Extremly bad tail vibration - resonance?

[Zoobie]

I lost one of mine too and I had the same vibration issues. I thought you could fly with out the tail support pipe - but obviously not on the hurricane. This begs the question - should we not investigate more rigid support pipes/rods, made out of CF, it could stiffen up the whole heli and take away some of the weird noises this heli makes on spool up??

[michael88997]

I thought you could fly with out the tail support pipe - but obviously not on the hurricane


every heli i have seen has to fly with supports or else the boom with crack and fail... i think carbon fiber would just cause problems because it would vibrate so much... as long as you get them tight they should be stiff

[mjdee14]

[quote=michael88997;680364]every heli i have seen has to fly with supports or else the boom with crack and fail.../quote]


ECO8 was an option.....it came without tail supports....maybe being the rpms were so slow it wasn't a major issue. I put them on after a while just to help and it looked better.

[dadde]

Ok, Im back and I have tried a few more stuff;

Changed to the T-Rex 600 Tail
H60043 - Tail Case
H60044 - Tail Rotor Control Arm
H60045 - Tail Rotor Shaft Assembly
H60046 - Tail Pitch Assembly
H60109 - New Tail Rotor Holder

And the results?

The exakt same tailvibs as the stock parts witout the head on and the exakt same vibs as the stock parts with the head on.

I do belive I have tried and failed everything I can do to fix it.

[dpa]

Don't know if this will help, but I've had the exact experience as Dadde, replaced esentially the entire heli, piece by piece, and bad tail vibration at about 1800 rpm never went away, there is a long thread about it here on helifreak.

However, I decided to fly anyway with the violent vibration and, after the inevitable crash, rebuilt the heli, and the vibration is now gone. The only thing that I can think that I did different is that made some some aluminum attachment points for the tail struts ('cause the stock plastic ones broke in the crash and I didn't want to wait on mail order), and pinned and super-glued them into the struts when I replaced the tail boom.

I have a rotowerks CF frame and a CNC tail, so other than the drive train and head there is not much "Gaui" left. Flies great, Z20 980 could probably be upgraded, otherwise I'm a happy camper. But it took about 4 months to track down the tail vibration, and then it really just sort of went away by itself. Strange, no?

You might try taking your struts apart and super-glue the plastic attachments points when you pin them back in place. Who knows? I have no idea why the vibration is now gone. Sounds identical to your problem, though.

good luck!
dpa

[dadde]

dpa: Thats a realy good idea! I'll have to try that out as soon as I can,
I'll report back when Im done.

[dpa]

Dadde, I just remembered one other thing that I changed after the last crash: the tail rotor belt. The other one was slightly damaged in the crash so I went ahead and replaced it. Don't know if that had anything to do with the vibration going away, but I guess anything is possible at this point.

dpa

[skigolfmike]

Up to 3 busted tail cases now. All broke in the same place. At least this time I might have an explanation why.

I had enough time last night to put on a new tail case. What I found was the new tail case didn't have as much twist on the shaft as the old one (about a third as much), so I looked at the case to figure out why. In every case the locating pin molded into the tail case had been cut into by the edge of the locating hole in the tube. When the tail vibrates and twists back and forth, it cuts into the plastic and give it more play. The more play, the bigger the vibration and eventually the tail case fails.

My experience with the stock tail case is you can tighten it all you wish; however, you cannot get it tight enough on the boom to keep it from twisting. I tried scotch tape; however that leaves some messy residue and I've seen the vibration spit the tape right out the front of the tail case. What I did this time was wick a little thin CA down the tail case before I put the fin on. Then I quickly put on the fin and tightened it down. It doesn't twist now. I've give this a try and see what's going on.

While I was at it I took apart the tail boom support pipes, CAed the ends in place and put CA on the screws that hole the ends on. I rechecked the belt tension. It's pretty tight, but it doesn't seem to be so tight that affects spool down.

Lastly, since I have the TR servo mounted on the boom, I flipped the TR servo last night. In doing so I got better alignment of the linkage down the tail boom. I went through that whole setup too. One of the things that was happening when the vibration got real bad was it actually pulled the TR servo towards the tail. Since the arms on the clamps are screwed on, they moved. it really made a mess of things.

Honestly, it's not making any sense to me why I have the vibration in the first place. Mechanically, everything looks pretty good. The TR shaft is straight, the blades track perfectly, belt tension is good, alignment is good. I just don't get it. I was thinking this might be a gyro problem, but I kind of doubt that. However, I wonder if I have a servo problem.

The setup is a JR G770 3D gyro running through a Spektrum stepdown with a JR DS8900G servo. The ball is 10.4mm from the center of the hole on the arm and the gain is 70%. I'm starting to wonder if maybe the servo is bad. Might have to get another one to check it out.

Lastly, I should have a CNC tail case soon. At least I won't be able to break that one.

My 550 flies great when it's working. I just can't seem to get it working for more than a flight or 2.

[Mikej]

I can't help much Mike, but just wanted to say good luck in getting it sorted - I knwo how frustrating it can be when you get so close but can't solve a recurring problem (fortunately in my case not with the Hurricane).

Cheers,
Mike.

[skigolfmike]

I put on the CNC tail case and bell-crank I got from HeliDirect and that seems to have fixed the problem. I think it may have had something to do with the combination of CF tail fin with the stock tail case creating a resonate frequency in the tail. When the head speed got to the right frequency, the tail went nuts. Since the CNC tail clamps to the boom and is more solid it damps the CF fin.

I'm wondering if the harmonic dissonance comes from the 2 stage gearing. I can hear dissonance coming from somewhere when I get the heli spooled up.

I think I'm getting things sorted out. I put on the CNC bell-cranks and the see-saw in last night. The head is all Gaui CNC now and the see-saw took some play out of the head as did the CNC bell-cranks. I also setup the head with the swash leveling tool and the zero degree alignment tool. I actually had to tweak the Travel Volume a little to keep the swash level at max/min pitch. Hopefully, I can get in a test flight or 2 tonight or tomorrow.

I am spinning up the head pretty well too. 2300 in normal and idle1 (100-75-100) and 2400 idle2 (100-80-100). I have plenty of power in idle1 and idle2 for the way I'm flying now and for the foreseeable future. However, I am down to 4:30 with the Gaui H18 motor.

[dadde]

I tried to glue the plastic-ends on the boom support pipes and changed the mountingscrews that goes throu the pipes into the heli to longer ones.
I also replased the Tail support clamp at the same time,

The results?
Vibrations still there, but they were a bit more manageble due to the more ridgid tail-suport wich made it possible to fly if I lowered the gyro sensitivety.
Im a litle happier now that I can fly the thing but its still vibrating BAD.

After that I tried replasing the tail-blades with blades from quick - No differense
Replased the mainblades to KOK 505mm CF blades - No differense
Replased the paddles to lightwheight ones - No differense

Atleast I can fly the thing now.

I'll update as soon as I've got somthing.

[mjdee14]

Someone mentioned adding washers under the bolts for the motor mount on the frame...assuming some vibs were coming from the motor mount being transmitted thru the frame....??

[skigolfmike]

The vibration may not be in the tail, it's just where you see it.

I rebuilt the head on my 550 the other night to put in the CNC see-saw. I also added the CNC bellcranks. Plus I used a new flybar when I rebuilt the head. When I did the test hop last night I noticed the heli was running a lot smoother. I ran it 4:30 like I normally do, but I only put a little over 1900mAh back in the batteries. Normally it's like 2200mAh. I'll have to do some followup testing WRT to see if I can increase my flight times.

The only thing I can think of is I may have had some misalignment in the paddles, or the flybar wasn't centered all that well before. The harmonic dissonance coming from the 2 stage gearing was less than before, which is probably a good thing. I didn't see any sign of vibration in the tail on spool-up like I did before either.

Just food for thought.

[mjdee14]

The vibration may not be in the tail, The only thing I can think of is I may have had some misalignment in the paddles, or the flybar wasn't centered all that well before.
Just food for thought.

Mike...you may be right ...about the paddles.....I wonder how many of us have it just an RCH off from one another....and unlike the main blades....out of track is not noticible to the eye but I would imagine it would still cause a vibration of sorts....

Definatel worth a try to check on those that have vibs and have done everything.

If you look at other heli forums....they are not without their own problems with vibs....

the real helis are always plauged with it also.

[skigolfmike]

I think the hardest part of setting up the head is getting the flybar in the see-saw right. one thing I noticed when I changed from the plastic see-saw to CNC was the CNC Stabilizer Control Set was a better fit. The stabilizer control set actually holds the flybar in place and before there was a little play there. That meant the flybar could slide back and forth a little, probably .1-.2mm, just enough you could feel it. That play is gone now.

I use the pitch gauge to setup the paddles and get them square to the control set. Setting up the stock flybar arms has got to be a real PITA.

[mjdee14]

I think the hardest part of setting up the head is getting the flybar in the see-saw right. one thing I noticed when I changed from the plastic see-saw to CNC was the CNC Stabilizer Control Set was a better fit. The stabilizer control set actually holds the flybar in place and before there was a little play there. That meant the flybar could slide back and forth a little, probably .1-.2mm, just enough you could feel it. That play is gone now.

I use the pitch gauge to setup the paddles and get them square to the control set. Setting up the stock flybar arms has got to be a real PITA.

I went to the flybar cage and added washers to the seesaw...but the cage is the best becuase i never felt I ever had both arms in perfect alignment.

I use the trex flybar and it has notches on both sides....allows you to line up perfectly on each side...then I use a micrometer to ensure both paddles are same distance...But I don't have a real acurte paddle gauge.

[Wazzer]

You guys seem to have tried everything
Jb had a tail vib on his heli that made the vertical and horizontal fins (trex600 fins BTW) vibrate like crazy. The vibes werent coming from the tail gearbox or anything else on the tail as thease were not vibrating. the trex600 fins are also very soft in comparison to the standard fins

It wasnt that bad and didnt effect flight, was more of an annoyance really.

Well I gave JB a Z20 980 for his birthday and when i installed it all the vibes went away and now the tail is silky smooth in flight.

I know theyhave tried chaning the motor but didntstate which motors were being swapped.

Just a thought as Bobs carbon Hurry Pro is now super smooth quiet and stable.

however i am just about to install a full trex 600 tail and boom as its just a better set up than the standard gaui so hopefully I wont come accross any of the above problems!

Cheers
Ben

[dadde]

The Vibs are there vitout the head on, witch leeds me to belive its not somthing in the head.

I have tried the stock Gaui 890kv motor a Align 600L and a Z20 motor, no differense.

But I do feel encuredged that there is people that are willing to take time to post sugestions!

Im going to try shanging the OWB and OWB shaft just for the sake of it, I belive I have changed nearly all things then.

Cheers,

[clayboy]

have u tried to bench test the heli and take part by part off to try to pin point the problem?
mvh
janne

[dadde]

Yeah I have,
First I removed the head - Still violent vibes at the tail
Then I tried removing the tailblades - still vibes but it feels like there is nothing to amplefy them to the point of "very bad".
Removed the belt and the vibrations seem to be less but is still there I think but it gets less and less as I remove spinning parts, but are still there.
Tried changing all gears exept the OWB and OWB shaft without any differense.
After that I tried changing all the ballbearings in the heli - no differense.
Tried changing the mainframe without succes.
Changed the mainshaft 3 of 4 times inbetween these things.
thats apart of the story alteast.

Anything I should have done different?

[skigolfmike]

If you took off the tail belt and the vibration was still there, then it's in the main drive train and getting transmitted down the tail. Look at the tail belt drive shaft, you might need to replace that. Also, check that you gears are round. Slowly spin then and look for tight/loose spots in the mesh.

It acts like there is a shaft bent somewhere, probably not the main shaft since you replaced that.

You did confirm one thing for me. I think the tail blades make a difference. I noticed the vibration in the tail was amplified more with the stock tail blades than with the lightweight tail blades. The lightweight tail blades are more flexible and probably dampened the vibration.

[clayboy]

yup sound like the pulley or gears

[ICCA]

I'm sure you have done it, but, just in case, make sure your boom-supports are tight.

Dave

[tornet999]

this was a long discussion :)

Anyhow, had same problem as Dadde described last year, changed EVERYTHING on my Heli, since I had two Hurricanes it was quite easy to swap compete tail, head etc. One of my Hurricane was working perfect the other one has terrible vibrations, was really annoying.

I finally swaped ESC as a last and voila all vibs gone.

[mjdee14]

this was a long discussion :)

Anyhow, had same problem as Dadde described last year, changed EVERYTHING on my Heli, since I had two Hurricanes it was quite easy to swap compete tail, head etc. One of my Hurricane was working perfect the other one has terrible vibrations, was really annoying.

I finally swaped ESC as a last and voila all vibs gone.

Wow ! that is a definate surprise. Did you swap the bad one to the other heli and see if that one then had the vibs...or swap it back in the original?

I think there are many reasons we can get vibs...but this is just one more area to investigate...just expensive if you don't have a spare.