another Autoflight gearbox failure - this time after 34 hrs

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pantdino

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No, this is not the same Autoflight gearbox that failed at 43 hrs.

My LS3 430-equipped Titan T-51 flew from Ohio to Los Angeles at 180 KIAS without problems, taking about 12 hrs at 3000 rpm at 22 inches MAP.
But after half an hour here the prop governor began to hunt, so the plane was landed.
Inspection of the oil in the governor showed a metallic appearance. It shares oil with the Autoflight PSRU.
Interestingly, the gearbox oil was changed in Las Vegas, only about an hour from LA by air.

I sent the gearbox back to their previous chief engineer , (Bill Koleno, who was also their chief test pilot, and is the one who flew it here), who said the idler bearing was installed 0.015" off axis, which caused the bearing to fail and make metal. The gears and everything else looked fine.
The plan is to install a slightly larger bearing on-axis.

0.015" off axis doesn't sound like much to me. Could it really cause a bearing to fail after 34 hrs? Most T-51s get flown at about 160mph for an hour or so, not 215 mph for 2 hr stretches. I wonder if that was part of the reason for this bearing failure-- it overheated locally. (Bill said the gearbox never felt too hot to the touch.)

And in case you're wondering, no, there is no warranty coverage.

Jim
 

BoKu

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...0.015" off axis doesn't sound like much to me...
It matters how they're measuring, but it sounds huge to me. Bearings are very persnickety about alignment, especially when the forces are high. An error that you can see with the naked eye is definitely going to make a difference.
 

Vigilant1

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Explicit warranty or not--the company won't make this right even though the gearbox failed at just 34 hours?
 

wsimpso1

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0.015" position error on a shaft is a bunch. 23 years doing automatic tranny engineering. If one or both ends of the idler shaft was off position that much, the bearings could be in serious trouble and I would be scared of the gears too. That is enough to trash bearings, and could result in gear tooth face pitting too. I would be really concerned about the entire box and the inside of the governor too.,

Billski
 

proppastie

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shares oil with the governor and engine?......could be an Engine OH, Governor OH, Prop OH.....
 

proppastie

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Explicit warranty or not--the company won't make this right even though the gearbox failed at just 34 hours?
they admitted it was fabricated incorrectly......and are going to try to fix it...... if they charge him no warranty, and time to post all the details, if they don't charge him does that mean there is a warranty.....not necessarily but it is not as bad as if they charge him. The real issue here is does anyone want to fly using this company's gearbox.
 

TXFlyGuy

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they admitted it was fabricated incorrectly......and are going to try to fix it...... if they charge him no warranty, and time to post all the details, if they don't charge him does that mean there is a warranty.....not necessarily but it is not as bad as if they charge him. The real issue here is does anyone want to fly using this company's gearbox.
The gearbox is well proven with thousands of trouble free hours, for the most part. We have the new HD version, rated for 600 hp. It is odd that with only 34 hours TT, Titan refuses to honor any warranty.
 

Pops

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That is huge. I have aligned a lot of electric motors, gearboxes and coupling in my life as a maintenance Millwright.
 

Voidhawk9

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So is it the old previously reliable box failing on the Titans, or is it the new HD design?
 

Deuelly

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Generally when you machine housings like this for bearings, all the bearings in that housing would be done in one setup. Prop bearing, idler bearing, any other bearings that need tight tolerances to each other. If one bearing was off are the others? If not, it sounds like poor design, or poor machining practice.

Brandon
 

TFF

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I feel that while .015 is a major miss in assembly. Depending on the gear type it should have had enough latitude to survive. While automatic gearboxes are precise, manuals tend to have to survive movement. Miss shifts, oil never changed, burnouts, teaching a new to standard shift. They tend to survive. You know when they get crunchy. The helicopter type I work on can have either a magnetic chip detector or one that has a warning light. The boxes are the same, but the old style magnetic chip box will not have anything checked for 100 hours, it has to survive just about everything that could happen. I have pulled out teeth on one that was newer. The perfect gearbox is designed by a Russian and built by a German. It’s got to handle hammer and sickle abuse with laser precision.
 

Chris Matheny

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All the bearing bores should be cut in the same setup on a CNC and should be within a few ten thousandths of an inch of each other by location and parallelism. Something is not right.
 

TXFlyGuy

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found that on the company web page?
No. I personally know and am good friends with many T-51 owners, including the former Chief Test Pilot for Titan Aircraft. My relationship with most of them goes back to 2011, including my association with Titan.

Looks like the website has been pulled.
 

TXFlyGuy

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I don't know who owned the gearbox that lasted just 43 hours, but here's the thread wher it was discussed: Gear Box Failure @ 43 Hours

And there was another that failed prior to that. Tex says it was because the prop was wrong for the gearbox.
Correct. I think it was a Vesta prop, way too heavy for the PSRU. The pilot survived the nearly straight in crash.
 
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