted for recognition as an American National StandardAIR4083 RE V. AIssued 1989-07
4、Revised 1997-06Superseding AIR4083H elicopter P ower A ssuranceFOREWORDChanges in this revision are format/editorial only.TABLE OF CONTENTS1. SCOPE . 22. REFERENCES . 23. POWER ASSURANCE OBJECTIVES . 24. REGULATORY BACKGROUND . 25. INFLIGHT-TO-PRETAKEOFF POWER ASSURANCE COMPARISON . 36. POWER ASSURA
5、NCE THEORY . 57. SUPPLEMENTAL PROCEDURES . 88. INFLIGHT POWER ASSURANCE METHODS 8FIGURE 1 . 11FIGURE 2 . 11FIGURE 3 . 12FIGURE 4 . 12FIGURE 5 . 13FIGURE 6 . 13APPENDIX A EXAMPLE 1 PROCEDURE (FIGURE A1) 14APPENDIX B EXAMPLE 2 PROCEDURE (FIGURES B1 AND B2) . 16APPENDIX C EXAMPLE 3 PROCEDURE (FIGURES C
6、1 AND C2) . 19SAE AIR4083 Revised A- 2 -1. SCOPE:This SAE Aerospace Information Report (AIR) defines helicopter turboshaft engine power assurance theory and methods. Several inflight power assurance example procedures are presented. These procedures vary from a very simple method used on some normal
7、 category civil helicopters, to the more complex methods involving trend monitoring and rolling average techniques. The latter method can be used by small operators but is generally better suited to the larger operator with computerized maintenance record capability.1.1 Purpose:This AIR discusses he
8、licopter turboshaft engine power assurance theory and methods. Several inflight power assurance example procedures are presented. These procedures vary from a very simple method used on some normal category civil helicopters, to the more complex methods involving trend monitoring and rolling average
9、 techniques. The latter method can be used by small operators but is generally better suited to the larger operator with computerized maintenance record capability.2. REFERENCES:There are no referenced publications specified herein.3. POWER ASSURANCE OBJECTIVES:3.1 Turbine engine power producing cap
10、abilities can be expected to decrease with time from the new production or overhauled zero-time engine condition. The primary objective of the power assurance check is to assure that the engine remains capable of developing the power necessary to achieve the helicopter performance contained in the f
11、light manual.3.2 A second objective is to assure that the engine power parameter relationships required to assure continued engine airworthiness are maintained.3.3 Substantial maintenance cost savings and safety benefits can be realized if the data obtained is recorded and monitored to detect power
12、deterioration trends. Engine power may be checked prior to takeoff (pretakeoff power assurance) or during helicopter cruise conditions (inflight power assurance).4. REGULATORY BACKGROUND:4.1 The Federal Aviation Administration (FAA) has required an applicant for a commercial helicopter type certific
13、ate to provide a means to permit the pilot to determine, prior to takeoff, that each turbine engine is capable of developing the power necessary to achieve the performance required by the type certification regulations. This longstanding FAA policy was formalized as a regulatory change to Part 27, N
14、ormal Category Rotorcraft, and Part 29, Transport Category Rotorcraft, by amendments effective November 6, 1984.SAE AIR4083 Revised A- 3 -4.2 This requirement to provide a means to assure adequate power prior to takeoff has generally been met by providing a pretakeoff power assurance chart. The pret
15、akeoff check is usually performed in an in-ground-effect (IGE) hover or light-on-the-wheels. An inflight power assurance chart is often provided but is not required for type certification.4.3 It should be noted that FAA type certification rules and policy do not require that a pretakeoff power check
16、 be performed, only that a means be made available to the pilot. Individual operational practices will dictate the frequency of the pretakeoff power assurance check.4.4 Although this regulatory background discussion cites FAA regulations, the general principles contained in this AIR may be applied t
17、o rotorcraft certificated by other authorities using other airworthiness requirements.5. INFLIGHT-TO-PRETAKEOFF POWER ASSURANCE COMPARISON:5.1 Ideally, a pretakeoff and inflight power assurance check will yield the same results. Varied operating conditions and possible induction system malfunctions,
18、 however, can cause a different power margin value to be obtained from the two types of checks. The decision to use either the pretakeoff or inflight procedure, or both, depends on the operations and the intended use of the information.5.2 Merits of Pretakeoff Power Assurance:5.2.1 As mentioned, the
19、 FAA has insisted on the availability of the pretakeoff power assurance information or other means to allow the operator to assure adequate power for rotorcraft flight manual (RFM) performance prior to commitment to the takeoff flight phase. If the check is performed in gusty wind conditions, or wit
20、h adverse winds which cause exhaust gas recirculation to the inlet, the power check on a newly delivered healthy engine may be unsuccessful. While these results do not indicate the need for engine maintenance, they do indicate that engine power may not be adequate for a critical takeoff under these
21、specific operating conditions.5.2.2 Certain inlet system service difficulty problems which result in loss of power at low airspeeds but adequate power at higher airspeeds may be detected by the pretakeoff check. The most common example of this type of failure would be the misinstallation or deterior
22、ation of seals which isolate induction system air from that in adjacent hot-air compartments. At low airspeeds, the reduced pressure in the inlet system would draw air from adjacent hot compartments resulting in a higher than normal inlet air temperature rise (or perhaps even inlet air temperature s
23、tratification) and an associated engine power loss. At higher airspeeds, the inlet ram pressure effect would minimize the entrainment of hot-air from the adjacent compartment, and the resulting engine power loss effect would be small. This and other low airspeed engine power loss causes may not be d
24、etectable by inflight power assurance procedures.SAE AIR4083 Revised A- 4 -5.3 Disadvantages of Pretakeoff Power Assurance:5.3.1 One obvious disadvantage of the pretakeoff check is the time required to accomplish the procedure at often uncomfortable operating conditions. While the procedure can be u
25、sed as simple “go/no go“ criteria (that is, as soon as the check parameters are positive the flight may commence), the flight manual may specify a dwell time to allow for engine stabilization. After changing from the low power ground operating condition to the hover IGE or light-on-the-wheels condit
26、ion, there is a finite time required for engine internal components to reach their optimal clearance and power producing capability. This stabilization time may vary from only a few seconds to 5 min depending on the engine model thermodynamics and individual engine build tolerances. While the data f
27、rom these lengthy power assurance checks may yield more useful power trend information and perhaps result in fewer engine rejections, the time delay in noisy ground proximity to stabilize engine power and read the power charts is not operationally desirable.5.3.2 In-ground-effect conditions such as
28、rotor downwash, variable wind direction, and exhaust gas recirculation may artificially influence the day-to-day variation in the pretakeoff power assurance margin when, in fact, no real change in engine power margin has occurred. This false power margin trend can lead to erroneous conclusions about
29、 the need for engine maintenance.5.4 Merits of Inflight Power Assurance:5.4.1 The inflight power assurance check overcomes the mentioned disadvantages of the pretakeoff check. Since the inflight check is usually made in cruise conditions, it may be performed with minimal or no delays in normal opera
30、tions. More accurate engine health information may be obtained at the stabilized cruise condition without the influence of rotor downwash, variable winds, and exhaust gas recirculation associated with the pretakeoff check. Stabilization time for accurate data is reduced since the engine components h
31、ave already been operating at relatively high stable temperatures just prior to the inflight check.5.4.2 The more accurate engine health information obtained from the inflight data can be utilized in a power trend monitor program to reduce operating costs. A carefully administered program can provid
32、e an early indication of the need for engine maintenance while at the same time eliminating unnecessary engine removals caused by an inaccurate power assurance check. Early engine maintenance can reduce overall operating costs by preventing premature failure of expensive engine components.5.5 Disadv
33、antages of Inflight Power Assurance:5.5.1 The disadvantages of the inflight power assurance are some of those mentioned as merits of the pretakeoff check. Positive power margins from inflight power assurance checks do not necessarily ensure that engine power is available for a critical takeoff if th
34、ere are inlet system malfunctions only evident at low airspeeds.SAE AIR4083 Revised A- 5 -5.5.2 Inlet system and engine installation maintenance errors, and foreign object damage (F.O.D.) which result in sudden power degradation, may not be detected until after the aircraft is committed to flight.6.
35、 POWER ASSURANCE THEORY:The safety objectives and some potential economic benefits of the power assurance procedures have been mentioned. This section will explain, in simplified terms, some of the considerations involved in constructing the power assurance charts.6.1 The power assurance charts are
36、typically constructed with the aid of the engine estimated performance computer program supplied by the engine manufacturer to the aircraft original equipment manufacturer. The performance program allows the helicopter manufacturer to input the helicopter model installation information for various f
37、light conditions. The resulting installed engine power available prediction is verified by helicopter flight testing and used to predict RFM performance and generate the power assurance charts. The families of curves on the various power assurance charts are intended to check the relationship of thr
38、ee engine power related parameters - gas producer speed, measured gas temperature, and power (or torque). The theory involved in assuring these relationships is explained in the following sections by considering a simplified operating line for turboshaft engine types.6.2 Minimum Specification Engine
39、:The new production or overhauled zero-time engine acceptance test procedure will specify that the engine produce a given set of required powers (rated powers) at not greater than a corresponding set of gas producer speeds and measured gas temperatures. A plot of these power levels versus gas produc
40、er speeds and measured gas temperatures defines the “minimum specification engine runline.“ A different engine runline could be generated for each ambient condition, but by the application of correction factors, a single normalized runline may be constructed which is representative over a range of a
41、mbient conditions. These corrected engine performance parameters are designated shaft horsepower corrected (SHP c ), measured gas temperature corrected (MGT c ), and gas producer speed corrected (NG c ) on the accompanying figures.SAE AIR4083 Revised A- 6 -6.3 Field Limit Engine:6.3.1 (Figure 1) At
42、a given gas producer speed (NG) or measured gas temperature (MGT), turbine engine power will deteriorate with service time. Some engine models will not specify a delivery power margin in the engine documents to account for this normal, expected deterioration. In this case, the MGTs and NGs associate
43、d with the rated powers in the engine performance program correspond to the limit values identified on the engine type certificate data sheet. The engine manufacturer may voluntarily or contractually deliver the engine with a power margin above the engine recognized in engine certification documents
44、. Because the designation of any power margin for service longevity is an economic rather than safety concern, the specification of a power margin is not required by regulatory authorities. Since to these authorities the minimum acceptable power versus MGT and power versus NG relationship for new de
45、livery engines is the same as that for engines which should be removed from service, the minimum specification engine for these models is the same as the “field limit engine.“6.3.2 (Figure 2) To account for normal, acceptable engine power deterioration, other engine models may specify a built-in per
46、formance margin or field margin in the engine documents, which may be considered as an allowable measured gas temperature increase or gas generator speed increase from a minimum specification engine. This field limit engine may be established in the engine documents (type certificate data sheet, eng
47、ine specification, installation manual, or computer predicted performance program) by stipulating that the engine rated powers will be produced at some MGT or NG below the limit values. This set of reduced MGTs and NGs may be referred to as “rated MGTs“ or “rated NGs,“ respectively.6.3.3 To avoid po
48、ssible confusion the term “field limit engine,“ rather than minimum specification engine, will be used to describe an engine which will produce rated power at the limits of MGT and/or NG identified in the engine documents. Power deterioration beyond the installed field limit engine, described below,
49、 would require that engine maintenance be performed in an attempt to restore power to acceptable levels.6.4 Installed Field Limit Engine (Figure 3):The effect of helicopter installation losses is to require a higher MGT and NG to produce a given power. The power assurance chart represents this installed field limit engine runline. Since RFM performance is also based on this runline, a comparison of an individual engine to the power assurance chart will indicate whether RFM performance can be attained.6.5 Power Assurance Data Extrapolation:SInce the power assurance check is often not perf
