1、a i i I I I. IN TER NATI O NA LW 400 Commonwealth Drive, Warrendale, PA 15096. .o001 AEROSPACE IN FOR MATION REPORT Submitted for recognition as an American National Standard JcpE AIR1603 Issued 1993-06-17 AUXILIARY POWER SYSTEM CONSIDERATIONS FOR ADVANCED MILITARY AIRCRAFT FOREWORD This document ha
2、s been assembled to aid the engineer in optimizing the auxiliary power system in advanced military aircraft. Frequently the engineer responsible for the early definition of the subsystems is only superficially acquainted with the various subsystems and is expert in one or none. progresses through th
3、e phases from conceptual design to production, the subsystem definition specified early in the program may remain, and become ever more firm. This AIR provides such an engineer with enough insight into the various components of the auxiliary power system to enable him to choose a combination that wi
4、ll best suit the projected aircraft. evolves, experts will review the design, and the requirements may change. original selection may, and probably should, be altered to a system that is more appropriate for the final aircraft. 1. SCOPE: Yet as the aircraft Understandably, as the design of the aircr
5、aft The This document provides a brief descr ption of the auxiliary power equipment that is available with enough description and pertinent comments to enable an engineer to make logical preliminary selection of the appropriate equipment for advanced military aircraft programs. brief as possible to
6、include the maximum amount of equipment in a relatively short document. detailed information available from the equipment suppliers. The information has been kept as It is not intended to replace textbook design analysis or The document describes auxiliary power equipment. Auxiliary power is defined
7、 as follows: “Those elements of secondary power defined as all aircraft nonpropulsive power generation and transmission related to main engine bleed air and shaft power extraction or power generation separate from the main engines. Included are engine bleed air systems, remote engine driven gearboxe
8、s, engine starting systems, auxiliary power units, and emergency power systems.“ Additional definitions may be found in ARP906A which is the source of this definition. SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering
9、 sciences. lhe use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.“ SAE reviews each technical report at least every five years at which time it may be rea
10、ffirmed, revised, or cancelled. SAE invites your written comments and suggestions. 1 Copyright 1993 Society of Automotive Engineers, Inc All rights reserved. Printed in U SA SAE AIR*Lb03 93 W 7943725 0517110 338 W SAE AIR1603 1. (Continued): Some closely related systems which are not discussed in de
11、tail, include thermal management, environmental control, electrical, and hydraulic systems. 2. REFERENCES : 2.1 SAE Publications: Available from SAE, 400 Commonweal th Drive, Warrendale, PA 15096-0001. AIR781 ARP906A AS943A AIR944B ARP949A AIR1174A AI R1467A AS1 606 ARP1607A Guide for Determining En
12、gine Starter Drive Torque Requirements Glossary, Aircraft Engine Starting and Auxiliary Power Start, Pneumatic, Aircraft Engine, General Specification For Pneumatic Ground Power Supplies for Starting Aircraft Turbine Engine Starting System Design Requirements Index of Starting System Specifications
13、and Standards Gas Energy Limited Starting Systems (DRAFT) Specification, Jet Fuel Starter Starter Control Valve Specification 2.2 Military Specifications: Available from DODSSP, Subscription Services Desk, Building 4D, 700 Robbins Avenue, Philadelphia, PA 19111-5094. Available from Standardization D
14、ocuments Order Desk, Building 4D, 700 Robbins Avenue, Phi 1 adel phi a, PA 19111-5094. MIL-F-94900(USAF) - 6 June 1975 - Flight Control Systems - Design, Installation and Test of Piloted Aircraft, General Specification For MIL-S-l9557D(AS) - 29 January 1988 - Starters; Aircraft Engine, Air Turbine,
15、General Speci fi cati on For MIL-V-38398A(USAF) - 8 July 1974 - Valve, Starter Control, Pneumatic, Aircraft Engine - General Specification For MIL-S-38399A(USAF) - 14 February 1975 - Starter, Pneumatic, Aircraft Engine - General Speci fi cat ion For MIL-P-85573(AS) - 1983 - Power Unit Aircraft, Auxi
16、liary, Gas Turbine, General Speci fi cat i on For MIL-A-87229(USAF) - 31 July 1985 - Auxiliary Power Systems, Airborne MIL-V-81995(AS) - 25 June 1980 - Valves, Starter Control, Aircraft Engine, General Specification For MIL-S-22518(AS) - 19 March 1982 - Starter, Air Turbine, Accessory Drive Combinat
17、ion A/C Engine, General Specification For MIL-S-22999B(AS) - 15 June 1981 - Starter, A/C Engine Hydraulic, General Specification For -2- SAE AIR*Lb03 93 7943725 05L7LLL 274 SAE AIR1603 3. 3.1 ENGINE STARTING AND AUXILIARY POWER GENERATION: System Configuration: The auxiliary power system on military
18、 aircraft has evolved from a few small mi scell aneous accessories conveniently mounted on the propul sion engines to a separate entity, often separately housed from the engines. In future high performance fighter aircraft the accessories probably will be remotely mounted in separate bays, as they a
19、re in current similar aircraft, to take full advantage of the benefits of divorcing them from the propulsion engines: a. Aircraft performance is improved by taking advantage of the reduction in a maximum cross-section area that may be achieved by careful arrangement of the accessories on gearboxes r
20、emote from the propulsion engines. The greatest cross-section area reduction is usually achieved by designing with mirror image gearboxes for a twin engine aircraft with fuselage mounted engines. b. Survivability is improved by removing sources of ignition (generators) and fl ammabl es (hydraul i cs
21、) from the engine environment. Combat experience in the 1960s showed that fires in the engine bays (caused by damage to electrical or hydraul ic systems in those bays) significantly contributed to aircraft losses. c. Overall aircraft survivability may be enhanced by locating the accessories where th
22、ey will protect more vital components (like engine fuel feed lines, for example). Uncluttered engine bays, with no requirement for disconnecting and connecting lines and wires for the accessories, minimizes engine removal and replacement time. d. e. Engines can be removed from shipping containers an
23、d installed in the aircraft with no requirement for quick engine change (QEC) kits. Among military aircraft other than fighter and attack aircraft, the B-1 and B-2 bombers have also been designed with remote accessories, as was the 8-70. The trend toward remotely mounted accessories can be expected
24、to become even more nearly universal in future military aircraft with the aim of maximizing performance and supportability. Military transport-type aircraft, on the other hand, which typically have pod mounted engines, have followed the traditional lead of the subsonic commercial transport aircraft
25、and mounted the accessories on gearboxes integral with the engines. Engine mounted accessories have been demonstrated to provide better accessibility and maintainability for this type of aircraft, particularly when engine replacements are rare. -3- SAE AIR+Lb03 93 m 7943725 0517112 LOO SAE AIR1603 I
26、 3.2 Drive Type Accessory: Historically, accessories have been driven by shaft power from the main engines, with a few exceptions, namely: Early B-52, A-3, F-105, and early A-4 (Partial). These aircraft used engine bleed air turbines to drive the accessories. This option, as well as electric and hyd
27、raulic drive are illustrated schematically in Figure 1 and should be considered in advanced military aircraft design. In selecting the method of providing power for the various aircraft services, the engineer must consider the total impact on the aircraft. Weight, aircraft performance penalty, heat
28、rejection, re1 iabil ity, and maintainabil i ty are all important considerations. 3.2.1 Shaft Drive: secondary power on most mil itary aircraft with accessories mounted remotely from the propulsion engines. Subcritical tube-type shafts, generally with diaphragm-type joints to allow for misalignment
29、and deflections, have usually been used between the engines and the airframe mounted accessory drives (AMADs). Shaft power from the propulsion engines is the source of a. Advantages (1) Maximum efficiency (2) Engine starter mounts on AMAD b. Disadvantages (1) Located close to engine (2) Speed varies
30、 with engine 3.2.2 Pneumatic Drive: Pneumatic drives for hydraulic pumps and generators normally are engine compressor bleed air turbines. Small positive displacement air motors powered by engine bleed air may be used for actuation (the nozzle actuation system on the F100 engine is an example), and
31、positive-displacement air motors powered by high pressure bottled air have been used for APU starting. for hydraulic and electric power generation on several aircraft in the past, and should be considered as a possible option for advanced military aircraft (particularly when the power is only requir
32、ed for a small portion of the mission or for emergencies). Bleed air turbine drives were selected a. Advantages (1) Flexibility of location (2) Can be constant speed (3) Can be powered from any engine b. Di sadvantages (1) (2) (3) Starter must be separate Much greater engine performance penalty than
33、 shaft power Requires high-temperature bleed air ducting to the air turbine mot or -4- SAE AIR*Lb03 93 N 7993725 0517113 047 SAE AIR1603 BLEED AIR BLEED AIR p-wwu.- “,.,.YI d 2- HYD GEN BLEED AND PUMP TARTER GEN MOTOR GEN MOTOR nI GEN HYD PUMP PNEUMATIC DRIVE FIGURE 1 - Accessory Drive Types -5- SAE
34、 AIR*Lb03 73 m 7943725 0517LL4 T3 m SAE AIR1603 3.2.3 Bleed and Burn: The engine performance penalty associated with bleed air extraction can be reduced from that incurred with a bleed air turbine by inserting a combustor ahead of the turbine because less bleed air is used to produce a given amount
35、of power when the temperature is higher. disadvantage is in the need to route fuel to the machine and the creation of an additional fire zone. bleed air turbine is considered. The This alternative should be weighed whenever a a. Advantages (1) Flexibility of location (2) Can be constant speed (3) (4
36、) Less penalty than bleed air turbine Can be powered from any engine b. Di sadvantages (1) Requires fire zone (2) Requires high temperature bleed air ducting 3.2.4 Hydraulic Drive: Since hydraulics are usually routed throughout the aircraft for flight control actuation and other high force applicati
37、ons, this source of energy may be convenient, particularly for emergency electric power sources. Most of the normal, shaft driven, electric power sources require minimum speeds near engine idle while hydraulic power may be available in even lower engine speed ranges, such as windmilling or engine li
38、ght off. drive and its driven accessory can be carried back to a centrally located heat exchanger by the hydraulic fluid. generally are relatively less efficient than direct shaft power driven generators. The inefficiency comes about, first, because the power has been converted from shaft power to h
39、ydraulic power through one inefficiency before it is converted to electrical power, and second, the hydraulic motor normally operates at part power to provide margin for the generator overload requirements, and finally fluid transmission losses contribute to the inefficiencies. The heat generated by
40、 inefficiencies in the hydraulic Hydraulic generator drives a. Advantages (1) Flexible location (2) Can be constant speed (3) Can be powered from any engine b. Disadvantages (1) Fairly heavy (2) Re1 ati vely inefficient (3) Starter must be separate 3.2.5 Electric Drive: Electric power is frequently
41、used to drive such devices as fuel pumps, flap actuators, cooling fans, or possibly high pressure air compressors. power to drive hydraulic pumps for intermittent use, such as during landing or takeoff. during the periods of peak hydraulic demand which are generally not coincident with electrical po
42、wer peak demand. In this way, the central hydraulic pumps can be downsized, reducing the engine power extraction and Electric motors remote from the engines also can provide These auxiliary electric-driven pumps would be operated only -6- SAE AIR*1603 93 W 7943725 0517LL5 917 SAE AIR1603 3.2.5 (Cont
43、inued) : accessory heat rejection during most of the flight. disadvantages are essentially the same as for hydraulic drives, except that there is no inherent provision for heat dissipation. The advantages and 3.3 Engine Start System Type: Early in the history of aircraft powered by large turbine eng
44、ines, air turbines were employed for engine starting because of their high power concentrated in small, lightweight packages. The air source was from ground power units that contained bleed-type small gas turbine engines developed to match the air turbine starters (ATSs). ATSs have continued to be c
45、hosen over other types of start systems in most military and commercial aircraft thereby providing excellent opportunities for many i terations of design improvements over the years. Still, in any new aircraft design it is wise to examine the various alternatives and select the one that is optimum f
46、or that particular appl i cat i on. 3.3.1 Pneumatic: for aircraft turbine engines. flexible engine starting system. In the F/A-18, for example, the ATSs are continuous duty units designed to drive their respective AMADs (disconnected from the respective engine) at speeds near engine idle for mainten
47、ance checkout electric and hydraulic power, as well as driving through the AMADs for engine starting, using bleed air from the APU, a ground power unit, or cross bleed from the opposite engine. On the other hand, versatility is only one consideration. In some applications a more important considerat
48、ion may be that the power transmission efficiency is relatively low; an APU compressor efficiency of 75% coupled with an ATS turbine efficiency of 75% yields a power transmission efficiency of about 50%. turbine through a special set of starting nozzles, is a simple, lightweight system that requires
49、 at least twice as much air horsepower as an ATS to start the same engine. sufficient propulsion engine starting is required with large engines because the APU weight increase will more than offset the saving due to el iminat i on of ATSs. As mentioned above, ATSs are the most common type of starter They provide an extremely versatile and Impingement starting, where bleed air is directed at the engine Impingement starting is not practical when self- a. Advantages (1) Lightweight (2) Versatile and flexible (3) Highly developed b. Disadvantages (1) Poor efficiency (2) (3) Overboard exhau
