Geared Turbofan

RC20 · Post by **RC20** » 30 Mar 2007, 04:55

Well, looks like P&W has the engine, now we just need the airframe!

(well it needs to prove itself), but Boeing and Airbus did ask for this, and now.........

RC20 · Post by **RC20** » 30 Mar 2007, 04:56

http://www.atwonline.com/news/story.html?storyID=8389

Link to the above

foxtrot_lima_yankee · Post by **foxtrot_lima_yankee** » 30 Mar 2007, 05:57

Cool!!!
So we gonna need a 3rd pedal to switch gears or is it gonna be an automated system?
Who says gears says problems.
The less factors, the better!!
Very interesting though from an ecological point of view!!

DFW · Post by **DFW** » 30 Mar 2007, 06:14

I'm not trying to turn everything into a Boeing vs. Airbus issue, but a 2012 entry date for geared turbofans appears to favor Boeing. By say 2010, the work on most 787 variants will have been completed (except for perhaps the -10), freeing up resources and capital for a 737 replacement. Airbus will still be expending resources, capital, and cashflow on the A350 through 2014. Might not be able to start back up on the A380F anytime soon either then.

regi · Post by **regi** » 30 Mar 2007, 10:41

foxtrot , please, gears are fine! How often do you hear these days about malfunctioning car transmissions? If something goes wrong, it is mostly with the auxilliary equipment such as oil pumps, electronics, seals,...
But the hardware gears are OK.

Bracebrace · Post by **Bracebrace** » 30 Mar 2007, 12:24

You cannot make that comparison. The geared turbofan is a single speed gearbox (afaik).The GTF "simply" disconnects the fan from the low pressure compressor. If you have a 3 megawatt turbofan, a gear with an efficiency of 99% will still create 30000W of heat losses in a very small section and this heat would destroy the lubricating oil inside immediatly. And gears have an efficiency (at very best) of 98-97%.

P&W is working on this engine for years and years (since before 2000 I believe)... says enough about the gearbox problem. I hope the final result will be reliable, but only entry into service will tell. Bit strange if you consider the GTF is similar to a cowled turboprop with a fixed pitch fan.

smokejumper · Post by **smokejumper** » 30 Mar 2007, 14:42

Let's assume that P&W is correct in saying that a new engine (GTF) will be available in 2012, will offer drastically lower fuel consumption, be relaible and, offer lower noise - all are requirements for an airframe manufacturer in order to make development of a replacement narrow-body plane attractive.

If it takes 5 years for a manufacturer to design, build and certify a new plane, the we could possibly see a new narrow body plane announced in 2008. This will allow the manufacturer enough time to market the new plane and continue to refine the design before any announcement.

I agree with the above post that this schedule might favor Boeing since their design work on the 787 and 747-8 will be largely completed and engineering resources willl be available. Airbus will be heavily involved with the A350XWB, but can outsource a large amount of the design, but I'd guess that they will lag Boeing in developing a replacemment for the A320.

Bilboone · Post by **Bilboone** » 30 Mar 2007, 16:32

Is this the PW8000 about we are talking ?

a 32000- shp gearbox should be ok,i think

link : http://www.sae.org/aeromag/techinnovations/1298t10.htm

achace · Post by **achace** » 31 Mar 2007, 02:14

It was reported a few weeks ago that we might see the GTF on a 320, because it has the necessary ground clearance.

Would be an interesting excercise if PW gave Airbus sufficient guarantees to underwrite the new wing that would be needed to optimize performance.

Could be a very cheap interim step for Airbus, because if they were smart, they could then at the right time design a new composite fuselage for the 320 replacement that would take the wing designed for the intermediate airplane, which in itself would have pretty attractive operating costs with GTF and a composite wing.

The existing 320 layout is popular because it carries a fair payload in the hold, so maybe any replacement will still have similar layout, but much better operating costs, so an all composite 320 with GTF may be a good move.

Remember Boeing have to start with a clean sheet of paper for the 797.

Something to think about.
Cheers
Achace

RC20 · Post by **RC20** » 31 Mar 2007, 20:17

foxtrot_lima_yankee wrote:Cool!!!
So we gonna need a 3rd pedal to switch gears or is it gonna be an automated system?
Who says gears says problems.
The less factors, the better!!
Very interesting though from an ecological point of view!!

Lets see, Fokker F27, P3 (Electra), C130 Herc, ATR, DH Dash7/Dash 8, A400, Navy Cruisers and Destroyers have what in common?

Yep, Turbines with gears! Now, we can add Aircraft carriers that have huge gears (what 250,000 shaft hp total?), not to mention the F-35 Jump jet (front flower gear driven fan), and I could go on for many hours.

The critical questions is it a force fit, or does it really work. They wanted props on turbines because they are more efficient than jets for some missions and they did it. They wanted turbines in ships because you get a huge bang for the size buck, and they did it. Many power generation plants used turbines (to make useful power you have to slow them down for all those applications)

Economics of jet engines favored a non geared approach. But when Boeing wanted the large alternators on the 787, WALLAH, RR discovered that not only could they do it, they could have taken that power off another section long ago, and done it better.
Reason, no one ever though to do it.

I have seen incredible improvements in diesels that lat 10 years, where everything before that was incremental improvements. Why? The application of electronics to diesels, where the wisdom was they would never work with them.

P&W feels that the reason that geared turbines were felt not to work was no one ever developed the machines that way. No research has ever been done in that direction, there is no knowledge base to work from (diesels borrowed their knowledge base from the electronics developed for gasoline engines) If you need a dramatic improvement, you have to look outside the box. The geared turbine may or may not work, but not because it has gears. Frankly it looks very promising.

I have heard to years that chain driven cycles are better than shaft because of the efficiency of chain. Actually that’s not right, chain is probably a bit more efficient than shaft, but it has its losses. Shaft a bit more, its mostly the weight a shaft adds (reducing performance, and it cost more). But if you are on a dirt road, a shaft lives a lot better, because it does not get eaten alive by the grit.

And the Boeing vs Airbus: That’s simply a part of the discussion. If its viable, who picks it up and does what first.

I agree, Airbus may be forced to do an interim step, but where it gets them I am not sure. Maybe helps keep existing, but who really wants to invest in a half way measure, when the CFRP wing and fuselage is coming along soon anyway?
Yes there are the American Airline types who simply need to move now, and all would take a look and try to figure what works best.
Long term, its usually better to bite the bullet and go all the way. The A350 if it continues on its present course (hybrid structure) will be a good model of how many are willing to invest in a technology that superseded it before it was even promoted.
I still go back to what Leahy said, he could have been selling a lot of A350s (first version) if they had left it alone (they would have had to commit to a CRFP in the future, but it would have cost a lot less as gap filler than what they have). Now they are stuck with it, as its not a gap filler, it’s the so called answer. If they only get 30% of the market, they are lost long term.

Boeing on the other hand not only is in the cat birds seat, they could actually start a all new aircraft beating Airbus, and still beat them to the market.

Mostly I think it depends on what kind of response Boeing gets from he customers on the narrow aisle and size, vs the mini wide body. Boeing has not been keen on the geared turbine, but figures like P&W have could change that.

The other issues is could they design a wing that can work equally well with both geared turbine and straight jet? I don't have that kind of knowledge. Boeing will hold that secret. Boeing would have to be completely convinced its viable before putting their eggs all in one basket. However, they certainly did on the 787.

It will be interesting.

mmciau · Post by **mmciau** » 31 Mar 2007, 23:42

RC 20,

Very interesting discussion by you - well done.

Mike McInerney

achace · Post by **achace** » 02 Apr 2007, 02:50

RC 20 has said it all in my opinion.

Existing turbines all have gearboxes, and size is not an issue.

There is nothing else on the horizon to match the GTF for fuel consumption, so if it is as quiet as they claim and has lower emissions, I believe GE and RR will be forced to follow this trend.

No doubt Boeing and Airbus will be led kicking and screaming into dropping their existing narrow bodies which still sell well and presumably make reasonable profits.

Apart from composites and probably the GTF, ther are no very obvious aerodynamic developments on offer within the timescale everyone is talking about, to complement a new airframe, unless they look at a slowed down Sonic Cruiser layout to accommodate a 767 cross section, and they introduce canards for pitch control, and I fancy those could be a bit damage prone around the airbridge.

It is going to be very interesting?

Cheers
Achace

smokejumper · Post by **smokejumper** » 03 Apr 2007, 15:38

Pratt & Whitney has started assembly of its geared turbofan demonstrator that will begin ground tests in November.

See: http://www.flightglobal.com/articles/20 ... -plan.html

Assuming the demonstration is succesful, development of production type should follow soon. Can an announcement for a new single aisle plane be far away?

RC20 · Post by **RC20** » 05 Apr 2007, 06:51

If it bears out its promise, its going to shake up the industry like the 787 did.

Huge kudos to P&W for persisting. Extremely tough with no outside research to support it.

P&W has been looking at becoming a second tier player. This would change that in the single aisle area. Could it be scaled up to mini wide body or the big guys? No comments on that yet, just 30,000 lb thrust class the upper limit right now.

Like the 787 it depends on them producing what’s promised, but it looks very good at this point.

RC20 · Post by **RC20** » 23 Oct 2007, 05:23

AV week had an article on the GTF and the (open duct, i.e. prop) option on the net.

http://www.aviationweek.com/aw/generic/ ... row%20Body

To me it looks like RR and GE are flailing away trying to convince people to wait for the open ducted thingy, while desperately trying to catch up with P&W.

If Boeing is convinced its a go, I think they will launch the aircraft knowing the engine will be there. P&W would bet the company to get an advantage like that. It would be the 787 all over again (a huge leap). Granted RR and GE would catch up eventually, but it would take time, and P&W would have a long lasting lead.

Open rotor, open duct, whatever they call it, just does not look to have a future in that sort of service. (737/A320 class aircraft).

achace · Post by **achace** » 23 Oct 2007, 05:50

Mitsubishi have already signed up for this engine for their proposed 100 seat rejional, which suggests the first vesion is short of the power a 737/A320 replacement would need, or P and W have a bigger version in waiting.

Cheers
Achace

smokejumper · Post by **smokejumper** » 23 Oct 2007, 15:10

In my opinion, Boeing is not in a position to start another new major program at this time to replace the 737.

It is now fully occupied with the 787 program, the 747-8i program and , a (posssible) major revamp or replacement of the 777. Also, throw into the mix, the 777F and the KC767 activity.

It will proably be the 2010-2011 time frame before they can devote a major effort to the 737 replacement, using whatever engine matches the requirement.