X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from wr-out-0506.google.com ([64.233.184.224] verified) by logan.com (CommuniGate Pro SMTP 5.1.11) with ESMTP id 2247586 for flyrotary@lancaironline.net; Tue, 07 Aug 2007 08:35:08 -0400 Received-SPF: pass receiver=logan.com; client-ip=64.233.184.224; envelope-from=msteitle@gmail.com Received: by wr-out-0506.google.com with SMTP id 58so1286748wri for ; Tue, 07 Aug 2007 05:34:29 -0700 (PDT) DKIM-Signature: a=rsa-sha1; c=relaxed/relaxed; d=gmail.com; s=beta; h=domainkey-signature:received:received:message-id:date:from:to:subject:in-reply-to:mime-version:content-type:references; b=pVaLUy6+PAVgD/E5ZNSZWIPr2/qXsTF4pkTa0Y2lqy4iC455ZhBJvnKDKamPXAB/09egSgS7d+kAALHxBXXcFdq1M87sIidQwkzkdOn/SWperY6O+RGqgsreOrhHcgDGp5nd/srXJ4dLdnoXHQsQVocOkW8Nq0rttHHwAQrazqk= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:to:subject:in-reply-to:mime-version:content-type:references; b=pnCY7PqP/fSRDAAU7QurYWkFkrSoHRIQ8G16ww7jj+mXSp9y90aP/57GoQ0iZ10/7USHx6KJNp3E0VIzK+zMZorFatlxitc3U293OtaX3TLA9O/Dxqu+PDTqTqDtVI8i+cDCDBSqHY8pgY3iYXclzyRnVIuyI8CyWK6Vo/dQA70= Received: by 10.90.25.3 with SMTP id 3mr5706199agy.1186490069086; Tue, 07 Aug 2007 05:34:29 -0700 (PDT) Received: by 10.90.115.6 with HTTP; Tue, 7 Aug 2007 05:34:29 -0700 (PDT) Message-ID: <5cf132c0708070534r6414b071ma52e0b6df879ddb4@mail.gmail.com> Date: Tue, 7 Aug 2007 07:34:29 -0500 From: "Mark Steitle" To: "Rotary motors in aircraft" Subject: Re: [FlyRotary] Re: RV -7A Cooling Update 8/6/07 In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_106676_19038734.1186490069040" References: ------=_Part_106676_19038734.1186490069040 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline Dennis, You've been too quiet. I was wondering what happened to you. Interesting theory (fins causing turbulence). Rather than turning the radiator 90*, another option might be to see if you can get a radiator with the fins angled 60* so the air would pass straight through. I remember someone looking into getting custom radiators done like that a while back. But I don't know what ever happened. It sure would solve the turbulence problem. I wonder if any auto manufacturers do it like that? Might be worth making a few phone calls. Keep us posted (I may be needing one of those special radiators soon). Mark S. On 8/7/07, Ed Anderson wrote: > > Hi Dennis, > > Send some of the wet stuff over to NC, we need it. Good to hear that > things have improved cooling wise. > > From my understanding of K&W and your radiator orientation, I would hazard > a "Yes", I think you may have found a significant reason for getting less > cooling than you would initially think you would get with that size > radiator. > > Rather than the larger, relatively more aerodynamic cross-tank tubes > turning the air, the air, as you point out, is meeting the sharp edge of > the fins between the tubes. This likely causes flow separation and that > turbulence at the entrance could, in effect, act as a barrier to good flow > through the core channels. So that may indeed be a reason why manipulation > of your airflow inside the duct does not appear to have as much effect as > expected. > > If the flow through the core channels is impeded , then the relatively > lesser amount of air flowing through the channels would be at a higher > temperature at exit than it would be if a larger air mass flow (more > velocity) carried the heat away. Might be one reason you are seeing such > high exit temperatures but cooling not as good as you might expect. Slower > moving air will pick up more heat per unit volume, but will carry away less > heat per unit time. So best air mass flow is always a compromise of > balance between those to opposing factors. > > Its my guess that K&W did not address the airflow alpha across the fins > because a professional and experienced designer of a cooling system for an > aircraft simply would not select that choice of orientation - but just a > guess. > > Perhaps the one good thing is that you appear to be getting adequate > cooling with this less than optimum orientation of the core, it would be > interesting to now switch the orientation and see the results - next time > you are looking for something to do {:>) > > Ed > > P.S. Really could use some of the wet stuff > > > > > > ., ----- Original Message ----- > > *From:* Dennis Haverlah > *To:* Rotary motors in aircraft > *Sent:* Monday, August 06, 2007 10:51 PM > *Subject:* [FlyRotary] RV -7A Cooling Update 8/6/07 > > > > > I've been busy with Family vacation, dealing with the exceptional wet weather in > central Texas and my tennis playing but finally I have some more > thoughts on radiators and cooling. *My cooling is marginal for Texas in > the summer.* I want to climb at 120 kts and 26 + inches MP on a 100 deg > F day without exceeding 215 on water and oil. > > I have the Griffin radiator (core 19 X 13 X 2.5 inches) and stock RX-7 > '89 oil cooler as shown on pictures I have previously posted. The > radiators are mounted under the engine at about a 30 deg. angle. My > latest test flight with OAT of 92 deg F on the ground was encouraging. > I had temp. probes on the outlet side of the oil and water radiators > to measure the temp. of the heated air. The temp. probes had an upper > limit of 160 deg. F. The air exiting the water radiator exceeded the > 160 Deg. limit soon after take-off. I estimate the air temperature > rise through the water radiator was at least 80-90 deg. Cooling water > temp. never exceeded 210 deg. F. > > The air exiting the oil radiator was at 135 - 140 deg. F. (A delta T of > about 40 - 45 deg F.) Oil temperature rose to 213 deg. F. max and at > cruse 24 in. MP, 160 mph at 5500 feet the oil temp. decreased to 210 deg. F. > > > I'm close to ideal cooling but I've been surprised how little effect my air > flow modifications have have had on overall oil and water cooling. After > studying K&W Chapter 12 some more I've decided I mounted my cooling radiators > incorrectly!! As mentioned above, the radiators are below the engine at about > a 30 Deg angle (alpha = 60 deg.) to the incoming air stream. The tanks are > orientated fore and aft. This positions the fins across the air stream. > > Ch. 12.2 of K & W Fig. 12.6 shows a radiator block at an oblique angle (*alpha*) > to the incoming air. The *tubes* are at the angle* alpha* to the flow. In the > K & W analysis the tubes are slightly aerodynamic in shape they turn the flow > as it enters the radiator fins. In the radiators I am using the tubes are > separated about 1/2 inch. My fins are separated by about 0.080 inch. Because > I mounted my radiator with the tanks fore and aft, the fins are at the angle*alpha* to the flow and the fins turn the air. The fins are very sharp thin metal > and I believe air flow separation and turbulence is occurring at the leading > edge of each fin. Because the fins are very close together the flow is restricted > through the entire radiator surface. *I believe the separated, turbulent flow at > the leading edge of the fins limits the amount of air flowing through the > radiator regardless of how "good" the diffusers are ahead of the radiators.* > > If I have to do it over, I will defiantly mount my radiators with the tanks on the left > and right side of the incoming air so that the tubes turn the air through *alpha* - not > the fins!! > > Any comments - Am I out to lunch on this one? > > PS. The end of the first paragraph in Ch. 12.2. states "We shall consider first the > simple case of parallel inflow at an angle *alpha* to the *tubes*, as shown in Fig. 12.6" > I have not found a consideration in Chapter 12 of the case of the *fins* being at > an angle *alpha*. > > Dennis Haverlah > > ------=_Part_106676_19038734.1186490069040 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline
Dennis,
 
You've been too quiet.  I was wondering what happened to you.
 
Interesting theory (fins causing turbulence).  Rather than turning the radiator 90*, another option might be to see if you can get a radiator with the fins angled 60* so the air would pass straight through.  I remember someone looking into getting custom radiators done like that a while back.  But I don't know what ever happened.  It sure would solve the turbulence problem.  I wonder if any auto manufacturers do it like that?  Might be worth making a few phone calls.  Keep us posted (I may be needing one of those special radiators soon).
 
Mark S.

 
On 8/7/07, Ed Anderson <eanderson@carolina.rr.com> wrote:
Hi Dennis,
 
Send some of the wet stuff over to NC, we need it.  Good to hear that things have improved cooling wise. 
 
From my understanding of K&W and your radiator orientation, I would hazard a "Yes", I think you may have found a significant reason for getting less cooling than you would initially think you would get with that size radiator.
 
Rather than the larger, relatively more aerodynamic cross-tank tubes turning the air, the air, as you point out,  is meeting the sharp edge of the fins between the tubes.  This likely causes flow separation and that turbulence at the entrance  could, in effect, act as a barrier to good flow through the core channels.  So that may indeed be a reason why manipulation of your airflow inside the duct does not appear to have as much effect as expected.
 
If the flow through the core channels is impeded , then the relatively lesser amount of air flowing through the channels would be at a higher temperature at exit than it would be if a larger air mass flow (more velocity) carried the heat away.  Might be one reason you are seeing such high exit temperatures but cooling not as good as you might expect.  Slower moving air will pick up more heat per unit volume, but will carry away less heat per unit time.  So  best air mass flow is always a compromise of balance between those to opposing factors.
 
Its my guess that K&W did not address the airflow alpha across the fins because a professional and experienced designer of a cooling system for an aircraft simply would not select that choice of orientation - but just a guess.
 
  Perhaps the one good thing is that you appear to be getting adequate cooling with this less than optimum orientation of the core, it would be interesting to now switch the orientation and see the results - next time you are looking for something to do {:>)
 
Ed
 
P.S. Really could use some of the wet stuff   
 
 
 
 
 
.,    ----- Original Message -----
Sent: Monday, August 06, 2007 10:51 PM
Subject: [FlyRotary] RV -7A Cooling Update 8/6/07

 


I've been busy with Family vacation, dealing with the exceptional wet weather in 
central Texas and my tennis playing but finally I have some more 
thoughts on radiators and cooling. My cooling is marginal for Texas in 
the summer.  I want to climb at 120 kts and 26 + inches MP on a 100 deg 
F day without exceeding 215 on water and oil. 

I have the Griffin radiator (core 19 X 13 X 2.5 inches) and stock RX-7 
'89 oil cooler as shown on pictures I have previously posted.  The 
radiators are mounted under the engine at about a 30 deg. angle.  My 
latest test flight with OAT of 92 deg F on the ground was encouraging.  
I had temp. probes on the outlet side of the oil and water radiators 
to measure the temp. of the heated air.  The temp. probes had an upper 
limit of 160 deg. F.  The air exiting the water radiator exceeded the 
160  Deg. limit soon after take-off.  I estimate the air temperature 
rise through the water radiator was at least 80-90 deg. Cooling water 
temp. never exceeded 210 deg. F. 

The air exiting the oil radiator was at 135 - 140 deg. F. (A delta T of
about 40 - 45 deg F.)  Oil temperature rose to 213 deg. F. max and at 
cruse 24 in. MP, 160 mph at 5500 feet the oil temp. decreased to 210 deg. F.


I'm close to ideal cooling but I've been surprised how little effect my air 
flow modifications have have had on overall oil and water cooling.  After 
studying K&W Chapter 12 some more I've decided I mounted my cooling radiators 
incorrectly!!  As mentioned above, the radiators are below the engine at about 
a 30 Deg angle (alpha = 60 deg.) to the incoming air stream.  The tanks are 
orientated fore and aft. This positions the fins across the air stream.  

Ch. 12.2 of K & W Fig. 12.6 shows a radiator block at an oblique angle (alpha) 
to the incoming air.  The tubes are at the angle alpha to the flow.  In the 
K & W analysis the tubes are slightly aerodynamic in shape they turn the flow
as it enters the radiator fins.  In the radiators I am using the tubes are 
separated about 1/2 inch.  My fins are separated by about 0.080 inch. Because
I mounted my radiator with the tanks fore and aft, the fins are at the angle
alpha to the flow and the fins turn the air. The fins are very sharp thin metal
and I believe air flow separation and turbulence is occurring at the leading 
edge of each fin. Because the fins are very close together the flow is restricted
through the entire radiator surface.  I believe the separated, turbulent flow at
the leading edge of the fins limits the amount of air flowing through the 
radiator regardless of how "good" the diffusers are ahead of the radiators.
 
If I have to do it over, I will defiantly mount my radiators with the tanks on the left
and right side of the incoming air so that the tubes turn the air through alpha - not
the fins!!

Any comments - Am I out to lunch on this one?

PS. The end of the first paragraph in Ch. 12.2. states  "We shall consider first the
simple case of parallel inflow at an angle alpha to the tubes, as shown in Fig. 12.6"
I have not found a consideration in Chapter 12 of the case of the fins being at 
an angle alpha. 

Dennis Haverlah

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