Return-Path: Received: from sccrmhc14.comcast.net ([204.127.202.59] verified) by logan.com (CommuniGate Pro SMTP 4.3c3) with ESMTP id 854555 for flyrotary@lancaironline.net; Mon, 04 Apr 2005 15:01:20 -0400 Received-SPF: none receiver=logan.com; client-ip=204.127.202.59; envelope-from=kenpowell@comcast.net Received: from 204.127.205.142 (unknown[204.127.205.160](misconfigured sender)) by comcast.net (sccrmhc14) with SMTP id <2005040419001501400dt9g1e>; Mon, 4 Apr 2005 19:00:30 +0000 Received: from [68.51.45.41] by 204.127.205.142; Mon, 04 Apr 2005 19:00:20 +0000 From: kenpowell@comcast.net To: "Rotary motors in aircraft" Subject: [FlyRotary] Re: A lot to learn / theory Date: Mon, 04 Apr 2005 19:00:20 +0000 Message-Id: <040420051900.10700.42518EC200089B16000029CC220700295304040A99019F020A05@comcast.net> X-Mailer: AT&T Message Center Version 1 (Dec 17 2004) X-Authenticated-Sender: a2VucG93ZWxsQGNvbWNhc3QubmV0 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="NextPart_Webmail_9m3u9jl4l_10700_1112641220_0" --NextPart_Webmail_9m3u9jl4l_10700_1112641220_0 Content-Type: text/plain Content-Transfer-Encoding: 8bit But Jim, some of us rather enjoy the theory of 'why' things work. I agree that we are dealing with so many variables that ultimately empiracal data must be gathered - but that is the 'testing' phase of scientific method. I think that this is a valid discussion for those who are interested in theory. We DO have engineers and scientists on this list who are BUILDING airplanes. Ken Powell Bryant, Arkansas 501-847-4721 -------------- Original message -------------- Is it possible we're dismissing some important factors getting a little out of our depth here? Dynamic pressure in the cores and across the cores would seem to be so highly dependent on surface friction and core density and passage size as to be impossible to estimate, much less quantify accurately. If the purpose of the plenum is pressure recovery (converting dynamic pressure into static pressure) and it's the static pressure drop that drives the mass of air through the radiator core, why not just forget about the molecular, boundary layer and core passage size considerations for the moment since we can't quantify any of that anyway. As Ed has stated so many times in so many ways, a good inlet/plenum design does a better job of converting dynamic pressure to static pressure than a bad one, and he's found out pretty much what he has to do to make a bad one good. If we measure static pressure at the forward and aft face of the radiator and we've got the pressure drop across the core. Period. We know how close we are to Ed's plenum. Then adapt the stuff that Ed has pioneered for us to make it better An Airspeed indicator I find is handier and more accurate than a water manometer. The Pitot connection on the upwind side and the Static connection on the downwind side should give me upwards of 100, maybe 120 kias drop across the radiator at cruise. More is better. If I don't have sufficient pressure drop across the radiator, I probably need to improve my intake and plenum to get rid of the eddies Ed alludes to. That is what I've got the most influence over. If I don't get enough pressure recovery, I study Ed's findings and approach implement them better. I think all this molecular stuff is more appropriate to the ACRE list where nothing ever really has to fly. This list (to me) is the guys who actually FLY. A sound qualitative analysis of the issues involved (which we already have) will lead me to a workable solution. That is very nice since an acceptably accurate quantitative analysis is not possible. To that end (to coin a phrase) I don't have to know how it works or why it works, I only have to know what I have to do to MAKE it work. And I have been blessed that Ed has found out most of this. Are we PVORT. again? ... Jim S. David Carter wrote: ----- Original Message ----- From: To: "Rotary motors in aircraft" Sent: Monday, April 04, 2005 7:07 AM Subject: [FlyRotary] Re: A lot to learn ! Re: Cooling -Learned a lot Charlie E wrote: At the risk of embarrassing myself with a display of misunderstanding the physics of it all, should your pressure sensors be measuring dynamic pressure or static? Seems like I remember Tracy's measurement pics having foam chunks over the pressure sensors to remove the dynamic component of the pressure measurement. I couldn't remember if your setup has that (& I really don't know if it should, either). Charlie --------------------------------------------- >> Homepage: http://www.flyrotary.com/ >> Archive: http://lancaironline.net/lists/flyrotary/List.html --NextPart_Webmail_9m3u9jl4l_10700_1112641220_0 Content-Type: text/html Content-Transfer-Encoding: 8bit
But Jim, some of us rather enjoy the theory of 'why' things work.  I agree that we are dealing with so many variables that ultimately empiracal data must be gathered - but that is the 'testing' phase of scientific method.  I think that this is a valid discussion for those who are interested in theory.  We DO have engineers and scientists on this list who are BUILDING airplanes.

Ken Powell
Bryant, Arkansas
501-847-4721
 
-------------- Original message --------------
Is it possible we're dismissing some important factors getting a little out of our depth here?  Dynamic pressure in the cores and across the cores would seem to be so highly dependent on surface friction and core density and passage size as to be impossible to estimate, much less quantify accurately.

If the purpose of the plenum is pressure recovery (converting dynamic pressure into static pressure) and it's the static pressure drop that drives the mass of air through the radiator core, why not just forget about the molecular, boundary layer and core passage size considerations for the moment since we can't quantify any of that anyway.  As Ed has stated so many times in so many ways, a good inlet/plenum design does a better job of converting dynamic pressure to static pressure than a bad one, and he's found out pretty much what he has to do to make a bad one good. 

If we measure static pressure at the forward and aft face of the radiator and we've got the pressure drop across the core.  Period.  We know how close we are to Ed's plenum.  Then adapt the stuff that Ed has pioneered for us to make it better  An Airspeed indicator I find is handier and more accurate than a water manometer.  The Pitot connection on the upwind side and the Static connection on the downwind side should give me upwards of 100, maybe 120 kias drop across the radiator at cruise.  More is better.  If I don't have sufficient pressure drop across the radiator, I probably need to improve my intake and plenum to get rid of the eddies Ed alludes to.  That is what I've got the most influence over.  If I don't get enough pressure recovery, I study Ed's findings and approach implement them better. 

I think all this molecular stuff is more appropriate to the ACRE list where nothing ever really has to fly.  This list (to me) is the guys who actually FLY.  A sound qualitative analysis of the issues involved (which we already have) will lead me to a workable solution.  That is very nice since an acceptably accurate quantitative analysis is not possible.  To that end (to coin a phrase) I don't have to know how it works or why it works, I only have to know what I have to do to MAKE it work.  And I have been blessed that Ed has found out most of this.

Are we PVORT. again? ... Jim S.


David Carter wrote:
----- Original Message ----- 
From: <jbker@juno.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, April 04, 2005 7:07 AM
Subject: [FlyRotary] Re: A lot to learn ! Re: Cooling -Learned a lot


  
Charlie E wrote:

At the risk of embarrassing myself with a display of misunderstanding
the physics of it all, should your pressure sensors be measuring dynamic
pressure or static? Seems like I remember Tracy's measurement pics
having foam chunks over the pressure sensors to remove the dynamic
component of the pressure measurement. I couldn't remember if your setup
has that (& I really don't know if it should, either).

Charlie
---------------------------------------------

    
  

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