Pratt & Whitney's surprise leap
`Interavia; Jun 1998; 53, 621; ABI/INFORM® Professional Advancedpg. 25
`
`Rated at 32,000shp, the
`PWBOOO gearbox is just
`17 inches (43cm) in
`diameter.
`
`Pratt &
`Whitney's
`surprise leap
`
`The announcement of the PW8000 geared
`turbofan caught the industry unawares.
`
`Planned as a follow-on to today 's V2500 and CFM56, pow(cid:173)
`ering future developments of the A320 and, perhaps, a new(cid:173)
`family 737, Pratt & Whitney's PW8000 breaks new ground
`in having a gear-driven fan and a higher bypass ratio than any
`current engine ( 1 1: 1, versus 9: I for the GE90).
`Together with the PW6000, a conventional turbofan with the
`same core, it will provide Pratt & Whitney with a family of
`modem , economical engines from 67 kN to 155 kN , that
`promise to offer significant improvements in airline operating
`economics. The PW8000, claims Pratt, will increase reliabil(cid:173)
`ity while reducing operating costs, fuel bum and noise.
`P&W will start detailed de sign of the engine this month
`(June), and could run the first engine as early as September
`1999. However, the actual timing will depend on when there
`is an application for the engine -
`and the main reason that
`the company's rivals did not see the PW8000 coming is that
`there is no clear application for such a family of engines.
`This may be about to change. The PW8000 will cover a range
`of25,000 to 35,000lb thrust, suitable for aircraft between 120
`and 180 passengers. With its 76-inch fan diameter the engine
`will fit the Airbus A320 family, but not under the wing of the
`
`current new-generation Boeing 737 . Talks are taking place
`with Airbus to flight test the PW8000 on an A320 in the time
`period 200 I, with production scheduled for two years later.
`An inservice date could be around 2005-7.
`Pratt & Whitney says that is trying to position itself ahead of
`the market, so that it can produce new engines quickly enough
`to match the airframe manufacturers' development schedules.
`Engine companies have not tried to do this since the 1980s,
`when both P&W and GE invested heavily in high-speed pro(cid:173)
`pel le rs for Boeing's aborted 7 J7 project. Now that Boeing and
`Airbus are taking less time to produce major derivatives and
`new ai rcraft, engine manufac turers may have to invest more
`in speculative technology developments unless they are con(cid:173)
`fident that they can win business with derivatives.
`P&W saw that it had few options left. The company' s share
`of the gigantic market for narrow-body aircraft is in single
`digits (comprising P&W's share of the V2500 program and
`the PW2000) while CFM's share of the business expands
`inexorably.
`
`Common core for a new family
`P&W's strategy is to invest its earnings from the wide-body
`market in a new family , based on a common core, which cov(cid:173)
`ers a huge range of applications -
`almost the entire narrow(cid:173)
`body segment from 80 to 180 passengers. The PW6000 core
`is already running. It shares some aerodynamic technology
`and design philosophy with the military Fl 19, with a sharp
`reduction in the number of blades and stages compared with
`earlier engines. The geared fan concept is important to
`P& W's strategy, because it allows the common core to cover
`a significantly larger thrust bracket. The cost of developing
`the gearbox is more than offset by the ability to cover most of
`the narrow-body market with one core.
`Gearing boosts performance because it eases a difficult com(cid:173)
`promise in engine design. The fan' s tip speed cannot go much
`above 450 m/sec -
`above that point, noise statts to become
`unacceptable. As the designers increase the fan diameter in
`pursuit of more thrust, the tip speed limit means an ever lower
`
`INTERAVIA June 1998
`
`25
`
`Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
`
`GE-1012.001
`
`Sweetman, Bill;Sutton, Oliver
`

`
`rotational speed, so that each
`blade and stage in the low-pres(cid:173)
`sure system can do less work.
`The result is that high-bypass,
`high-thrust engines have large
`and complex low-pressure com(cid:173)
`pressors and turbines. More(cid:173)
`over, as the rotational speed
`slows
`down,
`the
`torque
`increases,
`demanding
`a
`stronger, thicker LP shaft which
`makes a poor match with a
`small, compact core.
`
`Solid
`Shroudless Fan
`
`Fan Case
`Mount
`
`Fan Drive
`Gear Sy.stem
`
`PWSOOO Geared Turbofan
`
`5stage
`High Speed I High Pr
`HP Compressor
`
`but the 3: I ratio is modest, so the
`gearbox can be a straightforward
`planetary design. The ADP gear(cid:173)
`box underwent extensive test(cid:173)
`ing, including 1,000 hour in a
`full demonstrator engine.
`Gearbox design and history of
`failures in seven turbofan and
`turboprop engines and two heli(cid:173)
`copters were analysed back to
`1962. The results showed that
`most problems came
`from
`bearings, lubrication/cooling
`systems, and flexing of the gear(cid:173)
`box during normal flight. The
`new gearbox design features
`small, light self-aligning bear(cid:173)
`ings, a lubricating system that places oil only where it is
`directly needed, and which circulates it out of the gearbox
`to avoid a build up of heat. To cope
`as quickly as possible -
`with the flexing of the engine structure in flight, which tends
`to cause gear wear and cracking, engineers came up with a
`design to mount the gearbox on a kind of bellows, that
`resembles a large spring. This physically isolates the gear(cid:173)
`box from the normal bending loads and keeps gear align(cid:173)
`ment precise. The PWSOOO gearbox is just 17 inches (43cm)
`in diameter.
`Full-scale tests, the equivalent of
`18,000 flight cycles and 25,000 flight
`hours of normal service, were carried
`out by Pratt and FiatA vio, including a
`40,000shp gearbox that ran without
`problems for over 500 hours at its rated
`loading.
`The development of the PWSOOO could
`lead to an interesting situation among
`the airframers- Airbus Industrie could find itself able to
`offer significant economic advantages to operators with a
`PWSOOO under the wing of its A320 family. This in tum
`could push Boeing into the design of a totally new family,
`replacing the present 737, and possibly the 757, to accom(cid:173)
`modate the PWSOOO. This is the situation that CFMl will be
`seeking to head off.
`BY BILL SWEETMAN AND OLIVER SUTTON
`
`The fan .will rotate at about one-third compresso_r speed, and
`provide 90% of the engine's propulsive power
`
`Gearing does the trick
`Gearing solves the problem.
`The LP turbine and compressor
`spin faster, which means that they can be made smaller in
`diameter, shorter and simpler: the engine has 52% fewer com(cid:173)
`pressor and turbine blades than a conventional turbofan.
`according to P& W. The speed of the fan can be optimized for
`noise, efficiency and structural considerations (P& W is talk(cid:173)
`ing about a 300 m/sec tip speed for the PW8000) and the LP
`shaft shrinks back to a nomrnl size, making the core more
`compact and efficient. The low tip speed reduces noise -
`P&W claims a cumulative margin of 30dB below current
`rules -
`and the high bypass ratio boosts
`propulsive efficiency and reduces fuel
`bum by 9%. This is enough to make the
`A320 and A32 I into transcontinental
`aircraft, and get the attention of airline
`financial officers.
`The PWSOOO design draws on the tech(cid:173)
`nology that P&W, MTU and Fiat dem(cid:173)
`onstrated in the Advanced Ducted Pro(cid:173)
`peller (ADP) engine in the early 1990s,
`but it is not an ADP. It has a lower bypass ratio and a higher
`fan pressure ratio, which eliminates the need for variable
`pitch; and it has a conventional reverser and solid titanium
`blades. The fan, gear driven off the LP spool, will rotate at
`about one-third compressor speed, and provide 90 percent
`of the engine's propulsive power.
`Fiat developed the gearbox for the ADP and will be a part(cid:173)
`ner on the PWSOOO, as will MTU. It transmits 32,000 shp,
`
`THE PW8000 DRAWS ON TECHNOLOGY
`THAT P&W, MTU AND FIAT
`DEMONSTRATED IN THE ADVANCED
`DUCTED PROPELLER (ADP) ENGINE
`
`MTU SET FOR PWSOOO STAKE
`M TU President and CEO Rainer Hertrich is
`progress will also depend on Airbus's 100-seater
`preaching the advantages of its linear friction
`welding repair technology to the airline industry,
`project, either with the Chinese, where the PW6000
`is a prime candidate engine, or on the A319-MS,
`which today may be more comfortable with
`which could also take it.
`traditional blade repair methods.
`MTU is running a demonstrator core with a six-stage
`MTU's contribution to the PWBOOO will focus on
`HP compressor, while Pratt is trialling a five-stage
`capabilities in blisk technology, developed for the
`Eurofighler's EJ200 engine, on
`transonic
`core. On the PWBOOO, MTU will bid for the LP
`turbine and LP compressor, both MTU core
`compressor
`technology developed under
`competencies, which Hertrich stresses are
`Germany's Je engine programme, and on earlier
`work on the LP turbine and compressor for Pratt's
`equivalent to today's HP stages, since air flow will
`ADP demonstrator engine. MTU will also be
`be transonic.
`
`enthusiastic about the market potential far
`the PWBOOO, and, as a Pratt & Whitney preferred
`partner, intends lo toke a 20-25 percent stoke in
`the programme. MTU earlier declined to go with the
`PW6000, and Hertrich acknowledges that progress
`on the PWBOOO wi11 depend on Pratt's common core
`development of the PW6000, since Pratt does not
`intend lo start development of both engines
`simultaneously. The next priority is engineering
`design, and a demonstrator engine. The rate of
`
`26
`
`INTERAVIA June 1998
`
`Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
`
`GE-1012.002