Jesus bolt sheered

[Bamboo]

Yesterday while powering up i heard a kind of chaffing but it soon went and took off to hover. It hovered well so i took off again but this time it shot up like a bat out of hell and i couldn't control it. I cut the power and it landed in the tree tops. Now i believe that anything that happens is your own fault but it does not stop you having a post mortem. I was lucky to get it down. On inspection the blade had cracked and at first i thought the servo had gone but not so sure now. The last one was the Jesus bolt had sheared off. Not come loose but broken leaving the bolt and nut still in place. What could have caused it? I can only think the shaft had done it but i can’t see how unless the bolt was just weak. I know i will get a quick answer which is why i am in here...

By the way all main gear was fine?

[Si Goodchild]

Had my first Jesus bolt shear the other day with my Synergy during a minor prang. In my case the auto hub had seized so the sudden stop of the blades would have transmitted a large force to the bolt. You tree-top landing would have probably done similar.

Si G

[David Drew]

If it was loose the constant loading/unloading may have simply cut it in half!

[Bamboo]

it had loctite on it but i guess that could have been the issue with the tree. I have seen many just put any old screw in there to hold it although mine was in the align kit.

Still if it was lose then my fault i will be checking that before flight now....cheers

[Si Goodchild]

Nah! Stick a proper bolt in there and screw it up tight with a nylon nut then forget it - jobza goodun!

[crash-test-tomo]

I had one let go during flight on a 1 month old uncrashed 450x a few months ago, I have also spoken to another member over the last few days who had the same thing on a 300x. Mine has given me no end of bother since

[French Paul]

Hi guys, the Jesus bolt on any heli should or would be specified in the build manual that it's a serviceable part.
it takes a beating every flight and should be changed regularly.
The 300x and 450x are both prone to extra vibrations as was the 400 & 450 3d because as you'll notice the ail servos are a little too small to be tight together in the mounting square/frame gusset and as such don't brace the top of the frame as designed and never rectified!
push your mainshaft back and forth and you'll see the anti rotation pin move in and out of its guide!
a cheap mod is an old bank card wedging the servos or a lynx carbon frame!
These helis can and have snapped mainshafts in flight because of this!
What blade goes up will come down, but I'll always be thankful of the education they provide in and out of the air :-)

[hedge]

weired I can only assume the main shaft was slipping on the sheared bolt so you where not getting any power to the head, this meant you where not taking off so you had gone full collective trying to lift off, then it all suddenly caught, gripped and well shot up... My old blade 400 used to shear Jesus bolts after a couple of crashes just keep an eye on the both in future

[Varelco]

i. I have seen many just put any old screw in there to hold it although mine was in the align kit.

You need to use a shouldered bolt for the Jesus bolt. A regular full threaded bolt regardless of its grade won't have the same shear strength as a shouldered equivalent.

I've never had one fail but I tend to replace my jesus bolts after a crash. If you haven't hit the deck then they should last for a long time.

[Grumpy]

You need to use a shouldered bolt for the Jesus bolt.

FWIW.. A shoulder bolt is one that has a larger diameter shank and smaller diameter thread, so there is a step (shoulder) between the two different diameters. You wouldnt usually use one of these as a Jesus bolt.

I think what you are looking for is a straightforward 'bolt' . A bolt has threads over only part of it's length the rest will be plain shank, usually it's fitted with a nut. If it is threaded full length then it's called a screw, usually used for tapped holes.

[Varelco]

Yeah you're right my mistake!

[helijohn]

A bolt has threads over only part of it's length

Don't know if I agree with that.

To the OP I have had a jesus bolt shear just with regular use. Some of these weedy things in kits worry me to death.

[dillwhacker]

Remember that if the head Jesus bolt partially shears, and allows the head to slide up a bit, then the remains of the Jesus bolt grip again, it will have screwed up your collective pitch settings...
Agreed - a bolt has partial threads, a set screw is threadded all the way. Bolt is stronger when used as a Jesus bolt.
I have had them fail several times in flight on Trex 500s, prolly from re-using them after a crash...