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occom

Joined: 26 Aug 2006
Posts: 404

Posted: Tue Nov 30, 2010 1:50 pm Post subject: Losing rpm on takeoff

Looking for ideas here. My test pilot says he is  losing about 500 rpm upon becoming airborne. Has low rpm all during climb and is  doubtful of full power on cruise. EGT's appear fine, although he was not riveted  on the gauge having a few other things to watch. 

  

 I checked fuel flow and the function of the vacuum  fuel pump to be ok. I also had a look at the plugs and they look a little dark  but not wet and certainly not lean. 

  

 I did a one minute run at full power on the ground  with no loss of rpm, it pulls a little over 6200 static, EGT's run up to around  1100 but drop off quickly with only a little pull back on the throttle and  normally run around 1000-1025 on a Westach gauge. 

  

 Currently reviewing a my documentation for ideas.  Right now I'm leaning toward doubting the tach. 

  

 Engine has 82 hours and was recently checked  out by a service center.  

  

 Dave Goddard

KitFox IV 1050 / 582 /  Warp

   [quote][b]

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Tue Nov 30, 2010 4:01 pm Post subject: Re: Losing rpm on takeoff

 	  Quote: 	
		  Looking for ideas here. My test pilot says he is  losing about 500 rpm upon becoming airborne. Has low rpm all during climb and is  doubtful of full power on cruise. EGT's appear fine, although he was not riveted  on the gauge having a few other things to watch. 

  

 I checked fuel flow and the function of the vacuum  fuel pump to be ok. I also had a look at the plugs and they look a little dark  but not wet and certainly not lean. 

  

 I did a one minute run at full power on the ground  with no loss of rpm, it pulls a little over 6200 static, EGT's run up to around  1100 but drop off quickly with only a little pull back on the throttle and  normally run around 1000-1025 on a Westach gauge. 

  

 Currently reviewing a my documentation for ideas.  Right now I'm leaning toward doubting the tach. 

  

 Engine has 82 hours and was recently checked  out by a service center.  

  

 Dave Goddard

KitFox IV 1050 / 582 /  Warp

  	


Dave,   Your static RPM sounds in the right range 6000 t0 6300 IF your tach is correct - Get a Tiny  tach  if you do not have one. 



EGT gauge is only for reference not for actual temps but it might read accurate - WHO KNOWS !! Plugs will tell you  what is going on inside.

At cruise 5800 to 6000 RPM  plugs should be med to light brown. MEd or darker is too rich or too much pitch.  You should be be using NGK BR8ES. If you do not have the right plugs order some from Bob Robertson when you order the tiny tach  1-866-418-4164.

If your EGT are correct you should see 1100 to 1200 rpm in cruise no colder. Your EGT are calibrated for 70 F  right now the temps are about 20 to 30 F outside do you are reading 50 F  higher than it really is.



Cheers



Your needle clip should be in the 3 rd notch from the top but changing to the bottom notch once temps are below 0 C  ( 32 F)  for the winter.

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carlisle

Joined: 20 Jun 2009
Posts: 72
Location: Sioux Falls, SD

Posted: Tue Nov 30, 2010 5:28 pm Post subject: Re: Losing rpm on takeoff

Sounds like the prop is pitched a little too coarse.  Try backing off a degree or two.



Chris Carlisle

Model 2, 582, C box

Sioux Falls, SD

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Tue Nov 30, 2010 6:35 pm Post subject: Losing rpm on takeoff

I’d doubt the tach too.  My plane was doing almost the same thing as yours and one day I had an ivo set for a go around and after an hour on the ground firewalled the throttle for a takeoff.   Imagine my surprise when the plane leapt into the air and the tach spiralled up to the wrong side of seven grand, make that the low side of 8 grand!  I got a Tiny Tach and quickly found my Westach read a consistent 20% too high.

 

I often wonder how I was ever able to get the plane into the air with a true take off rpm of around 5400 rpm.

 

Noel

 

From: owner-kitfox-list-server(at)matronics.com [mailto:owner-kitfox-list-server(at)matronics.com] On Behalf Of Dave G

Sent: November 30, 2010 6:17 PM

To: kitfox-list(at)matronics.com; rotaxengines-list(at)matronics.com

Subject: Losing rpm on takeoff

 

Looking for ideas here. My test pilot says he is losing about 500 rpm upon becoming airborne. Has low rpm all during climb and is doubtful of full power on cruise. EGT's appear fine, although he was not riveted on the gauge having a few other things to watch. 



 



I checked fuel flow and the function of the vacuum fuel pump to be ok. I also had a look at the plugs and they look a little dark but not wet and certainly not lean. 



 



I did a one minute run at full power on the ground with no loss of rpm, it pulls a little over 6200 static, EGT's run up to around 1100 but drop off quickly with only a little pull back on the throttle and normally run around 1000-1025 on a Westach gauge. 



 



Currently reviewing a my documentation for ideas. Right now I'm leaning toward doubting the tach. 



 



Engine has 82 hours and was recently checked out by a service center.  



 



Dave Goddard

KitFox IV 1050 / 582 / Warp

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  [quote][b]

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Tue Nov 30, 2010 7:32 pm Post subject: Losing rpm on takeoff

Noel-



I often wonder why anybody would use a Westach....I haven't heard of  

much in the way of reliability from any of their products.



Lynn Matteson

Kitfox IV Speedster, taildragger

Jabiru 2200, #2062

Sensenich 62"x46" Wood (summer)

Electroair direct-fire ignition system

Rotec TBI-40 injection

Status: flying...1070 hrs (since 3-27-2006)

On Nov 30, 2010, at 9:31 PM, Noel Loveys wrote:



 	  Quote: 	
		   I’d doubt the tach too.  My plane was doing almost the same thing  

 as yours and one day I had an ivo set for a go around and after an  

 hour on the ground firewalled the throttle for a takeoff.   Imagine  

 my surprise when the plane leapt into the air and the tach  

 spiralled up to the wrong side of seven grand, make that the low  

 side of 8 grand!  I got a Tiny Tach and quickly found my Westach  

 read a consistent 20% too high.



 I often wonder how I was ever able to get the plane into the air  

 with a true take off rpm of around 5400 rpm.



 Noel

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

occom

Joined: 26 Aug 2006
Posts: 404

Posted: Wed Dec 01, 2010 2:34 am Post subject: Losing rpm on takeoff

My retired engine ran well beyond it's time and still looks like new using 

that gauge package. I have a digital instrument upgrade in mind, they are 

better, but mine have served well.



Dave Goddard

KF IV 1050 / 582 / Warp

---

occom

Joined: 26 Aug 2006
Posts: 404

Posted: Wed Dec 01, 2010 2:41 am Post subject: Losing rpm on takeoff

But even with that your rpm went up from static not  down, which is what I am experiencing. Tiny tachs have their issues also,  especially the older ones. Try wrapping too much of the sense lead onto  the HT lead, they hate that!. 

  

 Dave Goddard

KF IV 1050 / 582 /  Warp 

 [quote]   ---

Fox5flyer
Guest

Posted: Wed Dec 01, 2010 5:35 am Post subject: Losing rpm on takeoff

Elbie, I think what you are experiencing is prop  cavitation.  This happens at static when the prop gets the air stirred up  and "slips" through disturbed air, sort of like stalling, which increases the  rpms.  On takeoff roll and climbout the prop is now spinning through clean  air which gives it more "grab", depending on the amount of pitch, which reduces  the rpms.  Of course, the type and model of prop, along with pitch,  temperature, humidity, other factors has a role in this.

 Deke Morisse

 NE Mi and snowing

 S5

  

  

  

 Time: 01:45:18 PM PST US

From: EMAproducts(at)aol.com (EMAproducts(at)aol.com)

Subject:  Re: Jeffery Dill   RPM - 11/29/10

In a message  dated 11/30/2010 12:05:38 A.M. Pacific Standard Time,  

kitfox-list(at)matronics.com (kitfox-list(at)matronics.com)  writes:



I took  off about a 1 1/2 degrees from my prop and ran it up  to just short 

of  6600

RPM at full throttle. Then I went to fly, and  once again, I saw much  less 

during

takeoff roll, maybe 6100. In  cruise at wide open throttle and  level I saw

a higher RPM, 6400. So, at  least the static versus cruise RPMs  make more 

sense

this time. I  don't know why I twice have gotten a higher  RPM right after  

installation

test than later flight test. Different  conditions of  some type, but

not 

Remember, ANY change in Density Altitude will change  the perceived power  

output from your engine.  This goes for 2  stroke, 4 stroke, turboprop and  

pure jet.  Write down the temp  and altitude when doing tests, then compare,  

you will find what a  difference it makes.

Elbie

an old CFI, still teaching.  



   [quote][b]

rawheels

Joined: 09 Jul 2008
Posts: 89
Location: Westfield, IN

Posted: Wed Dec 01, 2010 1:21 pm Post subject: Re: Losing rpm on takeoff

In case none of the other ideas help you, you might check your fuel lines for any crimped or black rubber tubing.  I had a problem with my model IV where about halfway through the takeoff roll it would lose a couple hundred RPM.  Finally found that the problem was a ~2" piece of black rubber tubing that connected the header tank to the metal fuel lines.  After removing it, it swelled completely shut.  So while it was attached to the lines it was spread open allowing enough fuel to get through to run continuously at about 6000 RPM, but no more.  I suppose the reason I could get a little bit down the runway was because there was enough fuel in the carb bowls/lines to get that far before the "reduction" metered the fuel.

_________________
Kitfox IV-1200
Indianapolis, IN

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Thu Dec 02, 2010 5:31 am Post subject: Losing rpm on takeoff

Lynn: 

The only reason I can see to use the westach is it comes with the kit. (?)

I found the tinytach worked really well on the 582. When I get the 9122

going it's anyone's guess. 



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

mikeperkins

Joined: 22 May 2007
Posts: 123

Posted: Thu Dec 02, 2010 11:41 am Post subject: Re: Losing rpm on takeoff

I have never heard a discussion involving aircraft props that mentions cavitation, stirring air, humidity, or higher RPM during a static run-up. If you have some references, please let me know. 



A prop during a static run-up experiences a higher angle-of-attack than a prop moving forward through air. The higher AOA produces more drag, thus more load on the engine, and thus a lower RPM for a given power setting, not higher RPM. 



Some very high-performance aircraft with fixed-pitch props (long time ago) produced so little prop thrust (blade lift) during a static run-up that they had to be pushed to get them rolling - the prop was stalled. Once rolling, the AOA would gradually decrease and thrust (lift) would increase because the prop was un-stalling. 



A properly set-up Rotax 2-stroke will produce 5800 to 6200 on a static run-up (temp dependent), and max RPM of 6600 while climbing at Vx. 



I would not be looking at the prop pitch for this particular problem. 



Mike

lcfitt(at)sbcglobal.net
Guest

Posted: Thu Dec 02, 2010 12:10 pm Post subject: Losing rpm on takeoff

Mike,



I think you answered your own question.  Just substitute stalled prop for 

cavitating prop.  I think the concept is the same In each case the prop is 

pitched too high for conditions.



Lowell



--------------------------------------------------

From: "mikeperkins" <michael.perkins(at)rauland.com>

Sent: Thursday, December 02, 2010 11:41 AM

To: <kitfox-list(at)matronics.com>

Subject: Re: Losing rpm on takeoff



 	  Quote: 	
		   

 <michael.perkins(at)rauland.com>



 I have never heard a discussion involving aircraft props that mentions 

 cavitation, stirring air, humidity, or higher RPM during a static run-up. 

 If you have some references, please let me know.



 A prop during a static run-up experiences a higher angle-of-attack than a 

 prop moving forward through air. The higher AOA produces more drag, thus 

 more load on the engine, and thus a lower RPM for a given power setting, 

 not higher RPM.



 Some very high-performance aircraft with fixed-pitch props (long time ago) 

 produced so little prop thrust (blade lift) during a static run-up that 

 they had to be pushed to get them rolling - the prop was stalled. Once 

 rolling, the AOA would gradually decrease and thrust (lift) would increase 

 because the prop was un-stalling.



 A properly set-up Rotax 2-stroke will produce 5800 to 6200 on a static 

 run-up (temp dependent), and max RPM of 6600 while climbing at Vx.



 I would not be looking at the prop pitch for this particular problem.



 Mike





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=322085#322085

gpabruce(at)gmail.com
Guest

Posted: Thu Dec 02, 2010 1:55 pm Post subject: Losing rpm on takeoff

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.  We all know what is meant, we just have to be tolerent of each others linguistics. To be technical I really don't believe there is such a word as "un-stalling". It's either stalled or not stalled but correct me if I'm wrong. But I do not what you mean and what your getting at, it's like coming out of a stall condition.     

   

 Bruce

  

  

  

  

 



 

 On Thu, Dec 2, 2010 at 12:08 PM, Lowell Fitt <lcfitt(at)sbcglobal.net (lcfitt(at)sbcglobal.net)> wrote:

 [quote]--> Kitfox-List message posted by: "Lowell Fitt" <lcfitt(at)sbcglobal.net (lcfitt(at)sbcglobal.net)>

 

Mike,



I think you answered your own question.  Just substitute stalled prop for cavitating prop.  I think the concept is the same In each case the prop is pitched too high for conditions.



Lowell



--------------------------------------------------

 From: "mikeperkins" <michael.perkins(at)rauland.com (michael.perkins(at)rauland.com)>

Sent: Thursday, December 02, 2010 11:41 AM

To: <kitfox-list(at)matronics.com (kitfox-list(at)matronics.com)>

 Subject: Re: Losing rpm on takeoff   

 



 [quote]--> Kitfox-List message posted by: "mikeperkins" <michael.perkins(at)rauland.com (michael.perkins(at)rauland.com)>

 

I have never heard a discussion involving aircraft props that mentions cavitation, stirring air, humidity, or higher RPM during a static run-up. If you have some references, please let me know.



A prop during a static run-up experiences a higher angle-of-attack than a prop moving forward through air. The higher AOA produces more drag, thus more load on the engine, and thus a lower RPM for a given power setting, not higher RPM.

 

Some very high-performance aircraft with fixed-pitch props (long time ago) produced so little prop thrust (blade lift) during a static run-up that they had to be pushed to get them rolling - the prop was stalled. Once rolling, the AOA would gradually decrease and thrust (lift) would increase because the prop was un-stalling.

 

A properly set-up Rotax 2-stroke will produce 5800 to 6200 on a static run-up (temp dependent), and max RPM of 6600 while climbing at Vx.



I would not be looking at the prop pitch for this particular problem.

 

Mike





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=322085#322085

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[b]

occom

Joined: 26 Aug 2006
Posts: 404

Posted: Thu Dec 02, 2010 2:54 pm Post subject: Losing rpm on takeoff

I have received enough email to establish a plan of  action here. Despite the fact that reducing pitch WILL result in an overspend  situation with my particular experimental installation, I will reduce the pitch  and see what happens during high speed taxi and then climb. Many people actually  using Warp props tell me that I achieve the results I am looking for.  

  

 I understand it is counter-intuitive, but  apparently it is at least somewhat common. I have a couple of theories, but for  now I'll accept positive results and remain in doubt about the actual reason.  Over a long work life I've had to do that on many occasions, because results are  what really matters. 

  

 Thanks to Guy, Lucien and those who contributed  positive and helpful advice off list. To those who offered unhelpful advice and  lectures, thanks for the efforts. It all reminds me of a saying a friend  repeats from time to time. 

  

 "In theory, theory and practice are the same; in  practice they are quite different!" This may be one of those cases.

  

 Dave Goddard

KF IV 1050 / 582 /  Warp

 [quote]   ---

mikeperkins

Joined: 22 May 2007
Posts: 123

Posted: Thu Dec 02, 2010 2:59 pm Post subject: Re: Losing rpm on takeoff

I'm not sure, but I think the drag on the prop airfoil would decrease as airspeed went from 0 to climb. Then RPM should go up somewhat, not down, as airspeed increased. Would that be right?

gpabruce(at)gmail.com
Guest

Posted: Thu Dec 02, 2010 3:43 pm Post subject: Losing rpm on takeoff

I don't know if you're asking me or anyone, but as speed increases, engine RPM increases just like a car. If your climbing, your speed decreases and so does your rpm. This is because your prop is essentially one and the same with the air. When you are descending or diving your speed increases as well as your rpm. Regarding sitting still on the ground (static or stationary), the prop does lose efficiency because of stalling at higher rpms and typically doesn't move as much air. (the prop is not one with the air as when it's in motion) At that time the prop may stall or cavitate just as a boat prop does in the water. We can see a hydrofoil cavitate but we can't see an airfoil stall) This means that the air rather than be driven through the prop as does a fan, the air begins to rotate with the prop (stalled blades due to high angle of attack) thereby allowing the engine to run faster but exerting less power. Once the plane begins moving, the prop then becomes more efficient, the angle of attack from the prop to the relative air/wind becomes less, the efficiency increases thus making the prop more efficient thereby changing from a stalled blade to a non-stalled blade.  

   

 Does any of that make any sense? I'm trying to explain it in comparable terms between a hydrofoil and an airfoil terminology. The thing is to understand that when the difference between the prop and the forward airspeed becomes less, the lesser angle of attack and the more efficient the airfoil. Of course we have not discussed the variable angle of attack found on a prop where the angle is great towards the prop shaft than it is towards the tip. That's another topic for another discussion and it does play a part in the big picture. For the discussion we are only talking about a mean section of the prop. 

   

 I hope I didn't just confuse it even more. Sorry if I did. 

  

 Bruce

 



 

 On Thu, Dec 2, 2010 at 2:59 PM, mikeperkins <michael.perkins(at)rauland.com (michael.perkins(at)rauland.com)> wrote:

 [quote]--> Kitfox-List message posted by: "mikeperkins" <michael.perkins(at)rauland.com (michael.perkins(at)rauland.com)>

 

I'm not sure, but I think the drag on the prop airfoil would decrease as airspeed went from 0 to climb. Then RPM should go up somewhat, not down, as airspeed increased. Would that be right?





Read this topic online here:

 

http://forums.matronics.com/viewtopic.php?p=322107#322========================

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[b]

gpabruce(at)gmail.com
Guest

Posted: Thu Dec 02, 2010 3:50 pm Post subject: Losing rpm on takeoff

Dave

  

 Results is truly the main issue, no matter how you get them. If you want to try to understand it later, take a ride in a certified plane with a constant speed prop AKA variable pitch prop preferably hydraulic or electric actuated as opposed to fly-weighted. Then you can adjust it on the ground to see the effect or pitch. Then do it again in flight in acsending and descending conditions.  Now this prop is not like one found on the ultralites. Some ultralite props can warp by design to achieve different effects that a constant speed solid metal prop won't do so there is some difference. 

   

 Bruce

  

 



 

 On Thu, Dec 2, 2010 at 2:51 PM, Dave G <occom(at)ns.sympatico.ca (occom(at)ns.sympatico.ca)> wrote:

 [quote]  I have received enough email to establish a plan of action here. Despite the fact that reducing pitch WILL result in an overspend situation with my particular experimental installation, I will reduce the pitch and see what happens during high speed taxi and then climb. Many people actually using Warp props tell me that I achieve the results I am looking for. 

   

 I understand it is counter-intuitive, but apparently it is at least somewhat common. I have a couple of theories, but for now I'll accept positive results and remain in doubt about the actual reason. Over a long work life I've had to do that on many occasions, because results are what really matters. 

   

 Thanks to Guy, Lucien and those who contributed positive and helpful advice off list. To those who offered unhelpful advice and lectures, thanks for the efforts. It all reminds me of a saying a friend repeats from time to time. 

   

 "In theory, theory and practice are the same; in practice they are quite different!" This may be one of those cases.

  

 Dave Goddard

KF IV 1050 / 582 / Warp

 [quote]  ---

gpabruce(at)gmail.com
Guest

Posted: Thu Dec 02, 2010 5:34 pm Post subject: Losing rpm on takeoff

Guess what I just ran across . . . a discussion about "prop cavitation on takeoff". An interesting play on terminology again. Thought I would throw this in to confuse the doubting Thomas's even more 

   

 Bruce

  

 http://www.oshkosh365.org/ok365_DiscussionBoardTopic.aspx?id=1235&boardid=147&forumid=520&topicid=5819

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  Back To Ultralight Strip

 



 

   

 Propeller cavitation?  Posted By:

  

  

 David Lacy 

 Posted: 11/30/2010 15:15:08 

	
   	  Quote: 	
		   

Hello every one! I am new to this forum but have read several threads with some great info. I hope someone can help with my issue. 

I purchased a mid 90s Rans S 12 XL with a Rotax 582 and a four blade Warp Drive propeller about a year ago. Between me and my instructor, the plane has about 45 hrs flying time since purchase. The plane and the engine have performed flawlessly.  

The issue occurs during acceleration for take off and occasionally early in climb out. For a very brief moment (about 1 second or less) the engine will over speed (my normal rpm during climb out is~6,300; it jumps to~6,700).   

Or assumption is that the prop is cavitating due to disrupted air flow around the engine and muffler. If anyone has knowledge of this or solutions, I would be grateful. TIA  

  	


  

  

 On Thu, Dec 2, 2010 at 3:48 PM, b d <gpabruce(at)gmail.com (gpabruce(at)gmail.com)> wrote:   

 [quote] Dave

  

 Results is truly the main issue, no matter how you get them. If you want to try to understand it later, take a ride in a certified plane with a constant speed prop AKA variable pitch prop preferably hydraulic or electric actuated as opposed to fly-weighted. Then you can adjust it on the ground to see the effect or pitch. Then do it again in flight in acsending and descending conditions.  Now this prop is not like one found on the ultralites. Some ultralite props can warp by design to achieve different effects that a constant speed solid metal prop won't do so there is some difference. 

   

 Bruce

  

   

   

   



 On Thu, Dec 2, 2010 at 2:51 PM, Dave G <occom(at)ns.sympatico.ca (occom(at)ns.sympatico.ca)> wrote:   

 [quote]  I have received enough email to establish a plan of action here. Despite the fact that reducing pitch WILL result in an overspend situation with my particular experimental installation, I will reduce the pitch and see what happens during high speed taxi and then climb. Many people actually using Warp props tell me that I achieve the results I am looking for. 

   

 I understand it is counter-intuitive, but apparently it is at least somewhat common. I have a couple of theories, but for now I'll accept positive results and remain in doubt about the actual reason. Over a long work life I've had to do that on many occasions, because results are what really matters. 

   

 Thanks to Guy, Lucien and those who contributed positive and helpful advice off list. To those who offered unhelpful advice and lectures, thanks for the efforts. It all reminds me of a saying a friend repeats from time to time. 

   

 "In theory, theory and practice are the same; in practice they are quite different!" This may be one of those cases.

  

 Dave Goddard  KF IV 1050 / 582 / Warp

 [quote]  ---

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Thu Dec 02, 2010 10:47 pm Post subject: Losing rpm on takeoff

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

 	  Quote: 	
		   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.

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

gpabruce(at)gmail.com
Guest

Posted: Thu Dec 02, 2010 11:19 pm Post subject: Losing rpm on takeoff

Cavitation and stall are quite the same but with different mediums, it's still only semantics. And yes a sail luffs too yet another analogy to describe the same thing. Nothing new has been added. You only said the same thing the first feller said a long time ago but yet another way. We all get it. The horse is absolutely dead and has now been drug down the road several miles . . . 

  

 

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

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



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

  	  Quote: 	
		  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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