N5 - Inflight failure - Preflight check warning!!

[Britflyer]

Well I have had failures in the air before, but not seen anything like this before. The N5 design like the N9 and a few others does not tolerant play in the mainshaft (as you can see in the pics)!

This was about my 8 flight and it didn't last long! So far during the 8 flights I have had to remove play in the mainshaft twice, only a small amount that was never noticeable in the air but on the ground. Which gets be wondering if my locking collar is abit oversize.

Well you can see from the pics I lost tail and main drive, and as the swash moved it broke the antirotation guide, so I lost cyclic and pitch control too, in the air!! So about all I could do is hit the hold and watch it go in!!

It's one of the few bad bits about the design. Clearly play developed quickly, I'd only been flying about 20secs and it was enough for the shaft to move upwards and shaft pop out the bottom bearing and then the upper bearing popped out the upper bearing block. I've stripped the heli abit, and the mainshaft collar has moved but it wasn't what I would call loose like I was expecting. I couldn't move it by hand and the bolt was tight.

So I suggest you check your mainshaft for play before everyflight. I know I did before this flight and there was none. but still it happened. And I will be in the future if I decide to fly it again!!

It's going to need a full strip and rebuild as the frames are damaged in various places as a result of the mainshaft moving and need quite a few bits to but it right!! Not a happy bunny ATM!!

Paul

********* Thread Update ***************

Looks like the contributing cause has been established, see post 27 onwards of this thread:
http://www.rcheliaddict.co.uk/synerg...tml#post500267

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

[Kwickkwack]

Does the N5 have a recess in the main shaft where the collar fits? (never seen one) if not, it may be worth turning one in or dimpling the shaft with a pilot drill on assembly (if possible) where the grub screw goes, that looks a nasty crash and I feel you mate.

[Jamin_00]

Holy crap, thats not good.

Hope you get it back in the air soon.

[Tim Procter]

Damn that's a poor design.

Having a dumb thumb moment I can live with, Stupid mechanical faults like this really gets to me.

Hoping you get it fixed soon Paul. More expense that is not needed.

[jamiem]

Ouch! I've not had any movement appear on mine at all since building it, and I've put 44 flights on mine now. Will definately keep an eye on it though

[moonmanflyer]

Oh Paul thats not good at all, hope you get it fitted soon and is it the collar that stops it coming out the bottom bearing block? on others if it does come loose, yes you will get some travel but only a mm or 2

[rspblake]

This is not a pop at your building, Paul.

But surely the main shaft slipped because the locking collar was not locked... main shaft would lift up and everything would move..

Check the collar not cracked! thinking back we had a knight do the same thing 3 year back..

Whether its a bad design is debatable, it is one of the problem lockings from the underside..

Its quite important the main shaft is free of oil and so is the collar..in the area where it sits, I made sure the on the knight's a little locktite was used or a 3rd bearing to stop this if you was going to beat the crap out of it..

Agree a recess is a good idea.. thats something the Beam E4 uses..

[squeaky pete]

N5 - Inflight failure - Preflight check warning!!

I didnt think it was possible to move that far if it came loose, i thought the main gear wld bump the frames 1st

[mattie-lodge]

Its interesting because when I was building mine I was a little concerned about this locking collar. I remember my knight one was always coming loose. It used to really pee me off. However I've not had any probs with the N5 as of yet, I check mine every flight because I am slightly paranoid about aswell !!!!

Thanks for the heads up though Paul and really sorry to hear about your heli dude.

[moonmanflyer]

Is it that there is need for an additional spacer, so that if the collar does come loose the main shaft and gears will only move a bit

[Britflyer]

This is not a pop at your building, Paul.

But surely the main shaft slipped because the locking collar was not locked... main shaft would lift up and everything would move..

Check the collar not cracked! thinking back we had a knight do the same thing 3 year back..

Whether its a bad design is debatable, it is one of the problem lockings from the underside..

Its quite important the main shaft is free of oil and so is the collar..in the area where it sits, I made sure the on the knight's a little locktite was used or a 3rd bearing to stop this if you was going to beat the crap out of it..

Agree a recess is a good idea.. thats something the Beam E4 uses..

Yes clearly the shaft has displaced becaused the collar has slipped excessively and that is either a builder error or failed collar or undersize collar.

Either way the machine is pretty knackered and in the words of one of my Clubmates straight afterwards, 'Bet you wish you hadn't sold your Trex700 now Paul! :P' No kidding!


My post was to highlight the extreme possibilities of any play in the mainshaft as with most of the machines on the market this could simply never happen by design. As Pete pointed out I was shock that this could even happen, the maingear would hit the frames first before this happened surely.

Another suggestion might be to CA the bearings into the blocks, but I don't think that would be enough to stop it if it was going to happen anyway.

Paul

[Britflyer]

Is it that there is need for an additional spacer, so that if the collar does come loose the main shaft and gears will only move a bit

Yes, this is a good idea. You could get rid of the collar alltogether and have an adjustable upper bearing block with a spacer/sleeve that sits between the upper bearing and the inner sleeve of the auto unit.

I know a few other helis that do it this way and it works well.


Paul

[Grant_beltcp]

Sorry to see that Paul - you must be pretty gutted!
I have had to adjust mine once already, and i need to do it again as I have about 1mm of play again now. As i'm awaiting some main blades for mine, I will take a look at it and see if theres a simple way to sort the problem before I fly it next.

I was worried about tightening my locking collar any tighter incase I stripped the threads, especially keep tightening it - So anything to take abit of load off it would be good.

[Rctintin]

Would it be beneficial to add a second grub screw opposite to the first one on the collar, and when assembling it all, tighten the grub screws to mark the main shaft, remove the shaft, and grind (Dremel) a flat where those marks are. That way you have double fixings, and something for them to lock on to.

[Britflyer]

Anyone know where to get odd-ball size bearings?

The upper mainshaft bearing is 10x19x6, which is £10 for one for Synergy part number!! A search on Modelfixings, RC Bearings and Ebay finds nothing.

If there was one place on a heli to use 'standard' sizes, mainshaft bearings which get replaced quite often, would be one of them!!

I'll probably end up using 10x19x5 and a spacer unless someone can point me to a reasonable source.

Cheers

Paul