X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 73 [XX] (60%) SPAMTRICKS: long string of words (40%) RECEIVED: IP not found on home country list Return-Path: Received: from [201.225.225.167] (HELO cwpanama.net) by logan.com (CommuniGate Pro SMTP 5.1.7) with ESMTP id 1870551 for flyrotary@lancaironline.net; Mon, 26 Feb 2007 22:47:45 -0500 Received-SPF: none receiver=logan.com; client-ip=201.225.225.167; envelope-from=rijakits@cwpanama.net Received: from [201.224.94.164] (HELO usuario5ebe209) by frontend1.cwpanama.net (CommuniGate Pro SMTP 4.2.10) with SMTP id 103942261 for flyrotary@lancaironline.net; Mon, 26 Feb 2007 22:54:36 -0500 Message-ID: <052301c75a21$e5d39da0$a45ee0c9@usuario5ebe209> From: "Thomas y Reina Jakits" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Pinched ducts was : [FlyRotary] Re: cowl openings for water radiators Date: Mon, 26 Feb 2007 22:46:40 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0520_01C759F7.FB0DAC80" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3028 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.3028 This is a multi-part message in MIME format. ------=_NextPart_000_0520_01C759F7.FB0DAC80 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Joe, I hate to do that, but if you need even more study stuff, go to Paul = Lamar's site and read up on the cooling chapter. He put an impressive = collection of data there and a lot of ideas - at your own risk. There = some ways that work well too (obviously, as they are used...), but you = will not find it on his site, as these ideas do not agree with his = findings. If you need something like Ed has, then you will get a lot of info here: = http://www.rotaryeng.net/cooling.html (The quoted site belongs to Paul Lamar, all info on it was collected by = him and is provid to the public by him. Where applicable Paul Lamar = holds copyrights as noted on his site...) Best Regards, Thomas Jakits, "Slim ball parasite and low life jerk" PS: Whatever one thinks about him, he does have an impressive collection = of info! ----- Original Message -----=20 From: Ed Anderson=20 To: Rotary motors in aircraft=20 Sent: Monday, February 26, 2007 9:38 PM Subject: [FlyRotary] Pinched ducts was : [FlyRotary] Re: cowl openings = for water radiators Actually, there is, Joe. But, you are going to be sorry you asked = {:>). I spent quite a hit of time studying a tome (Kuchuman and Weber = better know as K&W) on air cooling of liquid cooled engines written = back in the hey day of high speed mustangs lightenings, spitfires, etc. = Sort of the liquid cooling bible. Chapter 12 (the one of most interest = to us) showed a duct that reportedly had the best pressure recovery (84% = or thereabouts) around for a subsonic duct that they had found. It was = called a "StreamLine Duct" (See attached graph - the graph a of the top = graph shows the shape of the duct (or at least 1/2 around the center = line - sorry for the poor quality). =20 After quite a bit of studying and thinking about what I had read = about cooling ducts, it finally became clear to me that the perhaps top = thing that is clearly detrimental to good cooling is having flow = separation in the duct. Most of the old drawings of a cooling duct = shape followed a sinusoidal shape - rapid expansion right after the = opening. It turns out that "traditional" shape is probably one of the = worst shapes for a cooling duct (the story why is too long to get into = here). Anyhow, Flow separation leads to eddies and turbulence which casts a = "shadow" of turbulent air on the cooling core. Like a shadow, the = further away from the core the separation occurs (like near the entrance = of the duct) the larger the shadow it casts on the core area. This = "shadow" adversely interferes with the flow of air through the core and = reduces the effectiveness of the core. What causes this separation is that as pressure is recovered by the = expansion of the duct, the build up of the very pressure recover we want = - starts to hinder the boundary layer flow near the wall of the duct. = It slows it down and causes it to lose energy and attachment to the duct = wall. At a certain point the flow separates and starts to tumble/rotate = and depending where (near the duct entrance or near the core) the flow = separates, determines how much of the core area is adversely affected. = So if the boundary layer's energy level (air speed of its molecules) is = maintained at a high level separation is less likely. So ideally, you would like to prevent any separation during pressure = recovery. The Streamline Duct is the so called "Trumpet" duct or "Bell" = duct . After the opening, there is a long section of non-expanding duct = followed by a rapid expansion into the "bell" shape just before the = core. The long non-expanding part of the duct maintains the energy (air = flow) of the boundary layer and separation does not occur until well = into the "bell" shape expansion.=20 In fact, it happens way up in the corner of the bell/core interface = and affects a very small area of the core. For full effectiveness the "Streamline duct" from K&W needs a length = of 12-17". Well, that's way more distance than I had. So I got to = thinking that if keeping the speed of the air molecules near the duct = wall helps prevent boundary layer separation and the cooling killing = eddy of turbulent air - what could I do with my short 3 - 6" (no jokes = you guys). We all know from Bernoulli that if an area is squeezed down = that the velocity of the air flow increases - right? =20 So I decided to try to maintain or increase the energy of the air by = pitching down the neck just before it goes into the bell shape = expansions in hopes that the increased energy will help the boundary = layer stay adhered to the duct wall until well into the corner of the = bell shape. So that's the story of the pinched ducts. There is no = question in my mind that this is not as effective as if I could have had = the 16" to build the duct - but, in this hobby, you work with what = you've got - right? Does it work? Who knows - but I seem to fly with less opening area = than most folks and have no cooling problems. So that's my 0.02 on the = topic - see told you, you would regret asking {:>). Ed ----- Original Message -----=20 From: John Downing=20 To: Rotary motors in aircraft=20 Sent: Monday, February 26, 2007 8:53 PM Subject: [FlyRotary] Re: cowl openings for water radiators Ed, is there some particular reason that you necked the inlet down = small, then enlarged it again. Thankyou for the pictures. JohnD ----- Original Message -----=20 From: Ed Anderson=20 To: Rotary motors in aircraft=20 Sent: Monday, February 26, 2007 3:39 PM Subject: [FlyRotary] Re: cowl openings for water radiators John, don't know if these photos will help. But, like you I only = have between 3 and 6" of duct distance on the radiators. You should do = Ok with 20 sq inch on each opening with a good diffuser/duct. Attached = are some photos of my current ducts. The openings are 18 sq inches = each. I have had one opening down to as little as 10 square inches - = but that was a bit marginal - so opened it back up. I have a generous = exit area for the hot air including a larger 4" x 12" bottom opening as = well as louvers on each side of the cowl. So you mileage could vary - = but Tracy has essentially the same size opening as well as several = others. Ed ----- Original Message -----=20 From: John Downing=20 To: Rotary motors in aircraft=20 Sent: Monday, February 26, 2007 12:12 PM Subject: [FlyRotary] cowl openings for water radiators What size openings do I need for the water radiators? The = Wittman Tailwind cowl I have has postal slots of 3' x 7 3/4" , which is = approx. 22 1/4 sq in. on each side. Sam James for the 160 Lycoming is = using 4 3/4' round holes which are 17.6 sq. inches on each side. My = radiators are quite close to the opening and I plan on making the = diffusers trumpet shaped, will the openings be large enough if I can = stay over 20 sq. inches on each side with a decent trumpet shape. JohnD = hushpowere II on order - hope to start in 2 weeks if weather = cooperates. ------------------------------------------------------------------------ -- Homepage: http://www.flyrotary.com/ Archive and UnSub: = http://mail.lancaironline.net/lists/flyrotary/ -------------------------------------------------------------------------= - -- Homepage: http://www.flyrotary.com/ Archive and UnSub: = http://mail.lancaironline.net/lists/flyrotary/ -------------------------------------------------------------------------= ----- -- Homepage: http://www.flyrotary.com/ Archive and UnSub: http://mail.lancaironline.net/lists/flyrotary/ ------=_NextPart_000_0520_01C759F7.FB0DAC80 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Joe,
 
I hate to do that, but if you need even = more study=20 stuff, go to Paul Lamar's site and read up on the cooling chapter. He = put an=20 impressive collection of data there and a lot of ideas - at your own = risk. There=20 some ways that work well too (obviously, as they are used...), but you = will not=20 find it on his site, as these ideas do not agree with his = findings.
If you need something like Ed has, then = you will=20 get a lot of info here: http://www.rotaryeng.net/c= ooling.html
 
(The quoted site belongs to Paul Lamar, = all info on=20 it was collected by him and is provid to the public by him. Where = applicable=20 Paul Lamar holds copyrights as noted on his site...)
 
Best Regards,
Thomas Jakits,
"Slim ball parasite and low life=20 jerk"
 
PS: Whatever one thinks about him, he=20 does have an impressive collection of=20 info!
 
 
----- Original Message -----
From:=20 Ed=20 Anderson
Sent: Monday, February 26, 2007 = 9:38=20 PM
Subject: [FlyRotary] Pinched = ducts was :=20 [FlyRotary] Re: cowl openings for water radiators

Actually, there is, Joe.  But, you are = going to be=20 sorry you asked {:>).
 
  I spent quite a hit of time studying a = tome=20 (Kuchuman and Weber better know as K&W)  on air cooling of = liquid=20 cooled engines written back in the hey day of high speed mustangs = lightenings,=20 spitfires, etc. Sort of the liquid cooling bible.  =  Chapter 12=20 (the one of most interest to us) showed a duct that reportedly had the = best=20 pressure recovery (84% or thereabouts) around for a subsonic duct that = they=20 had found.  It was called a "StreamLine Duct" (See attached graph = - the=20 graph a of the top graph shows the shape of the duct (or at least 1/2 = around=20 the center line - sorry for the poor = quality).  
 
 After quite a bit of studying and = thinking about=20 what I had read about cooling ducts, it finally became clear to me = that the=20 perhaps top thing that is clearly detrimental to good cooling is = having flow=20 separation in the duct.   Most of the old drawings of a = cooling duct=20 shape followed a sinusoidal shape - rapid expansion right after the=20 opening.  It turns out that "traditional" shape is probably one = of the=20 worst shapes for a cooling duct (the story why is too long to get into = here).
 
Anyhow,  Flow separation leads to eddies = and=20 turbulence which casts a "shadow" of turbulent air on the cooling = core. =20 Like a shadow, the further away from the core the separation occurs = (like near=20 the entrance of the duct) the larger the shadow it casts on the core=20 area.  This "shadow"  adversely interferes with the = flow of air=20 through the core and reduces the effectiveness of the = core.
 
  What causes this separation is that as = pressure=20 is recovered by the expansion of the duct, the build up of the very = pressure=20 recover we want -  starts to hinder the boundary layer flow near = the wall=20 of the duct.  It slows it down and causes it to lose energy and=20 attachment to the duct wall.  At a certain point the flow = separates and=20 starts to tumble/rotate and depending where (near the duct entrance or = near=20 the core) the flow separates, determines how much of the core area is=20 adversely affected.  So if the boundary layer's energy level (air = speed=20 of its molecules) is maintained at a high level separation is less=20 likely.
 
So ideally, you would like to prevent any = separation=20 during pressure recovery.  The Streamline Duct is the so called = "Trumpet"=20 duct or "Bell" duct .  After the opening, there is a long section = of=20 non-expanding duct followed by a rapid expansion into the "bell" shape = just=20 before the core.  The long non-expanding part of the duct = maintains the=20 energy (air flow) of the boundary layer and separation does not occur = until=20 well into the "bell" shape expansion. 
 
 In fact, it happens way up in the corner = of the=20 bell/core interface and affects a very small area of the = core.
For full effectiveness the "Streamline duct" = from=20 K&W needs a length of 12-17".  Well, that's way more distance = than I=20 had.  So I got to thinking that if keeping the speed of the air = molecules=20 near the duct wall helps prevent boundary layer separation and the = cooling=20 killing eddy of turbulent air -  what could I do with my short 3 = - 6" (no=20 jokes you guys).  We all know from Bernoulli that if an area is = squeezed=20 down that the velocity of the air flow increases - right?  =
 
So I decided to try to maintain or increase = the energy=20 of the air by pitching down the neck just before it goes into the bell = shape=20 expansions in hopes that the increased energy will help the boundary = layer=20 stay adhered to the duct wall until well into the corner of the bell=20 shape.  So that's the story of the pinched ducts.  There is = no=20 question in my mind that this is not as effective as if I could have = had the=20 16" to build the duct - but, in this hobby, you work with what you've = got -=20 right?
 
Does it work?  Who knows - but I seem to = fly with=20 less opening area than most folks and have no cooling = problems.  So=20 that's my 0.02 on the topic - see told you, you would regret asking=20 {:>).
 
Ed
 
 
----- Original Message -----
From:=20 John=20 Downing
To: Rotary motors in = aircraft=20
Sent: Monday, February 26, = 2007 8:53=20 PM
Subject: [FlyRotary] Re: cowl = openings=20 for water radiators

Ed, is there some particular reason = that you=20 necked the inlet down small, then enlarged it again.  Thankyou = for the=20 pictures.  JohnD
----- Original Message ----- =
From:=20 Ed Anderson
To: Rotary motors in = aircraft=20
Sent: Monday, February 26, = 2007 3:39=20 PM
Subject: [FlyRotary] Re: = cowl=20 openings for water radiators

John, don't know if these photos will = help. =20 But, like you I only have between 3 and 6" of duct distance on the = radiators.  You should do Ok with 20 sq inch on each opening = with a=20 good diffuser/duct.  Attached are some photos of my current=20 ducts.  The openings are 18 sq inches each.  I have had = one=20 opening down to as little as 10 square inches - but that was a bit = marginal - so opened it back up.  I have a generous exit area = for the=20 hot air including a larger 4" x 12" bottom opening as well as = louvers on=20 each side of the cowl.  So you mileage could vary - but Tracy = has=20 essentially the same size opening as well as several = others.
 
Ed
----- Original Message ----- =
From:=20 John Downing
To: Rotary motors in = aircraft=20
Sent: Monday, February = 26, 2007=20 12:12 PM
Subject: [FlyRotary] cowl = openings=20 for water radiators

What size openings do I need = for the water=20 radiators?   The Wittman Tailwind cowl I have has = postal slots=20 of 3' x 7 3/4" , which is   approx. 22 1/4 sq in. on = each=20 side.  Sam James for the 160 Lycoming is using 4 3/4' round = holes=20 which are 17.6 sq. inches on each side.  My radiators are = quite=20 close to the opening and I plan on making the diffusers trumpet = shaped,=20 will the openings be large enough if I can stay over 20 sq. = inches on=20 each side with a decent trumpet shape. =20 JohnD       hushpowere II on = order -=20 hope to start in 2 weeks if weather cooperates.

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