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  #11  
Old 07-19-2011, 01:02 PM
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Toobuilder Toobuilder is offline
 
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Originally Posted by elippse View Post
Sorry, Larry, but that's one of the well-known facts that is totally wrong and should have been eliminated long ago. The reason on a CS prop that a three-blade will be slower is that it usually has such draggy hub-shapes that the plane's total drag is much higher...
If the 2 blade and 3 blade are under the same 14 inch spinner, how does a "draggy hub" factor into the total drag of the airplane?
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  #12  
Old 07-19-2011, 08:45 PM
elippse elippse is offline
 
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Originally Posted by Flyfalcons View Post
How different were the biplane's prop designs?
The four-blade was for 250 rpm more than the three-blade, and the latest four-blade was for 250 rpm more than that!
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  #13  
Old 07-19-2011, 08:50 PM
elippse elippse is offline
 
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Originally Posted by Toobuilder View Post
If the 2 blade and 3 blade are under the same 14 inch spinner, how does a "draggy hub" factor into the total drag of the airplane?
Take and make up some foam shapes that have the same 3"-4" round airfoil as do most of the CS hubs about 4"-6" long and attach 2 or 3 of them on the side of your plane. Do you think they will add drag? You bet your bottom they will!
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  #14  
Old 07-19-2011, 08:54 PM
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Quote:
Originally Posted by elippse View Post
The four-blade was for 250 rpm more than the three-blade, and the latest four-blade was for 250 rpm more than that!
So, quite a bit different then.
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  #15  
Old 07-19-2011, 08:56 PM
Kyle Boatright Kyle Boatright is offline
 
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Originally Posted by elippse View Post
The four-blade was for 250 rpm more than the three-blade, and the latest four-blade was for 250 rpm more than that!
Then the engine was delivering more HP. Also, was the prop and subsequent rpm increase the only year over year modification or is the owner involved in a drag reduction program?

Without all of the pertinant details, it is impossible to evaluate prop performance claims.
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  #16  
Old 07-19-2011, 09:27 PM
ccrawford ccrawford is offline
 
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Originally Posted by Kyle Boatright View Post
Then the engine was delivering more HP.
I don't believe an increase in RPM automatically means an increase in HP, but I could be wrong here. Besides, aren't we suppose to be getting the goods on this 150 HP super fast RV6?
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  #17  
Old 07-20-2011, 04:39 AM
Kyle Boatright Kyle Boatright is offline
 
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Originally Posted by ccrawford View Post
I don't believe an increase in RPM automatically means an increase in HP, but I could be wrong here. Besides, aren't we suppose to be getting the goods on this 150 HP super fast RV6?
An RPM increase absolutely does result in more HP. Speaking of which, what were the before RPM on the RV-6?

My point with the biplane extends to the RV-6. We need all of the pertinant information - what portion of the speed increase was due to the cooling air fairing? What portion was due to more engine HP? What portion was due to the increased aspect ratio? What portion is due to the (my assumption) modern gear leg fairings and pressure recovery wheel pants, neither of which was available when Van's RV-6 spec's were published? And finally, once we back out those factors, what final improvement can be attributed to the prop?
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  #18  
Old 07-20-2011, 06:30 AM
F1R F1R is offline
 
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Default Bottom cowl for drag reduction



The photo of Vetterman's exhaust cowl is on his web site(at the bottom) along with the speed trials and flight test data.

Last edited by F1R : 07-20-2011 at 07:03 AM.
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  #19  
Old 07-20-2011, 11:45 AM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by elippse View Post
Take and make up some foam shapes that have the same 3"-4" round airfoil as do most of the CS hubs about 4"-6" long and attach 2 or 3 of them on the side of your plane. Do you think they will add drag? You bet your bottom they will!
So you're talking about the draggy root of the blade, rather than the hub mechanism itself... THAT makes sense.

...Still need an apples to apples comparison though - same RPM, conditions etc. to determine if "simply" having more blades hurt or help speed.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
______________
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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  #20  
Old 07-20-2011, 12:19 PM
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digidocs digidocs is offline
 
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Default They're wings right?

Paul,

I'm curious --- how do the total blade area and the aspect ratio change as you add more blades to your designs?
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