another Autoflight gearbox failure - this time after 34 hrs

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pantdino

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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.
The answer here also ties in with the "old, reliable" gearbox question.
The original gearbox was designed to work with the Suzuki engine, about 150 hp, and had a needle bearing on the idler shaft.
When they went to the Honda engine, about 250 hp, I believe they changed out the needle bearing to a roller bearing. The input and output bearings were already roller bearings.
But then some of those idler shaft roller bearings failed, so they went to a bigger one.
I'm not sure if they went to an even larger one with the LS3 (limited to 300hp) or not.
So the error in my gearbox was when the idler shaft bearing was replaced with a larger one, the center was off.

So when you speak of the "old" gearbox, you have to specify which iteration you are talking about.

Yes, the gearbox has had hundreds of hours flown on Suzuki and Honda-powered planes, but there are only a few LS3 powered planes in the air at this time. One does have 100 hrs, I believe, and Bill's factory prototype presumably has more than that.
 
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wsimpso1

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If one end of the shaft was 0.015 out of position while the other was dead on, and I assume a 3" separation between bearings on the idler, the rollers are running around 5 milliradian of error. Timken Engineering Manual https://www.timken.com/resources/timken-engineering-manual/ page 56 indicates max misalignment allowed on lightly loaded roller bearings (<20% of C) is 1.2 milliradians, moderately loaded (20-35% of C) is 0.5 milliradians. 0.015" out of position is a bunch for this type of bearing. I would expect at least one and possibly both bearings to be distressed.

Furthermore, a single bearing out of position by this amount with the other "on" position gives about 5 milliradian (about 0.28 degrees) of angular misalignment while the gear will be out of position about 0.008" (somewhere around 0.4%). Gears do not stand loss of conjugate action and edge loading for long. The AGMA provides lots of info to members, but engineering college libraries will have copies.

Then there is the issue of running with hard particle contamination. If contamination caused the governor to misbehave, you had a pretty fair load of hard particles in the loaded interfaces between parts that are supposed to be in clean oil and in rolling contact only. You had substantially higher contact pressures (edge loading) and sliding contact (loss of conjugate action) with hard particles in the oil - bad for these surfaces.

I personally would not accept reuse of any of the gears, shafts, bearings, or even the seals that ran in that misaligned condition. Perhaps the case can be machined to repair this and a larger bearing fitted that does not compromise the shafts. Replace the other parts subject to damage from the misalignment and contamination, and maybe it will be OK to fly. I would definitely not man-rate this box if any of the parts discussed were reused...

Billski
 

TXFlyGuy

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In a gear box, with this situation, why would the PSRU all of a sudden fail at 34 hours? Would it not have been a progressive failure starting at hour number one?

How do you know how much off the bearing was? By the time it was noted, it would have been well on the way to destruction, with no real and reliable way to get an accurate measurement.

How many times was the oil changed on this PSRU? Titan states you change it at 5 hours, and then at 10 hours initially?

Do you have log entries showing all of the oil changes? Were you invoiced by Titan for this work? If Titan did not invoice you, you can be 100% assured that the oil changes never happened.
 

pantdino

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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 owner of Titan stated "There is no warranty that would cover that."
One can only conclude he feels he is not responsible for the error of his employee.

I have sent the gearbox to their past Chief Designer and Machinist, who is the one who diagnosed the problem and wrote the programs for their CNC machines. I'll be paying for it.
 

TXFlyGuy

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The owner of Titan stated "There is no warranty that would cover that."
One can only conclude he feels he is not responsible for the error of his employee.

I have sent the gearbox to their past Chief Designer and Machinist, who is the one who diagnosed the problem and wrote the programs for their CNC machines. I'll be paying for it.
See post #26. Any input on this?

Do you have any evidence that Titan actually did the required oil changes, at 5 hours, then 10 hours, and each 10 hour interval until 50 hours?

Your engine log should show no less than 4 oil changes in the PSRU.

And there is no way Titan would have changed the oil without sending you an invoice for each oil change. Trust me.
 

pantdino

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If one end of the shaft was 0.015 out of position while the other was dead on, and I assume a 3" separation between bearings on the idler, the rollers are running around 5 milliradian of error. Timken Engineering Manual https://www.timken.com/resources/timken-engineering-manual/ page 56 indicates max misalignment allowed on lightly loaded roller bearings (<20% of C) is 1.2 milliradians, moderately loaded (20-35% of C) is 0.5 milliradians. 0.015" out of position is a bunch for this type of bearing. I would expect at least one and possibly both bearings to be distressed.

Furthermore, a single bearing out of position by this amount with the other "on" position gives about 5 milliradian (about 0.28 degrees) of angular misalignment while the gear will be out of position about 0.008" (somewhere around 0.4%). Gears do not stand loss of conjugate action and edge loading for long. The AGMA provides lots of info to members, but engineering college libraries will have copies.

Then there is the issue of running with hard particle contamination. If contamination caused the governor to misbehave, you had a pretty fair load of hard particles in the loaded interfaces between parts that are supposed to be in clean oil and in rolling contact only. You had substantially higher contact pressures (edge loading) and sliding contact (loss of conjugate action) with hard particles in the oil - bad for these surfaces.

I personally would not accept reuse of any of the gears, shafts, bearings, or even the seals that ran in that misaligned condition. Perhaps the case can be machined to repair this and a larger bearing fitted that does not compromise the shafts. Replace the other parts subject to damage from the misalignment and contamination, and maybe it will be OK to fly. I would definitely not man-rate this box if any of the parts discussed were reused...

Billski
Thanks for the detailed explanation, Billsky.
I discussed the idea of demanding a new gearbox with Bill, but he felt the gears looked fine and at least this way we know what we have and can fix it. Another gearbox would be an unknown that might have other screwups inside it that we don't know about.

Bill tried to explain to me in layman's terms what happened, and I gathered the machinist who put in the bearing didn't understand how to take into account the position of the bearings that had already been installed when placing the new one. He just put the case in the CNC machine and ran the program to place that bearing.

Would the gear tooth damage be something that would be visually apparent?

Jim
 

pantdino

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See post #26. Any input on this?

Do you have any evidence that Titan actually did the required oil changes, at 5 hours, then 10 hours, and each 10 hour interval until 50 hours?

Your engine log should show no less than 4 oil changes in the PSRU.

And there is no way Titan would have changed the oil without sending you an invoice for each oil change. Trust me.
I only received the Aircraft log with the plane, and there were very few entries in it. No mention of the engine that blew up, no mention of all the airframe mods made to accommodate the big engine, no mention of the change to the 3" gear, no mention of anything but an engine change and one oil change. I bought engine / gearbox and prop logs and have started them, but none came with the plane. Piss poor record keeping by Titan

EDIT- Actually I should clarify that the airplane made the cross country journey with LITERALLY NO PAPERWORK AT ALL- not a single document of any kind. I only got the paperwork and log after bugging several people to figure out where it was and send it to me. Everyone thought the other person had it.
 
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TXFlyGuy

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I only received the Aircraft log with the plane, and there were very few entries in it. No mention of the engine that blew up, no mention of all the airframe mods made to accommodate the big engine, no mention of the change to the 3" gear, no mention of anything but an engine change and one oil change. I bought engine / gearbox and prop logs and have started them, but none came with the plane. Piss poor record keeping by Titan

EDIT- Actually I should clarify that the airplane made the cross country journey with LITERALLY NO PAPERWORK AT ALL- not a single document of any kind. I only got the paperwork and log after bugging several people to figure out where it was and send it to me. Everyone thought the other person had it.
The tip-of-the-iceberg.

Did Titan invoice you for any PSRU oil changes? If not, the required oil changes never happened. And you can take that to the bank.
 

pantdino

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The tip-of-the-iceberg.

Did Titan invoice you for any PSRU oil changes? If not, the required oil changes never happened. And you can take that to the bank.
Well, they would have changed the oil when they took it apart after the prop strike incident at about 3 hrs and blown engine incident at about 8-10 hrs. So the 5 and ca 10 hr changes got done, indirectly. :)

In case viewers are wondering, the "blown engine incident" refers to the fact that there was a problem with the engine-gearbox adapter and / or the cap bolts used to hold the isolator which resulted in the crankshaft being forced against a thrust bearing, which eventually failed and welded itself to the crankshaft. Net result was a seized engine.
 

Vigilant1

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I think that's the customary deal: "Free oil change with engine rebuild/replacement."
At what point does a turboprop start to look cheaper than this craziness?
 

proppastie

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I'll be paying for it.
In case viewers are wondering, the "blown engine incident" refers to the fact that there was a problem with the engine-gearbox adapter and / or the cap bolts used to hold the isolator which resulted in the crankshaft being forced against a thrust bearing, which eventually failed and welded itself to the crankshaft. Net result was a seized engine.
You are a saint.......I hate to say this....do they put other engines in these birds? Like a big Lycoming or Continental?
 

Geraldc

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Bill tried to explain to me in layman's terms what happened, and I gathered the machinist who put in the bearing didn't understand how to take into account the position of the bearings that had already been installed when placing the new one. He just put the case in the CNC machine and ran the program to place that bearing.
So this is not a manufacturing fault but a poorly done modification.
 

pantdino

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You are a saint.......I hate to say this....do they put other engines in these birds? Like a big Lycoming or Continental?
The idea is to be more affordable and look like a Mustang. That wide engine would make it look like it had a birth defect or huge tumor. 😊
 
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