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Clocking the prop - 3-blade ?

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sarg314(at)comcast.net
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Posted: Sun Mar 02, 2008 6:47 am Post subject: Clocking the prop - 3-blade ?

I am willing to believe that clocking the (2-blade) prop makes a 

difference, though I am at a loss to understand why.  It must have some 

explanation in the dynamics - very small flexure in something occurring 

on each power pulse or something like that.



	But I have a Catto wooden 3-blade prop (not flying yet).  Are there any 

clocking issues with a 3-blade?



	Presumably the more blades, the less it matters.  Also, the total 

moment inertia of the wooden prop (17 lbs and 3" shorter blades) is much 

less than the moment of the metal 2-blade, so I'm guessing it's not an 

issue.  Can any of you Catto users confirm this?



Thanks,

--

Tom S., RV-6A

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sarg314(at)comcast.net
Guest

Posted: Sun Mar 02, 2008 10:27 am Post subject: Clocking the prop - 3-blade ?

Well, I can reply to my own posting in this case. I had also sent an 

email about clocking to Craig Catto when I posted to the list, but was 

not optimistic about receiving a reply any time soon.  Craig replied 

within a couple hours!



Craig says that wood props are less sensitive to clocking than metal and 

3-blades less sensitive than 2-blade - generally.  Sometimes clocking 

does make a difference with a wooden prop.   It's all a matter of 

harmonics.  He has no recommended clocking for the 3-blade wooden prop, 

but says if you sense any enhanced vibration at some rpm range, it is 

worth trying to rotate it one-hole to see if it helps.



tom sargent wrote:

 	  Quote: 	
		   

 

     I am willing to believe that clocking the (2-blade) prop makes a 

 difference, though I am at a loss to understand why.  It must have some 

 explanation in the dynamics - very small flexure in something occurring 

 on each power pulse or something like that.

 

     But I have a Catto wooden 3-blade prop (not flying yet).  Are there 

 any clocking issues with a 3-blade?

 

     Presumably the more blades, the less it matters.  Also, the total 

 moment inertia of the wooden prop (17 lbs and 3" shorter blades) is much 

 less than the moment of the metal 2-blade, so I'm guessing it's not an 

 issue.  Can any of you Catto users confirm this?

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Mark Phillips in TN

Joined: 10 Jan 2006
Posts: 431
Location: Columbia, TN

Posted: Sun Mar 02, 2008 8:34 pm Post subject: Clocking the prop - 3-blade ?

In a message dated 03/02/2008 8:49:10 AM Central Standard Time, sarg314(at)comcast.net writes:

  	  Quote: 	
		  Can any of you Catto users confirm this? 	


 I tried a re-clock on my Catto 3-blade during early testing as an experiment by shifting it one hole.  Not a major difference, but it did seem to shift from 90% smooth to maybe 95%, but then again, that may have been a placebo reward for my efforts.

  

 Much more importantly, be sure to wait until final paint is on the spinner, then decide what to do- after painting I picked up a noticeable vibration around 1900 rpm, most apparent when reducing power, that I hadn't noticed before.  One dynamic balance session later, it was running much to my satisfaction, and remains so after nearly 475 hours...

  

 From The PossumWorks in TN

 Mark



Delicious ideas to please the pickiest eaters. Watch the video on AOL Living.

  [quote][b]

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_________________
From The PossumWorks...

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