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Losing rpm on takeoff
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MichaelGibbs(at)cox.net
Guest

Posted: Thu Dec 02, 2010 11:51 pm Post subject: Losing rpm on takeoff

Bruce sez:



 	  Quote: 	
		  Cavitation and stall are quite the same but with different mediums, 

it's still only semantics.


	


Guy's explanation shows clearly that this is NOT the case.  From 

Wikipedia <http://en.wikipedia.org/wiki/Cavitation>: "Cavitation is 

the formation of vapor bubbles of a flowing liquid in a region where 

the pressure of the liquid falls below its vapor pressure."



No mention of angle of attack or separation from a surface.  And air 

doesn't changing phases in a stall!



 	  Quote: 	
		  You only said the same thing the first feller said a long time ago 

but yet another way. We all get it.


	


Apparently not...  



Mike G.

N728KF, Kitfox IV-1200 Speedster

Phoenix, AZ

 	  Quote: 	
		  On Thu, Dec 2, 2010 at 10:44 PM, Guy Buchanan 

<<mailto:gebuchanan(at)cox.net>gebuchanan(at)cox.net> wrote:




<<mailto:gebuchanan(at)cox.net>gebuchanan(at)cox.net>

On 12/2/2010 1:52 PM, b d wrote:



Yes, it's semantics, with a prop in a liquid (a hydrofoil) it's 

called cavitation and with an prop in air (an airfoil), it's called 

a stall but essentially the same-o same-o.

OOO I LOVE semantics. Actually, cavitation is quite different from 

stall. Cavitation involves a phase change from liquid to gas due to 

pressure drop over the airfoil. Since the gas is compressible it 

vacates the low pressure region of the airfoil destroying lift. 

Stall is where the streamlines in the low pressure region depart 

catastrophically from the airfoil surface. It can happen in liquids 

and well as gasses. Stalling the liquid does not result in gas 

formation, or cavitation, but results merely in turbulent flow. I 

used to do it in the sailboat all the time.



Guy Buchanan

Kitfox IV-1200 / 592-C / Warp 3cs / 500 hrs.

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gpabruce(at)gmail.com
Guest

Posted: Fri Dec 03, 2010 12:05 am Post subject: Losing rpm on takeoff

I've just had more fun out of this than anyone is entitled to have. We've drug this ol' carcass until there is just no hyde left on it. You guys take over now alright   God it's been fun but I have to go cavitate my stall . . .  LOL

  



 

 On Thu, Dec 2, 2010 at 11:49 PM, Michael Gibbs <MichaelGibbs(at)cox.net (MichaelGibbs(at)cox.net)> wrote:

 [quote]--> Kitfox-List message posted by: Michael Gibbs <MichaelGibbs(at)cox.net (MichaelGibbs(at)cox.net)>  



Bruce sez:



  	  Quote: 	
		  Cavitation and stall are quite the same but with different mediums, it's still only semantics.

	
 



Guy's explanation shows clearly that this is NOT the case.  From Wikipedia <http://en.wikipedia.org/wiki/Cavitation>: "Cavitation is the formation of vapor bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapor pressure."

 

No mention of angle of attack or separation from a surface.  And air doesn't changing phases in a stall!  



  	  Quote: 	
		  You only said the same thing the first feller said a long time ago but yet another way. We all get it.

 	




Apparently not...  



Mike G.

N728KF, Kitfox IV-1200 Speedster

Phoenix, AZ

  	  Quote: 	
		  On Thu, Dec 2, 2010 at 10:44 PM, Guy Buchanan <<mailto:gebuchanan(at)cox.net (gebuchanan(at)cox.net)>gebuchanan(at)cox.net (gebuchanan(at)cox.net)> wrote:

 

--> Kitfox-List message posted by: Guy Buchanan <<mailto:gebuchanan(at)cox.net (gebuchanan(at)cox.net)>gebuchanan(at)cox.net (gebuchanan(at)cox.net)>   

 

On 12/2/2010 1:52 PM, b d wrote:



Yes, it's semantics, with a prop in a liquid (a hydrofoil) it's called cavitation and with an prop in air (an airfoil), it's called a stall but essentially the same-o same-o.

 



OOO I LOVE semantics. Actually, cavitation is quite different from stall. Cavitation involves a phase change from liquid to gas due to pressure drop over the airfoil. Since the gas is compressible it vacates the low pressure region of the airfoil destroying lift. Stall is where the streamlines in the low pressure region depart catastrophically from the airfoil surface. It can happen in liquids and well as gasses. Stalling the liquid does not result in gas formation, or cavitation, but results merely in turbulent flow. I used to do it in the sailboat all the time.

 

Guy Buchanan

Kitfox IV-1200 / 592-C / Warp 3cs / 500 hrs.

	
  

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[b]

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hlang(at)bluewin.ch
Guest

Posted: Fri Dec 03, 2010 3:12 am Post subject: Losing rpm on takeoff

I think this is normal for self adjusting Warp Drives. My data for KF

IV-1200 R582, at full power are, static: 6800RPM, climb with 60mph: 6500RPM.

This setting is ideal for me. 

Regards

Heinz Lang

Switzerland

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occom

Joined: 26 Aug 2006
Posts: 404

Posted: Tue Dec 14, 2010 2:34 am Post subject: Losing rpm on takeoff

Problem solved, although what is actually happening is a subject of some 

debate.



Those who operate the Warp drive taper tip props or have experience with 

them were exactly right and ignoring static RPM was clearly the way to go. I 

ended up with a very nice smoooth prop after reducing pitch significantly. 

It is now pitched to allow 6200 rpm in full throttle climb at 0 deg temp. I 

expect we will have to revisit this when it warms up. The engine will 

overspeed quite easily on the ground until speed builds. I have spoken to a 

few others with the same type of prop and their expereince is similar.



Thanks to those who offered asistance, it would have taken somewhat longer 

to get it right without it. I still have the GSC but it requires a full 

service.



Dave Goddard

KF IV 1050 / 582 / Warp

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