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Mikado Modellhubschrauber . GrandRC . CanoMod

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Aerial Photography and Video > Main-blade-induced vibration ....?
 
 
Hogster
Key Veteran
Location: Surrey, UK

Right! Well I've just installed a new flybar, and used a pitch gauge to ensure both paddles were *exactly* parallel to each other. I then ensured the flybar was perfectly centred (did this before putting the paddles on the end, and after as well), and ensured the paddles were exactly parallel to the blades (again with a pitch gauge).

If they aren't level now ... well there's no hope

I've already made sure that the paddles weigh exactly the same too ...

Hopefully I'll be able to try it tomorrow morning! If it still doesn't improve the slight vibration, I won't worry too much, as I'm planning to go flybarless very soon anyway

Will report back soon


David
03-05-2008 07:54 PM
HOMEPAGE  
 
 
Hogster
Key Veteran
Location: Surrey, UK

Hmmmm not a big difference ... in fact almost no difference

I'm suspecting the blade grips now ... the blades are still split by a very small amount ...

It'll do fine until I upgrade to the flybarless head which should remove a a lot of the factors that could be contributing towards this problem.

Cheers for now,


David
03-06-2008 10:42 AM
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Hogster
Key Veteran
Location: Surrey, UK

Here's a video from the helicopter. The vibration isn't bad enough to affect the video quality (although it's only VGA), but I would still prefer it not to be there ...

http://www.vimeo.com/758304

Cheers,


David
03-06-2008 12:41 PM
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IKA photo
Senior Heliman
Location: Honolulu, HI

Thats pretty smooth David! Are you using soft dampers? On my Trex, I get nasty ground resonance while spooling down with the harder dampers, Even with no vibes while in the air.
03-06-2008 01:31 PM
 
 
Hogster
Key Veteran
Location: Surrey, UK

No I'm using hard dampers .... I think .... I think I've also got a set of soft dampers but the difference seems to be very slight ...

The vibration problem is mainly visible in the air, although also on the ground too.

It's most noticeable at the ends of the Askman undercarriage ... I guess the frequency of the vibration has hit the resonant frequency of the UC ...

Hmmm

Cheers


David
03-06-2008 01:55 PM
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rerazor
Elite Veteran
Location: Mich.

Video looks smooth to me besides "pilot induced stability" issues.

Must not have the Helicommand yet or else it would have been a level flight video thru out.

Is that still the old house, haven't torn it down yet?
03-06-2008 02:21 PM
 
 
Hogster
Key Veteran
Location: Surrey, UK

It was blustery too mate, not just shaky fingers

Nah it's all happening in 2009 ... still have several million tons of rubbish strewn around the house that needs to be sorted through first before it can be knocked down


David
03-06-2008 03:03 PM
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AceBird
Elite Veteran
Location: Utica, NY USA

Quote 
I guess the frequency of the vibration has hit the resonant frequency of the UC ...

I am not quite sure what you are trying to say here. If the frequency of the vibration has hit the resonant frequency of the anything the amplitude would grow and be very visible which it is not. I think there is still vibration in your video but it doesn’t show up much at a wide angle setting. Zoom in and you will likely see the vibrations. It is not something that you would normally want to do but if you are trying to make a comparison between different set ups it will give you a better comparison for you to tell which is better.

Ace
What could be more fun?
03-06-2008 05:59 PM
 
 
Hogster
Key Veteran
Location: Surrey, UK

Quote 
If the frequency of the vibration has hit the resonant frequency of the anything the amplitude would grow and be very visible which it is not.
This is what I'm saying. The tips of the undercarriage vibrate noticeably when the heli is flying.


David
03-06-2008 06:16 PM
HOMEPAGE  
 
 
tabbytabb
Elite Veteran
Location: seattle

Did you try loosening up the blades until they are sloppy loose?

Mine likes them so lose that I have to give it a hand prespin, anything tighter will give similar issues.


Tabb
03-06-2008 08:22 PM
HOMEPAGE  
 
 
Hogster
Key Veteran
Location: Surrey, UK

Hmmmm I haven't tried them that loose ..... I was worried that they would rattle in the grips then ....

Ah well, can but try! Will try it tomorrow

Thanks


David
03-06-2008 08:37 PM
HOMEPAGE  
 
 
cwd10
Veteran
Location: PA, - U.S.A.

If none of the other suggestions pan out:

Buy, borrow or steal another set of blades, and try them with all else being equal. It might be that your heli just doesn't like those blades, due to all the resonants and so fourth. Sometimes a perfectly good set of blades wont work on a certain heli, but will be fine on another. I had this problem with a Logo 20 that I had a couple years ago. New set of blades, and problem went away. Sold the blades to a local guy and they worked great. Go figure.
03-06-2008 08:55 PM
 
 
Hogster
Key Veteran
Location: Surrey, UK

Hmmmm ... the strange thing is that this heli has flown absolutely vibration-free before .... with those blades .... *thinks*

Will try having the blades less tight and see if it makes any difference.

I do have a set of 500mm blades I could try, but I would like to get this heli running the way it used to run ... with these blades

Cheers,


David
03-06-2008 10:53 PM
HOMEPAGE  
 
 
tabbytabb
Elite Veteran
Location: seattle

I bet it is the blade tightness,

Reason it is hit and miss is humidity and heat and expansion and contraction of the blade grips leading to lead lag problems and a small oscillating vibration.

All my logos and jokers do the same thing if the blades are too tight.

The german machines for some reason love the loosey goosey blade grips.


Tabb
03-06-2008 11:22 PM
HOMEPAGE  
 
 
Hogster
Key Veteran
Location: Surrey, UK

Just tried it with the blades very sloppy (pre-spin by hand required) and there's virtually no difference I later tried them very tight and it was the same.

I also tried swapping the blades over and it was the same.

I also tried an old set of 500mm blades and the vibration was still there.

I'm still suspecting the blade grips All the bearings seem in good working order and the feathering spindle isn't bent at all either .... neither is the main shaft.

Just waiting for a few cheques to come through before I can go ahead with the flybarless upgrade


David

Edit: Tracking is still out a touch ....
03-07-2008 02:41 PM
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Hogster
Key Veteran
Location: Surrey, UK

By the way, I don't know of how much significance this is but I thought I should mention it ... the vibration increases significantly when the pitch is increased when climbing.

Using my mad worn-blade-grip theory () I guess the extra load caused by increasing the pitch could be distorting one of the grips (assuming it's damaged somehow), causing a further imbalance in the system ...

Also, I tried lifting our camcorder with the heli (which is heavier than my normal payload), and again, the vibration was considerably worse (more load on the system).

Oh, and without the main blades there's no vibration ...

Cheers


David
03-07-2008 03:38 PM
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FCM
Elite Veteran
Location: Back in Blighty!

There's an outside chance that you could be locking up one of your blade grips. This can cause similar symptoms that you have just described.

Paul.
03-07-2008 03:40 PM
 
 
Hogster
Key Veteran
Location: Surrey, UK

How do you mean 'locking up'?

Thanks


David
03-07-2008 03:48 PM
HOMEPAGE  
 
 
rerazor
Elite Veteran
Location: Mich.

When is the last time you changed your main shaft bearings?
03-07-2008 04:03 PM
 
 
Hogster
Key Veteran
Location: Surrey, UK

Um ...... haven't


David
03-07-2008 04:08 PM
HOMEPAGE  
 
 
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Aerial Photography and Video > Main-blade-induced vibration ....?
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