Extremly bad tail vibration - resonance?

[dadde]

Hi!
I got a problem, I want to fly my hurricane but it has been grounded since over 2 months back.

The problem is that I got a bad tail vibration after an insident were the heli tipped over due to a faulty mixer on the new transmitter I was using. Several things broke, like the tailboom, tailblades, boom supports etc.

I replased all things that broke and thought it would fly greate as it did before. But ohhh so wrong I was.
Now I got a realy horrible tail vibration that is so violent that I think somthinge is going to brake.
Its impossible to lift due to the vibrations knocks out the gyro.
The wierd thing is that the vibrations arent that bad until I get above 1700rpm, there is a litle vibrations but over 1700 the whole tail shakes violently and a horrible sound starts.

I have read all the thread that I could find on the subject on this forum an tried some of the things that were mentioned.
One thing that I do belive that differs from most of the treads I have read is that my vibrations dont go away by incresing the headspeed, or maby I havent pushed it far enuff.

The vibrations are still there when I remove the head so I do belive it is somthinge in the tail or somthing in the drivechain, or maby a resonance.

In my hunt to kill these vibrations I have so far exchanged these parts:
Front gear
Main gear
3 tail output shafts
Tail Pitch Slider Bush
3 Main Masts
Tail Grips
Tail Hub Set
2 Tail Rotor Blade Set
Tail Rotor Belt
ALL the bearings in the heli (Yes I mean ALL)
Motor

And I have tried these things:
Balancing the tailblades
Tightening the tailblades
Tried atleast 10 diffrent belt tensions
I changed the motor to see if it was the culprit
I took apart the whole heli to check everything (The frame does take alot of time to take apart)
Tightening screws in the frame
Losening screws in the frame (around sertain bearings)
Cheked the tailcase for cracks (none found)
Tightening the screws in the tail
Losening the screws in the tail
CAing the tailcase to the boom
Adding spacers to the ballberings in the tail

I am starting to run out of ideas and hope.

What is the next step?

Changing the pullys?
Changing to the T-rex 600 tailcase?
Chaning to the CF frame?

I would appreciate if someone got some tips or have solved this problem already?
Thanks for your time

[Zoobie]

Main blades or feathering shaft? You did not mention them, or I missed them in your list, perhaps swop them out. Also flybar, paddles - it must be something big, not little like a bearing.
Generally if the tail vibes up and down it is the tail, if the whole heli vibrates it is something else. Dont give up I know how frustrating these things can be. The longest I ever took to isolate the problem was about 2 mts, turned out the electronics INSIDE my gyro had come free from their mountings in a crash causing a very bad tail drift.

[kahn10]

is the vibration up and down or side to side

[dadde]

Zoobie: The vibrations are still there when I remove the head. But yes I have changed the fetheringshaft, flybar, mainblades and bladegrips.

kahn10: Up and down I think but its realy hard to tell. Ill post a video of it and you can take a look.

[xodarap1]

Wow.. you changed darn near everything.
This may sound kinda silly and hate to even say it, but double check that your blades are all on correctly.

My friend had similar symptoms with two different 300 class helis. He finally showed up on my door step with the helis and the main blades were backwards on one and the tail blades were on backwards on the other.

I wish I could throw out more ideas to help you, but you sure covered a lot. Besides, warped gears, bent motor shaft, bogus pinion, the linkage being out of whack in some way, or the flybar paddles being on wrong or not balanced or making sure the blade grip tension is even on the main and tail blades, I can't think of anything else it could be at the moment. Sorry.

[kahn10]

have you replaced the cap screws that hold your tail grips to the hub?

[GatoVolador]

I had some bad vibes as well after a crash. My vibes were so bad that the landing gear and canopy shook off the frame! I finally narrowed down my vibes I believe to two things: notchy bearings and slightly bent washout arms (I have the CNC head). After I replaced the bearings things were better but I still had a vibe. I then spooled-up the heli without the main blades or tail blades at a low RPM and observed the head -- I noticed that the washout arms were not tracking indicating one or both were not true. I replaced them and the vibes went away. I suggest you do the same -- everything must be true on your head if you see any component not tracking straight then you'll probably get vibes. I doubt it's in your tail -- my guess it's in your head somewhere...

Oh, and disconnect your T/R linkage and manually move your pitch slider from the T/R linkage ball -- it should be very free and not bind anywhere along the range of travel. If it does either oil it or if that doesn't work spool-up the heli without the main blades and tail blade grips and burnish your T/R output shaft with some emery (sp?) paper until your T/R is moving butter smooth.

[Mikej]

Dadde,

I mentioned on the RCG thread some of the stuff covered here - the only other thing that I can think of is that when I have semi-stripped main gears that will produce bad vibrations.

Good luck,
Mike.

[dadde]

xodarap1: Good tip, but the blades are turning up into the boom with the leading edge like in the manual. Yeah I have soon changed the whole heli, atleast thats what it feels like :D It would almost been cheeper to have bougt another arf kit :D

kahn10: No I havent changed the screw but I have secured it with CA.

GatoVolador: I have changed all the bearings in the heli and some were notchy, but it dident help, I do dubt its in the head as the heli shakes very bad without the head on it.

Thanks for the input dudes! Im uploading a short clip of the tail shaking as I write this, Ill post it as soon as its done

Edit:
Mike: I posted on the RCG before I saw your reply here, Yeah I thougt that the maingear could be the bad egg so I changed it to a brand new -No improvment :(

[kahn10]

bro replace your cap screws.its nearly imposable to see if they are slightly bent but would put out a nasty vibration that would increase with rpm if they are.by the sound of it you've replaced everything else or ruled it out by still having vibration with complete head removed. also worth checking weight of new cap screws if you have access to sensitive scales(.oo). with the rpm the tail does its worthwhile

[BL]

If I read you correctly, you have vibes once you hit 1700rpm and getting worse when you go higher rpm.

I was having the same problem as you, but starting was from 1800rpm onwards.

I did almost the same thing as what you did, almost change the whole hurri.....

Finally found that is the tail blades that causing the problem, problem gone with a pair of new blades.
The problematic blades are like new, no dent, no scratches but it just vibes, I believed is due to uneven blade angle.

For your case, you have changed the tail blades, I assume that you have a good tail blades.
So I suggest the tail slider set, pls check whatever thing that may causes the tail blades to produce uneven forces.

[dadde]

Here is a link to the clip:
http://www.youtube.com/watch?v=zHv1wsiKQA8

Its hard to see but the tailvibes are very high frequensy. Listen to the sound it is verry clear when the vibs starts
It looks and sound alot worse IRL

kahn10: Do you mean the screws that holds the bladegrips to the fork? In that case I have exchanged them to a machine screws, I think i missunderstood you :D I I have checked the screws - straight as an arrow

BL: I have a brand new set of tailblades on but I get the same results with an old pair that I have used before witout an Issue. But thats an exelent tip! I shall check that noting is messing with the angel of the blades. I can try putting on 1 new blade and 1 old to see if it changes anything :D

[xodarap1]

heheh.. all i kept thinking about when i was watching that was if a tail blade would have blown out. Be careful dude.. that reminded me of that old movie "phantasm" with the killer spheres lol. Anyway, have you tried replacing the tail belt tensioner/roller thingy? It's a weird setup.. you would think they would have made it the same on both sides, but it isn't.

[dadde]

xodarap1: No I havent tried to change the belt guidewheel but mamby I should try :/

I tried changing the blades with the same result, maby I should try a new fork aswell.
I changed the machinescrews i had on the fork to the bladegrips with new ones just incase but it dident help either :(

[xodarap1]

I guess it's worth a shot. My belt guide wheel had a wobble to it that caused some vibration, so i put a thin washer behind it that fit inside of the guide wheel a little bit (put a washer only on the one side), then it worked smooth and still works fine. Sadly, your running out of things to try. :(

[BL]

As the hurri tail shaft is known to be longer than other heli, thus this could be one of the root cause that easily makes the hurri vibes.

I suggest that you do this test, unscrew the tail hub then shifted the hub closer to tail case by 3~4mm, lets see whether it has any improvement.

[dadde]

Tried to run the tail without the guidewheel - same vibrations.
Tried moving the hub closer to the tailcase by 4 mm - no diffrense
Tried moving it 9 mm (the maximum amount possible) Vibrations gone??? Bad thing thou - cannot control the tail without any throw :D

starting to give up soon :(

[BL]

From your 9mm test, it may shows that it causes by the tail blades angle or unbalance tail blades.

Have you check the slider? and the linkage to the tail grips? Just anything that can causes the tail blades to change angle.

[skigolfmike]

We've seen similar things on the Blade 400 with even a slightly bent tail shaft.

Take the Tail Boom and Main Blades off the heli and spool it up and see if you get the vibration.

If not, put the tail back on with no TR blades and spool it up. I run the belt on my 550 pretty tight. You can get it too tight though. Get it a little too loose and it will slip (makes an awful sound).

Make sure your TR linkage to the blade grips is on the leading edge.

It could also be the TR locking up. If the tail hit in the crash there could be some play now in the TR grip/hub interaction. It doesn't take much to cause tail locks. The TRex 600 TR hub and blade grips is a good, inexpensive solution to replace the stock hub and blade grips.

[Mikej]

starting to give up soon :(
It sounds as if you are almost there - don't give up now

[Zoobie]

Dadde, my TR blades went out of balance/tracking for no good reason and I did the same as you. Finally tried a new set of blades and the vibe was gone. Also check the capheads/bolts holding the bladegrips to the TR hub, these ben with a minor touch of the ground and will cause a nasty vibe.

[dadde]

I have tried a bunch of diffrent things for about 10 hours and I have goten nowere so I have decided to buy a new frame, pullys and driveshaft and see if that helps.

[J-Heli]

Your tail output shaft might be bent.

Nothing else I can think of really. Sorry about that.

[vicrc]

Are you using the lighter white tail blades? You can try them and see if its less with those

[skigolfmike]

Make sure the tail case isn't busted. If it is, it WILL flex under load and cause all kinds of vibration in the tail. I've busted two so far.

Also, if the problem is less with the lightweight blades, that's kind of another clue. The lightweight blades flex more; however, the stock blades will immediately show any tail problems.

Lastly, if your tail blade are too tight in the tail grips they won't straighten out evenly and you WILL get a nasty vibration when the RPM gets high enough.

Just a few of the lessons I've recently learned.:arggg: