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Aerial Photography and Video > Main-blade-induced vibration ....?
 
 
FCM
Elite Veteran
Location: Back in Blighty!

Rotor heads can lock up if they are overloaded typically when running heavy blades on a head that isn't designed for it. This used to happen a lot before most manufacturers started using thrust races in heads. Even with thrust races, if the bearings are pitted/dry, then a lock up can occur which normally only happens on one blade grip hence the out of track condition.

Paul.
03-07-2008 04:37 PM
 
 
AceBird
Elite Veteran
Location: Utica, NY USA

Quote 
I tried spooling it up without the blades, and although there's a strong buzz in the airframe, it's at the frequency of the tail rotor (I imagine).

I think you should revisit this. As the energy passes through the frame the frequency can change. Without the mains on the heli should be pretty damn smooth. Check gearing, belting, bearings, tail feathers. You may think it is in the head but maybe it isn’t.

Ace
What could be more fun?
03-07-2008 05:41 PM
 
 
CoastalTom
Senior Heliman
Location: Foley, AL (7 miles N of Gulf Shores/Orange Beach)

I still think it is as I thought before. More pitch is causing the blade with the worn grip to "flex" up, therefore out of track, thus vibration.


Quote 
David,

Another thing to consider is the actual blade grips. I don't know if yours are metal or plastic. I recently had problems with some raptor plastic grips in that they were old, and the bearings had actually worn the inside of the grips enough that there was considerable wobble when mounted. Replacing bearings/dampners/spindle didn't help until I replaced the grips.

Tommy Patterson - Gulf Coast Aerials
03-07-2008 07:58 PM
HOMEPAGE  
 
 
Hogster
Key Veteran
Location: Surrey, UK

Thanks for the input guys

I've ordered a new set of blade grips ... apparently the flybarless head upgrade doesn't come with them, so I will need a new set anyway.

By the way, yesterday I discovered that I'm running 580mm blades on this ship and not 550s as I thought!!! No wonder it auto'd so well last month!

I was given the blades second hand from a chap on this forum (thanks Garry ) and was told they were 550mm ... so I just accepted that. It was only yesterday whilst over at Gordon's (Tarling) place when comparing it to his 550mm heli that I realised my blades were longer!

So the head and grips have probably been put under undue stress all the time I've been running the 580s ...

The grips are a very old style apparently, and the newer ones are meant to be beefier .... which can only be a good thing

Will let you know how that affects the vibration problem

Cheers!


David
03-10-2008 02:39 PM
HOMEPAGE  
 
 
djdaveq
Senior Heliman
Location: new york new york usa

i have had situations where my dampers were too lose or too tight. and the same with my blades. i actually have a looser damper and blades than id like to have but it works! maybe you need to mess with that
03-10-2008 06:48 PM
 
 
Hogster
Key Veteran
Location: Surrey, UK

I've tried it with the new blade grips and it seems better .... although I've also changed the camera mount configuration ....

Will have more chance to test it in the coming days.

I have done a test where I've removed the rotor blades and tail blades and there's absolutely NO noticeable vibration if you touch the tailboom. I then put the tail rotor blades on and even then there was very little noticeable vibration. I added a small amount of tape to one tail blade which reduced it still further.

So now with the new setup I will experiment with blade tightness, CofG (I now have a battery mount which allows the CofG to be adjusted), tracking, and swapping the rotor blades over (that seemed to make a difference last time). The rotor blades have been balanced both in terms of both weight and CofG and they're fine ....

I'm running out of options!

djdave - what do you mean when you say dampers? The rubber o-rings in the rotorhead?

Cheers


David
03-13-2008 11:23 PM
HOMEPAGE  
 
 
rerazor
Elite Veteran
Location: Mich.

Worn out main shaft bearings.....?
03-14-2008 03:27 AM
 
 
rroback
Key Veteran
Location: Irvine (UCI), Ca

What's the vibration now look like? bent tail shaft? You've now balanced all the blades... shafts are true... bearings feel smooth?

Rhett... There's no power like E Power!
03-14-2008 03:43 AM
 
 
Hogster
Key Veteran
Location: Surrey, UK

SUCCESS!!!

I've just tried putting the blades on the other way round and there's virtually NO vibration anymore!

So much so, that for the first time I've been able to take a video from our SD camcorder which is a heavy beast - I've tried it on the heli before, and it produced hideous amounts of vibration! Now it's smooth!!

Here's an onboard video from the heli

http://www.vimeo.com/784240

I think the residual vibration might be caused by either CofG (although that's pretty much spot on) or maybe tracking ...

Yippeeee!


David

PS. Am running the blades loose now ....
03-14-2008 12:49 PM
HOMEPAGE  
 
 
IKA photo
Senior Heliman
Location: Honolulu, HI

Great David. Now make sure you mark a master blade and a master grip, and always put it back teh same way
03-14-2008 12:54 PM
 
 
Hogster
Key Veteran
Location: Surrey, UK

Have done already


David
03-14-2008 01:00 PM
HOMEPAGE  
 
 
eyeinsky
Senior Heliman
Location: Fall River, Nova Scotia, Canada

If you are still having some vibration issue after you have tracked and balanced the blades and this is your new fwd mount setup with the long Ask man landing gear. Try and remove the pool noodles, I had similar issue with my new landing gear setup. The vibration was caused by the down wash on the larger surface area.

Hard job competing with gravity.
03-15-2008 02:17 AM
 
 
Hogster
Key Veteran
Location: Surrey, UK

Mmmm ... I'm now in the process of shortening the legs and skids ... and I might consider putting thinner skids on too

Will post any update pics here

Thanks!


David
03-15-2008 02:21 AM
HOMEPAGE  
 
 
AceBird
Elite Veteran
Location: Utica, NY USA

Quote 
Here's an onboard video from the heli

David, did those blades always sound like that? How about everyone else, is that what your blades sound like on an electric? I think there is alot of flapping going on for a hover. It might just be that I am not used to electrics.

Ace
What could be more fun?
03-15-2008 02:02 PM
 
 
Hogster
Key Veteran
Location: Surrey, UK

It depends on the wind condition really .... if it's calm you usually won't get that, but if it's blustery you will ...

Having said that, they're not the quietest blades I've used ....


David
03-15-2008 02:14 PM
HOMEPAGE  
 
 
Hogster
Key Veteran
Location: Surrey, UK

Just to bring this thread to a neat conclusion, the vibes are pretty much 100% gone now!

See the bottom of this page:

http://runryder.com/helicopter/t416465p1/

Yippeee!!


David
03-16-2008 01:37 AM
HOMEPAGE  
 
 
FCM
Elite Veteran
Location: Back in Blighty!

Glad you got it sorted. Your heli does sound a bit sensitive but I guess that is how all of this model behave.

Paul.
03-16-2008 03:01 AM
 
 
Hogster
Key Veteran
Location: Surrey, UK

Hmmmm now that I've gone flybarless I've got a vibration problem again!

I would like to ask a few questions, if I may ....

When balancing rotor blades I know you need to get two main things the same .... their weight, and the distance of their centres of gravity from the roots (or tips).

I've got a good set of analog scales which can measure roughly in 0.2g intervals, and I've checked the CofG location by balancing each blade on a razor blade ....

So my question is, if both of these have been done successfully, is there anything else that regarding the blades that needs to be checked? Tracking of course, and blade tightness are two the come to mind ...

It's just, I've got the head of my heli off at the moment (just the main shaft is sticking out ... which is bent ... which is why the rotor head isn't on it at the moment ), and there is no vibration coming from the tail rotor. Being flybarless, there are only three components that could be causing the vibration - the blades, the rotorhead and grips (and the spindle, which is dead true), or the swashplate and swash driver!

Perhaps before the major vibration which bent the shaft (when testing my new front-mount), the main shaft was bent in a way that I couldn't see when spinning it in situe (no rotor head) and resting my finger on it ..... it did seem very straight though! ...

Any thoughts chaps?

Many thanks!


David
05-03-2008 03:28 AM
HOMEPAGE  
 
 
rerazor
Elite Veteran
Location: Mich.

What about the head dampening (spindle). Is it to soft/hard for flybarless? I haven't had to mess with that yet but I thought I read somewhere about it.

Sorry to add yet another variable.
05-03-2008 03:40 AM
 
 
Vortex Aerial
Senior Heliman
Location: Huntington Beach Ca

Ill second the head damping. My L10 has the stock spindle O-rings that came with the kit. They are the softest ones. I notice that when its hot outside the L10 will have a very minor shake to it that looks like an out of balance head (tail trans vibrates in the vertical plane). By the end of the first flight or the beginning of the second, its gone. I figure the o-rings cool down from the rotory motion and stiffen back up just a touch. Thinking of moveing to the next hardest o-ring set to prove my theory.
At any rate id have to be a mean out of balance situation that made yours come apart.
05-03-2008 06:24 AM
HOMEPAGE  
 
 
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Aerial Photography and Video > Main-blade-induced vibration ....?
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