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Crashed? Discussion and Photos > Air Accident Investigator Reqd!
 
 
Jungle Bob
Senior Heliman
Location: Borneo, Malaysia

Okay, you decide because we can't agree. The heli, Shogun 400 electric, canopy off and being test flown due to recent alterations and a misbehaving tail (belt drive), Modified gear box, ali, (Microheli I think?). Tail is wagging and noisy. The hover- it is being hovered at about three or four feet...it is windy.....full battery, Spectrum set up. I (I'm flying it while my buddy watches) attempt a piro which happens very quickly (clockwise), much faster than this heli has ever done before. I return to the hover....suddenly there is an audible 'CLICK', LOUD ENOUGH FOR US BOTH TO HEAR ABOVE THE MOTOR!! We notice the heli is suddenly smooth, quieter and much steadier!! I land it to check. Nothing visible!! Took off again and all seems well. Try another turn and suddenly lose tail authority, nose in, loss of height and ditch (powered down). On inspection we see that the tail gearbox is broken (one of four supporting arms detached and one bent.) No other damage!
So.....did the accident do the gear box or did the gearbox do the accident????
10-22-2007 09:38 AM
 
 
redvtr1000
Veteran
Location: covington, GA

I work in the safety department for an airline if that qualifies...

Sounds like something went wrong, the click obviously wasn't normal and from the way you described it, something wasn't correct before the accident. Lets see some pics of the carnage focusing on the tail control system.
10-22-2007 08:53 PM
 
 
Jungle Bob
Senior Heliman
Location: Borneo, Malaysia

Wasser!!! The guys want to see some pictures of your broken gearbox. Like a true friend I broke his heli, gave it back to him and left the scene, ha ha (over to you buddy...again!)redvtr1000, you sound like you are in an excellent position to judge....I will abide by your decision in respect of culpability!
10-23-2007 10:45 AM
 
 
Wazzer
Heliman
Location: Kota Kinabalu, Sabah, Borneo



Hope this pic up loads correctly

Unfortunatly i have already rebuilt the heli with a replacement plastic gear box but here is the best picture i could take of the damaged parts.

This pic attached shows the damage we found on the tail gear box.

There was no other damage on the heli and the heli has since been hovered on its new gear box and is pretty smooth.

its a microheli item and usually pretty tough.

If you look closely you can see that the lower section of the broken side plate has been bent up wards as if something has struck it, but the is no marks suggesting a strike.

Taking the direction of all the forces acting on this tail gearbox we cant work out how this could have broken if it was not damaged in the cash itself.

As Jungle mentioned the heli went in on its side, spun round and ended up up side down the tail never came into contact with the ground at all.

We were lucky there was no other damage to the heli not even main shaft or feathering spindle.

hope you guys can help

many thanks Ben

Lama V3
Shogun (heavily Modded)
DX7 +401
soon to arrive Hurricane 550 WOOHOO!!!!
10-23-2007 03:31 PM
HOMEPAGE  
 
 
TrexRookie
Key Veteran
Location: San Francisco, CA

I went through TWO microheli tail boxes. One of them induced a strange vibration out of the blue. No crashes... Just flying moderate 3d. And then my tail started acting funny. I eventually took it apart and found the gearbox with one entire side essentially snapped off. Replaced the tail box immediately... and immediately crashed that one. And that was a loss as well.. Mind you, the machine work isn't consistent, so I did notice machining flaws that could have resulted in the initial failure.
10-27-2007 12:20 PM
 
 
Jungle Bob
Senior Heliman
Location: Borneo, Malaysia

Many thanks Trexrookie, you have added a bit of crdibility to my arguement......."your witness Wasser"
10-27-2007 05:02 PM
 
 
TankDirt
Veteran
Location: illinois

Maybe the shaft was bent and it just vibrated it until one side gave up?
10-27-2007 05:43 PM
 
 
redvtr1000
Veteran
Location: covington, GA

I would have to lean towards crash damage after taking a look at those pictures. It looks like a "shear" (quick impact forces snapped it right off). A good microscope would answer this difinitively, at least to the type of break which could give you all the answers you need as to how it occurred.

I would say impact damage though without going any further.

Wierd that you heard a noise in flight. Possibly something was binding up on the tail. I had my servo slide slightly forward on the boom and hadn't noticed it. Caused the tail to bind up and the heli went flying off around the corner of the house. Lost control and never saw it go in. Heard it whack though

Crash wasn't too bad, it crashed into an "elephant ear" big leaved plant if you know what they are. Bent flybar, main shaft, CY Radix's survived!!!!

How often is that going to happen
10-27-2007 06:46 PM
 
 
TrexRookie
Key Veteran
Location: San Francisco, CA

In the instance of my microheli tail case, my tail blades never even came into contact with the ground. the tail just started vibrating and didn't hold like it did when I first installed it. I inspected it by unbolting one side plate, and after unscrewing 3 bolts, it came off the tail. I then realized that there were TWO MORE bolts to unscrew to properly remove the pieces. I'd have to blame the first failure on bad machining. When I got the second tail, I figured I'd take the pieces off that and use them on the old tail case... Thought it'd save me some trouble by not having to install the entire tail. Not a chance. And that was when I noticed the tail pitch slider. Found out that it wasn't machined totally flat on the first tail. Second tail was fine. So I ended up having to Frankenstein the second tail unit, and of course, that went down on its maiden flight due to pilot error... guess I got too ansy to fly my new stuff.
10-27-2007 07:36 PM
 
 
Jungle Bob
Senior Heliman
Location: Borneo, Malaysia

So, still inconclusive! I might add that the tail did not impact the ground which, coupled with the loud audible 'crack' just before the loss of air time, made me come to my conclusion. Happy to accept other explanations though. I have a Zap 400 which uses the same gearbox and it seems to be sound. The tail shaft was transferred from the damaged gearbox to a stock unit we had lying around and does not appear to be bent or a cause of vibration. I test flew the 'stock box' with the same shaft, tail blade grips and tail pitch slider after the rebuild.....smooth as silk. Possible that Microheli box was damaged previously and the source of the original vibration prior to 'letting go'?
10-28-2007 03:57 PM
 
 
Wazzer
Heliman
Location: Kota Kinabalu, Sabah, Borneo

Thanks for all the input guys.

Trexrookie your problems sounded very much like ours in that a previously smooth tail developed a vibration.

This bit that is throwing us is that the vibrations seemed to instantly disappear when we heard the crack, but then fail. its all a bit wierd really.

I must admit i think that the tail box damage was a result of the impact as opposed to failures in flight, especially when you can see in the pics the lower of the two Spars on the rights side of the box has been bent up and the other has just snapped. looks like impact damage to me.

Jungle, Looks like we will have to agree to disagree!!

Thanks all

Ben

Lama V3
Shogun (heavily Modded)
DX7 +401
soon to arrive Hurricane 550 WOOHOO!!!!
10-29-2007 12:54 AM
HOMEPAGE  
 
 
vinver
Heliman
Location: Enfield,NS Canada

How's the bearings??

Here's my .02$,
If say a bearing was misaligned it could cause stress and tension on the shaft (leading to a winding/unwinding effect on the tail drive, hence the vibration,etc before the break. ( Once the sidepiece broke, the tension released and all ran smooth, until it just spit apart (unavoidable really given the appearance of the damage). My speculation was poor machining on the original parts introduced a tension into the tail gearbox, either due to a misaligned bearing or tail shaft, metal fatigue due to vibration caused the part failure, and once it broke the rest is history.
Vince
03-19-2008 10:16 PM
 
 
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