ALIGN 500 TAIL ROTOR BOLT FAILS: WARNING!!

[flydude]

I have the HK500 GT TT with all the vitals upgraded to genuine ALIGN parts (main gear & bearing, torque tube and gearing, metal hillier arms etc and the complete tail rotor hub assembly with Align CF tailblades) The reason I upgraded to the Align parts was that the original tail holder bolts sheared off on maiden flight before take-off was achieved

The Align tail kit was fitted along with all the other upgrades

2nd flight, actual flight and hover was achieved, all perfect

3rd flight, in hover at 20', the tail bolt sheared (AGAIN) and I couldn't control it, everything haywire due to only one tailblade left and heli rocking/spinning violently - like a very bad piroflip...

I now need to buy more parts, I want KASAMA as I will never trust Align for anything again

BEWARE THE ALIGN METAL TAIL ASSEMBLY FOR TREX 500
it doesn't work

[dyin2fly]

Originally Posted by flydude

I have the HK500 GT TT with all the vitals upgraded to genuine ALIGN parts (main gear & bearing, torque tube and gearing, metal hillier arms etc and the complete tail rotor hub assembly with Align CF tailblades) The reason I upgraded to the Align parts was that the original tail holder bolts sheared off on maiden flight before take-off was achieved

The Align tail kit was fitted along with all the other upgrades

2nd flight, actual flight and hover was achieved, all perfect

3rd flight, in hover at 20', the tail bolt sheared (AGAIN) and I couldn't control it, everything haywire due to only one tailblade left and heli rocking/spinning violently - like a very bad piroflip...

I now need to buy more parts, I want KASAMA as I will never trust Align for anything again

BEWARE THE ALIGN METAL TAIL ASSEMBLY FOR TREX 500
it doesn't work

does that mean your going to change your avatar ?

[Larry227]

That's not a rare occurence on that tail. I've seen a few or more posts about it in the 500 forum over the last couple of years. I went to the Kasama tail rotor over a year ago and never looked back.

[trickybit]

I have a conjecture, based on tail blade grip bolts snapping on 550E's. Maybe y'all can shed some insight.

The tail grips have "slop" when tightened down, that is, they move in and out a bit radially. When the tail spins up they'll be forced outward so the play is not actually a problem.

But I think a lot of people try to eliminate that play, as well as minimize the chances of the bolt working loose, by really torquing down on it hard, too hard. Thus over strained, they snap in flight.

Do you recall how tightly you cranked it down (if we're talking about the same bolt) and if you were trying to remove "slop" that just wouldn't go away?

Cheers,
Jim

[Vinger]

This happens due to over torqueing the bolt. As you had two occurences of it, maybe the fault is not Align, but the over tightening of the bolt. Been flying a TRex 500 since it came out and NEVER had this happen.

See the Trex 500 thread as there are a lot of more on this.

[bad007]

Originally Posted by Vinger

This happens due to over torqueing the bolt. As you had two occurences of it, maybe the fault is not Align, but the over tightening of the bolt. Been flying a TRex 500 since it came out and NEVER had this happen.

See the Trex 500 thread as there are a lot of more on this.

Dido Never had an Align tail come apart. Loctitie and snug the bolt. Over tightening weekens them, I run my 500 2500 - 2700 head speed.

[Wildcards]

Same thing happened on two different brand helis?? my vote is that it was overtightened, I have never had this issue.

[nbells]

Originally Posted by Vinger

This happens due to over torqueing the bolt. As you had two occurences of it, maybe the fault is not Align, but the over tightening of the bolt. Been flying a TRex 500 since it came out and NEVER had this happen.

See the Trex 500 thread as there are a lot of more on this.

+100000000000 on the over tightning ....... and the fact that you had it twice tells me your doing something wrong.

If your using loctite ... DO NOT tighten the hell outta the bolts .... just nip them up and leave the loctite to do the rest. If you have used the proper loctite, they wont come loose.

nbells

[michael503]

First, sorry for your loss.

Second, are you running metal grips? The plastic grips don't do this.

Keep in mind that the centrifugal force on a plastic tail grip at 3000 rpm HS, with a light carbon blade, is about 125 lbs. With a metal grip, it is higher.

I agree about the over tightening, and the 500 is not famous for shedding grips, but it has been known to happen. The 600s and 700s are more prone to it

The issue is deeper than that.

The 600 and the 700s, as well as some older Synergy birds are prone to this and is a two-fold issue. First, there is only one radial bearing, and second, the bolt threads right up to the hub. There are no exposed threads, so all of the force is concentrated directly under the bolt head. Because of this the bolts elasticity range is near zero and if it is defective, or weak, or stressed, it will fail.

Your options, IMO, are..
-get a set of plastic grips
-get an aftermarket set of grips with 2 radials and 1 thrust bearing
-get a longer bolt and add a spacer under the bolt head it give it some elasticity
-don't tighten the next bolts anywhere near as much and take your chances

Most people have good luck with stock and others --- they crash.

Synergy solved the issue years ago when they added a second radial brg to the grip. Align has recently followed suit, but have omitted the shim between the thrust and outer radial brg, causing binding issues (You'd think they could figure this out, since they do it in the main grips)

I have a buddy, as do many others who know what they are doing, and they have shed tail V1 metal grips before, and it was NOT due to over tightening.. although over tightening will almost certainly guarantee that it will happen. When this issue surfaced with the 700s, peeps figured the bolts were the issue, so they went to harder bolts. Guess what? They failed quicker. There is something about the lack of elasticity and the single radial design that does not play well together. Fixing either solves the issue.

Personally, if it were me, I'd just get a plastic grip set. I've been running one for about 500 flights now. They are about due for their 4th set of thrust bearings. They also weigh less, and require less force for the tail servo to move (TR effect)

There has been a LOT of debate on this subject in the 700 forums.

[extrapilot]

Guys

In general, this over tightening theory doesn’t make sense for a practical install. Look at the numbers. For an 11.9 2mm bolt, it can be torqued to .15nM (assuming a reasonable coefficient of friction (read: wet with loctite)), and still have a margin of 1.4kn. At operating speed, the stock 500 grip/blade impose a load of approx 1kn, leaving a 40% margin.

.15nM is a pretty good chunk of torque- basically 4.4 lb/in. For any stock 500 grip I have touched, you put anything like that level of torque on it, and the grip bearings are beyond notchy. Im not saying someone is incapable of putting that much torque on a grip bolt, but I have had 3 failures on a 500 tail bolt, and NONE of them had that level of torque- they were simply snugged with the type of torque you generate with two fingers on a small hex driver (approx 1lb/in, or .04nM).

When you look at the bolts that fail, every one I have seen personally or via imagery show a fracture pattern parallel to the boom- which is to say, from bending fatigue.

And to the post that suggests grip play is not a problem- well, that is false. If you do the math, you will realize that it does not take a huge amount of force to cause a couple degrees deflection. It only takes about 2lbs to deflect the grips 1degree at operating speed. When you consider that the blades have no flap hinge, in forward flight they are loading and unloading that bolt at 150hz, and that is not good from a fatigue perspective.

The reality is that the base design is marginal. They should not have used a 2mm bolt, and any radial play from slop in the hub/thrust washers/grip body just compounds the problem by adding stress on that bolt, and causing stress reversals in flight (fatigue).

[flydude]

thanks for the interesting and helpful reply, it beats the heck out of "you did it" in the rest of them - here's more detail:
the VERY first time the tail holder bolt sheared was on my living room floor when I was first assembling it, just touched it with the allen screwdriver and bang!

after that I was VERY careful putting them on, when it next sheared on spin-up (both bolts went) it was with ALIGN bolts from my spare stuff

having thought I had learned the lesson, I then got the ALIGN PRO tail pack, using the bolts that came with it, thinking they should be fine... I can tell you I was more worried they would spin out they were so loosely put in, lots of loctite - the slop in this tail is unbelievable (for a 'pro' version) and with this loose setup it was worse, but it STILL sheared

- anyway, in my opinion, the tail design does not support the side-to-side (lateral) movement of the blades, the carbons are very stiff too and probably transfer all that force right to the root - therefore flexing the holder which in turn, bends the bolt back and forth until fatigue occurs and it shears...

All I know is it's a weak design with a bolt that is too small to do the job, I don't care if headspeed/tightening could be the problem too, it starts at the designed heart of the thing and it's costing me money

NB: if it IS overtightening, how am I overtightening it when any attempt to even get the bolt snug, results in this badly machined tail notching up immediately, any tighter than finger tight and the holders have siezed up, unable to turn at all?
I have also built these things for 5 years now, I like to think I've learned a little about bolts

does ANYONE know of a different design that fits the 500, besides the Kasama which seems to be unobtainable in the UK..?

BTW here is a similar post with a great solution- I think the poster's name is pxprep or something
Is anyone in the UK capable of making these? there's probably a market by now

""My 500 is a genuine Align and 'The exploding tail' issue happened to me twice. After it happened for the second time (collateral damage was severe both times) I decided to do something about it. This is over one year ago and I think that it will never happen again.
If you have acces to a lathe this mod can make the problem go away permanently: http://perweb.dk/HaleMod500/Index.htm
The thread is 3mm and I put in an extra ball bearing.
Another benefit is that there is no slop because it can be adjusted away by means of the self locking nut.""

thanks for the replies folks keep'em coming
cheers
Fly

[michael503]

yeah, I looked at the extra bearing solution, but the issue with it is that you can no longer fold the tail blades without damaging the blade root.

Seriously, the cheap plastic align grips don't shed bolts. Go figure.

[extrapilot]

My plastic grips failed (snapped a bolt)- hence the switch to metal, which failed twice...

[michael503]

well, shucks. There goes that theory

[JesusFreak]

Originally Posted by Vinger

This happens due to over torqueing the bolt. As you had two occurences of it, maybe the fault is not Align, but the over tightening of the bolt. Been flying a TRex 500 since it came out and NEVER had this happen.

See the Trex 500 thread as there are a lot of more on this.

Ditto

[koppterx]

another sound the alarm thread....3 600s, 2 700s, 2 550s, and of course a 500 lead me to conclude that the design is fine. yes, there will be failures but the number is so small relative to the number flying that in no way can it be concluded that there is an inherent design flaw.

sorry about your bad luck...fix it and fly.

[el guapo]

Originally Posted by flydude

NB: if it IS overtightening, how am I overtightening it when any attempt to even get the bolt snug, results in this badly machined tail notching up immediately, any tighter than finger tight and the holders have siezed up, unable to turn at all?

this is a red flag.... the bolt should bottom out on the hub, there should never be any tension on the bearing.. never.

are you putting in an extra washer or shim, or using a clone hub?

read this post if you want to learn....
https://www.helifreak.com/showthread.php?t=379423

[toonttm]

My foot is in the 'bolt over-torqued' camp (yes, I did read your response about putting the bolts in 'gently'). I have lost 3 tails on my 500, one very spectacular incident threw the entire metal tail directly at me, this was after the plastic tail unit had exploded due to the same reason. I have had better luck by not forcing the bolt in so tight and praying, maybe it was the praying?

I do think that the Align bolts are weak. They seem to round heads or break very easily. I have gone and bought a set of MIP drivers and I am hoping for better luck. I have tried some stainless bolts and they seem worse, is there any type of bolt that is stronger?

[extrapilot]

Originally Posted by koppterx

another sound the alarm thread....3 600s, 2 700s, 2 550s, and of course a 500 lead me to conclude that the design is fine. yes, there will be failures but the number is so small relative to the number flying that in no way can it be concluded that there is an inherent design flaw.

sorry about your bad luck...fix it and fly.

When you have a configuration that repeatedly demonstrates a single (unintended) failure mode, that is by definition a design flaw.

This is simple math, mate. The 550/600/700 run 3mm bolts, which have a rated strength something like 250% higher than the bolt used in the 500. You would have to run your 700 at a headspeed of 2600 to see its tail safety margin drop to that of a typical 500. Add to this, the 550/600/700 stock hubs are not stepped (read: are not the same design).

[Heli G]

Two schools of thought given the discussions I have seen, 1) overtightenng the bolts and 2) the quality of these bolts vary causing pre-mature failure in some which is aggravated by torque on the bolts.
I've never had a problem with mine (using the metal tail) flying hard 3D, but have also substituted the stock bolts with 12.9s as an extra precaution. I also agree there's slop in the stock tail, but the new V2 tail is really tight and smooth.