Predator T.R Gear box failure during flight.

[tuber]

During an easy flight just doing lazy 8’s the tail rotor gear box left the boom… needless to say I crashed. During post crash I found the little bumps on the gear box that go inside the boom were both sheared off. This means the TR box was forced off as apposed to having fell off. All gears were fine in both TR box as well as the main gears all bearings were good. In short I can’t see why this happened. Anyone care to offer an opinion?

[marked23]

That's weird. Can you tell if the bumps were sheared off by torque (around the shell radially) or by tension (popping the tailbox straight off the end of the boom)?

-Mark

[tuber]

I think it popped straight off as the tube was not twisted. The bumps on the gear box were just sheared right down to the sides. No bump left on the gear box. Holes is the tube were also torn out as well.

Randy

[DebianDog]

Almost sounds like it locked up, if the holes were torn out of it. :dontknow

[tuber]

Yes it does. I can't find anything else that could be the problem. The "T" on the end of the drive shaft was missing broke completely off. But not sure if this was done during flight or when it crashed as the drive shaft was full of dirt.

Randy

[WillJames]

ANy chane a previous tail strike could have sheered off the knobs then it failed a short time later while flying? I ahve seen this happen to a Raptor before by hitting my tail fin on teh ground during an auto, then on the climbout for the next auto the tail box slid off the boom as the knobs had been sheered off.

[Rodney]

Hitting the tail on the ground could have caused it. But I have had them leave the boom as well. Come to find out after talking with John Benerio, it is a vibration
problem in your tail. Either a bent output or input shaft, I have bent the input shaft and not noticed it until after rebuild. The vibration causes the boom to crack and fail thus letting the box come straight of the end and breaking the nipples the are molded on the box as well. Did you wrap your boom with special century Boom Sizing Tape, other words know as electrical tape. That helps it grip better and keeps it from moving for me.

[tuber]

Rodney,

Thanks for this information. This makes total sense as I did notice a vibration on the rear stabilizer fin that wasn’t there before. This was the second flight after assembly from shipping. I didn’t give it much thought. I found the steel hub on the tail rotor was bent. I didn’t notice if the out put shaft is bent. I will check that again just to be sure.

Thank you. I believe what you said is exactly what happen. I have an order in at Century……

Randy

[Rodney]

Glad to be of help. I learned that just the way you did. I lost the whole box in flight.
While at Ircha a met John Benerio he told me that the booms were cracking due to Vibration. Since then I have had no tail problems. The new box is coming out real soon, I think they are printing the instructions then they will be released. I built one today and have to say it is a nice peice of work. If you gotta have bling then try one out. Part number CN1006

[DebianDog]

Umm I am weak for bling.... :cool: