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newbie question re prop overspeed with constant speed prop

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rv7charlie

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This is a long way from what *should* happen with a gearbox making metal, but operating the prop in fixed pitch mode should be do-able; it's been done before, in the P-85

Fixed-pitch Lycs on fast a/c like RVs, etc typically turn 2200-2400 rpm, static; 81%-89% of WOT top speed rpm of 2700. Doing the math for that engine/reduction/rpm ranges, and settting the fine pitch stop for somewhere in that range of static rpm percentage, then setting the course pitch stop to lock the prop at that angle, would effectively give fixed pitch performance.

Legally, you shouldn't need any kind of modification to the oplims because the w&b hasn't been altered, the prop hasn't been 'changed', and there's technically no change in performance from what *could* be happening with (im)proper positioning of the controls.

Not saying that * I * would fly the plane in that condition....

edit: Just refreshed the thread & saw that the OP intends to install the new gearbox (hopefully, complete with a governor to control the prop). Excellent choice!
 

Toobuilder

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There is more than W&B to consider when looking at a "change". Making a former C/S prop into a "fixed" unit is a major procedural change from a pilot perspective. THAT is why a switch from C/S to fixed is considered a "major" change. That, and the new fixed prop invalidates the data collected during the initial test program. That will be a major change to the performance of the aircraft and the POH data is out the window.

To summarize: Significant change in procedures, checklists and performance... You MIGHT find a FSDO that would look the other way, but I sure wouldnt count on it.
 

TFF

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Good move. For your gearbox, you are not going to just buy your way through it. You might get lucky with a local transmission shop, but don’t say the word airplane; they will shut the door on you just being scared of being sued. There will be a couple of people who will be machine savvy in a sort of underground way. Hot Rodders and racers will know someone that is the miracle worker. Already every bearing needs to be changed.
 

pantdino

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I'm thinking it would be best to install the new gearbox without the governor connected and ground run it until the initial fines are cleared. Then install the governor. Otherwise the governor and associated plumbing are going to get contaminated by the initial fines.

Does that make sense?
 

pantdino

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Another question- Titan said the shaft the disintegrated bearing was on was damaged too, so the hardened surface of the shaft where it contacts the bearing was worn away. But instead of making a new shaft and having it hardened they somehow press fit the new bearing onto the shaft. Is that OK?

Regarding the other bearings in the box, I was told they would replace all the bearings when they had it apart, but I have nothing in writing saying that was done.
 

Dan Thomas

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Another question- Titan said the shaft the disintegrated bearing was on was damaged too, so the hardened surface of the shaft where it contacts the bearing was worn away. But instead of making a new shaft and having it hardened they somehow press fit the new bearing onto the shaft. Is that OK?
No. Not ok in an airplane. In a tractor maybe. Tractors don't crash when their transmissions fail.

That prop and governor and gearbox ALL need to come apart and get thoroughly cleaned and inspected. You put that contaminated prop back on a new gearbox and all the crud gets rinsed out of it into the gearbox and starts the whole problem all over again.

Running the thing to rinse out the crud is just wearing away more critical stuff like the hardened surfaces of gears and bearings. That's like trying to rinse sand out of your engine by changing the oil and running it a few miles and changing it again. You end up with a trashed engine.
 

proppastie

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you must be very frustrated.....try to think of all the money and time you have spent and getting this right is only a very small portion of that. I like to say "it's a hobby"........
 

crkckr

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Since the gearbox and governor share the same oil, I would not install the new gearbox until whatever lines run between them (if any) and the governor itself have been completely torn down and closely and professionally inspected. Leaving any metal residue in the lines or in the governor is just going to screw your new gearbox to death! It also sounds like the governor may have been damaged from the metal in the gearbox, so I would consider replacing it as well.

Considering the performance losses of the airplane without the gearbox/governor, I would personally suggest that they are require items, not something you can just bypass on a whim and prayer! Since this is potentially involving someone's life, do it right or park the thing as a museum piece.
Good luck!
Cheers,
crkckr
 

TFF

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You are going to fix it so this question is not really relevant, but did you have a pilot ok with flying it fixed pitch? Right off the bat, the pilot pool is going to be small to fly a plane like that without training. Someone qualified and willing to do unconventional things is rare in that group.
 

pantdino

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You are going to fix it so this question is not really relevant, but did you have a pilot ok with flying it fixed pitch? Right off the bat, the pilot pool is going to be small to fly a plane like that without training. Someone qualified and willing to do unconventional things is rare in that group.
My plan was to hire Elliot Seguin to fly it fixed pitch to determine the best compromise pitch, but after reading the posts on here I realize that is not a reasonable option. So that would be a waste of time and money.

My insurance company requires 10 hrs of training before a pilot can fly the plane solo, and the pilot I for whom I had paid $3K for training has now decided he doesn't want to fly it after all.

I'm afraid it is beyond me how the gearbox and governor can be returned to the factory and come back so full of fines it fails again after 30 minutes or so.

I'm pretty much emotionally burned out on this plane at this point and need to step back and look at the big picture.
For the time being I have a 75% scale model of a cool looking Mustang and I'm trying to look on the bright side.
 

Toobuilder

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Like others, I'm still baffled that you are taking this on at all... Why the hell isnt Titan (or the Mfg) on the hook for this gearbox issue? Seems to me this is just a matter of turning it back to them until its "right". What part of this story are we missing?

And it seems that you (as a non pilot or mechanic) have taken on a HUGE task without the experience to carry it through. If you just wrote a big check because you wanted a cool toy, thats fine, but please take a moment to evaluate your NEXT move very carefully. This isn't a finicky exotic car here - this thing WILL KILL the pilot in a heartbeat - even if its 100% functional. Trying to cheapscrew this thing to get some hours on it is the exact opposite of what is prudent. I feel for your position, but take a minute to think this through. On the ground, its only money.
 

MadProfessor8138

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Like others, I'm still baffled that you are taking this on at all... Why the hell isnt Titan (or the Mfg) on the hook for this gearbox issue? Seems to me this is just a matter of turning it back to them until its "right". What part of this story are we missing?
I've asked this question twice now and still haven't received an answer from the OP......
I am very curious as to what the "WHOLE" story is pertaining to this issue.
I'm old school so I think differently than others because I can tell you this......if I had spent that amount of money on the T-51 and the factory tried to pass their mistake onto me financially......my lawyer would either be filing paperwork against them or posting my bond for me when the judge showed up in the morning......possibly both.

So what's the "ENTIRE" story as to why the financial burden was passed onto the OP and why was this allowed to happen in the first place ??????

Kevin
 

Toobuilder

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To be fair, the OP does not OWE any of us an answer. But as "problem solvers",many of us look for the root cause and the fastest/best solution. In this case, it DOES SEEM that the gearbox is manufactured or designed poorly and does not meet performance requirements; AND; its time to call a lawyer.

Beyond that, dont fly as fixed pitch; dont fly AT ALL until the powerplant assembly is fully functional.
 

pantdino

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I think a review of that thread will help you understand. Titan is not a normal company. In this case it’s “ My employee made a mistake and caused your gearbox to fail. So I’ll sell you another one at a discount.” Absent here is any apology, by the way. Only by the grace of God did this problem occur in the pattern (twice) and this didn’t result in an off-field landing with the attendant damage and possible injuries. I have tried to just state facts and let people draw their own conclusions.
 

pantdino

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Regarding the lawyer, I live in California and Titan is in Ohio. The only one who would gain here is the lawyer.
 

TFF

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California should be the best place to find someone to crack the thing open. Lots of race shops and machine shops for industrial and aerospace. You do have to find someone who has the time and will understand your needs.
 

Dana

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I'm curious... how does a non pilot choose to buy a demanding experimental airplane like this?
 
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