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HelicopterMain Discussion › 2nd Mysterious Bent Main Shaft
07-13-2008 01:52 AM  9 years agoPost 1
DSW

rrApprentice

Oviedo, Florida​32765

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For the second time my heli bent the main shaft without hitting anything.

1st time, I went into FLight Mode #1 with a MultiGov set to 1800 rpm. The heli spooled up, began to violently shake. I shut it down, but not before bending the main shaft, spinlde, tail boom. I thought maybe the blades were not tight enough and swung back under the torque of the engine causing a seriou out of balance issue.

2nd time, after the replacing the mian shaft, spindle, tail boom, and removing the MultoGov; I started in normal flight mode to check out the blade tracking, all good, hover seemed stable. I decided to check it out in Idle up 1, engine spooled up, heli about 1 foot of ground, began a violent shake, I hit throttle hold, shut it down, but the main shaft was already bent.

The blades were checked on digital scale.
Entire head (blades attached) statically balanced.
Blades:Maverick G5 600's
Hyper 50

What am I missing??

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07-13-2008 02:08 AM  9 years agoPost 2
Dood

rrProfessor

Wescanson

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...

  ▲
▲ ▲

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07-13-2008 02:24 AM  9 years agoPost 3
tchavei

rrProfessor

Portugal

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Balance...

The only way I can see a mainshaft getting bend is due to something seriously out of balance.

We don't know what heli... it could also be a bad batch of mainshafts... somebody could have forgotten to harden them...

Tony


--------------------
"Perfection and patience usually walk side by side..."

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07-13-2008 03:30 AM  9 years agoPost 4
DSW

rrApprentice

Oviedo, Florida​32765

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The complete rotor head was statically balanced on a Du-Bro Balancer with and without the blades attached. The blades were also matched for root to tip CG and weight, as were the flybar paddles.

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07-13-2008 04:11 AM  9 years agoPost 5
Red-Rx7

rrApprentice

Olathe, KS - USA

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Dave,

I find this very odd.

PM user name "jbeech" and tell him of your issue. He will take care of you on this...

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07-13-2008 04:37 AM  9 years agoPost 6
David Blain

rrKey Veteran

Mt. Dora, Florida​(USA)

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How about this--
- What manufacturer of Main shafts are you using??
- Which helo the Raptor or Pantera??
- Are you using a dial indicator when you install the shafts
to check the lateral run out? How much is it at two points??
- Could be worn a worn frame that holds the bearings on the
Raptor or misaligned bearing allowing the lateral main shaft
run out.... I've seen that before!
- A perfect balanced head or not, IF that Main shaft doesn't Spin
on a true axis (or too much lateral run out) then it will transfer
it directly to the rotor head assembly.

Let us know....

Pull-n-Pitch

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07-13-2008 12:45 PM  9 years agoPost 7
DSW

rrApprentice

Oviedo, Florida​32765

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Didn't see it during inspection, but I beleieve I've found the problem. The upper main shaft bearing was coming out of the bearing block. I thought I used some CA to secure bearing during construction, but maybe It slipped by me.

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07-13-2008 02:05 PM  9 years agoPost 8
f14tomcatfreak

rrVeteran

rochester,ny us

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thats the culprit good job

shut up and fly

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07-13-2008 02:25 PM  9 years agoPost 9
Yug

rrMaster

UK. Herts

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The upper main shaft bearing was coming out of the bearing block
I'm puzzled as to how this could happen because even if it was a loose fit in the block, the mast collar would prevent it from escaping

Vegetable rights and Peace

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07-13-2008 02:59 PM  9 years agoPost 10
tchavei

rrProfessor

Portugal

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Maybe its mounted upside down?

And the proper way to secure a bearing is with threadlocker (unless its a plastic bearing block and then not even CA will help you)

Tony


--------------------
"Perfection and patience usually walk side by side..."

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07-13-2008 03:21 PM  9 years agoPost 11
ofir

rrApprentice

tel aviv - israel

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In my opinion, bad synchronized flips can bend the main shaft.

My name is Ofir and I am a helicopters addict...

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07-13-2008 10:41 PM  9 years agoPost 12
DSW

rrApprentice

Oviedo, Florida​32765

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Yug siad
[quote]"the mast collar would prevent it from escaping"

I feel like Homer Simpson, I had the mast collar between the top and middle bearing blocks.

When all else fails, look at the directions. Next time I'll look a little closer at the assembly illustrations.

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07-13-2008 10:47 PM  9 years agoPost 13
petmotel

rrKey Veteran

DeKalb, IL.

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I feel like Homer Simpson, I had the mast collar between the top and middle bearing blocks.
DOH!!! ROFLMAO

Mighty kind of you to fess up. That's the MANLY thing to do.

Jay

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07-13-2008 11:25 PM  9 years agoPost 14
tchavei

rrProfessor

Portugal

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I've seen guys installing the middle bearing block the wrong way (ie right side up instead of upside down) but installing the collar below the top bearing definitely qualifies to enter the Homer Simpson Heli Contest 2008

I'm glad you found the problem though... what sucks is when we don't find the culprit. Congratulations.

Tony


--------------------
"Perfection and patience usually walk side by side..."

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07-13-2008 11:52 PM  9 years agoPost 15
DSW

rrApprentice

Oviedo, Florida​32765

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OK, I'll start it "Homer Simpson Heli Contest 2008" in a new post.

Thanks for all the replies.

Dave

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07-14-2008 02:52 AM  9 years agoPost 16
petmotel

rrKey Veteran

DeKalb, IL.

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installing the collar below the top bearing definitely qualifies to enter the Homer Simpson Heli Contest 2008
Watch it now, that's the proper place for the main bearing block on a Knight 3D ya know!

Jay

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07-14-2008 03:00 AM  9 years agoPost 17
tchavei

rrProfessor

Portugal

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Hum.. really? A friend of mine has one but I never noticed the collar being there... I will check tomorrow

Anyway, I was obviously kidding. I did things just as stupid in my life

Tony


--------------------
"Perfection and patience usually walk side by side..."

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07-14-2008 03:23 AM  9 years agoPost 18
petmotel

rrKey Veteran

DeKalb, IL.

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Hum.. really? A friend of mine has one but I never noticed the collar being there... I will check tomorrow

Anyway, I was obviously kidding.
Well you're welcome to check, I own almost as many 3Ds as you have Vibe 50s, you can take my word.

I was well aware you were joking, my post was obviously a poor attempt at levity!

Jay

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07-14-2008 09:20 AM  9 years agoPost 19
tchavei

rrProfessor

Portugal

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I'm going to check to see if he mounted it wrong, not to check if you're right

Tony


--------------------
"Perfection and patience usually walk side by side..."

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07-14-2008 09:55 AM  9 years agoPost 20
Yug

rrMaster

UK. Herts

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It's sometimes beneficial to put collars on both sides of the bearing. A bit of insurance if the jesus bolt fails.

Vegetable rights and peace to lentils

Vegetable rights and Peace

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HelicopterMain Discussion › 2nd Mysterious Bent Main Shaft
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