N5 "Buzzing"

[Spanner]

Ok, balanced tail blades haven't cured it, but on spool down and closer inspection of the head, it appeared to be travelling in an almost imperceptible ellipse. so I've just removed the mainshaft and rolled it along a glass placemat! and sure enough there is a slight bend in the mainshaft, but without a dial indicator I can't say how much of a bend it is. Its probably only 1/4 mm, ish! could this be a cause ? Or is that amount of bend nothing to worry about?

I'd check the tail shaft but I've managed to round the set screw when I re installed it! I'll report back later!

[ROSSCO]

Without question!!!.. Any of the shafts, be it the main shaft or the tail output shaft running out of true will cause a vibration.

[Spanner]

even something so slight?

I'll get one on order then!

[ROSSCO]

Even something so slight, the shafts should run perfectly true especially at the RPM's they are spinning at which will exaggerate the problem.

Even so, its worthwhile changing it! Rules it out then, but it sounds like it could be the cause of your problem. I would probably get a new upper main shaft bearing too! just incase the vibration has killed it.

[Spanner]

Well the mainshaft is winging its way through the ether from fastlad, the bearing felt fine last night. I'll see tomorrow I guess! I did however manage to get all the lateral play removed from my tail hub last night too, and as that is where I'm seeing the vibes, it may also be causing it? I'll try in the garden later on, the neighbors must be fed up of a OS55 giving it beans outside!!

[Spanner]

I have a some shielded 10x19x5 bearings, the N5 ones are 10x19x6 though I think, would this make much of a difference? I certainly aren't paying £11/bearing from FL and Midlands! (other heli shops are available!)

[Spanner]

OK, after some more hunting for this vibe whilst I wait for the mainshaft to arrive. I've been spooling the head up slowly and watching the mainshaft/head. There is a definite wobble in the head that for some reason I must have ignored, I think when I first noticed it I put it down to the blades not being quite perpendicular on initial spool up, but after letting the head spool up and down and watching it closely there is a definite wobble that turns into a vibration that vibrates the whole canopy. The frequency a of the vibe increases as the RPM's do, and the effectiveness of the gyro starts to get affected and won't hold very well at all, IU 2 @ 2100RPM . I'm 95% certain now that the new main-shaft will cure it.

My only problem is how the main-shaft has been bent? I've not crashed it so I can only assume its as I've been stopping the head with my hand? or starting up in IU1........ (we've all done it!)

[ROSSCO]

On the bearing, i'm not 100% sure if the drop in width would make a difference but you may find if you go smaller that the collar may rub on the bearing block.

with regards to the bent shaft, i've seen heli's damaged by them falling over in the car etc....

[Spanner]

Ok, fitted the new main shaft and already I can see a difference. However, I've managed to strip the threads from the ally nylock nuts on the Jesus bolt and the belt gear!! trip to my LHS for him to tell me he has no stock, as per.................

You can use the 5 mm bearing, there is just enough room, 1mm all round. The old one didn't feel too bad, but was definitely used!

[jamiem]

I've managed to strip the threads from the ally nylock nuts on the Jesus bolt and the belt gear!!

They are nylocks for a reason - nip them up, they wont come undone No need to hang off those!

[Spanner]

Agreed, they won't come loose, but you still need to tighten them up where needed to be tight. You need to nip the Jesus bolt one up tight or the head wobbles on the mainshaft, and the manual/website says to do the belt gear bolt up tight aswell. I imagine the threads are buggered because of the amount of times the head/mainshaft has been in and out recently.

[ROSSCO]

I usually only use locknuts a few times and then replace them with new ones as the nylon looses its grip and if you are stressing the nuts by tightening them the threads do get sloppy or stripped. Always keep a bag of M3 lockNuts in the box.

[Spanner]

Ok, so its not the main shaft thats causing it!!

so leaving me with a few other avenues.

Tail blades
Tail output shaft
Clutch stack/starter shaft
Engine tuning


Having read a thread earlier about OS55 engine tuning and peoples needle settings, mine appears to be on the rich side, 1 1/2 main and 1 3/4 mid, could this be causing it? I've leaned them off to nearer the 1 1/4 that most people are quoting and will test later in the week.

I'll order some tails when I get back off my hols, if the wife sees any more "Fast Lad Performance" on our statements before we go away it won't be worth going!!

[sacko]

Tune yours individually.

Other people may be using lower % fuel, different pipes etc than you, so what they are running is irrelevant.

Just lean yours 2 clicks at a time until you get consistent smoke trails and power.

[Spanner]

Yeah, not thought about that, I'll back it off a bit and try from there. Frustration looking for an quick fix! Dumbass