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Old Apr 23, 2013, 02:47 AM
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This is what happens when your rotor falls off the helicopter in midflight.

Was doing mild pitch pumps and I heard a metallic POP, about a second later the rotor disk appeared to collapse and the helicopter dropped like a rock from about 100 feet up. This happened at the top of a pitch pump.

I barely had time to hit throttle hold before it hit. I found it sitting in the grass on it's skids with the rotor head sitting next to it. What wasn't apparent as it fell was that the rotor head had completely separated from the airframe and it free fell 100 feet to the ground with the rotor landing next to it. It appeared to have landed squarely on the skids. I wouldn't have thought even gorilla gear could survive that.

I believe what happened was that at some point during the pitch pumps the jesus bolt broke, then when the hub became unloaded at the top of a pitch pump what was left of the screw came out and the head came off the shaft a moment later. I really don't see how it failed though as I don't fly hard 3D. From now on I will be replacing the jesus bolt every 200 flights or so.



The shaft collar slipped when it hit the ground, the mainshaft is also bent. Probably caused by the force of the "landing". Gorilla gear is slightly bent but still in one piece and can be fixed by boiling and it and then reshaping.



Gouge in the swashplate and the bearing is also gritty so it needs to be replaced. Time to buy another Chaos 500 swash, at least they aren't expensive. Main gear has half a tooth missing and there is some scraped plastic on the auto rotation gear where it hit the edge of the frame when the collar slipped. Helioption single piece mainshaft block is undamaged and the main bearings are fine. One of the canopy locks is also slightly bent and will have to be replaced.



Swash driver arms are both bent and the loops on the plastic radius arms were ripped in half when the head came off. One head link is also completely missing. Feathering shaft is still true and the blade grip bearings are fine. There is a small scratch on each of the pitch control arms (no idea what caused that) but they are otherwise undamaged. Blades survived and are undamaged.



The rotor somehow managed to hit the boom. Boom seems to have slipped forward slightly because the belt is now loose. The tail rotor shaft is slightly bent even though the tail doesn't appear to have hit anything. As with the mainshaft this was probably caused by the sudden deceleration when it landed on the skids.
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Old Apr 23, 2013, 10:39 AM
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Could have been much worse, looks like you'll be back up pretty quick...

Was it a shouldered bolt for the Jesus bolt? You should never use a fully threaded bolt for a Jesus bolt....
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Old Apr 23, 2013, 10:59 AM
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What helicopter? Did you use the stock bolt that came with the heli?
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Old Apr 24, 2013, 04:07 AM
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Quote:
Originally Posted by aaronredbaron View Post
Could have been much worse, looks like you'll be back up pretty quick...
There's more damage than I first thought. The battery tray is bent and the left frame has stress fractures in it. The canopy locks turned out to not be damaged, it was only the screws that were bent. I was planning on stretching it to swing 520mm blades which involves a new head so I'm just going to wait for those parts to arrive before working on it. I had a backup set of frames laying around so that won't be a problem.


Quote:
Was it a shouldered bolt for the Jesus bolt? You should never use a fully threaded bolt for a Jesus bolt....
It was a shouldered bolt, the stock one that comes with the shaft. I have no idea why it broke like that.


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Originally Posted by rotoraddict View Post
What helicopter? Did you use the stock bolt that came with the heli?
Trex 500 with standard sized servos, the bolt was stock.
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Old Apr 24, 2013, 05:14 PM
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The broken frames are fixable, the extra bridge at the bottom of the motor hole is cracked so I'll just swap them with another set I have remove those bridges (so they are like normal Trex 500 frames) and set them aside as backups.
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Old Apr 26, 2013, 08:29 PM
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What happens is you were s$iting bricks oh I am sorry s$iting rocks lol! Christmas Vacation.
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Old Apr 26, 2013, 10:22 PM
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Originally Posted by mhills51 View Post
What happens is you were s$iting bricks oh I am sorry s$iting rocks lol! Christmas Vacation.
Hmmmmm..... I danno..Playing detective here. It looks like he just forgot to put the bolt in and after three months he tried to fly it. ~ The swash driver arms are bent because they were the only thing driving the head. Also the head would of been at least 50ft from the crash.
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Old Apr 28, 2013, 11:58 PM
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Good ol Jesus bold snapped form being over tighten or excessive wear
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Old Apr 29, 2013, 03:59 PM
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Originally Posted by Dejavu*Xion View Post
Hmmmmm..... I danno..Playing detective here. It looks like he just forgot to put the bolt in and after three months he tried to fly it. ~ The swash driver arms are bent because they were the only thing driving the head. Also the head would of been at least 50ft from the crash.
This is my main helicopter and I have been flying it regularly, also I heard the bolt break in midair (the loud pop) I didn't even know the head had come off when it fell, only found out when I walked over to where it crashed.

Quote:
Originally Posted by Dejavu*Xion View Post
The swash driver arms are bent because they were the only thing driving the head.
Without the jesus bolt the head isn't being driven by anything. I'm pretty sure they bent when the head came off the shaft. The plastic radius arms were also torn in half.

Quote:
Originally Posted by Dejavu*Xion View Post
Also the head would of been at least 50ft from the crash.
I would have thought that too but it wouldn't be the only time an accident or mechanical failure happens in a weird way that you wouldn't expect.


Sequence of events:

Pitch pumps, at the top of a pump I bear a loud pop and I know something is wrong. So I stop everything thinking to myself "what just happened?" and getting ready to bring it down fast. Before this can happen (about 1-2 seconds passed since the pop) it drops out of it's hover and I hit throttle hold as it falls.

As it starts to fall I see one of the blades turning to about 80-90 degrees, I didn't think of this till later but the only way to "see" it is if the blade were stopped, which must have been the case. I remember thinking at the time that it looked like the rotor disk "collapsed" (though the blades were straight out), I didn't really understand what I had seen till I thought about it.

Here is what I think happened. As the head pulled up the links pulled positive collective on the blades which increased drag and stopped the rotor because nothing was driving it. It still had just enough upward force to pull the links and swash drivers off, but not enough to go far (it wasn't actually turning at this point)
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Old May 28, 2013, 02:08 PM
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That is an amazing story. I hope to NEVER see it in person, especially if I have my fingers on the sticks. I would need to go home for a change if it does happen to me.

ROG

ps sounds like the reflex flip to TH did not help much. maybe a ballistic chute is what we need for our machines in case this happens again.
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Old May 31, 2013, 11:15 AM
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The fact that you were able to see your blades stop spinning reminds me of a friends one way bearing issue... does your one way spin freely? If not, the one way stopping the spinning of the head could have caused the Jesus Bolt to snap due to excessive pressure... Then everything else would be collateral damage...
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Old Jun 04, 2013, 10:16 PM
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Originally Posted by mrmj2u View Post
The fact that you were able to see your blades stop spinning reminds me of a friends one way bearing issue... does your one way spin freely? If not, the one way stopping the spinning of the head could have caused the Jesus Bolt to snap due to excessive pressure... Then everything else would be collateral damage...
One way bearing is perfectly fine (it's a SAB Goblin bearing so quality is not suspect). I'm pretty sure what happened was that the hub was freewheeling on the shaft while the links dumped a huge amount of positive pitch into the rotor disk as the hub and airframe separated, which stopped the blades due to air resistance.
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