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HomeAircraftHelicopterMain Discussion › flybarred heli and bad shakes
11-13-2014 02:12 AM  3 years agoPost 1
honda411

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Surprise, AZ USA

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Okay so I bought a trex 700n and it has a flybarred head. When in normal mode the whole airframe shakes and wobbles side to side. It's at about 1700-1800 hs and didn't really switch into idle up 1 because it was in front of the house. Any ideas? Now I remember why I went fbl. What a pain. I figured flybar would be fun again.

HeliDirect Field Rep, Synergy N7 w/ OS 105, Torq Servos, Cyclone/ Rail blades

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11-13-2014 02:20 AM  3 years agoPost 2
RM3

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Killeen, Texas - USA

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You could start by looking for loose links, too tight main blade grips, bell cranks loose, bent main shaft... etc.

showing a preference will only get you into trouble, 90% of everything is crap...

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11-13-2014 02:21 AM  3 years agoPost 3
JasonJ

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North Idaho

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Gotta balance the entire head assembly. I use a good prop balancer that I can put the whole mess in, mainshaft and all. Always had good smooth running helicopters.

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11-13-2014 02:47 AM  3 years agoPost 4
honda411

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Surprise, AZ USA

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I do wonder if it's the blades are too tight. I tend to run mine tighter than normal I think.
I'm gonna pull the head off and roll it on a prop balancer

HeliDirect Field Rep, Synergy N7 w/ OS 105, Torq Servos, Cyclone/ Rail blades

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11-13-2014 02:55 AM  3 years agoPost 5
Gearhead

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Vt

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check your Dampeners

Jim
Buzz Buzz Buzz

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11-13-2014 02:57 AM  3 years agoPost 6
honda411

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Surprise, AZ USA

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I was thinking about putting the harder green ones in. Aftermarket dampeners

HeliDirect Field Rep, Synergy N7 w/ OS 105, Torq Servos, Cyclone/ Rail blades

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11-13-2014 11:27 AM  3 years agoPost 7
Heli_Splatter

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USA

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Main bearings! Sounds like main shaft or feathering shaft... roll both.

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11-13-2014 01:40 PM  3 years agoPost 8
Pistol Pete

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Seffner, FL

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I would check for flybar rod not centered and or blades too tight.

~~Enjoying the hobby one flight at a time~~

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11-13-2014 03:05 PM  3 years agoPost 9
Aaron29

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USA

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I take it this is a used heli?

Buying a used heli isn't normally plug and play. People don't often get rid of perfectly good helis.

I'd do a pretty extensive inspection. Shaking is often crash damage. Look it over. Even if it's not crash damage, a well maintained heli doesn't shake, used or not. Again, people don't sell perfectly good helis. Seller probably flew it into ground or gave the poor thing a long hard life without enough maintenance, then sold here when it no longer fit their needs like a arched back mule.

At a minimum:

Check all shafts for straightness
Balance the main blades and tail blades
Replace dampers

And FWIW, shaking/wobbling problems are not unique to FB.

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11-14-2014 01:14 AM  3 years agoPost 10
RPM 1.5

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Cape May New Jersey

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Make sure paddles sure good straight level and even from head on both sides

Ray

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11-14-2014 02:00 AM  3 years agoPost 11
unclejane

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santa fe, NM, USA

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It's at about 1700-1800 hs and didn't really switch into idle up 1 because it was in front of the house. Any ideas? Now I remember why I went fbl. What a pain. I figured flybar would be fun again.
Yeah the 700N flybar will "belly dance" at certain rotor speeds (I know, I've had two of them. I even still have the old heads in the living room even tho the machines died a while back).

There's not a whole lot you can do about it, other than try to find a headspeed where it goes away. Mine seemed to sit still at higher headspeeds so that's what I'd try.

I kept the governor speed control on one of the swipers on my transmitter (CGY 750), so I could monkey with the headspeed in flight.

Really heavy paddles and blades also seemed to make it worse, so I ran really light Align paddles and 690 blades....

LS

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11-14-2014 04:15 AM  3 years agoPost 12
honda411

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Surprise, AZ USA

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Thanks for the replies guys! All of you!
The heli was bought used on here a while ago.
I did take every bolt off anf check and loctite them back in. The shafts i did not check if they were straight. I should do that now.
Maybe the blades are too tight also. The blade tracking is good along with flybar paddle tracking.
The flybar seemed to be neutral.
Im afraid to go higher head speeds since its shaking. But will try that also and all things mentioned.

HeliDirect Field Rep, Synergy N7 w/ OS 105, Torq Servos, Cyclone/ Rail blades

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11-14-2014 05:37 AM  3 years agoPost 13
AgentOrange

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Jacksonville, Florida

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Mine did that too. I just upped the head speed a little bit and it went away. It must be something with the head harmonics with the airframe at certain head speeds.

Trying not to put them in the dirt.

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11-14-2014 02:28 PM  3 years agoPost 14
JasonJ

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North Idaho

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Out of balanced tire vibration goes away too if you drive faster. Doesn't mean it isn't still doing damage. You have to fix the situation or it will lead to reduced bearing life or worse. Just take the time and balance the assembly. Make sure the main shaft is perfectly straight, roll it on glass. Put the head/main shaft assembly in a balancer. Make sure the dampeners are good and the feathering shaft can slide freely. Make sure the blade grips are assembled properly. Thrust bearings put in wrong on one grip can cause chaos. Take the paddles off and balance the head with just the flybar. Once it's perfect put the paddles on and balance again until perfect. Don't have the blades too tight or too loose. Make sure the main shaft bearings are good. Do all of this and you should have a smooth machine. Just powering through an unbalanced machine is frankly lazy and unacceptable, this stuff is fixable with a few hours work.

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11-14-2014 02:29 PM  3 years agoPost 15
Aaron29

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USA

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I had a TRex 700N. It didn't shake at any reasonable headspeed.

Fix your heli.

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11-14-2014 02:46 PM  3 years agoPost 16
AgentOrange

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Jacksonville, Florida

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What ever bro. My head was balanced and blades were balanced and it still had a small shimmy. So it does do with a balanced assy or not. Just becuase your head is perfectly balanced does not mean the machine will not vibe a little. So know who and what you are talking about first before you say someone is lazy.

Trying not to put them in the dirt.

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11-14-2014 02:51 PM  3 years agoPost 17
Aaron29

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USA

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No one said anyone was lazy.

Looking back at the posts more than one says change headspeed. Jeez. Seems like shoddy quality and doesn't speak well for Align, IMO.

Maybe the hub machining had excessive space creating a need for shims on the spindle to keep it from shifting? Or maybe bad machining on the main grip holes creating a spacing/length difference? Or perhaps the whole thing has improper damper design?

It doesn't take much to get a shake. But if this is an Align "design feature," I guess I got lucky with my old Rex. I'm glad I'm more into Mikado/Hirobo now.

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11-14-2014 03:22 PM  3 years agoPost 18
AgentOrange

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Jacksonville, Florida

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Ok guys here is the deal. You are now wanting to possibly blame bad equipment from Align. I say no to that. You guys say balance the head. Ok thats fine but hear this. Lets go back to the tire scenario. A tire place like Tires Plus or Goodyear or any tire place only balances your tires at 55mph. I doing so your tires are going to be balanced at 55mph. Any speed lower or higher then that could have a slight vibration. Same goes for your head. If you balance it for 1900 head speed then at 1900 head speen it will be rick soild smooth. Any rpm below or above that you could decelop a vibration. This does not mean that you have a out of balance head or bad equipment. I am a full size heli mechanic and am a vibration tech so balancing and vibrations are my thing. It is impossible to balance a head for all rpm ranges. So again if his idle 2 rpm is 1900 and his normal mode head speed is 1700 then his head could be balanced for the higher head speed and that is what is causing his shakes. But you guys do what you want just my 2 cents.

Trying not to put them in the dirt.

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11-14-2014 03:27 PM  3 years agoPost 19
Aaron29

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USA

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Upon further reading, this seems to be mast bumping.

So perhaps it's this:
the whole thing has improper damper design?
Many helis have mast bumping at 1500 or less RPM but this sounds to be happening at a more normal operating range. Disappointing and I feel for the OP. But don't blame flybars.

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11-14-2014 04:05 PM  3 years agoPost 20
unclejane

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santa fe, NM, USA

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Looking back at the posts more than one says change headspeed. Jeez. Seems like shoddy quality and doesn't speak well for Align, IMO.
Aw, c'mon, stop that, fellers.... There's nothing wrong with it, it's just how the 700N flybar model is. I've had two of them, balanced and tracked to within an inch of their lives searching for the same problem . It just does that, probably because of the higher rotor disk height to accomodate the flybar and the lower CG because of the presence of the engine.

Just crank up the headspeed until it goes away and it'll be fine. Don't spend days and days tearing it up - I've already done that for you LOL....

Do experiment with different paddles and blades, though. That can make a difference. I did find that lightweight 3d paddles and blades seemed to work a little better than heavy ones.

LS

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