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Old 11-08-2009, 08:58 AM   #1
Patriek
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Default Flying without tail boom supports; slight vibration in the tail - update

Hi,

I just came back from testflying my Trex 600 without the tail boom supports. I took them off for a testflight to see if there were any vibrations before I bolt the machine in a MD500E scale fuse (without the supports). Therefore I want it to be vibration free.

I had a tad of vibration on the end of the tail (the tail case). I replaced the tail blades with some Radix and it was a lot better, but still there. Last night I replaced all the bearings in the tail and put on a new tail shaft so I rule that out.

I do run my tail belt on the losse side of the spectrum - you can hear it slap on spool up and spooldown.

Is it normal for the tail to vibrate a bit without the tail boom supports of do I have to resolve this issue before its going into the fuse? (in the fuse the tail is going to be supported by a ring in the fuselages tail boom - but I dont want the fuse to shake itself apart )

Thanks for you help!
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Old 11-08-2009, 09:52 AM   #2
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Is your tail a TT drive or belt? If it's a TT, there are a couple of things you should check. Make sure that the TT isn't bottomed out in the drive gears at either end, you may have to back the boom out of the blocks 1-2mm to acheive this. Make sure that the TT is straight. Pull the tailcase off, rotate the head and observe the runout on the end of the TT. There should be little to no wobble at all. What I've found on my 600N is that, even w/ a straight TT, the orientation of the TT end splines in the drive gear can have a BIG impact on the runout at the end of the TT. If you see a wobble, pull the TT out slightly, rotate one spline while holding the head, re-insert and try again. You should be able to find a position which eliminates or at least drastically reduces the wobble. You can then slip the tailcase on loosely and turn the head again, look for movement at the tip of the vertical fin. Try different splines on this end as well until this is minimized/eliminated.

It sounds a little complicated, but it's really easy. It only takes a few minutes and really made a difference in the smoothness of my heli.
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Old 11-08-2009, 12:08 PM   #3
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Quote:
Originally Posted by Patriek View Post
I do run my tail belt on the losse side of the spectrum - you can hear it slap on spool up and spooldown.
He has a belt drive, it says it in his post.

I assume you have balanced everything. You didn't say if it is a nitro or electric. You'll just have to balance everything that rotates. Will the boom be riding in a foam insert at the tail end or a more solid mounting method? If the fuse is well built and the mounting points are solid, it will probably absorb a high frequency vibration. A low frequency shaking would be more troublesome.

Scalercheli.com is another good resource for info on this.
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Old 11-08-2009, 02:18 PM   #4
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It's an electric Trex 600. I have researched a couple of forums (scalerchelis too) but I couldnt find a topic about someone testfly the electric Trex 600 without the tail boom supports to see if there was any vibration before installing it in a scale fuselage.

The tail boom will be riding in a foam insert at the tail end, it feels like the same material as the main blade holders we fold our blades in. The fuse is a MD 500E by Funkey. It is known to be prone to vibrations.

I have balanced main blades, tail bades & flybar paddles. What else could I balance?

When I had the tail boom supports on, there was no vibration. Now that Ive taken off the tail supports I can see the tail case vibrate just a bit, but enough to worry me about the fuselage install.

May be I am too anal here, I hope the answer is out (t)here
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Old 11-08-2009, 02:52 PM   #5
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Oh and let me add that the vibration is not there when the heli sits on the ground, its only there when the ship is airborn
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Old 11-08-2009, 05:55 PM   #6
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You may want to check your headspeed - I had terrible vibes on my 500D until I realised I was running about 3k, when I set it up to 2,550 at hover it was fine.
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Old 11-08-2009, 06:30 PM   #7
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I run my 600E with shortened boom supports and Align carbon boom. Once after a crash I replaced it with an aftermarket carbon boom and the tail vibrated like crazy. Come to find out this boom was much thinner than the Align one. I could easily flex it with my hand, where the Align one I could barely flex. So make sure you are running a quality boom.

Probably not your issue but worth mentioning.
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Old 11-08-2009, 06:41 PM   #8
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The foam insert will absorb the small vibes. The fuse is rigid and the foam works as a damper somewhat.
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Old 11-08-2009, 06:42 PM   #9
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I'm test flying a 600 right now without boom supports. Running one of the 'imposter' CF booms that is CF only (no metal). It's smooth as butter. Running a 5000 mah 10S pack, just hovered it for 19 minutes. HS is about 1650, which is recommeded for scale setup. Make sure you run grey dampeners for the slower HS.
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Old 11-09-2009, 01:33 AM   #10
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Quote:
Originally Posted by Cul-tech View Post
I run my 600E with shortened boom supports and Align carbon boom. Once after a crash I replaced it with an aftermarket carbon boom and the tail vibrated like crazy. Come to find out this boom was much thinner than the Align one. I could easily flex it with my hand, where the Align one I could barely flex. So make sure you are running a quality boom.

Probably not your issue but worth mentioning.
Quote:
Originally Posted by heli-on View Post
I'm test flying a 600 right now without boom supports. Running one of the 'imposter' CF booms that is CF only (no metal). It's smooth as butter. Running a 5000 mah 10S pack, just hovered it for 19 minutes. HS is about 1650, which is recommeded for scale setup. Make sure you run grey dampeners for the slower HS.
Hmm Im running an Align alu boom, could this be the cause?

I have set it up for scale flight already. HS is 1440 -the vibration gets worse when headspeed increases (vibration wasnt there with the supports on). I am using the grey dampers.

Quote:
Originally Posted by richardshakan View Post
The foam insert will absorb the small vibes. The fuse is rigid and the foam works as a damper somewhat.
I hope so, I was thinking that the vibs would go from the tail into the fuselage. The Funkey .50 MD500e is known to be prone to vibs no?
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Old 11-11-2009, 09:06 PM   #11
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Any update on this? You might want to check your blade grip screw tension. Really think 1440 is gonna a bit on the slow side - esepcially when you add the additional weight. I've got mine installed in the fuse now and it's got a slight wobble. AUW is significantly higher than the bare airframe. I just upped the pinion a tooth, so I'm hoping a slight bump in HS will settle 'er down.\

PS - Just for piece of mind I'd get the Align CF boom. And for god's sake, don't be doing any tic-tocs with that bad boy.
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Old 11-12-2009, 10:07 AM   #12
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Yes there is an update but aaaaarrrrrrrrgghhh the tail vibration is still there

So far I have

- tensioned the belt a bit tighter
- balanced tail blades
- changed tail blades
- tightened main blades up (and made sure they are equally tightened!)
- try it without the vertical stabilizer

and made a couple of testruns with no result the vibrabtion is still there. Bearings are new, new tail rotor shaft, vibration is still there.

Its really stupid, with the tail boom braces on there it doesnt vibrate. But I want it smooth without the braces as its going in a fuselage. The low headspeed isnt the cause, when I up the headspeed the vibration gets worse.

When I hold the heli and wiggle the end of the tail boom I noticedd theres a bit of lex in the main frames in the back. But this is also the case on my other 600E - WITH tail boom braces.

I might change the main shaft for the sake of it (no crash on it though).

Its really doing my head in

Any more ideas?
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Old 11-12-2009, 10:31 AM   #13
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I know you said you balanced the blades, but did you ensure that the CG is the same on both blades before balancing?
I just solve a vibe issue on my Protos and it was due to the CG in teh tail blades being considerably off. Under 50% throttle, butter smooth, over 50% and it shook like a crackhead needing a fix.
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Old 11-12-2009, 11:05 AM   #14
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Good thought! But yes, I have balanced the tail blades like I would balance the main blades, firstly CG, then balance them out. My Radix tail blades needed balancing, Align tail blades did not need balancing. I had vibrations with both makes of blades

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Old 11-12-2009, 12:37 PM   #15
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This is a long shot...But could it be the gyro gain? I once had a similar problem with a 450, I won't bore you with the details, but I ended up test flying it without boom supports and had a vibration I could see in the tail fin, It wasn't a gain too high, wag the tail back and forth affair, but a maybe 2mm hi frequency vibration and turning the gain down a couple of points fixed it.
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Old 11-12-2009, 01:14 PM   #16
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Quote:
Originally Posted by andrewt1971 View Post
This is a long shot...But could it be the gyro gain? I once had a similar problem with a 450, I won't bore you with the details, but I ended up test flying it without boom supports and had a vibration I could see in the tail fin, It wasn't a gain too high, wag the tail back and forth affair, but a maybe 2mm hi frequency vibration and turning the gain down a couple of points fixed it.
Long shot or not, and although it doesnt appear to be a wag (the tail case is vibrating about 0.5cm (or 1/5 inch), may be 3-4 times a second), its on my "things to try" list

My AVCS gain is set at 37% (Futaba - equals 68.5% on other radios). Worth a shot

Thanks!

Keep 'm coming freaks, all your help is very much appreciated


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Old 11-12-2009, 07:36 PM   #17
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Maybe try spooling it up without the main and tail blades, then check for vibes.
If no vibes-install tail blades and spool-up again. Then with mains. Hope you figure this one out.
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Old 11-13-2009, 01:12 AM   #18
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I will try, hope that it will point me in the right direction.

Though when spooled up and on the ground theres no vibration. I only get vibs when its airborn. The whole heli is fine, just the tail case vibrates
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Old 11-13-2009, 09:53 AM   #19
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I would try green locktiting the tail shaft to the bearings to take care of any possible lateral play. Problem with doing that is you're going to need to be able to easily assemble/disassemble for installation in the fuse. I'd actually just switch over to a TT because it lends to a scale setup so well.

Careful spinning up your hei with no tail blades on it, it's gonna piro like mad.
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Old 11-13-2009, 11:10 PM   #20
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I would certainly try the Align carbon boom. I believe the aluminum one is stiffer but maybe it is resonating at a bad spot for you.
Mine did the same when I had the thinner boom. Smooth on the ground, even OK for a couple of seconds airborne. Then the tail box would turn to a blur with the vibrating and not stop until I landed.
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