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HomeAircraftHelicopterHIROBOOther › Help! Sceadu Evo50 vibration problem
10-14-2005 12:01 AM  13 years agoPost 1
GScott

rrElite Veteran

Lewis Center, OH

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I took my Evo50 out today and it seems to have developed a weird vibration/shake. First a little background. I'm still hovering with the training gear on and my Ev50 is running an OS50 Hyper. I took advantage of the bad weather last week to replace a bent spindle and flybar, the gear under the main, and I also tightened up the tail belt and put on some Tuff Struts II. Today was the first post repair flight.

When I bring the speed up it shakes violently when it becomes light on the skids. If I give it some more throttle/collective the shakes go away but it practically shoots into the air. If I get a handle on this I can hover it but it also makes a really high pitched whine type of noise. I really don't even know where to start to troubleshoot this. Anyone have any ideas?

Thanks.
Gary

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10-14-2005 12:47 AM  13 years agoPost 2
Professor Fate

rrKey Veteran

Goose Creek S.C.

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You might have a tracking issue. Check all links, tightness of link balls.

Welcome my son, Welcome to the machine

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10-14-2005 01:58 AM  13 years agoPost 3
Heli-pres

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American Fork

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Vibration
Your training gear is setting up the vibration. Make sure it is on evenly and even if it is, try moving it a little. The high pitch wine is probably the main gear. Most all Evos have this noise. Doesnt mean anything is wrong.
JOHN

Quick UK Flight Team

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10-14-2005 02:41 AM  13 years agoPost 4
Leif

rrElite Veteran

USA

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While I agree that Evos tend to make some gear noise, you really should check the model over carefully if it seems to be misbehaving.

If the fan hub comes loose from the crankshaft the con-rod will scrape the backplate of the engine. This also makes a very high-pitch whine. Of course, the hub will eventually back off to the point of seizing the whole clutch assembly.

Sounds like there are some things you missed after the crash. Best thing is to check it over again, even if you need to do some disassembly in the process.

Leif

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10-14-2005 07:48 AM  13 years agoPost 5
jamppa

rrNovice

Finland

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Please refer to this topic for further information ->
http://www.runryder.com/t189303p1/

Raptor 50, Evo 50, Evo 90, Trex XL CDE

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10-14-2005 08:12 AM  13 years agoPost 6
jkelly

rrVeteran

Bedford, PA

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Definately could be the training gear. I assume the blades are balanced and tracking.

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10-14-2005 01:24 PM  13 years agoPost 7
929pilot

rrApprentice

Jackson, OH

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This sounds stupid but make sure you didn't put one or both of the blades on upsidedown.

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10-14-2005 01:32 PM  13 years agoPost 8
JerryLu

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Gretton, Northants - England

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Question is .... "why did you have to replace the spindle and flybar"?

Obvious answer is blade contact with the ground??

If that is so you should also look for bent mainshaft and/or the alloy hub on top of the mainshaft. It is difficult sometimes to detect a bent hub but either of these items bent will cause a vibration which gets worse as the head speed rises.

Jerry

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10-14-2005 02:58 PM  13 years agoPost 9
GScott

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Lewis Center, OH

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Thanks for the suggestions.

The reason I replaced the flybar was a hard landing on my first gallon of fuel. It occured when I had the rotopod setup in the high position and I landed hard enough to smack the tail and chip a tooth out of the 2nd gear. The flybar was bent when I removed it but the spindle was not as obvious. I replaced it anyway since I had the heli down.

My blades are not tracking 100% but I also flew it for the first 2 gallons without perfect tracking and didn't have any of these problems. I don't think it is the training gear since I didn't have these problems before I replaced the damaged parts.

It is really strange the way it plays out. The shaking is there right before liftoff but disappears with a little more throttle/collective. The best way I can describe it is the shake you get during spool up as your main blades are straightened due to the centrifical force. I'm really concerned about the sudden power spike as it lifts off the ground. It literally shoots up and this causes the heli to rotate quickly to the left. I'm good enough now to catch it and I can hover but with the high pitched noise.

I also replaced the factory struts with the Tuff Struts II and they do sit lower. As a result the training gear is now "closer" to the heli. Could this be causing any of the issues?

Also, how tight should the tail belt be?

Thanks.
Gary

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10-14-2005 03:00 PM  13 years agoPost 10
GScott

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Lewis Center, OH

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I'm pretty sure I put the blades on correct (already done that once) but I'll check again this evening.

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10-14-2005 05:19 PM  13 years agoPost 11
JerryLu

rrApprentice

Gretton, Northants - England

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It's suprising but you can bend the mainshaft in a hard landing even without blade contact. Don't ask me how I know.

I think it is either that or the hub. Suggest you pull the shaft out and roll it on a flat surface to check. A tiny runout will give you this problem.

I do not think it is your training gear. This will shake with a harmonic even with a fully balanced heli. If in doubt, get someone to fly it without.

Cheers

Jerry

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10-14-2005 05:37 PM  13 years agoPost 12
Professor Fate

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Goose Creek S.C.

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Does it do it every time just before lift off or just the first flight? What I mean is my EVO will shake a little on spool up on the first flight after being shut down, that's normal. I can spool it up and let it spool down for a few sec. and it's fine. Have you tried changing the RPM at point of lift off?
Try this...Take the training gear off, see if you still have a problem. Myself...When I first started I couldn't fly with TG. Same way when I learned to ride a bike. Now I ride my motorcycle all over without TG.

Welcome my son, Welcome to the machine

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10-14-2005 05:47 PM  13 years agoPost 13
Leif

rrElite Veteran

USA

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I would recommend that you check the thrust bearings in the blade grips.

Improperly installed thrust bearings can cause binding. This would account for both the out-of-track problem and the rapid change in pitch you experience on lift-off.

Check the manual carefully. The inner diameter of one of the outer race disks is larger than the other, and these need to be positioned correctly for proper centering. If you have the bearing in backwards, it will bind.

Leif

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10-14-2005 10:53 PM  13 years agoPost 14
JerryLu

rrApprentice

Gretton, Northants - England

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I would agree with Leif. Also make sure you have the thin washer in the right place and in both grips. My boy managed to assemble his head once and found a thin washer/shim left over. So what??

What ..... was a nasty vibration, got worse with increased head speed. The shim is necessary to ensure all the bearings sit correctly and are free to rotate as needed.

Just another thing to look into

Jerry

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10-16-2005 11:22 PM  13 years agoPost 15
GScott

rrElite Veteran

Lewis Center, OH

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I took the head apart and rebuilt it. I had a friend look over it and he also found a loose Jesus bolt. It now flies like it did before the repair. Thanks for all the help.

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10-17-2005 02:25 AM  13 years agoPost 16
dkshema

rrMaster

Cedar Rapids, IA

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With regard to the thrust bearings in the grips, the INNER race is the one with the slightly larger inside diameter.

The two ball races have different diameter holes in them. The one with the larger hole goes closest to the MR hub. The race with the smaller hole goes on the outside, closest to the blade bolt.

If you assemble this in the wrong order, the bearings will bind and you'll get erratic collective response, instead of a smooth transition. There's an outside chance that the thrust bearing races themselves are at fault, having small dents where the balls ride in the groove. This will make the collective mechanism erratic and "notchy".

The whine you are hearing is most likely the sound of the plastic gears in the MR and TR drive system. The plastic gears of the Sceadu make quite a bit of noise.

If your thrust bearings are assembled correctly, and you have all the spacers and other parts in the correct place on the head, the wobble could be simply the blades being not lined up correctly as you spool up. This creates an out of balance head and at certain RPM, with the skids still on the ground, the heli can go into a somewhat violent wobble. It's called ground resonance. Getting the skids immediately off the ground will stop the shake, or immediately spooling down the head RPM will also kill the shake. If you remain at that RPM with the heli shaking, it could get bad enough to rip your heli apart.

You may want to check the tightness of your blade bolts to make sure that the blades aren't flopping around or held too tightly. My guess is that you need to tighten them down just a hair.

One other thing on the EVO that needs to be checked if you bend the spindle or main shaft in a hard landing or crash is the aluminum rotor HUB. Although this looks like a good beefy part, it is easily bent. This can make the heli wobble and shake, even if you have a straight spindle and main shaft.

Dave

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10-25-2005 01:50 AM  13 years agoPost 17
hellflyer

rrApprentice

Staten Island NY

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start from the top check your pitch

The first step in gettin help is admitting you have a problem ( yes I am addicted to helicopters )

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10-25-2005 02:27 AM  13 years agoPost 18
CT.Chopper

rrVeteran

Meriden, CT

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Check to see if your blades are to tight or to loose.

to tight they will fight to find there center on spool-up.

to loose they will rock foreward or back on spooldown.

both will cause a violent vibration in the machine
also check the blades for balance and c/g

i have had a set of blades thet were not matched from the factory.

Rob Landry.

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