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HelicopterThunder TigerRAPTOR 90 › A shaking of the pitch slider that I can't diagnose
09-12-2007 04:21 PM  10 years agoPost 1
RCHelicopterGuy

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Michigan

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Hi all,

I've been chasing a vibration in the tail of my R90SE for a while now, and I'm running out of ideas.

First off, a bit about the setup:

* R90SE (stock 8.45 gearing)
* .91 C-Spec pumped (originally), but with the pump removed and a standard 60K carb installed
* Century Silent Power 90 muffler
* OMI Fuel Magnet pickup and muffler pressure
* TJ Pro
* Radix 710 mains / stock plastic tails
* CF tail boom, but aluminum boom supports w/ plastic ends
* Other misc. radio hardware

So anyway, I have my headspeeds set at 1500/1850, and I have this vibrational problem at lower headspeeds. In Normal mode, there's no side-to-side shaking (i.e., the vertical fin is nice and still), but if I watch the pitch slider and bellcrank, they're blurred up-and-down about 1/2 inch. When I go to Idle-Up, things seem to smooth out.

There seems to be a spot around 1550-1600 rpm (just guessing) where the vibrations get so bad that I worry that the tail will come apart, but if you push through it to 1850, it seems to calm down. Likewise, slowing down from 1850 to Normal mode goes through that same violent shaking until I get down to 1500rpm, but the shake never really goes away at lower speeds. I've lowered the headspeed as low as my TJ Pro will hold on, and the shaking never fully disappears, though it gets pretty close.

I noticed that the fuel in the tank never foams - it sits there as placid as a mountain lake. Because of that, I started looking at things like main/tail blade balance. I've checked both spanwise and chordwise CG of my main blades, and they're identical to each other. Total weight is equal. The head was balanced with/without blades on a Hi-Point... all good. The tail rotor, same thing. I checked the runout on the fan... .0015" (can't get any better with this screw-on fan). The boom is fully inserted, then backed out 2mm. Gear mesh was good on the engine side, but tight on the tail tranny side (I have since monkeyed around until I got the tail tranny gear mesh in good shape... head spins more freely, too, which is no surprise). I wrapped 2 strips of electrical tape around the tail boom where the horizintal fin clamp grips the boom, thinking that maybe it might dampen movement - it doesn't (but I like the idea of isulating CF from aluminum anyway, so I'll leave it).

I had Colin and Stephen Bell examine and fly my machine at IRCHA. Colin believed that in Idle-Up, my machine was about as smooth as his, but he doesn't understand the low-speed vibration either.

I want this thing smooth. This is my F3C machine. I want to compete in Class 1 or 2 at the Nats next year, but I'm not going to do anything with a machine that won't even hover smoothly. About the only thing left that I can think of to try would be to put as long a set a boom struts as I can on it, without the tail blades hitting the horizontal fin. It's so odd to me that this thing seems to not have any problems anywhere else except the tail end.

Does anyone have any experience like this? Do you think that changing to an aluminum boom might help anything? I'm at a loss for ideas.

EDIT: I see that someone else on the forum is having problems that sound similar to mine. I then remembered a few things that I should add:

I used to use V-Paddles, and the vibration problem was worse. I put some flybar weights on once, and the vibes seemed to diminish a little. Thinking that maybe I had a set of mismatched paddles, I took them off and replaced them with the stock TT black paddles. The result was about the same as the V's with the flybar weights.

Yes, I already checked the tracking. Main blade, paddle, and tail blade tracking are all perfect. I also checked the runout of both the main and tail shafts - both were under .001".

Just thought I'd add that and save the questions.

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09-12-2007 05:19 PM  10 years agoPost 2
mbkite

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usa

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I have a 90 standard and found my tail shaft to be the problem.
same symptoms How i found it was a guy hear at rr told me to measure from the boom to both tail rotors.
Turn the tail rotors full pitch and line one up with the boom and measure.. Then do the other one.

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09-12-2007 05:24 PM  10 years agoPost 3
RCHelicopterGuy

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Michigan

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You mean a runout problem on the tail shaft?

What points are you measuring from? Are you using the end of the tail blade?

Oh wait, I think I just got a mental image of what you're talking about. Do you mean folding the blades over (like you're going to put it in the car for transport), and measuring from the tip of the blade to the side of the tail boom?

I'll check it again. I'll admit, it would surprise me if that proved to be the case (this is a brand new, never crashed tail shaft), but I've seen stranger things happen.

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09-12-2007 05:31 PM  10 years agoPost 4
mbkite

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usa

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No keep tail blades straight twist ant direction like turn right or left.
Set one blade at a time and ck the distance on both blades from the boom.
I also did the run out and rolled the tail shaft on glass and found nothing.
After a guy hear on rr told me to ck the distance of those rear tail blades i found it.. good luck.

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09-12-2007 05:34 PM  10 years agoPost 5
RCHelicopterGuy

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Michigan

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This might be a dumb question, but wouldn't your readings be affected by whether or not you have the blade pulled out completely straight?

I take it you just replaced your output shaft with a new one...

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09-12-2007 09:53 PM  10 years agoPost 6
mbkite

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usa

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Just get them straight as you can Don't re invent the wheel just check it the best you can. if its off you will be able too tell.

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09-13-2007 12:34 AM  10 years agoPost 7
Dino Spadaccini

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USA

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vib

first things the 8.45 is the wrong gearing for that motor, the 8.45 with put the motor in the wrong power band need the white main gear with is 8.27

Ok i like you to look at this first

the head on the main mast does it fit snugg is there any play there

look at you T tube both ends are they runnning true to do this pull the tail off the boom and the boom out of the heli the spin buy hand the T tube and see if the ends are running true no run out a hair of fun out is ok but if you can see the end moving off center not good

let us know what you find

RIP Roman JR
Capt USA Align Factory Team Align - Conquer Your heart
Team Futaba

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09-13-2007 04:56 PM  10 years agoPost 8
RCHelicopterGuy

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Michigan

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What is considered an acceptable amount of runout on the torque tube?

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09-13-2007 06:09 PM  10 years agoPost 9
Dino Spadaccini

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USA

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run out

max maybe a 1 thou

RIP Roman JR
Capt USA Align Factory Team Align - Conquer Your heart
Team Futaba

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09-14-2007 01:27 AM  10 years agoPost 10
Salby

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Christchurch New Zealand

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A friends 90SE had the same problem, he tracked it down to the spacing of the support bearings in the boom. Im pretty sure he moved the rear support bearing back a bit further. The carbon boom has a lot of flex in it. Grab the boom around where the horizontal fin is & the tail box- now flex it up & down (lots of movement aye) the tail seems to start the vibration & there is nothing to brace the boom from the horizontal fin back so it just does what it wants.

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09-14-2007 01:44 AM  10 years agoPost 11
Kinger

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Granville, OH

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You just might be on to something there Salby.

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09-14-2007 02:48 AM  10 years agoPost 12
RCHelicopterGuy

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Michigan

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Y'know, I remembered to put the bearing carriers in with unequal spacing, but I never thought of making sure that the aft one was far back enough. That's as good an idea as I've heard... I'll try it.

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09-14-2007 12:00 PM  10 years agoPost 13
Costas

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Adelaide - AUSTRALIA

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Another trick is to add an additional bearing spacer for a total of three.

Space them UN-EQUALLY along the length of the shaft to stop any harmonic oscillation/vibration issues.

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09-14-2007 07:44 PM  10 years agoPost 14
RCHelicopterGuy

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Michigan

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Well, I tried Salby's suggestion of moving the bearing carrier a bit further back. I made it worse - the vibrations seemed to die down a little bit in Normal mode, but now in Idle-Up it shakes so bad that I'm worried about the tail exploding!

That Gohbee belt driver conversion idea looks better and better every day. I never much cared for torque tubes.

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09-14-2007 10:12 PM  10 years agoPost 15
Salby

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Christchurch New Zealand

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Well thats sort of good, at least we have tracked the source down. Now how to fix it? I think Costas has got the right idea another support bearing should help. Or you could keep moving the bearings around untill you find the sweet spot. Or fit aluminium boom.

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09-14-2007 11:08 PM  10 years agoPost 16
mbkite

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usa

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Raptors go together blind folded even a cave man can do it.
I think your barking up the wrong tree.
How do i know I barked up that tree my self.

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09-14-2007 11:21 PM  10 years agoPost 17
Salby

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Christchurch New Zealand

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OK

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09-15-2007 02:35 AM  10 years agoPost 18
Ken Filloon

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Highland, Michigan

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Did the vib start after a crash or is this a new Heli?

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09-15-2007 03:08 AM  10 years agoPost 19
RCHelicopterGuy

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Michigan

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This heli's never seen dirt, and these are all the stock components with the SE90.

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09-15-2007 02:02 PM  10 years agoPost 20
Costas

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Adelaide - AUSTRALIA

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Normally these machines go together quite well without any vibe issues.

I suspect that you may have to go over all the rotating components and triple check them in regards to runout. Basically there has to be something that is causing your problem because on most builds (even novice ones) there are no vibe issues.

How about you start by removing the blades (main and tail) and run the heli up to a reasonable speed without over revving it and check to see if you still have vibe issues? You could start isolating the problem by trying to isolate various rotating parts.

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HelicopterThunder TigerRAPTOR 90 › A shaking of the pitch slider that I can't diagnose
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