1、AEROSPACE AIR4172 The Engineering Society IhA =io, Advancing Mobility SCOP E : INFORMATION - -Land Sea Air and Space INTERNATIONAL 400 Commonwealth Drive, Warrendale, PA 15096-0001 R E PORT Submitted for recognition as an American National Standard Thls Aerospace Information Report (AIR) revlews the
2、 requirements to be satisfied by the englne mount systems and provides an outllne of some sultable methods, mount crashworthiness, vibration Isolation, and other effects on the installation are discussed. Factors such as drlve shaft alignment, englne expansion, Issued 1991-05-23 REFERENCES : The fol
3、lowing publlcations form a part of this guide to the extent referenced herein. The latest Issue of SAE publications shall apply. The applicable issue of other publlcatlons shall be the issue in effect on the date of the purchase order. SAE ARP704 SAE ARP721 Turbine Drlve Shaft Connection SAE AIR1289
4、 SAE ARP1 507 MIL-P-17842 FAR29.571 FAR25.361(b Engine Sudden Stoppage Helicopter Engine-Rotor System Compatibility Evaluation of Helicopter Turbine Engine Linear Vibration Envi ronmen t Hel i copter Engine/Ai rframe Interface Document and Check1 i st Powerplant Vibration Isolator Design and Install
5、ation Requirements Fatigue Evaluation of Flight Structure DISCUSSION: SAE Technical Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any parti
6、cular 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 reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. - Reproduced By GLOBAL s=
7、 _._ ENGINEERING DOCUMENTS _C_ X Wlh The Petmission 01 SAE - Under Royalty Agreement Copyright 1991 Society of Automotive Engineers, Inc. All rights resewed. Printed in U.S.A. -= SAE AIR4172 1 3.1.1 General: A satisfactory engine mounting system performs seven primary functions as fol lows: a. Maint
8、ains engine location and alignment under loads encountered during any flight conditton. vertical and horizontal linear acceleration, pitch, roll and yaw angular acceleration, and gravity. Loads include those generated by axial, b. Limits engine movement under crash conditions, bird strikes, rotor se
9、izure, and potential engine uncontained failure. c. Reduces airframe vibrations and deflections that are transmitted to the engine during any flight condition. d. Limits engine vibrations that are transmitted to the airframe. e. Accommodates thermal expansion and tolerance stackup of the engine. f.
10、Attenuates structure borne noi se. g. Permits simple engine installation and removal. The engine structure performs mu1 tiple functions. necessary load paths such that maneuver imposed loads (inertial and gyroscopic) and gravity imposed loads are transmitted to the engine mounts where they are react
11、ed by the airframe. It provides drive shaft reaction torque and coupling transmitted load reaction to the mounts. Loads due to intake depression and exhaust thrust, although generally Insignificant, are transmitted to the mounts and the engine structure provides paths for loads generated internally
12、within the engine that are not seen at the mounts. It provides the Statical ly determinate (nonredundant) mounting schemes are preferred as they eliminate built-in loads and moments that can create mount overloads and bending problems in the engine components. The engine should be designed for maxim
13、um mounting flexibility. 1, 2, and 3 illustrate three mounting systems that are statically determi nate. Figures a. Mount System No. 1 (Figure 1): Mount System No. 1 utilizes 3 and 9 oclock main frame mount pads In conjunction with the rear mount points. The rear mount loads are applied and transmit
14、ted through two airframe-supplied links to the engine mount ring. Either one of the forward mounting pads can be the main engine mount which provides restraint in all three directions, while the other pad provides only vertical restraint. For the rear mounts, the recommended location for the vertica
15、l restraint is 6 oclock and for the lateral restraint is either 3 or 9 oclock. Other mount locations (the main frame 6 oclock mount pad and two additional rear mount lugs) may be utilized for redundant fail-safe mounts provided sufficient clearance is 4 -2- SAE AIR4172 Midframe rear Frame forward FI
16、GURE 1 - Mount System 1 -3- SAE AIR4172 FIGURE 2 - Mount System 2 FIGURE 2A - Mount System 2A -4- SAE AIR4172 FIGURE 3 - Mount System 3 -5- I SAE AIR4172 3.1.1 (Continued): maintained to assure no loads are transmitted unless a primary engine mount fails. Other combinations of aft mount restraints m
17、ay be used, but resultant moments caused by offsets from engine centerline need to be considered. Torque is reacted as differential vertical loads at the two forward mount pads. b. Mount System No. 2 (Figure 2): Mount System No. 2 utilizes torque shaft housing attached to the engine output drive pad
18、 which serves as the forward main mount providing vertical, lateral, axial, and torque restraints without any moment restraints in the vertical or horizontal plane (Gimbaled ring configuration). vertical and lateral restraint only, thereby al lowing for engine differential thermal expansion and for
19、tolerance stack-up variation of the engine mount points. Other mount locations, forward mount pads on the malnframe and rear mount lugs can be utilized as fail-safe redundant mounts, provided sufficient clearance is maintained to assure no loads are transmitted unless a primary engine mount fails. A
20、nother option is to create a Gimbal that is soft mounted to assist in tuning engine dynamics. This results in engine torque being reacted by the rear mounts that are, therefore, reoriented as per Figure 2A. The rear engine mount provides c. Mount System No. 3 (Figure 3): Mount System No. 3 utilizes
21、an airframe gearbox and torque shaft housing attached to the engine output drive pad that provides restraints for the combined powerplant, in the vertical, lateral, axial, and roll directions. In addition, they also provide shear and moment restraints due to the reaction torque of the gearbox applie
22、d to the engine output drive pad. rear engine mounts provide vertical and lateral restraints only, thereby allowing for thermal expansion and tolerance stack up in relation to the other mount points. mount pads on the mainframe and rear mount lugs can be utilized as fail-safe redundant mounts, provi
23、ded sufficient clearance is maintained to assure no loads are transmitted unless a primary engine mount fails. Note that the airframe gearbox output shaft will impose a pitch moment (if power takeoff is horizontally perpendicular to the engine centerline) or a combination of pitch and yaw (if power
24、takeoff angle is compound). The The other mount locations, foward A standardized mounting system for all engines would represent an ideal situation. In reality, unused structural mount pads cost, weight, and expense are not justified where normally the aircraft configuration dictates the system to b
25、e used. Generally, however, a symmetrical system that accommodates handed mounts in a twin engine helicopter is preferred The engine installation instructions must contain the approved mount location method of attaching the engine to the aircraft and the maximum allowable load for the mounting attac
26、hments and their related structure. I -6- SAE AIR4172 .I 3.1.2 3.1.3 Drive Shaft Alignment: The mount geometry must be arranged to maintain the engine drive shaft couplings wjthin their misalignment capability. Accommodation of engine thermal expansion and drive torque reaction is necessary. This ge
27、nerally requires that the fixed mount be located on the output housing in order to minimize load path length. In order to enable engine changes with minimum time out of service for the aircraft, prerigging of the mounts is desirable. pad pick-up locations are closely toleranced, or a rigging tool is
28、 used to position the mounts on the engine precisely with relation to the output shaft. connections into a standardized location, enabling precise location of any engine upon installation. align the engine can be a time-consuming process to provide both drive shaft concentricity and squareness simul
29、taneously. Either the engine mount Similarly a rigging tool is used to shim the aircraft mount If this is not addressed, mount adjustment to Most he1 icopters feature rotor gearboxes having mounts designed to control the transmission of rotor flight and dynamic loads to the airframe, and consequentl
30、y have significant flexibility. should be of sufficient capacity to withstand normal coup1 ing generated loads, and limits for these should be shown on the installation instructions for the engine. shaft as attached to the rotor gearbox, must not be permitted to exceed engine output shaft load capab
31、ility in the axial direction. shaft couplings must also be able to accommodate the resulting mi sal i gnment without exceeding eng1 ne output shaft load capabi 1 i ty in bending. and where soft mounting of the rotor gearbox is necessary, it may be required to mount the engine on an extension of the
32、rotor gearbox or a subframe attached to the rotor gearbox. drive shaft problems, now enables low frequency rotor vibration to be fed directly to the engine which may require development to operate in such an environment. Engine output shaft bearings The complementary movement of the drive The drive
33、This represents a prime challenge for the helicopter designer, This, al though overcoming most Allowance for Expansion: pads located on a magnesium alloy case with an ambient temperature variation of -65 to 1235F (-53.9 to 112.8“C) and over a 24 inch length would be 0.111 inch. Where the aft engine
34、mount is located behind the combustor case, it is not unusual to see an increase in engine length between mounts of over 0.25 inch from normal ambient stationary to operating conditions. The variation of center distance between mount Mount geometry must be able to accommodate these changes without i
35、mposing excessive loads on the engine or aircraft structure. Thermally compensating “scissor“ links should be used when mounting to hot structure to alleviate thermal stresses and point loading. If a mount arrangement as illustrated in Figure 1 is used, expansion between the main 3 and 9 oclock moun
36、ts would be accommodated by the use of an articulated link, free to pivot transversely at 9 oclock and between these and the rear mounts by links free to pivot fore and aft. To minimize drive shaft misalignment, the fixed mount would be offset cold by half of the expansion between the main mounts th
37、at would be experienced under average engine conditions. -7- SAE AIR4172 3.1.4 Flight Loads: Figure 4 illustrates a typical engine flight load envelope with values in g and radians per second and radians per second squared, to which an engine may be designed and capable of accepting the resultant mo
38、unt loads. The aircraft flight load limits may however, be different than these, for instance, 8 gl in the three perpendicular planes, up, down, fore, aft, and side. In other cases the aircraft requirements will set the engine capability which should always exceed these, e.g., specific crashworthine
39、ss requirements of 20 g vertical for certain U.S. military appl i cations. Forces generated by these loads together with others contributed by drive shaft torque reaction and any other significant force such as resulting from intake and exhaust differentials, etc., are used for mount design for the
40、specific engine application. Additionally, loads that are not associated with the above that result from bird strikes and engne sudden stoppage, should be considered. the engine is not protected from bid strikes, the momentum force for the heaviest bird and impact velocity, should be accepted by the
41、 mounts. Ultimate torque loads due to engine seizure may be calculated by the use of Figure 5 (Reference 7) for preliminary estimates; however, the engine manufacturer should be consulted for formal values. If Besides providing unlimited structural life, the mounting arrangement must be stressed to
42、limit engine deflection to acceptable values for drive shaft and other connective features such as control linkage, etc. Crash loads are assumed typically 1.5 times flight loads, and generally it is considered that mounts may deform under crash loads but must not fail, thus ensuring that the engine
43、stays in place in the airframe under any predicted situation. relationship for each specific design. The airframe manufacturer should determine this It is often found that If crash loads are met, torque requirements are acceptable without further change. The engine mount pads are generally designed
44、to use tight fitting trunions to withstand shear forces generated by combination of linear and angular acceleration, taking into account weight and inertia of the engine and its accessories. The englne manufacturer must be consulted if the aircraft mount systems impose bending loads beyond those spe
45、cified, on the mount pads, or if other portions of the engine structure are attached. and exhaust ducts and engine driven accessories if supported by the engine should not transmit unknown loads due to airframe connections. Intake In order to calculate mount stresses, the dry mass of the engine incr
46、eased by the weight of all mounted accessories and operating fluids, and the position of their combined center of gravity is required. In addition, it is necessary that the engine manufacturer provide values for the mass moment of inertia in three axis about the center of gravity for the purpose of
47、calculating yawing, pitching, and roiling loads. -a- SAE AIR4172 Flight (O to full power) 0 Y Y S.L.= 6 1- Applicable to complete .crosshatched area S.L.= Applicable to complete rectangle from 7 Up to 10 Down 0 1- UP Down 1. Load factors and angular velocities and accderatims should be taken at or a
48、bout the C.G. of the engine. 2. Side load factors (S.L.) act to either side. and accderatiwi. and acceleration. Fore 3.6 and 0 are pitching velocity 4. i and Y are yawing Velocty 5. Down loads occur during 6. S.L. 6, 0, , Y, must be stated. pull out. S.L.= 0 Y 6 Y Dwn UP I Landing Fore FIGURE 4 - Ex
49、ternally Applied Forces -9- SAE AIR4172 T u) 3 a d O b LL O SAE AIR4172 I 4 I I 3.1.4 (Continued): In the case where a quickly attachableldetachable (QUAD) engine module is used, which features a number of nacelle parts and accessories also supported by the mounts, these concerns become significant and close liaison between engine and airframe manufacturer is necessary. a mounting system enabling the engine to be swung out to gain access for maintenance but without destroying alignment or detaching services, is a further elaboration of the QUAD system. The use of
