Lost MY tail today

[DethWshBkr]

Fourth flight on the rebuild, odd noise, but everything SEEMED ok. I took it apart, and checked the torque tube, and all looked OK. Had a loose tail rod guide, so I thought the noise was just vibration from that.

Just doing loops, immelmans, inverted hover, and general forward flight, trying to identify the problem.
All of the sudden, the tail went out. I hit throttle hold, dropped her down, but she started tilting and was still spinning faster than I could compensate. Went in, but not too bad.
Broken main blade, broken skid, and bend main rotor grip, otherwise OK.

When I pulled it apart, this is what I saw. This is a new torque tube, two flights on it.

You can tell it did not fail in the crash, as there is no twisting in the break, but you can see the serious rubs at the break. Looks like the torque tube just failed on it's own.

Wonder if there is any warranty!






EDIT -
From the thread - Lost the tail today ( https://www.helifreak.com/showthread.php?t=403413 )

Originally Posted by NitroAl

I had a similar day losing the tail while rolling out of a big loop! At about 60m high the tail swung around 180deg then took off on a random journey of it's own!
Total damage was Canopy, receiver tray,blades, boom and torque tube. I thought it would be toast since it was already aiming at the ground at speed from altitude before the rudder went AWOL!
The cause was a broken torque tube, I'll be damned if I know how or why. It was about 150mm from the tail!

Interesting....My break is 6" (152mm) from the end of the actual torque TUBE, 7" if you add the insertion piece.

And then me -

Originally Posted by DethWshBkr

Are you sure the torque tube itself broke? That seems a bit scary if that is the case.

I know with my rebuild, putting the new torque tube in, I noticed the new one seems a bit bent. Not kinked, but not perfectly straight. It does have some wobble in it rotationally.
Figure the head spinning at 2000 rpm, and a 1:5 ratio, means that tail shaft is spinning 10000 rpms. If that torque tube is not PERFECTLY straight, or slightly off balance, I can see it just flinging itself all around and causing some good stress.
I will actually be ordering a pair of the bearings and red grommets, and putting a total of three torque tube bearings (PV1376) on the shaft to help eliminate the possibility of the shaft wobbling, especially at high speeds. Whether this is needed or not, I do not know, but I think it may cause me to be a little more confident. I can see no detriments to this modification either.

I did NOT get to add more of the torque tube bearings yet....and the torque tube I mention is the torque tube that broke.

[NitroAl]

That is exactly what mine looked like! The original one that came in the kit was worn where the bearing was to the point that when I held the two ends and and bent it a little it snapped like a twig!
I have rebuilt the tail now with one bearing right on the boom support clamp and the other just forward of the center of the remaining tube but I am thinking I should have used 5min epoxy instead of CA!

I'l let you know if the bearings wear the shaft or some other strange things happen!

[DethWshBkr]

I did put a heavy bead of CA around the bearing, and it was in the proper place. I am going to put three bearings on this new rebuild tube, with a light dab of epoxy. Again, the bearing did not move, that rubbing must be from inside the boom itself. I'll try to get a picture of the boom on the inside. Because the boom is not damaged, I am not going to disect it to see inside, as I will re-use it.

It's just a little interesting that the torque tube itself seems to have failed completely.

That cracking indicates metal fatigue to me. The slight bending in the torque tube, and the forces put on it by rotating so quickly very easily could have caused metal fatigue. I am hoping more support would prevent any issues.
I wish that tube was a little thicker though, it seems VERY thin.

[johnbs8]

Deth,

hobbicos TT support is top notch. any piec that broke irregularly on any of my X50's, ive gotten them replaced hassle free. They may ask for proof of purchase though. i bought mine on ebay and the store/user was authorized as dealer so all good. give them a call. my clutch bell broke in flight and they replaced no prob.

[rcflier1]

i wonder if we should pull the tube out from the rear and check once in a while. should only take a few minutes? might prevent a more $$ repair

[Elgyn]

Is the torque tube a common faill or a few isolated incidents? It's making me nervous about mt X50

[DethWshBkr]

I called Hobbico, and spoke with their tech guy, he said I am the first person ever to call in and say that a torque tube failed in normal flight. The only other issues, were from ground strikes, which make sense.....
I will see what happens on this rebuild.

[DethWshBkr]

Originally Posted by rcflier1

i wonder if we should pull the tube out from the rear and check once in a while. should only take a few minutes? might prevent a more $$ repair

I did that! I pulled the entire boom off, removed the tube, and checked everything out prior to this flight, due to the "noise". I could see NO scuffs or stresses on the torque tube at all.

[johnbs8]

so is hobbico taking care of it?

[DethWshBkr]

I already have parts on order, but they offered to send me some replacement parts. I will look her over hard and make sure nothing is seriously screwed. I'm not asking for a freebie or anything though.

[KouDy]

Do you think that as prevention for the crash it would be worth for us to add 2 extra bearings inside the tail boom?

[DethWshBkr]

Do you think that as prevention for the crash it would be worth for us to add 2 extra bearings inside the tail boom?

I am doing that. I don't see what it would hurt. I mean, it SHOULDN'T need it, but WHAT caused that failure otherwise?!

I will be putting the old one in the middle, and the two more coming half way from the center to both ends.
I do not think this is a "Problem", as again, the gentleman I spoke to said he never heard of this before. Regardless, the crack in the torque tube lengthwise indicates fatigue. For less than two FULL tanks on the tube, that's a concern though.

[Bob O]

Originally Posted by DethWshBkr

SNIP
I will be putting the old one in the middle, and the two more coming half way from the center to both ends.
SNIP

There's nothing wrong with two or three bearings, just make sure there is NOT an equal distance between all three. Just as with one bearing where you don't put it exactly in the center, multiple bearings should NOT be spaced evenly.

[KouDy]

What else do i need... Hmmmmm, getting just bearings... To justify faster shipping i need more parts

[YBNORMAL]

Originally Posted by Bob O

There's nothing wrong with two or three bearings, just make sure there is NOT an equal distance between all three. Just as with one bearing where you don't put it exactly in the center, multiple bearings should NOT be spaced evenly.

What is the reasoning behind that?

[JeffKollin]

My tail has done nothing but give me problems since day 1. I have gone from 1 bearing to 2 bearings and then to 3. I have tried to lengthen the torque tube using a 60 torque tube and still no luck. I would be soo happy to find a solution to why my tail is not smooth.. It holds fine in funnels, hurricans and tail slides but in a hover the tail twitches and drifts nose left. I have set mechanical in normal mode and played with gyro tapes. I am so disappointed with the torque tube version especially after reading of all the problems everybody else has been having. I had the tail control rod break on the 2nd flight due to a vibration that must still be hounding me. I hovered again tonight after changing torque tube and still not happy.

[Bob O]

Originally Posted by YBNORMAL

What is the reasoning behind that?

https://www.helifreak.com/showthread...82#post3761882

I never used more than one on my 450SEv3, 450Pro, 600LE, or Velocity 50.

[YBNORMAL]

Thanks! I ordered two sets of bearings from Tower the other day, I will have to install the second one when I get a chance. Kind of nervous about all this talk of TTs fatiguing........I have been reading up on what everyone else is doing to their Titan so that when it is go time all the bugs will be wrung out.

I wonder if a few short pieces of fuel tubing spaced along the length of the TT would help to dissipate some of the vibrations? Similar concept to the type of dampeners that bowhunters use on the bowstring?

YB

[NitroAl]

If you run one bearing set it biased to the tail and it should be fine!

[DethWshBkr]

Should be, yes. So then what caused my replacement to fail in the equivalent of two tanks of not hard flying?
Should be fine, I agree, but after seeing a failure such as I had, the little bit of work and cost to run an extra bearing or two puts my mind at ease.
Right now I have the stock one at 350mm (13.78") as the manual calls for, one at 152mm (6") from the nose end, and one at 171mm (6.75") from the tail end of the tube.

I do NOT believe it is a design flaw (single bearing), but I do believe I just got unlucky and got a bad tube. It happens. This is my insurance policy and my minds solution.