Geared Turbofan - the future?

[Torquelink]

With Mitsubishi having selected the PW GTF for their new RJ and Bombardier having done the same for the C Series - both against proposed new engines from GE and RR: neither of which were GTFs, does this mean that the GTF is the way of the future - at least for narrowbodies? If so, where does this leave GE and RR: do they skip a generation and go straight to unducted fans and risk missing out if Airbus and Boeing go for more conventional engine installations on the A320/737 replacements, or do they play geared fan catch-up?

And hasn't the ALF502/LF507 got a geared fan which hasn't been a huge success?

Any equally sad engine enthusiasts got any thoughts?

:)

[Rainboe]

Hard to comment when there aren't any actually out there operating successfully and reliably! Need more than a testbed on a DC9. They have to prove themselves all the way- fuel economy, noise, reliability. We're waiting!

[twistedenginestarter]

I'm a sad engine watcher a well. Here's some notes I found:

The PW8000 was supposed to be a geared fan section on a PW6000 power core but the PW8000 never went anywhere despite ten years of research and $350 million in development money.
The latest iteration of the geared fan concept from Pratt is their GTF Demonstration program. It is a PW6000 core with a revised planetary gearbox that is alleged to save weight and be more efficient than the stillborn PW8000. Time will tell whether the market will reward P&W's devotion to the geared turbofan concept, or whether it is a technological blind alley for them.
The last time I looked, the big problem as ever was designing a gearbox that can take the loads. Quite some time ago the manufacturers were looking at weird techniques unlike those used in everyday machines. It looks like P&W are using a more conventional arrangement so school's out on whether they can get the wear and failure rates down to manageable proportions.
With regard to RR, I guess the extra shaft partly alleviates the need for other gearing.

[Torquelink]

I guess PW must be pretty confident that they have the gearbox technology licked - as must Mitsubishi and Bombardier - especially given that, for shorthaul, engine maintenance costs and reliability are at least as important as fuel burn. I agree that RR's third shaft partially addresses speed mismatch concerns but I see that their new offering in this sector (the RB282?) as selected by Dassault for their next gen twin is a two-spool engine. As ever, it's a high-stakes game but IF they pull it off and IF Airbus/Boeing select "conventional" engines for the A320/737 replacement (admittedly both big IFs) it could really put them back in the game - back to where they were when the JT8 was predominant. But I can't see GE or RR taking this lying down - maybe the V2500 replacement will be a GTF with PW doing the fan/gearbox and RR, MTU etc doing the rest?

[FE Hoppy]

Electric fan is the way ahead. Core drives Genny Genny drives fan. If it hasn't been done I hearby claim IPR on the concept. :O

[angelorange]

NASA have already looked into electric fan.

http://www.grc.nasa.gov/WWW/RT/2004/RS/RS19S-johnson.html

[Torquelink]

Pratt & Whitney said its Geared Turbofan demonstrator engine "successfully completed its first series of engine runs, reaching full power [of] 30,000 lb. thrust" at the company's test facility in West Palm Beach. The GTF has been selected as the exclusive engine for the proposed Mitsubishi Regional Jet and has been chosen by Bombardier for its planned CSeries 110/130-seat jet family (ATWOnline, Nov. 14). Both aircraft are scheduled to enter service in 2013. VP-Next Generation Product Family Bob Saia said the GTF is "performing flawlessly" and now is undergoing "a series of performance tests to validate the game-changing performance characteristics of the Geared Turbofan engine including low fuel burn, engine noise and environmental emissions." Ground tests will run through May after which flight testing commences on Pratt's 747 flying testbed.

[old,not bold]

the big problem as ever was designing a gearbox that can take the loadsIf you experts will forgive the intrusion, can someone please explain why the loads are so different to those experienced in, say, a large turbo-prop engine and propeller combination?

Is the reduction ratio very different?

Is the fan weight and/or load much greater, relative to engine power?

I know these are technically ignorant questions; that's because I'm technically ignorant!

[Intruder]

I suspect it's more a question of weight vs performance...

I can't imagine there would be any more torque/power going through such a gearbox on a small turbofan than that going throught the contr-rotating propellor gearbox in a Soviet Tu-95 Bear bomber (http://www.fas.org/nuke/guide/russia/bomber/tu-95.htm)!

[barit1]

In the end -- it will be a balance between fuel costs vs maintenance costs.

Consider this: If alternative fuels begin to seriously threaten the crude oil market, OPEC could decide to open the spigot and drive down the price of oil to quash the interlopers ("predatory pricing"). If so, the GTF and the UDF (http://en.wikipedia.org/wiki/General_Electric_GE36) will no longer be very attractive.

[Torquelink]

So, 737 and A320 replacements - UDF or GTF? Presumably a UDF will need some sort of a gearbox anyway not to mention variable pitch blades/rotors. I suspect that installation complexities, weight and noise will favour GTF or, at least, will not favour UDF. Watch out for GE/Snecma launching gearbox demonstrator programme and RR conceding that PW can put a geared fan on V2500 replacement?

[keesje]

If PW can get it to work providing significantly lower noise and use say 10% less fuel then the newest CF34 and CFM56's there will be interest by Boeing, Airbus, Embraer or a combination of those..

The large cross section of high BPR engines will probably force them up from under the wings. The tail, wings and fuselage could play a role in further reducing noise exposure.

http://i191.photobucket.com/albums/z160/keesje_pics/LRJ_Boeing_Embraer_Y1_narrow_body_7.jpg?t=1196956983

high resolution: http://i191.photobucket.com/albums/z160/keesje_pics/LRJ_Boeing_Embraer_Y1_narrow_bod-1.jpg?t=1196957150

[chornedsnorkack]

The large cross section of high BPR engines will probably force them up from under the wings.
There are known disadvantages to putting all your engine weight in the tail. GTF makes the matters only worse!

What does the GTF do with 13 and half tons of thrust? Mitsubishi MRJ 70 is supposed to have just 7 ton engines, and Bombardier C130 has 10 and half tons of thrust each engine!

[Swedish Steve]

In this weeks paper copy of Flight there is a long article on GTF and UDF.
The test GTF runs on a PW6000 core at 30000lbs.
The Mitsubishi and Bombadair engines will have different cores and smaller fans.

[Torquelink]

If Boeing sticks to this timetable, it's going to be GTF:

FT article today - Boeing to push on with new aircraft ranges

Boeing is pushing ahead with plans for its next multi-billion dollar aircraft development programmes, putting additional pressure on its troubled European competitor, Airbus.

Scott Carson, head of Boeing's commercial aerospace division, yesterday told the Financial Times the group could launch a programme to develop a new generation single aisle aircraft to replace its long-standing 737. The programme could be started in about 18 months, aimed at achieving entry into commercial service around 2015. He said Boeing was sounding out customers over their demands for a new aircraft to replace the 737, whose earliest models were rolled out 40 years ago.

"There will be a new narrow body. The question is, how far down in passenger count do you go," he said. New competitors had en-tered the niche for much smaller jets of fewer than 110 seats where the "operating economics are tough", he said.

However the group was also looking at launching a programme to develop a new wide-bodied aircraft by 2012 aimed for entry into commercial service by 2020.

And Mr Carson warned that the group's priorities could change depending on market conditions.

Boeing was always expected at some stage to renew its long-lived single aisle family of aircraft. However, a decision within the next 18 months will further complicate the predicament at the rival Airbus, which is already struggling with the painful consequences of a weak dollar, a politically controversial cost-cutting plan and several difficult development programmes.

A decision to press ahead with a new 737 that uses the latest technology and add-resses growing environmental concerns could force Airbus to take an earlier than desired decision on revamping its own A320 range - a popular and cash generative family of aircraft.

In recent weeks Louis Gallois, chief executive of Airbus parent EADS, has warned that the group must accelerate its cost-cutting programme and shift more production to dollar-linked economies if it is to survive the currency crisis.

However, there was some uncertainty yesterday surrounding its plans to sell seven factories in Europe amid growing political concerns over the job implications of any disposal.

Mr Carson said Boeing was not reviewing its own production process in the light of its troubles with the new 787 Dreamliner, the highly popular rival to Airbus's A350.

Boeing was recently forced to announce a six to seven month delay in deliveries of its new aircraft after problems emerged in the assembly process.

The Boeing executive insisted that there was no question, at least given the information available today, of any further delays to the programme.

[Torquelink]

Pratt to test Geared Turbofan on A340
Tuesday April 22, 2008
In a rare development, Airbus and Pratt & Whitney yesterday announced an agreement to flight test Pratt's Geared Turbofan engine on Airbus's A340 testbed, although the engine does not have an application on an Airbus airframe.

Testing will occur during the fourth quarter. The GTF has been chosen by Bombardier and Mitsubishi for their respective new aircraft programs, the CSeries and Mitsubishi Regional Jet, and Pratt has touted it for the successors to the A320 and 737NG families (ATW, February 2008).

Approximately 20 years have passed since commercial engine and airframe makers last collaborated to test fly an engine without an application on the airframe OEM's platform. These were the McDonnell Douglas Ultra High Bypass Demonstrator that featured a General Electric Unducted Fan demonstrator engine mounted on an MD-80 and the Pratt & Whitney-Allison Engine Propfan Demonstrator, which also flew on an MD-80.

"We are delighted at the opportunity to partner with Airbus on flight testing the Geared Turbofan engine," said Pratt & Whitney Commercial Engines President Todd Kallman. According to the company, "the flight testing will provide first-hand experience with the performance of the [GTF], which targets double-digit improvements in fuel burn, environmental emissions, engine noise and operating costs."

Airbus said in a statement that the trials "are an example of [its] commitment, as an eco-efficient company, to look at all new technologies and innovations that could potentially bring environmental and economic benefits to the aviation sector for the longer term."

A Pratt spokesperson noted, "The flight testing does not imply a business or technical agreement with Airbus for current or future aircraft. That said, we are excited for the opportunity to demonstrate the performance of this engine to Airbus."

The GTF demonstrator engine, which has logged approximately 150 hr. since ground testing began in November, recently started Phase II testing focusing on engine performance and acoustic characteristics with a flight-capable nacelle system (ATWOnline, April 11). First flight of the engine is expected around mid-year on Pratt's 747 testbed.


by Perry Flint

[chornedsnorkack]

on Airbus's A340 testbed,

Which model?

340-500/600, or 340-200/300?

340-300 makes do with as little as 31 200 pounds thrust (CFM56-5C2). And note that GTF is supposed to offer lower cruise fuel burn. If you reengine an A340-300 with 30 000 pound GTF-s, you will lose some of the takeoff performance, which you compensate for by decreasing MTOW. This limits your fuel load, but the decrease of cruise burn could mean you can achieve equal or longer range with less total fuel load. Which means that the MTOW and fuel economy of A340-300 may approach or improve from the performance of A330-300 twin.

Underwing space is a solvable problem. CFM56-5C has fan tip diametre of 72,3 inches. A330 and A340-500 manage to accommodate Rolls-Royce Trents with 97,4 inches fan diametre under the same wing.

So... are any airlines interested in buying GTF A340-300?

[Torquelink]

Interesting thought -I'd assumed it was just for general evaluation with a view to possible application on the A320 replacement. In fact, and I can't remember why, I seem to recall that GTF benefits are maximised on short haul high frequency ops rather than over long ranges.

[barit1]

For what it's worth:

Typical helo overall gear ratio: 40:1

Typical turboprop ratio: 14:1

Probable GTF ratio: 2:1

[airfoilmod]

I'm new to this discussion so if I sound ignorant, I may well be. I've watched the cold side gather more attention since the Turbojet hit its wall in the 50's. The idea is to turn blades efficiently and economically to produce the most thrust per wt. Fuel. Gears work, but the "load" originating aerodynamically ends up gnashing the teeth of the gearset. Petrol electrics have been used for 70 years in locomotives, but are heavy. Since N1 is just a big multiblade propellor anyway, an obvious thought would be varying the pitch of the vanes (blades). Another (Old) solution to isolating gear teeth from each other is Hydraulic drive. It's analogous to Generator to Motor drives, but substitute a Fluid pump for the generator and a driven turbine for the electric motor. The Hydraulic fluid absorbs the slam of the changing loads, the Hot Core can run at its most balanced power/fuel ratio continuously, the Pump changes out put to the Fan by directing fluid flow to separate vane incidence areas of the driven turbine, changing the RPM of the Fan.
There, I've wanted to put that out there for twenty years. Thanks for listening.

[airfoilmod]

cool thing about electric or hydraulic is it isn't absolutely necessary to put the Fan next to the power supply. Put the Hot Core on the tail, the Fan on a very trim nacelle on the Wing. Spread the weight around. Having seen JT-9's generate 4 MegaWatts on a Powerplant Gang, I would like to think that the new ultralight electric motors might have a place in some new aero application also.