PILOT SPIN
Pilot Zone => Pilot Zone => Topic started by: invflatspin on July 18, 2017, 08:15:43 PM
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This has been a project for decades. I was involved in some of the FFT analysis long ago on the gearboxes. It was complicated, and I was just part of the team that determined where to instrument the fan, the gearbox, and the turbine. The technology for the gearbox is mind-blowing. It's a planetary setup with helical cut gears, under tremendous stresses. They had an engine stand that would run the thing at 100% thrust and were able to pivot the engine on a gimbal frame at about 20deg/sec in any axis. not widely known, but this is what led to thrust vectoring in the F35, and that is another game changer.
Good on them for getting this done. Who would have thought that adding a gearbox with its own losses can result in some great overall efficiency of operation.
https://www.forbes.com/sites/lorenthompson/2017/07/17/pratt-and-whitney-surges-u-s-hiring-investment-as-geared-turbofan-ramps-up/#6001367a86a6
I wish the topic were more technical in nature, because the tech part of it is fascinating, but at least it's out there.
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I hope they have the problems solved..
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I hope they have the problems solved..
Do you have any specific problem in mind? I am quite sure they have solved thousands of them, and I am quite sure more will pop up as time goes on.
BTW, My brother is a lead engineer on this project, but he is one of those that says if he tells me too much about it, then . . .
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This has GOT to be complex as hell. I can't imagine.
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Do you have any specific problem in mind? I am quite sure they have solved thousands of them, and I am quite sure more will pop up as time goes on.
BTW, My brother is a lead engineer on this project, but he is one of those that says if he tells me too much about it, then . . .
These problems:
https://airlineaftermarket.com/pratt-combustor-oil-seal-top-geared-turbofan-reliability-issues/
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These problems:
https://airlineaftermarket.com/pratt-combustor-oil-seal-top-geared-turbofan-reliability-issues/
From the fist sentence in that link (from Feb 1 of this year)
Pratt & Whitney plans to introduce redesigned combustor liners and oil seals for the PW1000 geared turbofan (GTF) family this year, addressing the two components causing the most in-service reliability issues in the wake of well-publicized start-up challenges that have been solved.
And later in the article:
the problem seal “has nothing to do with the gear system” that sets the engine apart by allowing the engine’s fan and turbines to operate at different speeds. “The gear system has performed flawlessly,” Hayes said.
I'd say they must feel they have addressed those problems, or are well on the way.
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"The gear system performed flawlessly" was only a recently true statement.
Again, I was peripherally involved but I recall the following general issues;
1. Harmonics - Holy cow was there a ton of harmonics that had to be taken into account. One pernicious deal had to do with the ratio of the spur, or planetary gears to the outer ring gear. It was some convoluted equation where someone missed a sign and caused four iterations.
2. Gyroscopic gear loading - Not only must the gears remain in constant pressure load under fixed conditions, but they must remain under constant load during A. Acceleration, B. Deceleration, C. Overrun(fan driving engine). And all of those must be applied during climbing, turning, shock, vibration, turbulence, and all of those forces combined.
3. Gyroscopic fan loading - Different than the load applied to the shafts, bearings, and gears, the big giant fan on the end presented its own components of torque and flexing under all those conditions.
There was other stuff, but those were the big hitters. With our vibration and acoustic sensor array, we could tell engineers what forces and vectors were being applied to the structure, but it was up to them to get it all sorted out without adding gobs of weight. In an industrial setting, we would just increase the size of a shaft, or bearing, or disk to stiffen it. With aircraft engines, of course that's not possible. Some interesting solutions were developed.
FF to about 3:40, you'll see some bits of the gearset. Neat stuff, and I'm not a mech engineer;
https://www.youtube.com/watch?v=aMd0nbGHi4w
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"The gear system performed flawlessly" was only a recently true statement.
Again, I was peripherally involved but I recall the following general issues;
1. Harmonics - Holy cow was there a ton of harmonics that had to be taken into account. One pernicious deal had to do with the ratio of the spur, or planetary gears to the outer ring gear. It was some convoluted equation where someone missed a sign and caused four iterations.
2. Gyroscopic gear loading - Not only must the gears remain in constant pressure load under fixed conditions, but they must remain under constant load during A. Acceleration, B. Deceleration, C. Overrun(fan driving engine). And all of those must be applied during climbing, turning, shock, vibration, turbulence, and all of those forces combined.
3. Gyroscopic fan loading - Different than the load applied to the shafts, bearings, and gears, the big giant fan on the end presented its own components of torque and flexing under all those conditions.
There was other stuff, but those were the big hitters. With our vibration and acoustic sensor array, we could tell engineers what forces and vectors were being applied to the structure, but it was up to them to get it all sorted out without adding gobs of weight. In an industrial setting, we would just increase the size of a shaft, or bearing, or disk to stiffen it. With aircraft engines, of course that's not possible. Some interesting solutions were developed.
FF to about 3:40, you'll see some bits of the gearset. Neat stuff, and I'm not a mech engineer;
https://www.youtube.com/watch?v=aMd0nbGHi4w
Can't even imagine. Wonder what the TBO is going to be.
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Word is, the trans is a 'lifetime' component of the engine. I'm not too sure about that definition, but basically about 18 years of operation with regular lube changes, and no degradation in the torque transmitted. Planetary gear systems have a kind of remarkable wear pattern compared to ring, pinion, or para shaft, or other types of gear systems. I don't know much about it, but they are supposed to last a long, long time compared to other gear sets.