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HomeAircraftHelicopterAlignT-REX 700N › 700 Exploded today/POLL how many have had this happen??
01-17-2010 12:18 PM  8 years agoPost 181
RussJ

rrApprentice

lockport, new york usa

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No, I am not using any kind of spacer to fill in the gap in the feathering shaft. The only thing the gap in the feathering shaft does is help locate the bolt. Thats why align gives you collar bolts. The collar fits inside the gap. My bolts from align were not even straight, they were slight bent and had runout in them. The important thing is that the bolt and washer tighten up square to the bearing. With the align bolts this is not possible because of the bolts having runout in them. Also, if you use an allen cap screw bolt and washer, make sure the washer o.d. matches the inner dia. of the bearing and that the washer is kind of thick too. The thickness of my washers are about 1/16 . And go with a good grade tempered and hardened bolt like a 12.9 , no less than that. Do not use stainless steel bolts. This is working out well for me so far.

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01-18-2010 02:12 AM  8 years agoPost 182
PC12DRVR

rrKey Veteran

USA

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Here goes another one !!!!!!!! I just emailed QUK to see if they can help..

https://rc.runryder.com/t565013p1/

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01-18-2010 10:55 AM  8 years agoPost 183
rockrand

rrApprentice

west bloomfield mich

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Mine just exploded yesterday.
Same thing,a loud bang and that was it.This is not right.

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01-18-2010 12:17 PM  8 years agoPost 184
stuartmp74

rrApprentice

Gold Coast, Australia

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Hi Guy's,

I have Just bought a 700 LE kit and I am waiting for it to arrive.
I did some quick calculations on the forces on the bolt.

This is what I can up with.

Feel Free to correct any of the input values as I do not have my Radix 690 SB Blades Yet.

Single Blade Mass = 185g (Radix 690 SB)
Blade Holder approx. = 80g
Blade Bolt = 5g

Max Head Speed = 2200 used for Caculation purposes
(I will run at 1950)

Minor Pitch diameter = 4.773mm (Bolt that is snapping M6x16mm)

*************************************************************

Step 1. Calculate the force on the Bolt

Force on bolt = Rotating Mass X Radius to C.G. of Blade X
Angular Velosity in Radian/sec^2

Rad/Sec = Pi X RPM/30
Rad/Sec = 3.14159 X (2200/30)
Rad/Sec = 230

Force on bolt = 0.270 Kg X 0.435 mm X 230 Rad/Sec^2
Force on bolt = 6213 Newtons (This is 633 Kg)

Please note: This does not take into account any forces put on the bolt during the initial tightening.

***********************************************

Step 2. Calculate The Stress on the Bolt is.

Stress in Mpa = Applied force in Newtons / Area of Minor Pitch
diameter in MM^2
(pi*d^2)/4

Stress on Bolt in Mpa = 6213 / ((3.14159 X 4.773^2) / 4)
Stress on Bolt in Mpa = 6213 N / 17.892 mm^2
Stress on Bolt in Mpa = 347 Mpa

**************************************************************

Step 3. Calculate Safety factor.

Now I don't know what the grade of the bolt Align is using but.

a UNBRAKO metric socket head cap screws made to property
class 12.9 have a minimum ultimate tensile strength of 1300 Mpa

Ultimate tensile strength = 1300 Mpa
Yield Stress = 1170 MPa

So To see what type of safety factor these bolts would give use.

Factor of safety = Ultimate tensile strength / Working Load
Factor of safety = 1300 Mpa / 347 Mpa
Factor of safety = 3.75

Please note: This does not take into account any stress put on the bolt during the initial tightening.

************************************************************

Hmmmmmm Not much of a safety factor even with a 12.9 Grade bolt.

Maybe someone else who knows Engineering as well can check my calculations.

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01-18-2010 02:58 PM  8 years agoPost 185
PC12DRVR

rrKey Veteran

USA

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Wow ok I like it but So a grade 12.9 bolt is enough to cover the applied force, stuart you calculated a 3.75 safety factor, so thats 3.75 times the actual force, why would that not be enough of a safety factor? Thanks for doing that btw, any way you could come up with a torque value for tightening?

I just went to Lowes and they have a selection of 12.9 grade M6 hex socket bolts that range from 12-30mm length I went with 20mm and going to double the washer for strength. Is there something better than grade 12.9?

This has to be a better quality bolt than the align ones I'm assuming? Any input guys? I checked the Align bolts on a brand new feathering spindle I have, and they have a wobble in the head and runout in the head, visible to the eye,, yuck , Junk!!

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01-18-2010 03:07 PM  8 years agoPost 186
jschenck

rrProfessor

La Vista, NE.

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Don't you think it'd be a good idea to put a spacer on the bolt? Without that shouldered area the bolt would be allowed to flex on the end. Myabe JBWeld a properly sized piece of copper or brass tubing there?

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01-18-2010 03:22 PM  8 years agoPost 187
PC12DRVR

rrKey Veteran

USA

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I bought some hard nylon spacer that fits in the spindle, going to have to drill out the ID and cut it to length to allow the bolt to fit but it should provide some support.

The other guys that are using aftermarket bolts said they are not using any spacer so I don't know whats better? Is it really critical? hard to tell? Its a very short distance, will it really allow flexing of the bolt?

JB welding some brass tube sounds like a good option too.

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01-18-2010 07:35 PM  8 years agoPost 188
da_man

rrKey Veteran

Central NC

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I know XCell has been using an M5 bolt for 20 years without ever a problem. AN M6 like in a align trex 700 should have not problem. The problem is the Ultimate tensile strength of the bolts.

Another issue is fatigue. Generally after an infinite number of cycles or uses, metal is 50% as strong as it was initially.

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01-18-2010 08:24 PM  8 years agoPost 189
stuartmp74

rrApprentice

Gold Coast, Australia

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Hi Guy's,

3.75 is a value base on my calculations and the assumptions made within.

Please don't take my word for it that you have a safety factor of 3.75

Because there are other thing to consider.

If the tension on the bolt once torqued added a further 3000 Newtons or 305 Kg (I have no Idea at this stage)

This would increase the working stress to lets say 515 mpa

So the resultant safety factor would be 1300 / 515

Which is only 2.52

This does not include any extra forces applied during 3D flying.
This is just sitting on the ground with a head speed of 2200 RPM

I need to check up how to calculate the Torque value for tighten the bolt. etc etc

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01-18-2010 08:44 PM  8 years agoPost 190
Fernando

rrApprentice

Madrid

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The other guys that are using aftermarket bolts said they are not using any spacer so I don't know whats better?
I would recomend without the spacer, the head of the bolt should be enough support. The support for the bearings should always be the spindle itself so that the head of the bolt only support axial forces, never radial.

Any shim/spacer can shift axial into radial forces to the neck of the bolt itself. This could have been the problem of the explotions first instance, I do not know for sure…

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01-18-2010 09:22 PM  8 years agoPost 191
Thumpernator

rrKey Veteran

Senoia, Georgia, USA

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The support for the bearings should always be the spindle itself so that the head of the bolt only support axial forces, never radial.
Exactly!! And with these better bolts, you can tighten them down without the fear of damaging them in the process. That is, unless you are the "Hulk."

I trust these new bolts made in the good ole USA versus Taiwan crap bolts. Reminds me of when some cheap "Made in China" AN bolts got circulated within the aviation industry some years back.

Dave
I keep on thinking, but nothing's happening. Knuk, Knuk, Knuk

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01-18-2010 09:27 PM  8 years agoPost 192
jschenck

rrProfessor

La Vista, NE.

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I would still be concerned about that open space between the head of the bolt and the start of the threads in the spindle. Think about putting an 800 lb. pressure on one side of the bolt head it could move just a fraction. A bit of that and it'd fatigue. Put a proper filler in there and that can't happen.

Doing a bit more thinking about this I wonder if a copper "gasket" washer between the spindle and bolt could help out here. This would give a crush item and allow the force to be evenly distributed across the face of the bolt.

I still think the best solution would be a spindle that is threaded to the end and uses a normal bolt like every other heli I own.

EDIT: This is really concerning me - almost ready to ground my 700.

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01-18-2010 09:47 PM  8 years agoPost 193
Ladymagic

rrKey Veteran

South Korea

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Have a question. Have we polled to see exactly how many 700's have exploded due to the blade grip bolt failing? Have any one of you had your bolts fail on more than one ocassion? Maybe some could start a poll thread for this.

Maybe the first course of action should be to find that out. That way we can better asses whether or not this is really an epidemic. From what I've seen so far is this seems more like just a handful have encounted this unfortunate experience. Before this particular thread, i've never heard of this occuring so frequently. In fact, I was never really aware that I should keep an eye out for my bolts. I've not had the issue and I fly very hard around 1950 in FM2, maybe now i'm getting slightly paranoid. If in fact this really is a problem, it could end very badly for someone and I would prefer that not to be me.

This problem is hard to isolate. There are too many factors involved to really come up with the most intelligent solution. Factors such as the condition of the bolt before installation, how the bolts were installed, and most importantly, what variables actually were in play at the exact time of the failure. Things like air temparture, age of the metal, head speed, and over all flying style of the pilot are good to know too.

More simply, why are some bolts failing while others do not under similar conditions? My 700 has been very good to me and I have no complaints about any part of the kit. Everything is still orginal and I built mine almost a year and half ago. It was one of the orginal kits.

I'll keep checking in i'm interested to hear what you guys find out. Good luck and I hope this doesn't turn out to be real problem.

Maybe the best solution is to simply be aware that this could possible occur and to keep a close eye on that particular area for the time being. We need to pay more attention to the conditions during our flights for a while in case it happens so that we can let everyone here know. Maybe that will give better clues as to why.

Mellisa

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01-18-2010 10:32 PM  8 years agoPost 194
Thumpernator

rrKey Veteran

Senoia, Georgia, USA

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Maybe the best solution is to simply be aware that this could possible occur and to keep a close eye on that particular area for the time being.
The problem with that, Mellisa, is that you really can't tell if the bolt is defective by just looking at it. And remember, it all works great, up to the point where it breaks. So far, no one has reported an injury and I dread the day someone does get hurt because of this.

As far as a poll goes, it's in the title of this thread.
I would still be concerned about that open space between the head of the bolt and the start of the threads in the spindle. Think about putting an 800 lb. pressure on one side of the bolt head
JS,

The side loads aren't taken up by the bolt, it's all on the bearings. The only force the bolts have on them (unless I'm missing something) is tension against the head. It's not a side load. Also, even if the shaft was threaded to the very end, the way the threads are cut in the shaft and the bolt, there is still some play. That play is taken up when you torque the bolt.

I really don't think we need to worry about that small gap. Like you, though, at first I was concerned. But after looking at the whole assembly, I don't think it's a problem.

And where are all the Align Reps? Tell us what kind of testing or quality control Align does on their parts. Does Align make their own bolts?

Dave
I keep on thinking, but nothing's happening. Knuk, Knuk, Knuk

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01-18-2010 11:31 PM  8 years agoPost 195
rockrand

rrApprentice

west bloomfield mich

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Exploding Trex 700,most or all LE kits?
I wish Align would replace my Heli.I think it is just a bad batch of bolts,I see most or all are LE kits correct?

Rocky

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01-19-2010 12:18 AM  8 years agoPost 196
rudyy

rrElite Veteran

E. Amherst, NY

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So far, quite a number of same incidents have been reported. This is obviously a manfacturing defect. Guys, please check all your 700s and rectify the problem to prevent any fatal accident from happening.

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01-19-2010 12:42 AM  8 years agoPost 197
jschenck

rrProfessor

La Vista, NE.

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please check all your 700s and rectify the problem
that's the real problem, we don't know what to check for or how to prevent the failure!

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01-19-2010 01:01 AM  8 years agoPost 198
stuartmp74

rrApprentice

Gold Coast, Australia

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Why is someone from Align not commenting on this very important issue?

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01-19-2010 01:24 AM  8 years agoPost 199
PC12DRVR

rrKey Veteran

USA

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most or all are LE kits correct?
Mine is not an LE it is about a year old, and 20+ gallons of fuel, no crashes, all original parts.
This problem is hard to isolate. There are too many factors involved to really come up with the most intelligent solution. Factors such as the condition of the bolt before installation
Its not hard, these bolts are junk, wobbling side to side, runout in the head, its pretty obvious, and they are failing in the same exact spot, at the shoulder where the threads start. I have owned MA, Robbe,and built and flown the Kasama Srimok 90, they all use a straight threaded M5 bolt that never failed for me. EVER, I had over 55 gallons of hard 3D through a Millenium 3 and nothing ever let go, I crashed it. MA too, never had a bolt fail in ten years. They all used a high quality full thread bolt, and washer combination.
Why is someone from Align not commenting on this very important issue?
I agree, why ignore it? And I have directly emailed them and Alan Szabo and have been ignored.

And before anyone jumps on and says mine are fine,It does not matter if it is only a small number that it has happened to, or that it has not happened to you or anyone in your club, what if you are next?? Do you want to get hit anywhere with a 700mm carbon blade? Good luck to you if you choose to ignore it, its a big gamble.

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01-19-2010 01:35 AM  8 years agoPost 200
stuartmp74

rrApprentice

Gold Coast, Australia

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If it was a strength problem it would happen on your first flight.

But it seams it is a fatigue failure due to the head of the bolt not
being inline with the axis of the thread causing Bending Stress this repeated bending stress causes the bolt to work harden and BREAK

At this stage I am probably going to machine up a shouldered bush
insert it into the end of the shaft and then use a M6x16 Unbrako Cap screw 12.9

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