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AIAA-91-1905
Design Of The High Reliability GMA 2100
Reduction Gearbox
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J. Black and E, Pfaffenberger
Allison Gas Turbine Division
Indianapolis, IN
27th Joint Propulsion Conference
J u n e 24-26,1991 / Sacramento, CA
For permission to copy or republish, contact the American Institute of Aeronautics and Astronautics
370 LEnfant Promenade, S.W., Washington, D.C. 20024
AIM-91-1905-CP
DESIGN OF THE HIGH RELIABILITY GMA 2100 REDUCTION GEARBOX
J. D. Black
E. E. Pfaffenberger
Allison Gas Turbine Division
Indianapolis, Indiana
curring and nonrecurring costs providing significant improvemcnt in initial and operating costs.
Design and dcvclopment of a modcrn reduction
gearbox is critical to mcfting stringent requircmcnts for
ncxt gcncration commcrcial/military turboprop propulsion systems. Next generation gearboxes require significant rcliability impmvcmcnts, bctter power-to-weight ratios, highcr power capability, lower user cost, and simplification of maintcnancc tasks. Thcsc objcctivcs havc bccn
achicvcd in the GMA 2100 rcduction gearbox through advanced design tcchniqucs, rcduccd part count, improved
materials, simultaneous cnginecring, and "lessons
Icarncd" through ficld expericncc.
To minimizc aircraft development cost for rc-cngining opportunitics, any ncw gearbox must maintain the T56
external envelopes and interfaces. Emphasizing multi-application commonality both in military and commcrcial
gcarboxcs also provides cost bcncfits through volumc
bcncfits.
Design Obiectivc
The overall objectives of the engineering effort is to
design and dcvclop a new turboprop reduction gearbox
family capable of operating with single o r two-shaft turbine engines in a variety of installation arrangements that
meets thc following design goals. Thcsc goals reflcct a
significant improvemcnt ovcr the TSh/501 gcarbox basclinc shown in Figure 1.
Introduction
Dcsign and dcvclopment of a modern turboprop
gearbox in the 4000-7000 SHP class is nccdcd to satisfy
currcnt military f commercial propulsion requircmcnts.
Systems, such as thc T56 gearbox, havc bcen incrcmcntally dcvclopcd into highly reliablc units through dcsign
improvement programs ovcr thc years. Howcvcr, currcnt
ficldcd gcarboxcs cannot mect all modcrn customer requircmcnts in operational statistic areas such as reliability, maintainability, weight, and cost.
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A modcrn gearbox and propcllcr system arc key to
achievement of thcse statistics. Future reliability lcvcls
dcninnd systcms with unprcccdcntcd gcarbox unschcdulcd rcmoval and inflight shutdown rates. Many applications demand rcliability lcvcls u p to 35,000 hours mcan
timc bctwccn unscheduled rcmoval (MTBUR).
reliability improvcmcnts providing mcan timc bctwccn
unscheduled rcmoval (MTBUR) rate o[ 05,Oflfl hours
and significant inflight shutdown rate improvcmcnts
ratcd powcr incrcascs over 6000 HI' (25% morc than
basclinc)
mission mean cffcctivc power utilization incrcascs of
30%
wcight dccrcasc over 10%
incorporatinn of modern maintcnancc conccpts.
maximum application versatility by maintaining a T56sized cnvclopc and nacelle intcrfaccs
unit cost cqual to the T56
I'ower lcvcls cxcecding 6000 HP arc being considcrcd for applications such as 1
'3 rc-cngining. Commercial
systems are demanding highcr mission mean cffcctivc
power lcvcl capabilities.
Thcsc objectives have been achicvcd through an cxtcnsive analytical effort. Thc design, shown in Figure 2,
mccts all reliability, maintainability, six?, weight, and cost
goal.;.
Maintainability, in particular, would greatly benefit
from a new gearbox and propcllcr design using modcrn
maintcnancc conccpts. For instance, thc amount of
downtimc caused by complctc gearbox rcmoval or tasks
that rcquirc shop visits could be eliminated by incorporating on-wing maintenance in thc design.
Ccncral Arranpcmcnt Sclcction
Thc gcncral arrangement was sclected through CXtensivc tradc studies and analysis of gearbox ficld data. A
numbcr of dual stagc reduction arrangements, including
planctarics, simple offset, and split powcr path (such as
dual compound idler) arrangements, were evaluated in
thesc studies. T56 gearbox ficld data studies wcrc conducted to cstablish a rcliability and maintainability basclinc. This basclinc provided a bcnch mark to cvaluatc lhc
reliability and maintainability (R&M) lcvcls of the new
gearbox and ensure that thc R&M requircmcnts are
achicvcd within the weight, s i x , and cost constraints
spccificd.
Weight reductions arc nceded to increase payload
cs and/or improve spccific fuel consumption.
'Thcsr: improvcmcnts providc longcr range capabilitics,
lowcr fuel usage, and incrcascd payload capabilities.
Oldcr systems have not significantly bcncfitcd from
cost savings associatcd with modcrn simultaneous cnginccring dcsign approachcs uscd on ncw system designs.
This approach focuscs closer attention to minimizing rc-
Thcsc studies showed that all objcctivcs would bc
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Copyright 0 1991by the h e t i c a n Instilule of
Arrunaiitics and A..1TOnauti~s,Inc. All rights resewed
w a s au!ii!ids
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The general arrangement selected employs a two
stage speed reduction. The first stage is a simple pinion
gear offset design while the second stage is a fixed ring
planetary with a sun gear input and a camer output. The
carrier system drives a modern flange mounted propeller.
This approach allows different propellers to be accommodated easily through simple flange size changes. Transfer
of propeller loads and gear loads to the gearbox structure
requires only five cylindrical bearings, one ball bearing,
and five spherical planet bearings. A front housing, main
diaphragm, and aft cover are the structural members
used to react engine loads. A line replaceable gearbox
mountcd accessory drive (GMAD) is mounted to the aft
cover and driven by the main drive gear. The GMAD
supports the gearbox oil pump, propeller pump overspeed governor, alternator, hydraulic pump, and the propeller pitch change unit. The power section is attached to
the engine through a stiff torquemeter CTM) housing and
dual interconnect strut system. The gearbox, GMAD, and
propeller system are lubricated and scavenged by the
multi-element gearbox oil pump. The propeller system
also incorporates a pump to boost gearbox oil pump pressure to levels required for pitch change control.
accessory train components (27%)
The study was based on Model 501-D22Aengine
field data representing over 962,000 flight hours accumulated over the most recent, available five year period. The
501-D22A engine is a commercially certified engine used
on the L382 Model Hercules aircraft.
As shown, bearings are the most significant reliability driver and demanded the most attention in the design
of the GMA 2100 gearbox.
A planet bearing design with a life improvement factor over 6 relative to the T56 gearbox design was incorporated. This factor also includes the effects of the more severe duty cycle. This design is shown in Figure 3 with a
T56 planet as a comparison. These results were achieved
as summarized below by
increased dynamic capacity
improved materials
improved surface finishes
closer roller/race conformity
Reliability
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The 35,000 hour MTBUR and inflight shutdown requirements demanded significant attention to specific key
design areas. These requirements are a significant inw
crease over currently fielded gearboxes. The reliability
requirements are further complicated by the multi-application
objective. The reliability goals are to be met for ape'
plications with duty cycles 30% more severe thanT56 duty
cycles (on a torque basis) as shown below:
Application
501-D22A
(Commercial Fleet)
C130 &. CI3flJ
1'3
P3 Re-engining
Regionallcommuter
IdOY.IOI,wCZVL(
AS1OVIWIIIJ
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Mean Effective Torque
(IN-LBS)
120,000 - 135,000
lDY,".,
120,floo - 140,030
120.000 - 160.000
120030 - 170,000
130,003 - 205,000
GauiBnOCNU)
1561501
These results were achievcd with a design that fits
within the radial envelope of a T56 planet gear and bearing assembly.
Significant design improvements to the pinion
bearings resulted in overall bearing life increases of over
4.0 times the T56 bearings. This factor also includes the effects of the more severe duty cycles. This design is shown
in Figure 4 with a T56 pinion system for comparison. The
following summarized the design actions taken:
The field data studies showed that improvements in
four key areas would provide significant reliability increases. Eighty percent of classified inherent failures requiring a gearbox removal wcrc comprised of the following:
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Figure 3. Design features of the new planet bearing
provide an L10 life over six times higher than its
501-D22A counterpart.
Rcgional/commuter applications demand the highest effective power levels because of high torques associated with the low prop speeds selected for noise control
and the high speed, short stage length flights required to
transfer passengers quickly. Therefore, the reliability
goals wcrc targeted for the commuter applications whilc
less demanding applications enjoy greater reliability benefits.
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planet bearings (26%)
pinion front bearings (19%)
pinion rear bearings (7%)
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better load sharing between bearings
increased front and rear bearings' capacity
improved materials
improved surface finishes
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out-of-round outer rings oriented for improved load
distribution
line-borcd bearing seats to minimize misalignment
ficient accessory drive arrangement. In addition to the
high reliability levels achieved through low part counts,
this arrangement provides further improvements through
a multiple torque path approach. Multiple accessory
gears branch from a center gear eliminating the high
stage loading associated with in-series designs.
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Reliability improvements were identified through ultraclean gearbox oil. Three micron filtration has demonstrated two to six times life improvement relativc to
coarser mesh systems in both military and commercial
evaluations. To be conservative, these life benefits wcrc
not included in the reliability analysis.
Thc selected design has even addressed low frequency reliability drivers identified in the field data study
Examplcs include life improvements in the main drivc
gear bearing, rear carrier bearing, and prop bearings
through use of VIM/VAR processing; incorporation of
proven damper coatings to eliminate damper ring wear;
and serpentine O-rings at splitlines to eliminate oil lcaks.
Figure 4. Innovative design features provide pinion
beating lives over 4.0 times those of the industry
standard T56/501
Through surveys of gearbox users and ovcrhaulcrs
design areas not causing unscheduled rcmovals but affecting the useful life of gcarbox componcnts wcrc idcntificd. Examples include gearbox structures wherc ZE41
magncsium was used to promote creep resistance, climinatc loose fasteners, and improve bearing/gcar misalignment. These structures, plus improved datum fcatures and fasteners, were designed to creep allowablcs in
addition to fatigue/yicld/ultimatc allowables uscd in thc
T56 design. This approach promotes long term bore/ datum fcature alignment.
The acccssory train design shown in Figurc 5 and
Figurc 6 contributed significantly to the overall reliability
improvements. A more simplified design and the isolation of the accessory train from the reduction gcarbox result in a significant improvement in rcliability and also isolates the two systems from cach other. Thc simplified
GMAD contains only 6 gears and 12 bearings, compared
with 19 gcars and 24 bearings in the T56 gearbox. The
simplifications were accomplished by devising a more ef-
Figure 5. The new gearbox mounted accessory drive requires 50% fewer gears and bearings than the
counterpart T56/501 accessory drive train.
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Advanced design techniques and tools allowed better optimization of tooth flash temperatures, bending
stresSes/contact stresses, rim/web stresses, and dynamic
resonance response. Finite element techniques were key
to achieving these optimized levels. Other analytical tools
such as tooth deflection techniques grounded by empirical data were used to further enhance the design and minimize development test cfforts.
Splitline fretting was minimized by integrating the
gearbox mount pads with the front housing and incorporating a main diaphragm mounting splitline internal to
the front housing. This approach eliminates splitlines between load application and load reaction points thus
eliminating a potential oil leak path.
Further enhancements over T56 include line boring
of the housing bearing bores and optimizing the gearbox
structure through finite element analysis. The line-bore
approach reduces bearing and gear misalignment thus
promoting higher lives. The gearbox structural members
were finite clement modelled using 20 n d e d solid elements. This model is one of the most extensive and dctailed models ever constructcd at Allison and permits
much better control of stresses and deflections. This approach also greatly reduces development casting changes
and static load requirements. The structure can be optimized prior to initial hardware and strain gage locations
identificd for static load tests. A more extensive matrix of
load conditions can be evaluated more efficiently than
possible with static tests. This analysis will be verified
through static and rig tests.
Main Power Train Bearine Desien
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Since the bearings are key elements in achieving the
desired GMA 2100 reliability, the design process must
carefully consider all aspects of the application. Broadly,
we may consider the design proccss to consist of the following:
Basic Design
Materials
Internal Details
Fitting Practice
The following paragraphs describe the application of
years of field experience with the latest rolling bearing
technology to these steps in the design of the high reliability GMA 2100 reduction gearbox.
Basic Dcsien
In order to attain certain cost and risk benefits, an
initial design goal for the bearings was interchangeability
with existing T56 bearings in terms of envelope dimensions and bearing types. Trade studics and field data
analysis determined this was achievable except for thc
planet and pinion bearings. Accordingly, the pinion front
bearing capacity was increased by 17%. The same bearing
cnvelopc is used in the rear position. In the T56, the rear
bearing is smaller and farther from the pinion than the
front, causing the latter to carry the highest load. By relocating the accessory drive takeoff and moving the rear
bearing forward, Figure 4, the loading is more nearly
equal, increasing the life of the front bearing. Utilizing thc
larger rear bearing compensates for its higher load and
yields an overall greater set life for the two pinion bearings. It also affords a small economy by using the same
bearing in two positions.
Figure 6. The accessory drive train is isolated from
the reduction gearbox to improve reliability and
maintainability.
Studies of field data show very high reliability levels
and very low failure rates for T56 gears. The GMA 2100
gears were configured to be very similar to the T56 gears
to ensure that the high reliability levels were maintained.
Additional life improvements have been gained through
improved materials and analysis techniques.
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The spherical roller bearing type is ideally suited for
the planet application. Its self-aligning capability allows
the spur gears to determine alignment for uniform tooth
loading with no detrimental effect on bearing performance. However, in order to achieve the required level of
reliability, a new roller complement was necessary. Bearing size changes were confined to the bearing width and to
the radial thicknesses of the gear and journal. This a p
proach allowed the T56 gearbox envelope to be maintained. A comparison of the two designs is shown in Figure 3. The width of the bearing is limited by the outer
raceway. As the width of that raceway is increased, the diameter of the great circle at the edge of the raceway becomes smaller. This diameter in turn determines the O.D.
Spur gears were selected for the GMA 2100 gearbox.
Instrumented testing of T56 A427 gearbox showed dynamic tooth loads of less than 3%of the applied loads are
maintained with highly accurate spur gears. These accuracies are consistently achieved with the modern grinding
machines used today.
Double vacuum melted (VIM/VAR) AIS19310 steel
was selected for gears to provide over a two time life improvement relative to T56.
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of the cage, which must pass through it when the bearing
is assembled.
Other factors that influence the roller complement
design are minimum allowables for the circumferential
space between rollers, the axial space between rows, and
the ring thickness. The latter is determined by the effect of
ring deflections on roller load distribution and life, and by
resultant stresses in the ring. Again, the experience base
for these characteristics is the T56 gearbox. For example,
Figure 7 shows the comparative ring distortions for the two
outer rings due to gear tooth and roller loads at the maximum load condition for each. Obviously, there is little difference. Finite element analysis was used to evaluate
stresses and deflections across the raceway and, again,
they were held within the bounds of the T56. Arriving at a
final design requires simultaneous consideration of all
these parameters, in addition to the contact angle and
roller length to diameter ratio. A proprietary computer
program was used to accomplish the necessary iterative
calculations and efficiently achieve an optimum design.
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The same material was chosen for the rollers in order to
benefit from the residual stress pattern of the case hardened material.
Since the pinion bearings are very important in establishing gearbox reliability, and since the maximum
bearing size had already been incorporated, M50 NiL
VIM/VAR was chosen to maximize life. The main drive
gear bearing in the GMA 2100 gearbox will experience
slightly higher loading than in the T56. Thus, to improve
upon it's very high reliability without changing size, it was
targeted for the same material.
M50 NiL is a carburizing alloy that provides a hard
case that is resistant to rolling contact fatigue and a softer
core that has excellent fracture toughness. M50 NiL can
provide twice the fatigue life of M50 for two reasons: first,
there is a high residual compressive stress in the case that
effectively retards the formation and propagation of fatigue cracks; and second, the M50 NiL microstructure features a much finer and more uniform carbide distribution.
This has been shown to provide improved fatigue life compared to the relatively large and randomly distributed
carbides that typically occur in MSO. There are additional
benefits from the case-hardened material as discussed
under Rtting Practice.
Once a case hardening material has been selected,
one must be careful to apply the optimum case depth. Too
shallow a case can lead to sub-case fatigue failures, while
too deep a case can lead to less than optimum residual
stress patterns and core hardness, not to mention excess
cost. The case depths specified for the GMA 2100 gearbox
bearings are based upon maintaining an appropriate
Hertzian shear yield stress to shear yield strength ratio as
illustrated in Figure 8.
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Figure 7. Comparison of GMA 2100 and T56 planet
gear deflections due to roller and gear tooth loads.
Materials
For the planet bearing, the outer ring functions as
both gear and raceway. Therefore, it is important that the
material for this component have a demonstrated history
of good performance in both functions. As seen in Figure
2, the journal is a structural member holding the prop
shaft, as wcll as the inner race for the planet bearing.
Consequently, this member should possess excellent
strength and fracture toughness as well as good rolling
contact fatigue resistance. All requirements for both components are well satisfied by case hardened 9310, as
demonstrated by the years of experience in the similar
T56 application. For the GMA 2100 application, reliability
is further cnhanccd by specifying VIM/VAR' processing.
* Vacuum Induction Melting/Vacuum Arc Remelting, a
mclting process that produces exceptionally clean steel,
free of the harmful non-metallic impurities that can cause
prcmaturc failure.
Field data shows that neither of the prop shaft bearings fails by fatigue, and that the rear carrier bearing docs
so only infrequently after a long time in service. Together
they do not significantly effect overall gearbox reliability.
Since 52100 has been used extensively for these positions,
it was selected as the optimum material. 52100 has excellent fatigue and wear properties at low cost for operation
below about 300" F, a tempmature only occasionally approached in the gearbox. VIM/VAR processing was spccified to further enhance reliability.
Internal Desinn
Minimum stress and maximum life is achieved for
roller bearings when the footprint of the roller on the ring
raceway is approximately rectangular, with a uniform distribution of pressure along it's length (parallel to the roller
axis). For actual (finite length) rollers, this occurs when thc
theoretical contact ellipse is approximately 1.4 times the
effective roller length. This can only be achieved by using
crowned rollers, and even then only for one load. Heavier
than optimum loading results in a concentration of stress
at the ends of the roller, while lighter loading shortens the
actual length of contact and concentrates the stress at thc
center. For bearings that operate over a range of loads
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applied load direction to provide the optimum distribution
of load among the rollers.
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FILM PARAMETER
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A
Figure 9. ASME lubricant-life correction factor as a
function of the lubricant film parameter, A.
Cage designs for the ball and cylindrical roller bearings follow conventional practices that have been proven
successful over the years in the T56 and many other applications. All cages are land-riding, and are piloted on the
stationary (or lower speed) ring for maximum dynamic
stability. Pilot and pocket clearances were all carehlly
chosen on the basis of past successful experience.
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The planet bearing cage for the GMA 2100, however,
is of a differept type than the T56 as shown in Figure 3.
Over the years since the inception of the T56 gearbox, it
has been learned that a roller-riding cage will provide better performance than an inner land piloted cage for the
epicyclic type motion of a planet bearing. While it has not
been a major problem, heavy wear has been experienced
from time to time on the cage and ring pilot surfaces. This
is because the ring and rollers are vying with each othcr to
control the motion of the cage. By eliminating the landriding feature that source of friction and wear is eliminated. The rollers can then freely position the cage. Also,
because of the gcometry of the two row angular contact
bearing, radial loading tends to cause the two rows of
rollers to move very slightly toward each other. By careful
control of the cage '%backbone"thickness within the space
between the rows, optimum roller guidance is achieved
without relying on the sides of the pocket. Running clearances required in the cage pockets make the latter a
much less effective guiding surface.
In the T56 gearbox, the pinion front bearing is lubricated by oil jet, while the rear bearing is lubricated from
under the inner race through holes that ensure a good
supply of oil to the inner race rib/roller end contact. Occasional wear problems have been experienced with the
front bearing where the roller end contacts the inner ring
rib. To be sure this d w s not happen with the GMA 2100
gearbox, both pinion bearings are under race lubricated.
The lubrication arrangements for both gearboxes are evi. "@'re
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bearing outer ring has been controlled with respect io the
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FittinE Practice
It has been typical aerospace industry practice for
many years to use rather light interference fits or transition fits (i.e., where one end of tolerance range results in a
clearance fit) on rolling element bearings. This is due to
the high speeds that are often encountered that can result
in very high circumferential tensile (hoop) stresses when
combined with the stress due to an interference fit. Such a
highly stressed condition yields the potential for catastrophic ring fracture as either a primary or secondary failure mode. The lighter fits also make for easier installation
and removal of bearings at initial assembly and overhaul.
The downside, as indicated by field history, is that wear
and fretting often occurs at the shaft/bcaring interface,
necessitating rework or replacement at overhaul
With new, carburized materials, such as M50 NiL
described above, tighter fits are now feasible. This is because the residual compressive stress reduces the effect
of the applied tensile stress, and because the fracture
tough core precludes the fracture failure mode. Thus each
bcaring has been carefully fitted to the shaft to provide
thc necessary minimum interface pressurc to assure satisfactory pcrformancc, while kceping thc hoop strcss within
appropriate limits fo- .he given material. A proprietary
computer analysis w i s ised to accomplish this, taking
centrifugal furccs and ? r a m a l effects into account as well
as interference fits. This analysis also predicts effects of
these factors on operating int m a l clearance. This allows
the specification of an appropriate initial clcarance so that
the final operating clearance results in the best possible
roller load distribution consistent with adequate clearance
to prevent a thermal imbalance type failure.
Gearbox Maintainability
Major improvements in maintainability were gearbox achieved. A number of systems were configured and
located to permit on-wing replacement without removal of
the gearbox or other modules. This approach minimizes
secondary damage by isolating primary failure sites from
adjacent components and reduced operational costs by
minimizing major module removals. Based on reliability
studies, the following systems/components were configured as line replaceable units (LRUs): GMAD; propeller
components including pitch change unit (PCU), oil
pump/governor, and auxiliary feathering pump; gearbox
supply and scavenge pump; oil sensors; oil filter; prop
drive lip seals hydraulic pump pads; and struts and strut
fittings.
Maintcnance actions have also been reduced or enhanced through incorporation of borescope ports for internal gearbox evaluation; seal drains separately routed to
ecology tanks to delay action for minor leaks and to identify the leak source; integrally cast oil passages to climinate labor intensive tubes and fittings; and V-band accessory attachments.
Part cuunt was reduced b y over 50% relative toT56
lending to further maintenance improvements through
lower handling requirements. Part count was reduced by
integrating multiple functions into a single part, arrangement simplification and elimination of systems such as
negative torque systems (NTS), which are not required In
modern designs.
Gearbox Size and Weiqht
The T56 gearbox envelope and interfaces were successfully maintained in the new design. This approach
minimizes development costs to the military for re-cngining applications such as the P3 and C130J.
Significant weight reduction was also achieved in the
improved gearbox design, meeting the design weight goal.
The GMA 2100 gearbox is over 12% lighter than a TSh
gearbox.
CostIConcurrent EngRequirements for recurring and nonrecurring cost
were included in the design effort. Recurring cost at maturity was to match the current cost of thcT56 gearbox.
This requirement was made more difficult by cust incrcascs associated with improvements such as’ M50 NiL
and VIM/VAR materials selected for reliability improvcments and by the loss of dedicated, fixed sctup machines.
Many of the T56 machincs are dedicated to a part and operation. These machines d o not possess the versatility
demanded for today‘s manufacturing operations.
To reduce gearbox cost, a concurrent engineering
approach was applied with manufacturing and quality engineers participating in the design effort. This effort was
successful in meeting the cost goals by eliminating numerous fabrication operations and maintaining many cxisting gages and fixtures. An example of this cost savings
effort is shown in Figure 10. The initial GMA 2100 ring
gear system was designed to provide significant weight
and nun-recurring cost benefits relative to a T56 system.
Manufacturing studies showed that this suffered from a
significant non-recurring cost penalty due primarily to required changes to the spline ring bolt circle diameter.
Through simultaneous enginccring studies a design was
conceived which salvaged the T56 bolt circle. This design
allowed the use of current T56 gang drill machines and fixtures and reduced the non-recurring costs by over
$170,000. Recurring costs were reduced another 2% while
the weight savings was reduced only slightly. In addition,
commonality with other gearbox hardware also was
stressed wherever possible to further reduce cust. This cffort requires reevaluation of every fabrication and spccification requirement used in previous designs to determine
its applicability to the new design.
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Test Verification
To verify the dcsign, an extensive development
testing effort was initiated in 1990. The gearbox successfully demonstrated a 6000 NP and 100%speed capability
and matched performance predictions (such as 98.7%cfficicncy at 6ODO HP) during back-to-back testing. This test-
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Conclusion
ing has dcmonstratcd thc high specific power-to-wcight
gearbox capability establishcd in the overall objectives.
Follow-on testing in 1991 will lead to further performance
improvements and demonstration of the endurance capabilities of the gearbox.
The GMA 2100 gearbox design will significantly advance the state of the art in rcliability, and maintainability.
Significant improvcments in industry power-to-wcight levcls have been achicved through advanced design techniques, and better materials.
* BASELINE - T56 DESIGN
RECURRING COST- BASELINE
NON-RECURRING COST - $0 BASELINE
* WEIGHT- BASELINE
* INITIALGMA 2100 DESIGN
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RECURRING COST 18% DECREASE
NON-RECURRING COST - $210,000 INCREASE
* WEIGHT- 38% DECREASE
PERFORMANCE- MORE FLEIBLE
FINAL GMA 2100 DESIGN
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FIVE DESIGN ITERATIONS WITH SIMULTANEOUS
ENGINEERING STUDIES
PRODUCTION RING GEAR USED
* RECURRING COST- 20% DECREASE
* NON-RECURRING COST $40,000 INCREASE
WEIGHT- 37% DECREASE
* PERFORMANCE MORE FLEXIBLE
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Figure 10. GMA 2100 ring gear coupling system cost reduction effort.
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