Monday, April 17, 2006

The Short Life and Untimely Demise of the PW8000

When I started in the Garrett engine shop back around 1980, Garrett was coming to the end of a long hard development slog, getting the gearbox right on the TFE731 turbofan. There had been numerous failures, service bulletins and planetary reworks, and every engine in the field had gone through the rework program. As I recall I was given a special tool for removing a large anti rattle washer on the sun gear, which was one of the last big service bulletins. The whole mess cost Garrett a lot of money, downtime, and ill will.

All of which made it more interesting when Avco Lycoming tried more or less the same thing on the ALF502-which also had significant teething problems and nearly sunk the Canadair Challenger program. The ALF502 was supposed to be a quick and dirty spinoff of the T53 military turboshaft engine-but it took a lot of engineering to make it serviceable.

The handwriting was and is on the wall-gear reduction fan drives in turbine aircraft engines are damned difficult to bring off. They're expensive, quirky, and beset with problems not easily fixed, and the development dollars mount rapidly.

So when I heard that Pratt & Whitney was working on geared fans, my ears perked up and I wondered whether the boffins at East Hartford were smarter than everyone else or just didn't bother reading the newspapers.

The PW8000 was supposed to be a geared fan section on a PW6000 power core, and the article in the SAE journal archives is most interesting. The engine was scheduled for certification two years on, which would have put the release date about 2001. There is also a very nice article in Flug Review which described the history and construction of the PW8000.

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 which they are currently working on at this writing. 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 news about planetary reduction gearboxes in aircraft engines is not new. The old man once told me about looking for photographs of busted planets that he could use in a report after yet another reduction gear failure at Wright Aeronautical in the 1940s. He said they had a broken gearset for any occasion. I am sure that any of the engineers and technicians at Garrett that sweated bullets making the TFE731 a going proposition could have told the folks in East Hartford as much.

http://www.flug-revue.rotor.com/frheft/FRH9810/FR9810h.htm

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

3 Comments:

At 10:00 AM, Blogger Maury Markowitz said...

So is the GTF really a different engine than the GW8000? Or is it simply a renamed further development? They both seem to be about the same power ratings and the overall design is similar, of course.

Out of curiosity, do you happen to know the gear ratios of the TFE713 and ALF502?

 
At 9:50 PM, Blogger SMSgt Mac said...

I am waiting for someone in the trade press to pick up on the ALF502 being a geared turbofan. In fact, the ALF502 was based on Lycoming's earlier experince with a research engine project.

Yes, it had teething problems because of it's added complexity, but they were overcome. Mechanically, it was a very advanced engine and the design was probably a little ahead of the materials. I know of only two 'problems' with the -502 that gained any notoriety. The first did involve the Challenger, and Canadair sued Lycoming over failure to meet range and SFC specs. Canadair lost. I can't remember if it was in a pre-trial hearing or actual trial, but Canadair lost when an expert witness pointed out that the reason the plane didn't meet specs was not because the engine didn't perform, but because the Challenger 600 had gained 6000 lbs 3 tons!) over target weight. That expert was my Father.
The second problem involved a new synthetic lubricant that was certified for the engine and it NEVER should have been.
The ALF502's biggest problem was that the USAF was subsidizing GE's CF-34 through the constant quest for more thrust out of the TF-34. Everywhere the -502 went, sooner or later there would be a GE salesman sniffing around asking the aircraft builder if they were sure they wouldn't like a little more static thrust the early GE P.O.S. could provide. Never mind that when the AF started engine warranty programs, the first engine they went after was the TF-34

 
At 6:06 AM, Blogger Robert Luedeman, attorney at law said...

Interesting comments all, fellows. I agree that the ALF502 was not ready for prime time when it was released for service. I worked in engineering at Airesearch Aviation at the time and Canadair was indeed known as "The House of Unreasonable Demands". They had a huge weight problem with the CL600 as I recall and as they were making unreasonable weight demands on completion centers like Airesearch they were also making unreasonable demands on Avco Lycoming as well.

The Challenger was an interesting project that was a lot like the A380-"positions" were going for $5,000 in the early stages of the program.

I cannot say as I share your analysis of the CF34 as a POS. I worked for Atlantic Aviation for a time, and they sent me to CF34 school at GE in Linn. You know, "Linn, Linn, the city of sin, you don't come out where you first went in!"? It was a military engine abd built like the Portuguese phonebooths that dot the area south of Linn.

Maury, I think the GTF is indeed a different project from the 8000. Pratt dropped a bundle on both projects but with the price of jet fuel, they're going to clean house because they've done the development work. Building a geared fan that can live is a black art as Garrett and Avco Lycoming learned and as Rolls and GE will learn if they try a quick and dirty geared engine.

 

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