600SE tail vibes. ideas?

[cudaboy_71]

200+ flights on a 600SE. i've been plagued over the last 50 or so with some bad tail vibes that manifest with the heli (vbar 5.3) veering hard right on liftoff.

first it was the flange bearings in the tail box going out and wearing down the main shaft. replaced both bearings and shaft.

then, it was the tail servo pushrod wearing thin in the guide. I put on a new guide, new pushrod, and sleeved the pushrod with shrink as a bushing.

both of these seemingly fixed the issue, allowing another 20 or so flights between repairs. but, i'm starting to think these are symptoms of a larger issue.

two weeks ago, the problem returned. vibration analysis shows a huge spike (to the top of the graph) at 10,296 RPM with all blades off. My heli is configured for 2200RPM on the head swinging 620s/95s, and this 10296 coincides perfectly with a tail rotation assembly.

Tail is fitted with quick UK tail. I just replaced: flange bearings, tail shaft, radial and thrust bearings. but, when I spool up--still with blades off, I get the exact same 10296RPM vibration spike.

What else on this heli spins that fast? Any ideas? I was hoping to fly tomorrow. But, looks like she's down for another week unless I find something simple.

thanks.

[Mentalic]

Sounds like you found it, something on the tail. Perhaps tail hub bent or bearings in grips not fully seating. Make sure the hub fits very sung on the tail shaft otherwise is can vibrate. Could also take off parts until the vibration stops, pull the hub and run it, still vibrate?

[cudaboy_71]

hub's about the only thing i haven't replaced. this heli hasn't taken a hit. not sure what could have bent it. but, i'm out of ideas. this should just be a wear item. i've rebuilt the grips several times. and, it's not like this is a new build. radial bearings all seated fine, thrust bearings double confirmed installed correctly, but, i can't find it :-(

[MS60]

I had a similar problem with a 600 sx, I changed tail blades and that resolved it. 2200 is fairly high for 630s. I run my 606s at 2150, at 2200 it starts feeling squirrely.

[Mr.Andersen]

If its there with the grips on without blades then its either grips ore hub ore shaft.
The shaft is simple to investigate as its just to remoove the tailrotor and spool up the heli without blades and just the tailshaft spinning.
Now put a screwdriver against the spinning shaft and feal for vibes.
If the screewdriver feal smooth along the shaft its just hub and grips left to investigate.
I have had tailvibes on my 600sx these summer before slamming it big time and during the investigation i changed hub, balanced blades and changed shaft just in case witgout anything helping.
I use Ikon so dont have any analizing tools other then my finges but even without blades on it had vibes in the rear part of the tailboom.

[cudaboy_71]

still working through this issue with no resolution. my reluctance in swapping out the hub has been because it is a quickuk tail. as far as i know you can't just buy the hub, but need the entire $75 tail. is this correct?

or can i use the stock logo hub?

i've searched through the forums and don't see any reference. i got this airframe used and have never seen a stock tail.

might be easier to switch to the more robust SX tail now if the repair is replace the whole tail.

[Mentalic]

Originally Posted by cudaboy_71

still working through this issue with no resolution. my reluctance in swapping out the hub has been because it is a quickuk tail. as far as i know you can't just buy the hub, but need the entire $75 tail. is this correct?

or can i use the stock logo hub?

i've searched through the forums and don't see any reference. i got this airframe used and have never seen a stock tail.

might be easier to switch to the more robust SX tail now if the repair is replace the whole tail.

Don't think the Mikado parts will be compatible with a quick uk. The SX parts would be less expensive as well.
Mikado SX parts:
http://shop.mikadousa.com/04615-Tail...set_p_612.html
http://shop.mikadousa.com/03030-Tail...ges_p_211.html

[cudaboy_71]

Maarset (my flying buddy) gave me his tail today when we finished flying. i need to get my bird back together to test it. i have it torn apart to replace the bearings on the belt tensioners at the moment. but, i should be able to tell if it's my hub/grips pretty quickly when i put on his that were flying fine this afternoon.

i'll update the saga by tomorrow evening.

thanks for all the suggestions.

[cudaboy_71]

I took Mike's working tail off of his Logo, put it on mine, and I still get the same exact vibration spike at 10,290 RPM, with or without blades. So, I'm confident it's not the tail. So, $75 saved. Thanks, Mike.

I took a caliper to the tailbox sides to confirm it's square.

So, I started pulling things off:

servo to pitch slider rod and guide (same vibration)
boom supports (same vibration)
removed the idlers and replaced bearings, looked for flat spots
inspected the belt

with everything else exhausted, i checked the one last link in the chain....the sensor mounting tape. it felt solid (i've had the adhesive give way before on other helis. it was still sticking. oh well...replace it anyway.

keep in mind i've only ever used mikado tapes. so, the one on it was mikado. the one i just put on was mikado--though from a newer batch.

vibrations are gone. G.O.N.E. I guess I just wore out the damping of the tape. this is a new one on me. i built this airframe in march of '12. i guess 2 years between tape changes is too long

whatever...i'm gonna quit typing and go fly.

[Mentalic]

Well glad ya found the problem. So after all this time you had been chasing a vibration that is not visible on the heli but you saw it on the vibration analysis screen... Well if I had understood that was the case I would have had you check the foam. I inspect the sensor foam every now and then to see if its pulling apart on the corners. They do wear out.

[cudaboy_71]

Hindsight is always 20/20

The Heli was definitely reacting to the vibration. I don't make it a habit of looking for potential problems just for drill....Though there's nothing wrong with that. But this Heli started veering off to the right when it got up to 2200rpm.

As far as the physical looks of the foam it was fine, though it didn't the much pressure at all to delaminate it down the middle.

I got two perfect flights on it this morning without a hint of a cyclic drift.

[maarset]

Awesome!