Tail rotor vibration

[dpa]

Having a problem with violent vibration of the tail when the heli spools up. Z20 980 motor, 14T pinion, stock gears, 25C 2500 MAh packs , Gaul 50 amp esc. With 85% throttle curve, Eagletree gives a head speed of 2100 RPM hovering in my driverway.

As the heli spools up and passes through 1900 rpm, the tail begins to vibrate violently, (enough to actually break a rotor off at the hub). Once it gets to about 2000 rpm, vibration goes away.

I took the bird apart and spooled up without head or tail boom/belt, no vibration. So I started adding things, looking for the vibration, and eventually isolated the vibration to the tail blades themselves --- when they are removed, vibration goes away.

Tail rotor blades are balanced, not damaged. I tried another set, same thing. I replaced the tail case/rotor/grips with a CNC one. Same thing. Could it be belt tension? Bad bearings?

Any thoughts?

thanks,
dpa

[mjdee14]

Most likely it's the belt tension......we have had lots of problems with it.....the reason you don't have it with the tail blades off is because there is no load on the belt with the blades off.

Tighten up the belt and see if that cures it....now this is assuming the tail shaft is straight and the bearings are good.

Do a search on tail wag...or wag and you'll see a lot about vibrations....

also some people have noticed the tail gear box is either loose on the boom...or has developed stress cracks....

[istandalone]

yup, your search of "hurricane tail vibration" will yield alot of like issues. belt tension seems to be key, the hurri likes a tighter belt then normal. also, hold your heli down on the table, one hand pressing on the head button. grab your tail case and give it a twist. there is a good chance you'll get a mm or two of movement. mine would not go away, even with the screws as tight as they'd go. i just put a drop or two of thin ca where the boom goes into the case- holding the heli nose up. thin ca will wick into the suface imperfections of the boom and case and will hold it nice. both belt tension and the ca seemed to cure mine.

[helvetic]

Well, I got it as well!
I discovered the following:
You may get rid of the vibrations by getting the belt tighter.
But I think this is like a pill against headache. You got rid off the pain, but the cause is still there.
When I spool up the heli with tail belt but no blades, I have vibrations! Not as much as with the blades, and not with that dangerous hmmmmm-sound. But the vibrations are already there!
Spooling up without the tail belt, the whole system is quiet, no vibs at all.
Ok, I believe the vibrations are caused by the pulley and the belt, don't know yet, wheter both pulleys or just the tail or the front pulley are involved.
Those small vibrations may be the cause of the "big" vibrations with belt and blades on.
I will examine this issue and report the results.

I think GAUI has to take a stand about that.

[dpa]

Today I tore down the heli and examined/replaced all the bearings. One of the main bearings was notchy, and the bearing in the engine mount that captures the top of the one-way-bearing shaft was very scratchy as well. One of the tail drive bearings was notchy (ah ha!) and the tail shaft bearings were fine. I replaced them all anyway.

With all new bearings and no boom or belt, runs smooth and quiet at 2300 rpm.

Adding the tail boom and belt, also nice and smooth.

Adding the tail rotor and blades, violent vibration around 1900 rpm, just like before. Vibration goes away when tail blades removed, as before.

Adjusted belt tension from very tight to very loose in tiny increments, never seemed to effect the vibration at all, one way or the other.

I've replaced all the bearings, all the shafts, the tail boom, belt, and struts, the tail rotor, the tail blades, the stock tail case with another stock case, and also with a CNC case. It still vibrates violently enough during spool up to break things.

I'm about to give up on this heli.

dpa

[helvetic]

T
I've replaced all the bearings, all the shafts, the tail boom, belt, and struts, the tail rotor, the tail blades, the stock tail case with another stock case, and also with a CNC case. It still vibrates violently enough during spool up to break things.

I'm about to give up on this heli.

dpa

this really scares me !:thumbdown:

[mjdee14]

Today I tore down the heli and examined/replaced all the bearings. One of the main bearings was notchy, and the bearing in the engine mount that captures the top of the one-way-bearing shaft was very scratchy as well. One of the tail drive bearings was notchy (ah ha!) and the tail shaft bearings were fine. I replaced them all anyway.

With all new bearings and no boom or belt, runs smooth and quiet at 2300 rpm.

Adding the tail boom and belt, also nice and smooth.

Adding the tail rotor and blades, violent vibration around 1900 rpm, just like before. Vibration goes away when tail blades removed, as before.

Adjusted belt tension from very tight to very loose in tiny increments, never seemed to effect the vibration at all, one way or the other.

I've replaced all the bearings, all the shafts, the tail boom, belt, and struts, the tail rotor, the tail blades, the stock tail case with another stock case, and also with a CNC case. It still vibrates violently enough during spool up to break things.

I'm about to give up on this heli.

dpa

dpa..

I would get with John at Redi heli and speak with him...since he is the USA distributor he might be able to help.

This has been a big enough problem with enough people that Gaui might need to make some changes or pin this problem down with a good fix....

[concept1]

we went thru this many months ago, and I concluded it might acctually come from resonece starting from the motor and going thru the tail, different motor/esc combo's will react differently, so don't assume you need to tighten your belt, you might need to loosen it!. my H/18 Needs a loose belt guys I talked to in the past solved it with a tighter belt running the 75 amp esc and 1500w motor. but we are getting a resonence that is being amplified at certain RPM, a bad bearing will deffinatly make it much worse, and the plastic frame will react differently then the Carbon versions, but we do know it shows up in the tail belt! so try different tensions till you get it gone

[dpa]

Hi Concept1. Yes, I read your posts concerning belt tension and, as mentioned in the previous post, I have:

"Adjusted belt tension from very tight to very loose in tiny increments, never seemed to effect the vibration at all, one way or the other."

as well as changing out the belt itself, among other things.

My Hurricane550 has the short tail boom extension. I wonder if the resonance is better/worse with the longer tail boom? Just thinking out loud. I'm running out of things to try.

thanks for the help,
dpa

[concept1]

I assume since you have removed the tail case you did inspect it? I mean not just look at it but flex it to make sure isn't cracked? mine was cracked but it was not visually noticable, I was shocked when i finally found it! do you have any other esc to use? or a different motor? plastic or carbon frame? how is your gear mesh? do you have a tail mounted servo or frame mount? i do beleive this is starting fromthe motor/esc and making it's way back to the tail, so look hard at what could be causing this starting from a minor vib/resonence at the motor to the end of the tail. with the stock esc, you can't adjust the timming, but you can try gov/non gov! send me a pic of your setup

Edit! i see you did replace the tail case so, I would check motor/esc! I see a lot of Z-20 powered Hurri's having a problem, this might be a coincedence, but worth a look.
Also what blades are you using, have you tried different main blades? have you tried a different manufacturer of tail blades?

[bbagle1]

Make sure you check the Gyro mount as well. I forgot to tack mine in place and it was sliding/twisting in the frame. This is on the CF gaui frame.

[helvetic]

I checked my theorie about belt and pulley... I couldn't find any reason for vibrations.
But since I put everything together (with a loose belt, this time !) I have much less vibs and no tail issues anymore.

I don't know what exactly helped me out, but it could be a sum of little changes.

I have a Z20-1470 and a 5s setup, btw.

edit: after a few tests, the flutter came back.... so lets start again...

[dpa]

concept1, I think you may be right about the source of the vibrations.

With the belt removed but the tail boom attached, I can place my hand lightly on the boom and feel the same vibration as the heli spools up just as it passes through 1900-2000 rpm.

Following on your comments, today I swapped out the Gaui 50 amp ESC for an Align 100 amp ESC, but got same vibration as before. I tried both mid and high timing but no help.

Next I swapped out the Z20-980 for the stock Gaui motor, tried it with both the Gaui and the Align speed controllers, still same problem: violent vibrations on spool up going through about 1900 rpm, smooths out above and below that speed. But at that speed seems like it will shake itself apart, and indeed it has broken the tail rotor already so I'm not willing to fly it again until I get this straightened out.

You asked about the main blades (500mm CF) but neither they nor the head itself are attached for these tests looking for the source of the vibration. So far the only real difference I can make at all is to remove the tail blades. I can still feel the vibration in the tail boom as the heli spools up, but it is not violent without the blades attached. I have tried three different sets of Gaui tail blades, but none from another manufacturer. Who do you suggest?

Best I can tell I have now replaced the entire heli save the plastic frames and tail blades. There some pictures of it on the eagletree thread halfway down the page at:

http://www.helifreak.com/showthread.php?t=62013&highlight=eagletree&page=2

except it now has carbon fiber boom and CNC tail case, but vibrations are the same with metal boom and plastic tail case.

thanks for the help,
dpa

[concept1]

well, I really can't say if this will help, but do you have any other gears? main and tail drive? I know some of the Gaui gears are out of round a bit, I am using the revco gears and haven't had any problems since, but I haven't made any other changes either. but in theory you could get some vibs with the gears out of round or balance, I wouldn't think it would be enough though, but something is causing the motor to resonate and some motors are worse then others, gear ratios could maybe make some sence here???? my H/18 is better then the stock motor I had, but I am also now running the revco gears and a 21 and 22t pinion vrs stock???? when my tail case busted I also stripped the rear gear, at that time I swaped it out for the revco gear as well, I have had no vibs since? but like I said I have made no other changes to belt tension either so who knows. I am in the process of completeing my Rotorworkz frame conversion, will test it this weekend, I will play with the tension and see if i get any vibs.

You are running it without the head at all? or just without blades, if thats the case I assume you have pulled your head and balanced it? balance it with the flybar and paddles on. I use a prop balancer and balance the head and then with head with everything on down to the swash. should not make any difference with or without swash. I don't know if I have never had one balance correctly without some minor adjustments.

[concept1]

I saw your pics, in the one pic your main gear looks worn? is it? and are all the teath worn the SAME?
also tape on one of the paddles, did you balance the head?

[dpa]

Hi Concept1,

yes, blades and head removed completely for these tests. Main gear has been replaced with brand new Gaui gear along with all the other gears. ALL gears, shafts, and bearings, as well as the motor and ESC, have now been replaced over the last week, without effecting the vibration at all.

As mentioned in the last post, I've now replaced the entire heli, part by part, except for teh plastic frames and tail blades. I even took the frames apart and glued the bearings in place with plumbers "goop" a la Finless. No difference.

The head is balanced but not attached for these tests, so the vibration is not related to the head or main blades.

This is really a drag. I like flying this heli quite a bit and the Z20-980 motor is just right, but I can't get the bird back in the air, and I've been trying for weeks now. Maybe Finless was right.

I'll order up a set of Revco gears today and keep my fingers crossed that it will make some difference, but other than that I really have run out of things to try.

Anyway, thanks for sticking with me through this with all the ideas and advice.

Damn. I had a lot of plans for this heli.

best,
dpa

[concept1]

well hold off till monday, I will get some testing on my Rotorworks frame! maybe a good time for a frame upgrade!!!!

[dpa]

Well that's a thought. New gears and new frame. What else is left?

I shot some video this morning just to document the problem and help assure we are talking about the same thing. Check out (20M mpg):

http://geology.heroy.smu.edu/~dpa-www/heli/gaui/hurri550_tail_flutter.mpg

which shows the heli in its current enlightenment on the bench spooling up with and without tail blades and with and without the tail flutter. This is the same vibration that broke the tail rotor in flight and threw a tail blade at me --- why I'm not eager to get back into the air until its fixed.

thanks again,
dpa

[concept1]

what tail fin do you have? how stiff is it? by your vid the sound I hear is just the tail fin vibrating, I don't see or hear any tail flutter, nor do I see any tail servo movement. I hear a high pitch vibration. most of the flutter I have seen and got from mine was more of a lower pitch loud Flutter that shook the WHOLE tail back and forth 1/2 to 1 inch, watching yours it seems to come fromt the tip of the fin up to the tailand tail blades seem to stay in place. but the end of the fin vibs. remove the fin and fly it. I do think you are getting some resonence into your tail fin, but remove the fin and hover it, does the tail shake?

[dpa]

Ah! Good idea. I'll try that when I get home this evening.

Tail fin is CF.

thanks,
dpa

[concept1]

I watched this again a few more times, you do get a tail shake, but i only hear the fin vibration. it does start at the tip of the vin, try removing it, you might have done this already. I will play with mine this weekend and see if i can make it do it. with and with out blades

[helvetic]

I had a few good tests with a loose belt, but then, the flutter came back again....

After reading the posts of concept1, I began to search at other parts than belt and pulley . I took away all moving parts, one by one, until the vibrations stop.
But, it never stoped. At the end, I had only the motor (!) turning alone, no gears, nothing. Interesting, when I start the motor, it begins smooth and quiete, but with 70-80% throttle, a self-resonance begins and the whole frame loads up. More throttle, and the resonance stoped.

I discovered both bearings from the oneway gear were defect, there is a crunchy sound when it is turning. Remember, I have not one flight, the bird is complete new!

@concept1: Is it possible when the motor loads up the frame with the self-resonance that some bearings are going in pieces?

I know now, the Z20 has this bad behaviour when starting up. I'm going to replace the bad bearings. But what next? I'm afraid this is going to be a never ending upgrade...

Only the motor is installed, but still vibrations:
40421

those bearings were crunchy:

40420

[dpa]

Helvetic wrote:

"At the end, I had only the motor (!) turning alone, no gears, nothing. Interesting, when I start the motor, it begins smooth and quiete, but with 70-80% throttle, a self-resonance begins and the whole frame loads up. More throttle, and the resonance stoped."

I've seen exactly the same thing. It's why I swapped out both the Gaui ESC with the Align and eventually the Z20 motor for the Gaui stock motor as well. All combinations produced the same resonance. I wondered if maybe it was a timing thing with the ESC having incorrect timing at one point in the spool up.

I can add another data point from watching the Eagletree logger, and that is that the current consumption goes up significantly during the resonance, then drops abruptly when the rpm increases past the point of resonance. I thought this was caused by the flutter but perhaps it is itself the cause.

best regards,
dpa

[mjdee14]

I can add another data point from watching the Eagletree logger, and that is that the current consumption goes up significantly during the resonance, then drops abruptly when the rpm increases past the point of resonance. I thought this was caused by the flutter but perhaps it is itself the cause.

best regards,
dpa

dpa....now that is a major find....this is happening with more than one type of motor right ?.....does it happen on other helis using he same motors we are...maybe we should do a poll or forum search...

My other thoughts were how about the mount? it's pretty flimsey the way the motor is mounted with the two screws on the side....and they mill down the surface to just a couple of ears...

I wonder if anyone has the capability of drilling two more holes/slots in order to use the other two motor mounting holes to secure the motor to the plate.

As it is now....I wonder if the motor is rocking back and forth on the plate..?.

But with that latest news from dpa about the increase in power comsumption...that has me wondering....

Does anyone have a way to mount the motor on something different and see if it does the same thing...

I just can't believe it would be the motors....or this would be a MAJOR topic of all E heli flyers...I have to believe it is a Gaui engineered in problem...

I sure hope john at RH is monitoring this thread and giving a little feedback to Gaui...


**edit*** just thought of something...if the motor was rocking back and forth it would allow the gears to tighten up, MAYBE causing the increase in power comsumption...just a thought...

** edit #2 ** http://www.helifreak.com/showthread.php?t=55459&highlight=tail+vibrations
Go look at he Trex 600 guys...they are having the same problem....do a search on tail vibrations and you will get a bunch of hits....so we are not alone.

[dpa]

Howdy mjdee14.

I'm not certain if the peak in pack amps is a cause or effect of the vibrations, and therefore significant.

Here's an eagletree graph of the Hurricane 550 spooling up with the Z20 motor. Look at the second spool up starting at 80 seconds. The vibrations happen right at 1800 rpm, and I held it there for a while both on spool up and spool down (rpm in pink and amps in purple).

You can see that the current draw is greater at 1800 rpm for the violent vibrations than either higher or lower rpm.

In the previous trace, where I increased and decreased throttle several times across the resonance, you can see the current peak each time it crosses the 1800 rpm range.

edit: here's a second maybe better graph, this time with the main blades and head removed, and with the boom/tail rotor/tail blades attached, showing spike in current each time head speed passes through 1800 rpm.

edit #2: By my calculation the HS for the Z20-980 on 6s with stock gears and 14 tooth pinon should be about 1800 rpm. However the eagletree logger shows the heli actually hovering at about 2100 rpm in my driveway. Is it significant that the vibrations happen when exceeding the calculated head speed?

dpa