Document
NASA CR-151932 Copy number Reportnumber w)C A4551 LIFT/CRUISE FAN V/STOL TECHNOLOGY AIRCRAFT DESIGN DEFINITION STUDY VOLUME 11 PROPULSION TRANSMISSION SYSTEK DESIGN Revision date Revision letter Issuedate 18 November 1976 contract number NAS2-9245 Wm. J. O’Brlen Prepared bv MCDONNELL AIRCRA- COMPANY
BOX 516, Soin* Louis, Missouri 63166 - Tal. 1334J232-0232
MCOONNELL CORpdRAIlOU W C A4551 VOLUME I1 INTRODUCTION A i m SUNWARY This report presents results of Task 111 of a study by McDonnell Aircraft Company (MCAIR) for NASA Ames Research Center and the U . S . Navy to conceptually design two types of Liftkruise Fan Technology Aircraft.
One aircraft used turbotip fans pneumatically interconnected to three gas generators and the other aircraft used variable pitch fans mechanically interconnected to three turboshaft engines. The objective of Task I11 was to analyze and design the components of each propulsion transmission system to the depth necessary to determine areas of risk, development methods, performance, weights and costs.
The types of materials and manufacturing processes were identified to show that the designs followed a low cost approach. The lift/cruise fan thrust vector- ing hoods, which are applicable to either aircraft configuration, were also evaluated to assure a low cost/low risk approach.
The turbotip propulsion system consists of three General Electric ( G . E . ) LCF459 turbotip fans powered by three G . E . YJ97 gas generators through the Energy Transfer and Control (ETaC) system. The ETaC system consists of ducting, bellows and control valves. The ducting system for an operational aircraft would be a MCAIR developed light weight, composite design; however, stainless steel was selected for the RTA to assure a low cost/law risk approach. The stainless steel ducting is approximately 500 lb heavier than a composite con- struction but the excess thrust margin available in the turbotip RTA allows this approach to be used. A single duct was installed for the lift fan to reduce cost. The operating temperature, 1260°F, is nearly the same as that An evalua- already demonstrated by the XV-5 aircraft thereby minimizing risk.
tion of the ETaC system components indicated that all could be fabricated from existing materials using standard fabrication proceduree.
The mechanical propulsion system consists of three Hamilton Standard variable pitch fans powered by three Detroit Diesel Allison (DDA) XT701 turboshaft engines through a mechanical transmission system. This system includes shafting, supports, combiner gearbox, lift fan clutch and an over- The design and analysis of the mechani- running clutch for the third engine.
cal transmission system was subcontracted to DDA to utilize their expertise as a leading designer and fabricator of power transmission components. Based on MCAIR guidelines, which included the use of standard materials and state-of-the- art sizing criteria, DDA arrived at a low risk design for the mechanical trans- mission system.
MDC A4551 VOLUME 11 TURBOTIP RTA PROPULSION SYSTEM
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W I N TURBOIlP FAN U C VECTORING The design and analysis of the turbotlp and mechanical transmission systems and the thrust vectoring hoods demonstrated that state-of-the-art materials and fabrication procedures can be used, thereby assuring a low cost/law r i s k approach for the RTA.
MECHANICAL RTA PROPULSION SYSTEM VC VECIORINO MDC A 4 5 5 1 VOLUME I1 .
TABLE OF CC'YTENTS .
Sect ion Title pa_ge
INTRODUCTION AND SUMMARY . . . . . . . . . . . . . . . . . . ii
L I s T OF FIGURES . . . . . . . . . . . . . . . . . . . . . . V
1 . TURBOTIP TRANSMISSION SYSTEM . . . . . . . . . . . . . . . . 1
1 . 1 General Description . . . . . . . . . . . . . . . . . . 1
1 . 2 System Selection . . . . . . . . . . . . . . . . . . . 3
. . . . . . . . . . . . . . . . . . . 4
1.3 Ducting System
1 . 3 . 2 Elbows . . . . . . . . . . . . . . . . . . . . . 4
1 . 3 . 3 Transition Sections . . . . . . . . . . . . . . 4
1 . 3 . 5 Thermal Insulation . . . . . . . . . . . . . . . 6
1 . 4 Valves . . . . . . . . . . . . . . . . . . . . . . . . 9
. . . . . . . . . . . . . 1 . 4 . 1 Engine Isolation Valve r
1 . 4 . 2 Engine ETaC Modulation Valve . . . . . . . . . . 9
1 . 4 . 3 Engine ETaC and Shutoff Valve . . . . . . . . . 9
1 . 4 . 4 Interconnect Isolation Valves . . . . . . . . . 12
1 . 4 . 5 Diverter Valve . . . . . . . . . . . . . . . . . 12
1.5 Engine Diffuser and Alignment Bearings Section . . . . 12
1 . 6 Component Materials Selection . . . . . . . . . . . . . 14
2 . LIFT/CRUISE FAN THRUST VECTORING DEVICES . . . . . . . . . . 17
2 . 1 General Description . . . . . . . . . . . . . . . . . . 17
2 . 2 Thrust Vectoring Hoods . . . . . . . . . . . . . . . . 17
2 . 3 Yaw Doors . . . . . . . . . . . . . . . . . . . . . . . 19
3 . MECHANICAL TRANSMISSION SYSTEM . . . . . . 20
3 . 1 General Description . . . . . . . . . . . . . . . . . . 20
3 . 2 Transmission System Design . . . . . . . . . . . . . . 21
APPENDIX A SHAFT AND TRANSMISSION DESIGN STUDY BY DETROIT DIESEL
ALLISON . . . . . . . . . . . . . . . . . . . . . . . . . . A-1
LIST OF PAGES Title ii through v 1 through 21 A-l through A-31 MDC A 4 5 5 1 VOLUME I1 LIST OF FIGURES Page Title Number .
.
Gas RTA ETaC System .....................
2 Ducting Configuration . . . . . . . . . . . . . . . . . . . .
3 M260-RT.4-1 Gas Distribution System ' Y ' Duct Assembly . . . .
4 Main Anchor Support . . . . . . . . . . . . . . . . . . . . .
5 Swinging Support . Linkage . . . . . . . . . . . . . . . . .
6 Swinging Support . Hinge . . . . . . . . . . . . . . . . . .
7 Sliding Support . Bolt Type . . . . . . . . . . . . . . . . .
Directional Anchor . Rolling Support . . . . . . . . . . . .
M260-RTA-1 Engine/Fan Gas Distribution Angulation Bellows . . 10
10 Engine/Fan Coupling Arrangement . . . . . . . . . . . . . . .
11 M260-RTA-1 ETaC modulation & Gas Distribution Valve . . . . .
12 ETaC + Shut Off Gas Distribution Valve . . . . . . . . . . .
Engine Diffuser and Alignment Bearing Section . . . . . . . .
14 I ' D " Vented Nozzle Wall Temperature Measurements . . . . . . . 18
15 M260-RTA-1 Lift/Cruise Fan Hood Design . . . . . . . . . . .
16 M260-RTA-1 Lift/Cruise Fan Yaw Door Design . . . . . . . . .
17 Model 260-RTA-2 Propulsion System . . . . . . . . . . . . . .
MDC A4551 VOLUME I1 1 . TURBOTIP TRANSMISSION SYSTEM 1 . 1 GENERAL DESCRIPTION The Energy Transfer and Control (ETaC) system is used to distribute and control the exhaust gas from the General Electric ( G . E . ) iJ97 gas generators to the three G . E . LCF459 turbotip fans. This integrated duct system, Figure 1, consists of: ducting, valves for control and/or shutoff, and a system of bellows joints for thermal expansion compensation.
The ETaC system distributes the high energy gas from the engines to perform the following functions: Distribution of the gas tc the turbotip fans (a) (b) Provides the proper distribution for control during takeoff and conversion Provides for gas transfer in the event of an engine failure (c) Isolates and bypasses the failed portion of the system from the (d) active portion Provides the proper distribution of gas for cruise and high speed (e) flight Allows the third engine to be isolated from the main system after (f) "V" takeoff or to be brought back on line for a "V" landing.
To assure a low cost/low risk approach, two major guidelincs were established: (1) use stainless steel ducting, and (2) use only one duct for the lift fan. The use of stainless steel ducting results in a weight penalty of approximately 500 lb as compared to the MCAIR developed composite ducting but provides for a low risk development program using state-of-the-art fabrica- The single duct to the lift fan is a low cost approach tion procedures.
This single duct approach also allowed the scrolls of employed for the RTA.
all fans to be identical with the exception of the entry segment.
The overall ETaC system design was coordinated with various speciality manufacturers to assure simplicity of fabricacion. These manufacturers in- cluded Metal Bellows Co., Stainless Steel Products, and kiLowhead Products.
A layout of the ETaC system, Drawing RTA 260-001-4, wa8 p'sparsd to assure that the system components interfaced properly with each o t h r and with the Each of the major com- fan scrolls. This design i - s coordinated with G . E .
ponents were designed and evaluated and are discussed in the following paragraphs.
M-LL A#UCRAPT COMPANY MDC A 4 5 5 1 VOLUME I1 M C O O U W E U . AIRCRAFT COMPLINV MDC A4551 VOLUME I1 1.2 SYSTEM SELECTION In an aircraft power transmission system, it is necessary to make provisions for misalignments in the energy transmitting components. In order co compensate for these misalignments in the turbotip system with essentially no leakage, bellows are installed at the required locations. The bellows serve to relieve the effects of misalignment which are caused by differences in thermal expan- sion between the ducts and adjacent fuselage structure, nominal manufacturidg tolerances in the vehicles, and normal aircraft structural deflections during flight.
The design of an optimum ducting system, providing these futctions, includer consideration as to the type of bellows system to be installed, i . e . , a compression or tension system.
A compression system, which may appear attractive because of its apparent simplicity in utilizing unsophisticated ducting components, is one in which the bellows are not restrained. The insertion of the bellows in the line, however, destroys its ability to cancel the duct pressure loads against each other chrough axial tension in the ducting walls, since the bellows will stretch rather than carry the tension. This necessitates strong brackets and backup structure to react these loads. In the RTA system with a maximum working (for a 17-inch pressure of 63 psia and an effective bellows area of 257 diameter duct), this columnar action amounts to a design load of 24,300 lb.
The fact that the pressure reaction bracketry and reacting fuselage structure becomes necessarily heavy is apparent from the magniiude of the design load.
In addition to this undesirable feature, the system also places the ducting in column action requiring strength in the walls of the duct beyond that re- quired to carry the hoop tension created by the internal pressure.
A tension system I s one in which the thermal expansion bellows components are restrained from stretching while under internal pressure, by means of self- contained tensiou links, or by means of an interlocking system of bellows to balance the pressure separeting load. The tension system drastically reduces the number, complexity and weight of the ducting supports and allows a reduc- tion in gage of the duct walls by eliminating the column action on the ducts The tension system was considered the when compared to a compression system.
lowest risk approach and therefore was selected for the RTA.
MDC A4551 VOLUME 11 1.3 DUCTING SYSTEM The ducting system is of s t a i n l e s s steel c o n s t m c t i o n , wrapped with a thermal i n s u l a t i o n blanket, and c o n s i s t s of s t r a i g h t s e c t i o n s , t r a n s i t i o n sections, elbows and supports.
1.3.1
DUCTING - Figure 2 i l l u s t r a t e s t h e d u c t k g configuration selected f o r
t h e gas d i s t r i b u t i o n system.
The duct c o n s i s t s of a continuous inner w a l l covered by a second w a l l or lamination which is beaded every six t o e i g h t inches. These beads provide s t i f f n e s s t o p r o t e c t a g a i n s t collapsing from conditions of high i n t e r n a l pressure d i f f e r e n t i a l o r from handling during i n s t a l l a t i o n o r inspection. The inner and o u t e r w a l l s are joined together by seam welds between t h e beads t o improve t h e sectional s t i f f n e s s . Pressure buildup between t h e inner and outer s h e l l is relieved 1 , venting t h e o u t e r s h e l l t o ambient through small holes d r i l l e d i n t h e beads. The e n t i r e duct is wrapped with a n i n s u l a t i o n blanket which is wire-laced i n place.
1.3.2 ELBOWS - Dlscussions with duct component f a b r i c a t o r s and MCAIR produci-
b i l i t y s p e c i a l i s t s !.udicated t h a t t h e most p r a c t i c a l and simple process f o r f a b r i c a t i n g t h e elbows is by hydroforming s h o r t sections, and then b u t t welding each s e c t i o n t a the o t h e r t o form t h e cnmplete elbow. Thicker material w a s used i n t h e elbow area t o compensate f o r any thinning which may occur during t h e hydroform process. I f a weight reduction becomes d e s i r a b l e , selective chemical milling can be used t o reduce t h e weight of t h e heavier sections.
1.3.3 TRANSITION SECTIONS - The ' Y ' t r a n s i t i o n s e c t i o n w i l l be hydroformed from f l a t stock (Inconel 617 o r equivalent) i n t o s e c t i o n s and then b u t t welded This n e u t r a l i n a f i x t u r e t o make t h e required assembly ahown i n Figure 3.
assembly is used i n both t h e r i g h t hand and l e f t hand application.
The t r a n s i t i o n s e c t i o n a t the inLersection of t h a t h i r d engine duct with t h e crossover duct can likewise be fabricated by hydroforming.
The weight of each of these sections could a l s o be reduced, i f desired, by s e l e c t i v e chem milling.
1.3.4 SUPPORTS - I n order t o e s t a b l i s h t h e types and l o c a t i o n s of t h e bellow8 assemblies i n t h e system, c e r t a i n fixed p o i n t s were cssumed, and supports were designed a t these p o i n t s t o provide f o r operation i n t h e antic?.pated maneuvering I n order t o provide p r o t e c t i o n for t h e duct8 and and v i b r a t i o n a l environments.
adjacent s t r u c t u r e , fixed, s l i d i n g and swinging aapports are required. These supports are designed t o absorb t h e a c c e l e r a t i o n loads but not i n t e r f e r e with The types of support which have t h e d e f l e c t i o n c a p a b i l i t i e s of t h e ducts, MDC A4551 VOLUME I1 FIGURE 2 DUCTING CONFIGURATION
. 020mt.- INCONE L'617
FIGURE 3 M260-RTA-1 GAS DISTRIBUTIC'I SYSTEM ' Y ' DUCT ASSEMBLY
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MDC A4551 VOLUME I1 been designed are illustrated in Figures 4 through 8 and indicate the simpl%citp of the assemblies.
1 . 3 . 5 THERMAL INSULATION a - The following requirements and operating condicioncl were used in the heat transfer analysis to determine the thickness ard weight of the ducting external insulation: Duct temperature 1 2 6 0 ' F Ambient temperature* l O O ' F Duct diameter 17 Inches Maximum external insulation temperature 300°F *Natural convection only was assumed, and the fuselage was constantly purged of hot air to maintain lCOOF ambient conditions The result8 indicated that in order to remain within the specified surface temperature of the insulation blanket, 0.53 inch of rfin-K insulation was re- quired around the periphery of the duct. In addition, a high emissivity coating was required on the external surface of the blanket.
The insulatian aasembly consists of remvab3.e blankets of foil-encapsulated batting, with capstans provided for installation by wire lacing and bre*+.her vents to equaljze pressure variations. The calculated weight of the blanket for the 17 inch diameter duct is 5.72 lb/ft run.
Mln-K insulation exhtbits the lowest thermal conductivity of the available materials for this application; however, other insulations could provide the same protection at a lower weight $f increased thickness were acceptable. For exaaqde, a thickness of 0 . 9 0 inch of KAOWOU (8 PCF) could be used and the insulation system weight would be reduced t a 4.33 lb/ft run. Due to installa- tion consideration Min-K insulation was selected.
1 . 3 . 6 BELLOWS - The bellows assemblies designed for the RTA fall into two
One group of bellcws absorbs the thermal expansion by angulation categories.
movements, the other group through axial motion.
The joints which absorb thermal growth by angulation are referred to as Thn, pin joint type which is capable angulation bellows and are of two types.
of deflection or angulation in one direction only and the fully articulated or ginbal joint which al.lowe for deflection in any direction.
The joints which abaorb - h a m 1 grmth by axial motion are called compen- satore since a system of interlocking and balanced bellows can compensate for the ducting pressure load or thermal growth without exerting its compressive The gimbai end load on the adjacent duct sections or the eupporting etructure.
FIGURE 5
SWINGING SUPPORl -
LINKAGE FIGURE 6
SWINGING SUPPORT - HINGE
FIGURE 7
SLIDING SUPPORT - BOLT TYPE
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FIGURE 8
OIRECTIONAL ANCHOR - ROLLIWG SUPPORT
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MDC A4551 VOLUME I1 j o i n t is detailed on Figure 9.
In addition t o the above mentioned bellows components the RTA gas d i s t r i - bution system makes use of two sets of f r e e bellows, called bellows sets. This component allows the enginelcruise fan assembly t o move f r e e of t h e i n t e r - connect system without inducing excessive bending moments i n the engine case.
This arrangement of bellows c o n s i s t s of s p l i t t i n g one long bellows i n t o two halves and putting an intermediate spool between them so t h a t t h e bellows can a d j u s t t o a p a r a l l e l o f f s e t condition with reduced shear loads and end moments.
The piston load in the bellows is reacted by the main anchor point on t h e c e n t e r l i n e of the a i r c r a f t and t h e d i r e c t i o n a l anchor on t h e ' Y ' duct, t o which t h e bellJws set is attached. This arrangement s h a m i n Figure 10.
A l l bellows components on t h e RTA are equipped with i n t e r n a l sleeves t o reduce t h e pressure drop across the j o i n t .
1.4 VALVES A l l the valves i n the d i s t r i b u t i o n system are of the "butterfly" type, .
consisting of a valve body with attaching flanges, a ciosure o r modulation vane mounted on a torque s h a f t , and a s h a f t s e a l i n g gland. Since t h e RTA w i l l have ample t h r u s t t o permit s m a l l amounts of leakage without penalizing the o v e r a l l t h r u s t schedule, a simple low c o s t approach which will permit s m a l l amounts of leakage w i l l be employed i n t h e design of t h e valve seats. The valves, which provide f o r the i s o l a t i o n of components o r modulation of t h e gas flow, are described i n t h e following paragraphs and are shown i n s t a l l e d MCAIR Drawing RTA 260-001-4.
on
1.4.1 ENGINE ISOLATION VALVE - The two engine i s o l a t i o n valves operate only
during t h e engine out condition. The valves r o t a t e through an angle of 90 degrees t o prevent a back flow of hot gas through an inoperative engine. The i n s i d e diameter of the valves is 1 7 inches.
1.4.2 ENGINE ETaC MODULATION VALVE - These two valves modulate gas tr, t h e
1 i f t J c r u i s e fan s c r o l l s and are not required t o close against t h e valve case.
They r o t a t e through an angle of approximately 30 degrees, depending on the modulation required f o r control. The valve design is i l l u s t r a t e d i n Figure 11.
1.4.3 J N G I N E ETaC AND SHUTOFF VALVE - This valve serves t o both modulate and
It is located on the c e n t e r l i n e of the Tircraft j u s t for- close o f f the flow.
ward of the interconnect duct, preventing pressurization of the nose fan .Scroll ducting during the c r u i s e mode o r modulating t h e flow t o t h e nose fan i n powered 90 degrees f o r sealing.
l i f t operation. The valve r o t a t e s through an angle of The valve design is i l l u s t r a t e d i n Figure 12.
-L AlRCRIIPT EoMpL9Ny HDC A4551 V O L W I1 FIGURE 9 M260-RTA- 1 ENGINEjFAN GAS DISTRIBUTION ANGULATION BELLOWS W\TER\t,L: \\:CONEL 617 OL CQUCL EST.WEIrGU1~ t 6O\_%S- FIGURE 10 ENGINE/FAN COUPLING ARRANGEMENT . - -- - .
MAIN ANCHOR w)C A4551 VOLUME 11 FIGURE 1 1 F1260-RTA- 1 & GAS DISTRIBUTION VALVE ETaC MODULATION &xtowr *SAC A s u n SHIFT SEN IN(^ GIAHO k s m .
MAT€g\AL: \%ONEL tit7 OS EQJk EST. W E I G H T : 6 0 C B S .
IUWhTrOu 3puup ? h T . - z I R C O N I A CONTROL SHRFT VALVE BLADE
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CUT-OUT TO CLEAR SCROLL VALVE - # A A-RAFT CoMpylWY MDC A4551 VOLUME I1
1.4.4 INTERCONNECT ISOLATION VALVES - These two valves a r e used during engine
strrt-up and i n the c r u i s e mode t o I s o l a t e the l i f t / c r u i s e fans when no modula- ':?fm is required. The valves r o t a t e through an angle of 90 degrees t o close o ' f t h e flow. The i n s i d e diameter of the valves is 14 inches.
.4.5 DIVERTER VALVE - The d i v e r t e r valve is used t o d i r e c t the hot turbine
e x h a u s t gases from the t h i r d gas generator e i t h e r t o t h e nose l i f t fan (and t o the cruise ran in engine-out emergency) o r tc conventional fixed engine exhaust nozzles. The d i v e r t e r valve has a bifurcated valve body, two closure doors and s ' a f t s , an i n l e t d i f f u s e r cone, and a closure door actuation system. The i n s i d e d ameter of t h e valves is 17 inches. This valve is e s s e n t i a l l y i d e n t i c a l t o t . e design used in t h e XV-5 a i r c r a f t .
The closure doors are actuated by a set of linkages located outside t h e valve body.
When t h e doors are in t h e diverted position, t h e exhaust gases are directed through t h e diverted l e g of the valve t o t h e nose f a n system, and the exit t o the engine exhaust nozzle is sealed o f f , as shown on MCAIR Drawing RTF. 260-001-4. In t h e straight-through (or cruise mode) position, the ducts t o the f a n system are closed o f f and t h e engine exhaust is directed through t h e exhaust nozzle.
1.5 ENGINE DIFFUSER AM) ALIGNMENT BEARINGS SECTION The engine d i f f u s e r section, Figure 13, c o n s i s t s of t h e following items: (a) A .ffuser plug (b) A d i f f u s e r f a i r i n g (c) Antiswirl vane supports (d) Two b a l l bearing assemblies An a r t i c u l a t e d bellows set assembly (e) [f) Two attachfag flanges.
The ecgine dit:iaer s e c t i o n serves a twofold purpose i n t h e RTA gas d i s t r i b u - t i o n sy.s+-.n F i r s t it d i f f u s e s the hot gases from t h e engine turbine exhaust, a s i n a normal i n s t a l l a t i o n , and expands it t o f i l l t h e 17 in. diameter duct a t % of 0.30; and second, it prevents t h e thermal growth of t h e attached aucting from imposing extraneous bending loads on the engine case.
The d i f f u s e r plug is supported by t h e d i f f u s e r f a i r i n g thrcugh t h e anti- s w i r l vanes. fhe b a l l bearing assemblies, which allow t h e complete assembly t o rotatc, and/or t r a n s l a t e through small angles as the downstream ducting a l i . m s i t s e l f t o meet temperature and loading conditions, is sealed against sds leakage by the bellows arrangement shown on t h e reference drawing. The w)C A 4 5 5 1 VOLUME I1 FIGURE 13 ENGINE DIFFUSER AND ALIGNMENT BEARING SECTION ENGINC ATTACHMENT FLANGE GE.
SUPPORT VANES
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1 . 6 COMPONENT MATERIALS SELECTION The maximum duct system operating temperature of 1375OF and normal opera- ing temperature of 1260°F makes available a variety of materials which have the required characteristics of supericr corrosion resistance, resistance to creep, high stress rupture strength, and superior oxidation resistance. These service temperatures are more significant with respect to long term metallurgical sta- bility since this is in the range conducive to carbidL precipitation and the formation of brittle intermetallic phases. A number of available superalloys were screened as possible component materials, including the following: 21-6-9 Inconel X-750 .
N-155 (Multimet) Inconel 718 Inconel 600 Hastelloy X Inconel 601 Haynes 188 Rae' 41 Inconel 625 Inconel 718 Inconel 617 L-605 The austenitic 21-6-9 is one of the new stainless steels offering better Its oxidation resistance I s more than adequate strength than the 18-8 class.
for the application; but even with its low carbon content, there is a tendency for carbides to precipitate with long time exposure at the service temperature.
This behavior would result in reduced intergranular corrosion resistance and ductility. Typically, 21-6-9 is used in a cold worked condition for improved Strength; and since welding reduces the local area to annealed properties, the alloy is not competitive for welded applications. Since this application re- quires welding, 21-6-9 offers little advantage over the 18-8 stainless steel For these reasons, 21-6-9 was not attractive for this application.
grades.
N-155 is one of the oldest superalloys and contains roughly 20% each of It has excellent oxidation resistance well above chromium, nickel and cobalt.
the service temperatures, but its high carbon content raises the question of intergranular corrosion resistazce and ductility after long time elevated temperature exposure. While it would probably perform satisfactorily In this application, it is not judged competttive with the other candidate materials.
Inconel 600 and 601 exhibit superior oxidation resistance to temperatures Typical application8 for these alloys above 2000°F, but they have low strength.
MDC A4551 VOLUME I1 are therefore nonstructural, such as heat-treating baskets, fixtures.and furnace components. They both would be more than adequate for the application in.terms of oxidation resistance and metallurgical stability, but they would not be weight competitive with the other higher strength candidate alloys.
The remaining alloys can be divided into two classes: those which are Strengthened through precipitation heat treatment and those that are solid solution strengthened.
"he precipitation hardening alloys included Rene' 41, Inconel 718, and Inconel X-750 but the higher strength they offer is offset somewhat by the difficulty experienced in fabrication. The aging treatment required after fabrication creates a distortion problem which is related t o the complexity of the formed part. For simple parts, use of these alloys may be feasiFle; for moMt complex parte, the increased fabrication costs will make their use im- practical. As with the previous alloys, these exhibit more than adequate oxidation resistance and metallurgical stability for the RTA application. The service temperature, 1260°F, approximately represents the limit for long term exposure of Inconel 718.
The solid solution strengthened alloys are much easier to fabricate into complex structures, because they require no thermal treatment after forming or welding. The alloys in this category include Hastelloy X, Haynes 188, Inconel 625, Inconel 63.7, and 6605. Any of these alloys, all of which are readily available, will function satisfactorily in the system environment.
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MDC A4551 VOLUME iI A. LIFT/CRUISE FAN THRUST VECTORING DEVICES ?. 1 GENERAL !"-.SCXIPT' The t h r u s t vectoring devices used f o r the l i f t / c r u i s e fane were selected f o r evaluation t o determine the f e a s i b i l i t y of t h e b a s i c design concent i n regard t o state-of-the-art f a b r i c a t i o n techniques. The t h r u s t vectoring ele, e n t s consist of a n inner and an o u t e r hood and a set of yaw doors. The hoods are stow& during aerodynamic f l i g h t and are r o t a t e d i n t o t h e fan air stream during The yaw doors are closed powered l i f t f l i g h t f o r t h r u s t deflection.
'ng aerodynamic f l i g h t and form t h e f l o o r of the Exhaust nozzle. During red l i f t f l i g h t , t h e doors are opened and by d e f l e c t i o n i n t o t h e fan air .3 prcduce yaw moments f o r the a i r c r a f t . The estimated temperatures expected 03 these elements are shown i n Figure 14 and a r e based on t h e 36 inch t h r u s t vector nozzle tests recently rompleted a t NASA Ames Research Center. The b a s i c design concepts f o r the hoods and yaw doors were coordinated with t h e &tech Company t o a s s u r e t h a t state-of-the-art f a b r i c a t i o n procedures can be used.
2.2 THRUST VECTORING HOODS These dual r o t a t i n g hood segments provide f o r t h e l i f t / c r u i s e f a n t'rust inner a n t d e f l e c t i o n during a l l modes of a i r c r a f t powered l i f t f l i g h t . The o u t e r hoods r o t a t e independently of each o t h e r and can be moved from a 0" vector position (cruise) t o -105" vector p o s i t i o n ( v e r t i c a l ) . The design conLept of t h e hoods proviLes f o r s h i e l d i n g from the exhaust g?.s temperature during c r u i s e f l i g h t . The i n t e r n a l hood pressure and exhaust gas temperature, which imping? on t h e hoods during vectoring, are low enough t o allow t h e construction materials t o be e i t h e r 2219-T87 aluminum honeycomb o r polyamide graphite sand- wich. The aluminum was selected f o r t h i s application.
The inner hood canopy r o t a t e s about the fixed nozzle and t h e o u t e r hood r o t a t e s about t h e inner hood. The hoods are 1-1/8 inch uniform thickness. Guide Seals r o l l e r s are used between the hood segments t o control t h e clearance.
are provided between t h e outer hood and t h e fixed nozzle m d between t h e inner and o u t e r hoods. The pivot f i t t i n g €or both hoods is an slurt~num machining A l u g 2roJecting from t h e s i d e which is bonded i n t o the honeycomb sandwich.
of t h e pivot f i t t i n g is used as t h e attnchmen; point f o r the hood d r i v e link.
State-of-the-art The inner and outer hoods are i l l u s t r a t e d i n Figurc 15.
f a b r i c a t i o n methods are used.
W-LL AlRCRAFI COMI40NV MDC A4551 VOLUME I1 FIGURE 1 4 'ID" VENTED NOZZLE WALL TEMPERATURE MEASUREMENTS 11 2 O GEOMETRIC ?OSITION 840 VECTOR ANGLE NF/* = 95% .._.
_ _ - . . . -. ..
FIGURE 15 M260-RTA-1 LIFT/CRUISE FAN HOOD ' -!;IGN MDC A4551 VOLUME I1 2 . 3 YAW DOORS The yaw doors function both as closure doors during c r u i s e f l i g h t and as yaw moment producing devices i n powered l i f t f l i g h t . Since the doors are exposed to the high exhaust gas temperature duxins c r u i s e f l i g h t , Inconel 617 or equivalent was selected as the construction material. Seals are p r w i d e d forward l i p and exit nozzle.
on t h e fixed interface structure: hinge plane, State-of-the-art fabrication procedures are employed. The yaw doors are i l l u s t r a t e d i n Figcre 16.
I.
MDC A4551 VOLUME I1 3. MECHANICAL TRANSMISSION SYSTEM 3.1 GENERAL DESCRIPTION The propulsion system is composed of three Allison XT701 engines driving The engines and fans are inter- three Hamllton Standard variable p i t c h fans.
connected by a mechanical transmission system shown i n Figure 17, and c o n s i s t s of shafting, combiner gearbox and forward fan clutch.
The l i f t / c r u i s e fan assemblies (two) are located above t h e wing and adjacent t o the fuselage. The engine, mounted d i r e c t l y behind t h e fan, is integrated i n t o t h e l i f t / c r u i s e nacelle. Fan supercharged air is inducted i n t o the engine and exhausted together with the fan by-pass air through the t h r u s t vectoring nozzle. L i f t / c r u i s e fan speed is reduced below f r e e turbine speed by a planetary gear set. An overrunning clutch i n s t a l l e d ahead of the engine between the engine and the planetary set permits overrunning in t h e event of an engine f a i l u r e . The Allison XT701 engine is coupled with a Hamilton Standard variable pitch fan t o form the compound t u r b o f a d s h a f t engine u n i t i d e n t i f i e d as t h e Allison PD370-25A. The fan assembly includes a s p i r a l bevel gear set t o transmit power t o the other two fans f o r control power, o r power transmission during an engine out condition.
The Hamilton Standard variable p i t c h l i f t fan is located forward of the The fan assembly includes a s p i r a l bevel gear set t o transmit power cockpit.
t o the fan from the forward drive s h a f t . Power is transmitted from the combiner gearbox t o the l i f t fan through a w e t disk clutch t o provide f o r disengagement FIGURE 17 MODEL 260-RTA-2 PROPULSION SYSTEM COUBINER GFARBOX MDC A4551 VOLUME I1 of the fan during ground operation, i f desired, o r i n t h e c r u i s e mode.
The t h i r d engine (center) d r i v e s i n t o t h e combiner gearbox through a spur gear set i n t o the transmission system. The combf-er gearbox a l s o accepts power from the two l i f t / c r u i s e engines f o r d i s t r i b u t i r - during control excursions and engine out operation.
3.2 TRANSMISSION SYSTEM DESIGN The e x p e r t i s e and experience of Detroit Diesel Allison (DDA) in power transmission systems w a s employed in t h e study of t h e design, development and estimating of the RTA mechanical transmission system with a subcontract arrange- m e n t . The work t o be performed under t h e contract was defined i n MCAIR Work Statement WS-SDPS-960. The ground rules established by MCAIR f o r t h e con- t r a c t e d study are defined below:
Power Requirements - The system w a s sized f o r an a i r c r a f t requiring
(a) a normal t o t a l t h r u s t of 28,275 pounds and an engine out thrust of 25,740 pounds.
Control Margin - The control margins specified were 27% a t normal
(b) (3 engine operation) power and 13% during engine out.
Duty Cycle - The operational duty cycle t o which DDA designed t h e
(c) is defined below: system 40% of time a t normal standard T.O. power 30% of t i m e a t high c r u i s e power (75%) 20% of time a t normal c r u i s e power (60%) 10% of t i m e a t i d l e power.
G e a r Design - The gears i n t h e transmission system were designed f o r
(d) i n f i n i t i v e l i f e a t normal power p l u s f u l l control.
Under the terms of t h e subcontract, DDA supplied design d a t a f o r a power trans- mission system which, per agreement with MCAIR, emphasized a l o w c o s t , low r i s k The design and did not include excessively low weight advanced technology.
component weights which resulted from t h i s study are as follows: Component W-f ght (lb) Combiner Box Assy. (including clutch) 412.8 Cross Shafts (including support bearings) 19.4 Center Engine Shaft 15.7 98.2 Fan Shaft (including support bearings) Total 546.1 Complete r e s u l t s of t h e DDA e f f o r t i n response t o the MCAIR work statement are presented i n Appendix A.
-ma. AHWCRAPT COMFWNV 2 1 I9DC A 4 5 5 1 Volume I1 APPENDIX A MCI)ONNELL AIRCRAFT COMPANY V/STOL RTA SHAPT AND TRANSMISSION DESIGN STUDY By DETROIT DIESEL ALLISON A-1 MDC A4551 Volume I1
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omton 01 G e n m tors coruoretlan ineimnamtis. tndtana 46206 MC DONNELL AIRCRAFT COMPANY V/STOL RTA S H A F T AND TRANSMISSION SYSTEM DESIGN STUDY EDR 8 9 7 6 Part I November 1 5 7 6 A-2 MDC A4551 VOLUME I1 1.0 Introduction This report w a s Trcnarcd in response to ticUoniie11 A i r c r a f t Go. (MCALR) Purchase Or-:er Z6OC91 vnnrz'r? 9eetroit Diesel Allison (3DA) w a s t o conduct a propulsion s y s t e n r:ocf..ncip-i Zransmission study for the V/STOL-Research and Technology k.5rcrz.r: {RTA!. The complete w r i t t e n response by DDA in- cludes t h i s report (P3z-c i ) ri-d P a r t 2 covering estimated c o s t s of a shaft.
s y s t e m developmext pro.cr3r.i.
"he e f f o r t described herein w a s accomplished during the period July-August 1976 m d e r t h e DDA P r o j e c t Ninnber E76030.
The RTA V/STOL a i r c r a f t incorporates a propulsion s y s t e m ae shown i n Figure 1.1.
This study h a s as its o b j e c t i v e s the i d e n t i f i c a t i o n of technical risks and preparation of estimates f o r design, f a b r i c a t i o n and t e s t i n g of assemblies and components f o r a research and technology a i r c r a f t propulsion system mechanical transmission. The components t o be covered are those shown i n Figure 1.1 and i d e n t i f i e d a s combiner box and c l u t c h and t h e four s h a f t s leading to the combiner box.
Design study 2 .o A design study w a s conducted t o define a s h a f t i n g system i n the d e t a i l ade- quate t o i d e n t i f y technical r i s k s and estimate costs f o r design, fabrica- t i o n and t e s t i n g . This design study is defined herein.
2.1 Power and Speed Requirements P r i o r t o t h e a c t u a l s h a f t i n g system design e f f o r t , i t w a s necessary t o obtain estimates f o r RTA s y s t e m powers and speeds. This e f f o r t was conducted at DDA making use of t h e known data f o r a Hamilton Standard 62" varlable-pitc4i fan and the DDA XT701 engine. The s t a r t i n g p o i n t for t h l n effort w r i n I t i t .
required t h r u s t and control t h r u s t margin e s t a b l I ~ h e d by M:hlK 0 Total Thrust Required (normal) 2 8 , 2 7 5 l b s . (margin 22x1 0 Total Thrust Required (1 engine out) 2 5 , 7 4 0 l b s . (marpin If)?)
These t h r u s t l e v e l s a r e t o be achieved on 90°F day a t s e a l e v e l s t a t i c condi- t i o n s .
It w a s assumed f o r the purpose of t h i s study t h a t the engines would be f l a t rated below 900F and t h a t s h a f t horsepower would therefore not exceed those determined f o r the s t a t e d conditions.
Performance calculations were made €or the RTA system f o r V.T.O. operation with t h r e e engines operational and with an outboard engine out.
A-3 MDC A4551 VOLUME I1
OstrpIt Diesel Allison
Onrldon ol General Motors Coqtomtlon ItulmnawUS. Indiana 46206 A-4 MDC A4551 VOLUME 11 These c a l c u l a t i o n s were then extrapolated t o t h e nine conditione shown ia Table 2.1 and s h a f t horsepower was determined f o r each component i n the s h a f t i n g system.
Actual mechanical design speeds f o r t h e RTA t o be used I n t h i s study were e s t a b l i s h e d in the following manner.
1. The 100% mechanical fan speed w a s set at 3,543 W M .
2. The reduction gear f o r t h e l i f t / c r u i s e engines w a s assumed t o be t h e T56 planetary set with a r a t i o of 10:3. This e s t a b l i s h e d t h e 100% l i f t cruise power t u r b i n e speed a t 11,810 RPM.
Cross s h a f t i n g from the l i f t / c r u i s e engines t o the combiner box 3.
was set close t o power turbine speed - 11,805 RPM.
4. The input speed to t h e l i f t fan gear box was determined t o be 8,432 RPU based on t h e l i f t fan gearbox ratio of 2.38:l e s t a b l i s h e d i n earlier s t u d i e s and coordinated v i t h Hamilton-Standard and McDo&ell- Douglas.
(100%design Figure 2.2 is A schematic showing the RTA power system speeds point) f o r each p o i n t i n t h e system.
this Although o t h e r speeds could have been s e l e c t e d f o r each component I n study, it is believed t h a t t h e overall resultb would b e t h e same relative t o conclusions on costs, risk and development time.
2.2 Combiner Gearbox Design 2.2.1 General Arrangement and Function The combiner box t r a n s f e r s power from t h r e e engines t o the t h r e e fane during the powered l i f t mode. During conventional f l i g h t t h e l i f t fan is disengaged by the combiner box clutch; t h e combiner box clutch accel- fan t o operating speed p r i o r t o powered l i f t o f f and during erates t h e l i f t t r a n s i t i o n from conventional f l i g h t t o the powered l i f t mode.
is through a set of h e l i c a l The center engine input t o the conblner box gears with a 1 . 4 : l reduction r a t i o . (See Figure 2 . 3 . ) The output gear of t h i s set mounts d i r e c t l y on the s h a f t d r i v i n g folward to the l i f t fan.
Each outboard engine is coupled t o the l i f t fan s h a f t with a r i g h t angle set of s p i r a l bevel gears; reduction r a t i o of 1 . 4 : l . Here again the output gear is mounted d i r e c t l y on t h e s h a f t d r i v i n g forward t o t h e l i f t fan.
Output from the combiner box t o t h e l i f t fan is through a disk clutch provided with a mechanical lockup f o r f u l l power transmission. The com- b i n e r box is provided with i t s own l u b r i c a t i o n and cooling system, the oil cooler being the only airframe equipment. Controls for clutch actuation A-5 MDC A4551 VOLUME I1 0 0 hl 0 m U 9 0 d 4 h N N 0 (Y m N hl (Y (Y In VI 0 00 00 0 00 03 U In m d In d I 0 0 Qo 0 \o 9 cr) N N 9 9 0 9 M N N 9 9 9 m m 0 0 00 00 V e \o m m 9 I 0 0 9 9 c3 Q, 0, 0 N N 0 d d h 0 Y N hl 0 N N m 00 00 In 00 03 In In u) N N In I 00 0 N CCI 0 0 Q, m G d U N 0 (Y m 4 h d d 0 9 9 In r- 9 rg In r- U \o M OI U 9 h In I I U h 00 0 a0 0 00 0 rn U d 9 00 0 0 m d In d 0 d 9 OI 9 hl 0 9 9 br h U U 9 U In h 9 I I d a0 O 9 m m 9 0 0 4 N 4 U 0 N 9 QD h d N In In In In 0 d 9 9 h In In In m In b In 0, I I d d Q) m h 0 r- U 00 N d d U U c, OI 0 9 U In r- 9 0 r( In 9 9 U b U d 9 9 IP U 00 9 N In 9 I I 4 d 00 0 0 0 U U 00 m 4 9 9 d U U 0 0 0 9 r- r- \o In In 9 9 0 0 9 d 9 9 In I n m a r( In 00 I d d a0 0 0 0 m 00 F) H In r ) In .d U 0 0 0 p3 I- h 9 d 4 U U In 9 U 9 0 In 9 9 9 U In 9 Lc U P) Lc Y A Y P) W 00 c 3 Q) r( 9) 0 cl oc W pc .) n U Lc Lc Lc W Q) a! 91 3 E 0 :
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Eo I N c N i A- 7 MDC A4551 VOLUME I1 To LIFT FAN BEVEL SET f
1 . 1 A
I -INPUT FROM RIGHT ENGINE HELICAL GEAR SET r
7 - 1 OVER - CLUTCH RUNNING
OIL PUMP DRIVE G E A R S 7 INPUT FROM I CENTER ENGINE
FIGURE 2 . 3 - COMBINER GEARBOX GEAR SCHEMATIC
A-a MDC A4551 VOLUME I1
Datanit Diesel Allison
Olvldon of General Motors Corporation IndIanaDob. lndrna 46206 are mounted d i r e c t l y on the combiner box. Figure 2.4 is t h e canbiner box as designed f o r t h i s study.
,2.2.2 Combiner Box Gearing S p i r a l Bwel The s p i r a l bevel gear set w a s designed t o meet t h e power and speed re- quirements defined i n Section 2.1.
Allowable stress levels were s e l e c t e d t o produce i n f i n i t e l i f e f o r t h e s p i r a l bevel gearing. Stressee a r e calculated according t o methods set. f o r t h by Gleason Gear Works.
The pawrr levels in Table 2.1 were reviewed zo determine t h e maxiatrrm power on t h e s p i r a l bevel gear set. This w a s not& t o be 6,663 horsepower i n t h e contingency maximum r o l l mode. Gears are designed t o produce i n f i n i t e l i f e a t t h i s condition. This approach a f f o r d s low r i s k plus eruwth for t h e r e s u l t a n t gear set. (The s p i r a l bevel gears do not have t o be inspected a f t e r contingency operation.)
!ho d i f f e r e n t gear arrangements were evaluated. The one shown in Figure 2 . 4 and an alternate arrangement that incorporated an i d l e r bevel gear, The arrangement shown i n Figure 2 . 4 was selected because it offered t h e most compact, low-weight design f o r t h e RTA design parer. (It should be noted t h a t higher power 1 vels may not r e s u l t i n t h e same conclusion.)
S p i r a l beve: gear calculations were made with a DDA-developed computer a n a l y s i s t h a t follows from the Gleason methods shown i n t h e i r publica- tions and used at DDA f o r same time. The r e s u l t i n g gear set d a t a is shown in Table 2.5 f o r t h e design point power level.
Comparisons f o r stress and p i t c h l i n e v e l o c i t y were made with other s p i r a l bevel gear a p p l i c a t i o n s calculated i n a s i m i l a r manner. These a r e shown i n Figures 2.6 and 2 . 7 . It can be noted t h a t t h e RTA design is within t h e l i m i t s of successful e a r l i e r designs.
MDC A4551 VOLUME I1 A- 10
~sl;roit Diesel Alllson
Dlvlslon ol General :lotom Corgoratlon
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Indlanapolk Indiana 46206 A-11 Nw: A 6 5 5 1 YOLUNE 11 m x x
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A-12 M#: A6551 VOLUME I1 m
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0 0 0 m m 0 m cu d cu CONTACT STRESS--KSI A-13 ?fDC A4552 VOLUME I1 l z l i c a l Gear Set The h e l i c a l gear set was designed t o provide i n f i n i t e l i f e at t h e amximan powFr levels established i n Section 2.1. This is 7610 horsepower.
A DDA-developed computer a n a l y s i s w a s used t o evaluate numerous h e l i c a l gear sets and t h e r e s u l t i n g selorction is Shawn i n Table 2.8. Bending stress is calculated with t h e modified Lewis formula.
Accessory G e a r s An accessory gear set is provided t o d r i v e t h e o i l pumps f o r the combiner box.
Design goals f o r t h i s set are t h e same as noted previously f o r t h e h e l i c a l gear set.
Gear Materials A l l t h e RTA ctmbiner gearboxes are designed of AMs 6265 (CEVM 9310) material which is t o be carburized and ground. This gear material has accumulated 64,000,000 f l i g h t hours I n DDA designed gearboxes and has demonstrated its c a p a b i l i t y q u i t e s a t i s f a c t o r i l y .
2.2.3 B e a r i n g s Each bearing position i n t h e combiner box w a s examined t o determine t h e maximum load f o r any of t h e power conditions established i n Section 2.1.
The minimum bearing static capacity w a s then required t o be no less than the msttimum load under any c o n t r o i condition (including contingency).
See Figure 2.9 f o r t h e l o c a t i o n o f , and numbering system f o r , the can- b i n e r lox bearings.
I n order t o estimate a f a t i g u e l i f e f o r each combiner box bearing and f o r t h e systrm, a duty cycle w a s established by which t h e mean bearing loads could be evaluated.
The duty cycle was biased heavily toward t h e high power conditions s i n c e the RTA is expected t o spend a l o t of time at high power.
The duty cycle used iras: o 40% of t h e a t normal standard T.O. paver o 30% of time a t high c r u i s e paver (75%)
(3 engines running - lift f a n off)
o 20% of time a t normal c r u i s e power (40%)
(3 engines running - l i f t f a n o f f )
o 10% of time a t i d l e power A- 14 M)C A 4 5 5 1 VOLUME I1 A-15 MDC A4551 VOLUME 11 Bearing f a t i g i e life was calculated based on a modification of the AFBMA method. This procedure includes the e f f e c t of material, processing, lubrication, speed and misalignment t o produce a more realistic estiaate of f a t i g u e l i f e f o r the a c t u a l bearing design and operating conditions.
This procedure w a s used f o r t h e twelve combiner box bearings that are sensitive t o transmitted load; f o r t h e other six bearings, a combined m a t e r i a l and l u b r i c a t i o n f a c t o r of f i v e w a s used.
The r e s u l t s of this a n a l y s i s are shown in Table 2.10.
2.2.4 L i f t Fan Clutch Function The l i f t f a n clutch is provided t o accelerate t h e l i f t f a n t o combiner box output s h a f t speed.
This is accomplished with an 011-actuated, o i l - cooled multiple d i s k clutch. G i l f o r cooling and actuating t h e ciutch is transmitted t o t h e clutch by tubes passing through t h e combiner box from a clutch c o n t r o l valve mounted a t t h e rear of t h e canbi.net box.
The power requirements f o r the disk clutch are only those developed by t h e l i f t f a n while operating at minimm blade p i t c h p l u s the inertia f o r t h e fan. Those are: o
*Fan i n e r t i a - 475 pound f t
o *Fan windage l o s s - 1000 horsepower a t f u l l speed
* E s t i m a t e s from Hamilton-Standard A-16 MDC A4551 VOLUME I1 TO LIFT FAN
t
OIL PUMP
FIGURE 2.9 - COMBINER BOX BEARINGS SCHEMATIC
A-17 -mru nrrtnCv*-n,
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MDC A4551 VOLUME I1 MvlsM d Geneml Motors Corpontlon Indianapolis. Indhne 46206
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L 9-4 rl r ) rl 4 d rl d d Qo 00 Qo co a0 a U U d 4 rl d rl 4 d 94 4 OI OI Qo a0 N In In a0 Qo 9 00 aD m OI d 9 4 (3 N d cv cv N N N Pl (3 m (3 N U U rl 4 X X X X X X x x X x X X X W W X X 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 cv N w p r ) 9 0 9 c3 N N N J 0 0 0 a0 C I d r ( 94 4 N N d rl c . l N 4 h ( N -4 \o rg X X X x X X X ?t x W X X X x x X X In ln In In C 0 0 In 0 In In u) 0 0 0 0 u) d 4 r( 9-4 r( u7 In In 9 e m 0 0 In (7 0 m r( r( 4 rl d d d r( r( 4 N U ln 9 h Q) c ( 0 N m U In 9 Q) r ( d r ( d rl 4 4 c) A-18 MDC A4551 VOLUME I1 A mechanical lock-up device is provided in the clutch mechanism t o permit transmittal of f u l l l i f t f a n power a f t e r t h e d i s k c l u t c h has brought the f a n t o combiner box speed. The lock-up device senses d i s k clutch tnput and output speed and i n h i b i t s lock-up u n t i l r o t a t i o n a l speeds are matched.
Once speeds are matched, lock-up occurs automatically and a signal is generated t o t h e a i r c r a f t c o n t r o l system t o permit t h e l i f t f a n blade angle t o be advanced in order t o develop t h r u s t .
Clutch D i s k Materials The l i f t fan c l u t c h has been designed t o make use of a Teflon based d i s k facing material recently developed a t DDA f o r a General Motors i n d u s t r i a l application. It has shown i t s e l f t o be q u i t e satis- f a c t o r y f o r use at high power loadings w h i l e running i n i n d u s t r i a l transmission o i l s . For the RTA application, where it is expected t h a t o i l s per MIL-L-23699 or MIL-L-7808 will be used, it will be necessary t o run o i l compatibility tests. Data a v a i l a b l e a t t h i s time does not suggest any incompatibilities between a i r c r a f t oils and t h e material but t h i s will be substantiated by test.
Clutch D i s k S i z i n g The clutch d i s k s i z e selected f o r the RTA design is a 7.88 inch diameter p l a t e that is a v a i l a b l e from o t h e r clutch designs on test and i n produc- at DDA. This s i z e y i e l d s a 17,400 f t . per minute omximum rubbing t i o n speed which is w e l l within the l i m i t s of high speed clutches designed For example, the T-40 clutch ran at 18,000 ft/minute.
by DDA.
D i s k Clutch Details The c l u t c h as designed f o r the RTA mission is described as follows: o Clutch plate O.D. = 7.88 in.
o 13 p l a t e s - 26 f r i c t i o n surfaces
o engagement time 6 seconds o approximately 1700 BTU t o t a l heat r e j e c t i o n A-19 MDC A4551 VOLUME I1
Oetrolt Oiesel A I I I ~ O ~
OMdon ol General Motors C o m l b n Indbnepolls. Indiana 46206 The previously mentioned clutch development e f f o r t a t DDA f o r an i n d u s t r i a l clutch provides good guide l i n e s f o r required clutcb coolant flow rate.
This is .042 GPH/in2 vr 24 CPM for the disk c l u t c h . This flcw rate is only required during clutch engagement and f o r approximately 2 4 seconds following clutch lock-up, a t which t i m e the coolant would be turned o f f .
Clutch piston pressure required t o achieve the 6-second engagement t i m e would be approximately 100 p s i maximum.
2.2.5 Over-Running Clutch The o v e r r u n n i n g clutch w a s provided a t the center engine input t o the combiner box t o allow f o r planned o r emergency s h u t dawn of the center engine.
as shown i n Figure 2.11 is similar t o one designed and developed The clutch i n the T56-A-18 program. Normal power t r a n s f e r through t h e c l u t c h fs accomplished by a double set of h e l i c a l s p l i n e s t h a t do not permit dis- engagement with a p o s i t i v e torque application. When the c e n t e r engine is shut down and clutch torque goes negative, the h e l i c a l s p l i n e s force disengagement. While running i n the disengaged mode, r a t c h e t i n g of the s p l i n e is inhibited by an a x i a l l y unbalanced centrifugal o i l head within the over-running c l u t c h . The clutch design w i l l permit an In-flight start- up of t h e center engine.
The combiner box over-running clutch is the same b a s i c design as would be used i n the l i f t c r u i s e engine gearboxes.
2.2.6 Lubrication and Cooling System The combiner box design contains a completely integrated lubrication aitd cooling system ( t h e o i l cooler would be airframe supplied and mounted).
i n the s y s t e m a r e t h e following: Included o Low pressure pump f o r cooling and lubrication 0 High pressure pump f o r clutch c o n t r o l and gear lubrication 0 O i l f i l t e r 0 Pump regulators o Pump and f i l t e r relief valves 0 Scavenge pumps 0 Clutch control valve o O i l tank ( s l g h t g l a s s - f i l l e r ) This system is shown schematically i n Figure 2 . 1 2 .
A-20 MDC A 4 5 5 1 VOLUME I1
Dotmit Dirsel Allison
OMslon ol Oenen Motors C o w l o n lndianepolk hdlana 46206 INPUT
FIGURE 2 . 1 1 - OVER-RUNNING CLUTCH
A - 2 1 MDC A4551 VOLUME I1
Ostrolt Diesel Allirren
Oivlslon ol General Motors CorWnlron hdlanapok tatem 46206 MDC A4551 VOLUME I1
Detmit Diesel Allison
OMabn ol General Motors Corpontlon Indianapous. Indiana 46206 The o i l system cooling rc-quircments arc' estimated i n t h e following manner.
1 . Combiner box windage losses a t f u l l speed - 1700 B'IU/min
2. Gear and bearing s y s t e m losses ( 1 / 2 % of p a r e r in each gear mesh)
at T.O. power (normal) - 1400 BTU/min
3 . Gear and bearing s y s t e m l o s s e s a t contingency T.O. condition -
3560 BTU/ml:t
4. Clutch h e a t rejection for each engagement cycle - 1700 BTU
The gearbox cooling s y s t e m was designed t o handle t h e normal T.O. power heat r e j e c t i o n with a 100°F o i l s y s t e m 4 1. This suggests a normal flow rate of 10 GPM through the gearbox at a l l times except when the clutch is engaged. During clutch engagement and f o r 24 seconds t h e r e a f t e r an a d d i t i o n a l 24 CPM is added t o t h e system flow t o absorb the clutch heat r e j e c t i o n of 1700 BTU.
An approximation of t o t a l heat rejection a t the tfme of clutch engagement is shown i n Figure 2.13.
It is suggested t h a t the oil cooler be sized t o handle t h e normal T.O.
paver heat r e j e c t i o n of 3100 BTU/min and t h a t the clutch heat r e j e c t i o n be t r e a t e d as a t r a n s i e n t , i . e . , allow the s y s t e m temperatures t o rise during clutcn engagement and d i s s i p a t e t h i s heat gradually over a period of t i m e . The l a r g e thermal mass of the combiner box w i l l keep the peak temperatures w i t h i r . .asonable limils.
Total oil contained i n the sump is s i x gallons. This quantity is neces- s a r y t o permit deairation of the o i l when the f l o w rate is 34 GPM.
O i l pumps for the system a r e conventional spur gear pumps control!.ed by by-pass regulators and protected by pop-off type relief valves.
2 . 2 . 7 Case Structure and Mounts The main combiner box case s t r u c t u r e is made up o f three rnnjpe?'!i,w c . 0 ~ 1 - ings (two covers and a diaphragm). The magnesium would be coated for corrosion protection. Mounting pads are c a s t i n t e g r a l w i t h t h e case and could be located t o be compatible w i t h t h e l o c a l airframe s t r u c t u r e . The o i l tank is mounted d i r e c t l y on t h e combiner box.
2 . 2 . 8 Materials Figure 2 . 1 4 shows the various materials t h a t have been s e l e c t e d f o r c o b ponents of the combiner box.
A-23 MDC A4551 VOLUME I1 MDC A4551 VOLUME I1
Detmit Diesel Allison
0)vlblcIt ol Oenerel Motors Corwretlon IndianaDolls.lndiene 46206 Table 2.14 RTA V/STOL PROPULSION SYSTEM MECHANICAL D R I V E MATERLALS T B U U T I O N Shaft i n & Shaft AMT5512 Support Bearings SAE 52100 Damper Rubber .
Couplil?gS AMs6512 S e a l Plates AMZ5504 Housing AMs5350 Combiner Box Rous ings Ais4434 Shafting lNS64500 Steel Gears AM66265 Bearings AMs6444 Oil Tank AMs5646 Clutch Input-Output AMs6415 Clutch Plates M 6 3 5 5 Seals Carbon Fasteners ~ - 2 8 6 Brackets, Plates AMs6415 Spanner Nuts AMs64 15 A-25 NDC A6551 VOLUME I1 2.3 S h a f t i n g The s h a f t i n g for the R T A propulsion s y s t e m was designed t o m e e t t h e speed and load requirements established i n Section 2.1. S u b c r i t i c a l design points were selected t o minimize development e f f o r t and r i s k .
(The weight increase fa- 'I is approach is s l i g h t . ) Figure 2.15 is t h e R T A shaft system.
S h a f tdesign d e t a i l s are shown i n Table ?.16.
C r i t i c a l speeds were calculated f o r each s h a f t assuming simple supports.
The l i f t f a n s h a f t L ; $ evaluated f o r a number of d i f f e r e n t segments and it as found that t h e ninirmrm weight f o r t h e shaft(inc1uding intermediate support bearings) w a s achieved with four s e c t i o n s of sh. 'ting. It should be noted that t h e l i f t f a n s h a f t discussed herein does not include t h e por- t i o n of t h e shaft that passes through t h e l i f t f a n air stream stat.
A support bearing and coupling assembly was designed f o r use a t each inter- m e d i a t e point of support f o r t h e l f f t f a n s h a f t . See Figure 2.17. The support bearings nre lubricated by grease t h a t is c i r c u l a t e d through t h e bearing by a built-in viscous pump. Bearing loads are law f o r t h e shafting and t h e r e are not any rubbing grease seals t o wear out, therefore t h i s type of assembly is expected t o give a long trouble-free l i f e . Routine main- tenance would not be required of t h i s asse&ly.
The coupling incorporates a diaphragm t o alluu f o r s h a f t angular misalign- m e n t and limited axial displacement. The number of diaphragms 1n the coupling can b e varied t o account f o r misalignment. Airframe a t t a c h points f o r the l i f t f a n support bearings would not r e q u i r e p r e c i s e machining tolerances, r a t h e r it is planned that t h e supports would be shimmed t o f i t at i n s t a l l a t i o n .
A reasonable c o n t r o l on the combiner gearbox t o l i f t f a n distance would be expected and t h e tolerance f o r t h i s would be taken up i n t h e end fittings a t assembly.
Each Lft fan s h a f t coupling assembly is estimated t o weigh 12 p o u d s .
Shafting materials are shown i n Figure 2 . 1 4 .
A-26 MDC A4551 VOLUME I1 , - - -.
A-27
ORIGINAL PAGE I S
OF POOR QUALIlr
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DAWER -
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! ,’ LGREASE RESERVOIR
FIGURE 2.17 - LIFT FAN SHAFT MOUNT BEARING
A-29 MDC A4551 VOLUME I1 2.4 Weifit and CG Weight and center of g r a v i t y f o r the main s h a f t system components were de- termined and t h e r e s u l t s are presented i n Table 2.18.
TABLE 2.18 RTA V/STOL SHAFT =STEM WEIGHTS AND C . G . ' S CG Weight Location (lbs) (Station)* Combiner Box Assembly 412.8 278.0 Cross Shaft (each) 9.7 274.2 Center Engine Shaft 15.7 310.3 Fan Shaft (includes 98.2 166.2 support bearings) Totals 546.1 258.7 *Station Numbers are referenced t o Figure 2.14.
2.5 Maint;inability 2.5.1 Routine Service RTA s h a f t system and combiner box w i l l be l i m i t e d Routine s e r v i c i n g of the t o periodic checking of the oil l e v e l , normal oil changing and f i l t e r maintenance. The oil f i l t e r is provided with a pop-out indicator t h a t w i l l i n d i c a t e the occurrence of high pressure drop across the f i l t e r .
The combiner box w i l l not be an o i l consumer.
O i l change intervals are expected t o be a function of the number of clutch engagement cycles and t h e r e s u l t i n g high bulk o i l temperatures.
There are no components i n the combiner box t h a t w i l l require periodic adjustment.
The grease lubricated bearings supporting the l i f t fan s h a f t are not ex- pected t o require s h o r t time i n t e r v a l maintenance. Their service require- ments w i l l , i n p a r t , be a function of t h e local temperature.
The higher the temperature i n t h a t part of t h e afrframe, t h e s h o r t e r a service i n t e r v a l predicted.
Development t e s t i n g of these bearings w i l l provide good guide- l i n e s f o r grease lube l i f e .
A-30 MDC A4551 VOLUME 11 2.5.2 Overhaul Requirements I n a production program, the combiner box would be subject t o on-condition r e p a i r . This same approach. for a minimum cost program, would generally apply t o the RTA program. It is expected t h a t the combiner box would re- ceive routine boroscope inspections with some disassembly being required for f u r t h e r inspection andfor r e p a i r s .
Combiner box disassembly and r e p a i r w i l l require a limfted number of s p e c i a l t o o l s and technicians experienced i n a i r c r a f t transmission r e p a i r pro- cedures.
Combiner box components such as the disk clutch, over-running c l u t c h oil regulators and c l u t c h c o n t r o l valve can be removed vithout a complete pump, disassembly.
A-31