N5 "Buzzing"

[Spanner]

Right this niggle is starting to **** me off!!! And without a video of it happening its going to be hard to describe. She's never been crashed, and has done it from the start, I think.

I'm getting a really annoying buzzing through the heli which is manifesting itself into the tail, causing it to blip to the right every so often, as though its affecting the gyro.
I've gone through the heli eliminating any slop in anything that I can find and now is better than when I built her but still I get it, its as though at this particular RPM (1950-2100) is finding some kind of harmonic and vibrating the heli.

On idle the exhaust seems to be making the buzzing sound, and if I grab hold of it the buzzing goes away. It's bolted on securely, the sound seems to be coming from inside the pipe.

Get head-speed up and that's when it starts happening, every 5 seconds or so there is a buzzing sound and the tail loses its heading for 10 degrees or so and comes right back.

I've changed the back bearing and the auto-hub, but doesn't seem to make any difference. I've got the gyro mounted pretty much above the engine, but can't see why this would make the buzzing noise.

Like I said without a video its hard to explain!

Anyone had anything similar? Any ideas how to progress finding the problem? Am I just looking at a red herring with the buzzing from the exhaust @ idle?

Cheers chaps and chap-esses!

[mark Taylor]

I'm pretty sure it was down to the boom support length ??
There was a prob with harmonics,
Saying that mine was fine

Also what tail blades you running??
Hope you get to bottom of it

Cheers

[Spanner]

radix 95's

[challis349]

The problem is, your poor n5 is getting jealous of the wot4

Hope you get it sorted Ian

[mark Taylor]

I was running radix
Can't remember if 92 or 95mm ?

I know someone had a similar problem to you
They fitted the N9 supports which solved the problem
Possibly worth a try

Cheers

[Spanner]

well, just had a small blade balancer on my tail blades and one is heavier than the other, may be causing it. Have to balance them tomorrow and wait till tuesday!

[Steve]

radix 95's

There is much talk on American forums of Vibe 50s suffering the 'Vibe Hum' where they get a similar affect and ultimately fail where the tail boom basically snaps off in flight due to harmonic resonance fatigue!!!! Fortunately, I've never suffered this with mine, but the general consensus across the pond is to use Radix 92mm tail blades rather than the 95s on the tail, and it seems to work a treat. I've always had Radix 92s on my Vibe and never had a problem in several years from new.

I know it's a different heli, but the symptoms sound similar. Maybe worth a try for £20 or so.

[Spanner]

thanks chaps, I'll give it a try I think, can't hurt.

[Steve]

thanks chaps, I'll give it a try I think, can't hurt.

Keep us informed of the outcome please.

[Spanner]

will do mate, I'll order them tomorrow, I just balanced the 95's and they took over an inch of selotape to balance................

[Steve]

I have a set of Radix 92s on my Vibe, and Radix 95s on my Sceadu SDX. Both work perfectly on their respective machines.

I'm not suer it was a balance problem with the Vibes, more of a harmonic problem.

Don't wish to see the Radix tails get slated where the problem is a combination of many facets that are particular to the heli, if you know what I mean.

But, yes balancing the blades (or even better - the whole tail hub) and having another go would be a sensible, cheap and easy starting point.

[Spanner]

No, not slating the tails at all, like you say could/probably be a combination of things. Does bracing the boom supports make any difference to vibrations in a heli?

[ROSSCO]

Hi,

If your tail blades are out of balance then this could quite easily be the root of your problem, my N5 is from the first batch and i've not had any vibration issues with it although i do run the radix 92mm tails on it. As it already has been mention it may be worth trying some 92mm Radix tails on your to try and solve the problem.

Generally i don't use bracing for the boom supports as the cause of the vibration is still there and the bracing just disquises the problem or shifts it to another area.

First thing i would try is the tails, it may simply be your tails blades been out of balance causing you issue. I find 92mm Radix to be a perfect match for the N5.

If that does'nt solve your problem, check your main rotorhead for blade/paddle tracking as these can cause similiar issues too. Next thing is to check things that rotates so these mean checking the tail output shaft, main shaft and things like that. Even though the machine has not been crash the tail may have been caught damaging the shaft.

I was going to suggest checking the engine bearings but you mentioned you changed the rear bearing in the engine and this did'nt solve the problem.

Another thing to check is maybe the engine housing itself, check for proper alignment of the engine/clutch stack and fan housing making sure nothing is catching or check for if the fan has caught the fan housing, check the fan blades are all intact. It's very unlikley that it has as there is plenty of clearance. Although there is very little adjustability in the clutch stack assembly if the system is stressed it could cause a harmonic vibration. Best thing to check is the freeness of the start shaft, if its free and smooth then the alignment is good if its grabby and tight then the alignment is off slightly. To achieve a good alignment, what i usually do is with the engine bolted to the engine mounts but the mounts left loose on the frames and also same for the clutch stack i push the clutch stack towards the maingear with a slip of paper inbetween to give correct gear meshand thenmoving the engine slightly while spinning the start shaft till if feels free, once it feels smooth i tighten up a few of the mount bolts to hold it in place. Check and then go round and loctite and tighten.

Hope this helps and let us know how you get on and if you find the cause.

[debrooker]

Try taking a look at your fan assembly and see if it is in balance, mine wasn't if your on the hunt for vibes.

[Spanner]

Thanks for the advice gents, I'll let you know. Got the blades balanced, just a case of getting it flown during daylight! Work sucks!