X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from ms-smtp-03.southeast.rr.com ([24.25.9.102] verified) by logan.com (CommuniGate Pro SMTP 5.1.11) with ESMTP id 2248002 for flyrotary@lancaironline.net; Tue, 07 Aug 2007 11:28:26 -0400 Received-SPF: pass receiver=logan.com; client-ip=24.25.9.102; 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-03.southeast.rr.com (8.13.6/8.13.6) with SMTP id l77FRVNu000238 for ; Tue, 7 Aug 2007 11:27:32 -0400 (EDT) Message-ID: <002901c7d907$9a0d9b90$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: RV -7A Cooling Update 8/6/07 Date: Tue, 7 Aug 2007 11:28:27 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0026_01C7D8E6.12AD6660" 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_0026_01C7D8E6.12AD6660 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable I agree, Tracy. =20 Our flow is without doubt never laminar, a boundary layer of laminar = flow has only(mostly?) the molecules next to the metal absorbing = significant heat. Those molecules in the middle of the stream have = no(little) opportunity to pick up heat. A boundary layer with = turbulence on the other hand has molecules shuffling all over the place = and every one (most?) get an opportunity to contact the hot metal and = take away some of the heat. So turbulent flow is better for conducting = away heat. Chaotic macro flow (boundary layer folding over itself, eddies, etc) on = the other hand impedes pressure recovery, increases drag and overall = adversely effects cooling. My research and experiments leads me to believe that many factors are = relative minor compared to the large scale adverse effect of poor duct = design which leads to early boundary layer separation. However, = significant macro turbulence at the entrance to the core channels might = have a large effect - just speculation on my part. Ed ----- Original Message -----=20 From: Tracy Crook=20 To: Rotary motors in aircraft=20 Sent: Tuesday, August 07, 2007 11:03 AM Subject: [FlyRotary] Re: RV -7A Cooling Update 8/6/07 No scientific analysis here, just my sum total of gut feel after = reading & experimenting. In my understanding, the airflow through the common rads we use is = fully turbulent. the little louvers in the fins are there to guarantee = this. So what difference does it make whether the air goes turbulent at = the leading edge of the fins of a dozen or so thousandts later. Again = according to my very fallible gut feel, the whole story is whether or = not you converted the air velocity to air pressure. Either you did or = you didn't. I can't remember if you have measured pressure at the face = of the rad or not but that will tell the whole story. Angle of tubes, = fins, face of rad, etc is all relatively insignificant.=20 The motorcycle rad stuff someone mentioned is not a good indicator. = They do not depend on high pressure recovery the way we do so the design = and operation of their rads is not necessarily applicapable. As always, YMMV and I will gladly amend my gut feel to match reality = if you find it is wrong. Tracy =20 On 8/6/07, Dennis Haverlah wrote:=20 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_0026_01C7D8E6.12AD6660 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
I agree, Tracy. 
 
Our flow is without doubt never laminar, a = boundary layer=20 of laminar flow has only(mostly?) the molecules next to the metal = absorbing=20 significant heat. Those molecules in the middle of the stream have=20 no(little) opportunity to pick up heat.  A boundary layer with = turbulence=20 on the other hand has molecules shuffling all over the place and every = one=20 (most?) get an opportunity to contact the hot metal and take away some = of the=20 heat. So turbulent flow is better for conducting away heat.
 
Chaotic macro flow (boundary layer folding over = itself,=20 eddies, etc) on the other hand impedes pressure recovery, increases drag = and=20 overall adversely effects cooling.
 
My research and experiments leads me to believe = that many=20 factors are relative minor compared to the large scale adverse effect of = poor=20 duct design which leads to early boundary layer separation.  = However,=20 significant macro turbulence at the entrance to the core channels = might=20 have a large effect - just speculation on my part.
 
Ed
 
 
----- Original Message -----
From:=20 Tracy=20 Crook
Sent: Tuesday, August 07, 2007 = 11:03=20 AM
Subject: [FlyRotary] Re: RV -7A = Cooling=20 Update 8/6/07

No scientific analysis here, just my sum total of gut feel after = reading=20 & experimenting.
 
In my understanding, the airflow through the common  rads we = use is=20 fully turbulent.  the little louvers in the fins are there to = guarantee=20 this.  So what difference does it make whether the air goes = turbulent at=20 the leading edge of the fins of a dozen or so thousandts later.  = Again=20 according to my very fallible gut feel, the whole story is whether or = not you=20 converted the air velocity to air pressure.  Either you did or = you=20 didn't. I can't remember if you have measured pressure at the face of = the rad=20 or not but that will tell the whole story.   Angle of tubes, = fins,=20 face of rad, etc is all relatively insignificant.
 
The motorcycle rad stuff someone mentioned is not a good = indicator. =20 They do not depend on high pressure recovery the way we do so the = design and=20 operation of their rads is not necessarily applicapable.
 
As always, YMMV and I will gladly amend my gut feel to match = reality if=20 you find it is wrong.
 
 Tracy

 
On 8/6/07, Dennis=20 Haverlah <clouduster@austin.rr.com>= =20 wrote:=20 


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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