X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from ms-smtp-01.southeast.rr.com ([24.25.9.100] verified) by logan.com (CommuniGate Pro SMTP 5.1.11) with ESMTP id 2247583 for flyrotary@lancaironline.net; Tue, 07 Aug 2007 08:23:26 -0400 Received-SPF: pass receiver=logan.com; client-ip=24.25.9.100; envelope-from=eanderson@carolina.rr.com Received: from edward2 (cpe-024-074-103-061.carolina.res.rr.com [24.74.103.61]) by ms-smtp-01.southeast.rr.com (8.13.6/8.13.6) with SMTP id l77CMWLm010537 for ; Tue, 7 Aug 2007 08:22:33 -0400 (EDT) Message-ID: <002101c7d8ed$c2675870$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] RV -7A Cooling Update 8/6/07 Date: Tue, 7 Aug 2007 08:23:27 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_001E_01C7D8CC.3AF65A60" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3138 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.3138 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_001E_01C7D8CC.3AF65A60 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Hi Dennis, Send some of the wet stuff over to NC, we need it. Good to hear that = things have improved cooling wise. =20 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 =20 ., ----- Original Message -----=20 From: Dennis Haverlah=20 To: Rotary motors in aircraft=20 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=20 central Texas and my tennis playing but finally I have some more=20 thoughts on radiators and cooling. My cooling is marginal for Texas in=20 the summer. I want to climb at 120 kts and 26 + inches MP on a 100 deg=20 F day without exceeding 215 on water and oil.=20 I have the Griffin radiator (core 19 X 13 X 2.5 inches) and stock RX-7=20 '89 oil cooler as shown on pictures I have previously posted. The=20 radiators are mounted under the engine at about a 30 deg. angle. My=20 latest test flight with OAT of 92 deg F on the ground was encouraging. =20 I had temp. probes on the outlet side of the oil and water radiators=20 to measure the temp. of the heated air. The temp. probes had an upper=20 limit of 160 deg. F. The air exiting the water radiator exceeded the=20 160 Deg. limit soon after take-off. I estimate the air temperature=20 rise through the water radiator was at least 80-90 deg. Cooling water=20 temp. never exceeded 210 deg. F.=20 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=20 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=20 flow modifications have have had on overall oil and water cooling. = After=20 studying K&W Chapter 12 some more I've decided I mounted my cooling = radiators=20 incorrectly!! As mentioned above, the radiators are below the engine at = about=20 a 30 Deg angle (alpha =3D 60 deg.) to the incoming air stream. The = tanks are=20 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)=20 to the incoming air. The tubes are at the angle alpha to the flow. In = the=20 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=20 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=20 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=20 radiator regardless of how "good" the diffusers are ahead of the = radiators. =20 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=20 an angle alpha.=20 Dennis Haverlah ------=_NextPart_000_001E_01C7D8CC.3AF65A60 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Hi Dennis,
 
Send some of the wet stuff over to NC, we need = it. =20 Good to hear that things have improved cooling wise. 
 
From my understanding of K&W and your = radiator=20 orientation, I would hazard a "Yes", I think you may have found a = significant=20 reason for getting less cooling than you would initially think you would = get=20 with that size radiator.
 
Rather than the larger, relatively more = aerodynamic=20 cross-tank tubes turning the air, the air, as you point out,  is = meeting=20 the sharp edge of the fins between the tubes.  This likely causes = flow=20 separation and that turbulence at the entrance  could, in effect, = act as a=20 barrier to good flow through the core channels.  So that may = indeed be=20 a reason why manipulation of your airflow inside the duct does not = appear to=20 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=20 would be at a higher temperature at exit than it would be if a larger = air mass=20 flow (more velocity) carried the heat away.  Might be one reason = you are=20 seeing such high exit temperatures but cooling not as good as you might=20 expect.  Slower moving air will pick up more heat per unit volume, = but will=20 carry away less heat per unit time.  So  best air mass = flow is=20 always a compromise of balance between those to opposing = factors.
 
Its my guess that K&W did not address the = airflow=20 alpha across the fins because a professional and experienced designer of = a=20 cooling system for an aircraft simply would not select that choice of=20 orientation - but just a guess.
 
  Perhaps the one good thing is that you = appear to be=20 getting adequate cooling with this less than optimum orientation of the=20 core, it would be interesting to now switch the orientation and see = the=20 results - next time you are looking for something to do = {:>)
 
Ed
 
P.S. Really could use some of the wet=20 stuff   
 
 
 
 
 
.,   =20 ----- Original Message -----
From:=20 Dennis Haverlah
Sent: Monday, August 06, 2007 = 10:51=20 PM
Subject: [FlyRotary] RV -7A = Cooling=20 Update 8/6/07



I've been busy with Family vacation, =
dealing with the exceptional wet weather in=20
central Texas and my tennis playing but finally I have some more=20
thoughts on radiators and cooling. My cooling is marginal for Texas =
in=20
the summer.  I want to climb at 120 kts and 26 + inches MP on a 100 =
deg=20
F day without exceeding 215 on water and oil.=20

I have the Griffin radiator (core 19 X 13 X 2.5 inches) and stock RX-7=20
'89 oil cooler as shown on pictures I have previously posted.  The=20
radiators are mounted under the engine at about a 30 deg. angle.  My=20
latest test flight with OAT of 92 deg F on the ground was encouraging. =20
I had temp. probes on the outlet side of the oil and water radiators=20
to measure the temp. of the heated air.  The temp. probes had an upper=20
limit of 160 deg. F.  The air exiting the water radiator exceeded the=20
160  Deg. limit soon after take-off.  I estimate the air temperature=20
rise through the water radiator was at least 80-90 deg. Cooling water=20
temp. never exceeded 210 deg. F.=20

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=20
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=20
flow modifications have have had on overall oil and water cooling.  =
After=20
studying K&W Chapter 12 some more I've decided I mounted my cooling =
radiators=20
incorrectly!!  As mentioned above, the radiators are below the engine at =
about=20
a 30 Deg angle (alpha =3D 60 deg.) to the incoming air stream.  The =
tanks are=20
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)=20
to the incoming air.  The tubes are at the angle alpha to =
the flow.  In the=20
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=20
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=20
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=20
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=20
an angle alpha.=20

Dennis Haverlah
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