X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from ms-smtp-02.texas.rr.com ([24.93.47.41] verified) by logan.com (CommuniGate Pro SMTP 5.1.11) with ESMTP id 2246828 for flyrotary@lancaironline.net; Mon, 06 Aug 2007 22:52:28 -0400 Received-SPF: pass receiver=logan.com; client-ip=24.93.47.41; envelope-from=clouduster@austin.rr.com Received: from [10.0.0.99] (cpe-70-113-77-184.austin.res.rr.com [70.113.77.184]) by ms-smtp-02.texas.rr.com (8.13.6/8.13.6) with ESMTP id l772pZZq027481 for ; Mon, 6 Aug 2007 21:51:36 -0500 (CDT) Message-ID: <46B7DE32.4070204@austin.rr.com> Date: Mon, 06 Aug 2007 21:51:30 -0500 From: Dennis Haverlah User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 (ax) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Rotary motors in aircraft Subject: RV -7A Cooling Update 8/6/07 Content-Type: multipart/alternative; boundary="------------040001060408020102070307" X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. --------------040001060408020102070307 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit 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 --------------040001060408020102070307 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit 

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
--------------040001060408020102070307--