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harmonic vibration new prop Yak 55m

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Steve Geard

Joined: 09 Dec 2013
Posts: 36

Posted: Mon Jul 07, 2014 4:21 am Post subject: harmonic vibration new prop Yak 55m

Hello all. I've just fitted a set of Whirlwind W530 composite scimitar blades to my Yak55m. Both blades are in 7 turns on the original hub, and set the same pitch. They're about 1mm different from hub to tip. The engineer removed all the balance weights and are running without a dynamic balance. 

I have a harmonic vibration between 80%-99%, a beat frequency if you like.

This seems to indicate both a prop and engine vibration. It's worst at 90-99% at low power setting such as on approach decent.

Should I be worried about the engine possibly having issues, or just dynamically balance the prop?



Cheers Steve.

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SteveO

cjpilot710(at)aol.com
Guest

Posted: Mon Jul 07, 2014 4:38 am Post subject: harmonic vibration new prop Yak 55m

Try dynamically balancing the prop first.  That usually cures a lot of  problems.

  

 Jim "Pappy" Goolsby

  

  In a message dated 7/7/2014 8:22:49 A.M. Eastern Daylight Time,  stevegeard(at)xtra.co.nz writes:

  	  Quote: 	
		  -->    Yak-List message posted by: "Steve Geard"    <stevegeard(at)xtra.co.nz>



Hello all. I've just fitted a set of    Whirlwind W530 composite scimitar blades to my Yak55m. Both blades are in 7    turns on the original hub, and set the same pitch. They're about 1mm different    from hub to tip. The engineer removed all the balance weights and are running    without a dynamic balance. 

I have a harmonic vibration between 80%-99%, a    beat frequency if you like.

This seems to indicate both a prop and engine    vibration. It's worst at 90-99% at low power setting such as on approach    decent.

Should I be worried about the engine possibly having issues, or    just dynamically balance the prop?



Cheers    Steve.



--------

SteveO





Read this topic online    here:



http://forums.matronics.com/viewtopic.php?p=426233#426233

	


 [quote][b]

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dsavarese0812(at)bellsout
Guest

Posted: Mon Jul 07, 2014 5:04 am Post subject: harmonic vibration new prop Yak 55m

Where on the hub are you making             the measurement?  Try making the measurement from the lip             under the counterweight clamp to the same point on both blades.                  Next, recheck the blade angles.  Also make             absolutely certain the counterweight clamps are perfectly flush against lip under the clamp all the way around.  Even a fraction of a mm off from the                         lip under the counterweight will cause an                         imbalance.  If all checks good, them do a                         dynamic balance.

                         Dennis  

        	  Quote: 	
		  A. Dennis Savarese

334-285-6263

334-546-8182 (mobile)

www.yak-52.com

Skype - Yakguy1 	
       On 7/7/2014 7:21 AM, Steve Geard wrote:

     

     [quote]        	  Quote: 	
		  --> Yak-List message posted by: "Steve Geard" <stevegeard(at)xtra.co.nz> (stevegeard(at)xtra.co.nz)



Hello all. I've just fitted a set of Whirlwind W530 composite scimitar blades to my Yak55m. Both blades are in 7 turns on the original hub, and set the same pitch. They're about 1mm different from hub to tip. The engineer removed all the balance weights and are running without a dynamic balance. 

I have a harmonic vibration between 80%-99%, a beat frequency if you like.

This seems to indicate both a prop and engine vibration. It's worst at 90-99% at low power setting such as on approach decent.

Should I be worried about the engine possibly having issues, or just dynamically balance the prop?



Cheers Steve.



--------

SteveO





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=426233#426233



	
     [b]

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wlannon(at)shaw.ca
Guest

Posted: Mon Jul 07, 2014 8:37 am Post subject: harmonic vibration new prop Yak 55m

Steve;



Does the 1 mm represent the blade track?    If so that is within limit. 

Track is the difference between each blade tip passing a fixed point during 

rotation.



As Dennis noted make sure the counterweight clamps are positioned as far 

outboard as possible.



When you say "the engineer removed all the balance weights"  are you 

referring ONLY to the dynamic balance correction attached to the spinner 

back-plate?  That would be the correct action if you were sending a prop in 

for overhaul or blade replacement.   If he has removed ALL balance weight, 

including that attached to the hub,  you do have a problem.



In the first case a dynamic balance is in order.



In the second the prop needs to go to an overhaul facility for static 

balancing.   This is done and corrected in both the horizontal and vertical 

planes.   Dynamic balance should then be done to correct any engine/prop 

imbalance.



One other item that may be a factor is the difference between blade angle 

settings.   This must not exceed 0.1 deg.  I would expect info on this with 

the blades from Whirlwind.



Walt

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Steve Geard

Joined: 09 Dec 2013
Posts: 36

Posted: Tue Jul 08, 2014 2:11 am Post subject: Re: harmonic vibration new prop Yak 55m

Thanks guys, all good info.

Walt I better add a bit of detail. 

My engineer removed the original V530 wooden blades and all the weights on the hub that were used in the dynamic balance on the 55. At that stage there was no spinner or back plate.

These blades were then fitted to a Yak52 and the weights used to dynamic balance the Yak 52.

The blades from Whirlwind that we fitted to the 55 are brand new carbon composite supplied as a matching pair. The agent told me they "should be" with in 2 grams of each other. My engineer didn't weigh them :-/

The 1mm was the difference from center of hub to rear tip of each blade. We are also fitting a matching whirlwind backplate and spinner. They weigh next to nothing are extremely light. 

I was told by someone who had also fitted some carbon composite blades to a Yak55 that they were very smooth without a dynamic balance. 

I'm thinking we should check the angles, check the clamps and do a dynamic balance without the spinner. See how it goes. Are we on the right track? Cheers Steve

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SteveO

Steve Geard

Joined: 09 Dec 2013
Posts: 36

Posted: Tue Jul 08, 2014 2:30 am Post subject: Re: harmonic vibration new prop Yak 55m

Just reread your post Walt.

Are you saying the weights attached to the hub (the flat plates shaped to fit round the hub) are part of the hub static balance, and not used to dynamically balance the blades? That wouldn't be so good, since they're now on another plane LOL.

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SteveO

wlannon(at)shaw.ca
Guest

Posted: Tue Jul 08, 2014 8:07 am Post subject: harmonic vibration new prop Yak 55m

Hi Steve;



Yes.   But not just the hub,  that is the static balance correction for the 

propellor.

Horizontal static balance is corrected first and weight attached.  Then with 

the prop vertical on the balance ways vertical imbalance is corrected by 

moving that weight circumferentially on the hub.



On a rare occasion you may find one of these props with corrective balance 

weights on both sides of the hub.   In that case the vertical unbalance 

correction exceeded the horizontal and additional weight was added  to both 

sides in the correct location to maintain the horizontal correction and 

correct the vertical.



Unless there is a spinner on the propellor dynamic balance may or may not be 

of any value.   Since this is intended to correct mass imbalance of the 

power plant assembly corrective weight may be required in any position from 

0 to 360 degs.

Without a spinner backplate or at least three blades that is a crap shoot.



Walt

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Steve Geard

Joined: 09 Dec 2013
Posts: 36

Posted: Fri Jul 25, 2014 3:07 pm Post subject: Re: harmonic vibration new prop Yak 55m

Well we've dynamically balanced this prop installation. We have a whirlwind  20" carbon composite spinner and it only needed 28grams about 18" out to get the dynamic spot on.

Runs sweet on the ground. But in the air that harmonic is quite evident. 

Especially at high RPM but low power settings such as approach, its so shocking, I'm flying approaches at 80%.

The engineer is thinking a reduction gear issue, these blades are lighter than the standard blades so maybe hide any engine issues less? We have double checked the pitch and diameters are within half a millimeter (1/64 for you Americans   the clamps are right out to the edge.

The only thing we didn't do was a static balance because the blades are supposedly very accurate in dimension and weight. Any more hints guys before we pull the prop off and start again?

Thanks Steve New Zealand.

P.S. in flat spins I get pitch hunting of around 5% i.e(98%-93%) Not sure if thats relevant, could the fault be in the governor. Oh boy we could be here awhile.

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