X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 50 [XX] (100%) SPAMTRICKS: long string of words Return-Path: Received: from ms-smtp-05.southeast.rr.com ([24.25.9.104] verified) by logan.com (CommuniGate Pro SMTP 5.1.7) with ESMTP id 1871296 for flyrotary@lancaironline.net; Tue, 27 Feb 2007 07:47:52 -0500 Received-SPF: pass receiver=logan.com; client-ip=24.25.9.104; 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-05.southeast.rr.com (8.13.6/8.13.6) with SMTP id l1RCklIc009436 for ; Tue, 27 Feb 2007 07:46:47 -0500 (EST) Message-ID: <004301c75a6d$5f7cd4a0$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Pinched ducts was : [FlyRotary] Re: cowl openings for water radiators Date: Tue, 27 Feb 2007 07:46:59 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0040_01C75A43.76666840" 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 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0040_01C75A43.76666840 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Thomas is right, Joe.=20 Lots of good stuff on cooling on Paul's site - if you want your own = copy of K&W they are long out of print. However, there was (may still = be there) a place in the Philippines that would make you a bound Xerox = copy of the book for somewhere around $30. Unless you like pouring over = a lot of math thought it makes for heavy reading {:>). =20 Ed ----- Original Message -----=20 From: Thomas y Reina Jakits=20 To: Rotary motors in aircraft=20 Sent: Monday, February 26, 2007 10:46 PM Subject: [FlyRotary] Re: Pinched ducts was : [FlyRotary] Re: cowl = openings for water radiators 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_0040_01C75A43.76666840 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Thomas is right, Joe. 
 
 Lots of good stuff on cooling on Paul's = site - if=20 you want your own copy of K&W they are long out of print.  = However,=20 there was (may still be there) a place in the Philippines that would = make you a=20 bound Xerox copy of the book for somewhere around $30.  Unless you = like=20 pouring over a lot of math thought it makes for heavy reading=20 {:>). 
 
Ed
----- Original Message -----
From:=20 Thomas y=20 Reina Jakits
Sent: Monday, February 26, 2007 = 10:46=20 PM
Subject: [FlyRotary] Re: = Pinched ducts=20 was : [FlyRotary] Re: cowl openings for water radiators

Joe,
 
I hate to do that, but if you need = even more=20 study stuff, go to Paul Lamar's site and read up on the cooling = chapter. He=20 put an impressive collection of data there and a lot of ideas - at = your own=20 risk. There some ways that work well too (obviously, as they are = used...), but=20 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=20 get a lot of info here: http://www.rotaryeng.net/c= ooling.html
 
(The quoted site belongs to Paul = Lamar, all info=20 on it was collected by him and is provid to the public by him. Where=20 applicable 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 = does have an impressive collection of=20 info!
 
 
----- Original Message -----
From:=20 Ed Anderson
To: Rotary motors in = aircraft=20
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=20 be 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=20 lightenings, spitfires, etc. Sort of the liquid cooling = bible. =20  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=20 subsonic duct that they had found.  It was called a "StreamLine = Duct"=20 (See attached graph - the graph a of the top graph shows the shape = of the=20 duct (or at least 1/2 around the center line - sorry for the poor=20 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=20 duct 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=20 here).
 
Anyhow,  Flow separation leads to = eddies and=20 turbulence which casts a "shadow" of turbulent air on the cooling=20 core.  Like a shadow, the further away from the core the = separation=20 occurs (like near the entrance of the duct) the larger the shadow it = casts=20 on the core area.  This "shadow"  adversely = interferes with=20 the flow of air through the core and reduces the effectiveness of = the=20 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=20 wall 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" duct or "Bell" duct .  After the opening, there is a = long=20 section of non-expanding duct followed by a rapid expansion into the = "bell"=20 shape just before the core.  The long non-expanding part of the = duct=20 maintains the energy (air flow) of the boundary layer and separation = does=20 not occur until 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=20 I had.  So I got to thinking that if keeping the speed of the = air=20 molecules near the duct wall helps prevent boundary layer separation = and the=20 cooling killing eddy of turbulent air -  what could I do with = my short=20 3 - 6" (no jokes you guys).  We all know from Bernoulli that if = an area=20 is squeezed down that the velocity of the air flow increases - = right? =20
 
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 = 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. =20 So that's my 0.02 on the topic - see told you, you would regret = asking=20 {:>).
 
Ed
 
 
----- Original Message ----- =
From:=20 John Downing
To: Rotary motors in = aircraft=20
Sent: Monday, February 26, = 2007 8:53=20 PM
Subject: [FlyRotary] Re: = cowl=20 openings for water radiators

Ed, is there some particular = reason that you=20 necked the inlet down small, then enlarged it again.  = Thankyou for=20 the pictures.  JohnD
----- Original Message ----- =
From:=20 Ed Anderson
To: Rotary motors in = aircraft=20
Sent: Monday, February = 26, 2007=20 3:39 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=20 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 = 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=20 marginal - so opened it back up.  I have a generous exit = area for=20 the hot air including a larger 4" x 12" bottom opening as well = as=20 louvers on each side of the cowl.  So you mileage could = vary - but=20 Tracy has essentially the same size opening as well as several=20 others.
 
Ed
----- Original Message ----- =
From:=20 John Downing =
To: Rotary motors in=20 aircraft
Sent: Monday, February = 26, 2007=20 12:12 PM
Subject: [FlyRotary] = cowl=20 openings for water radiators

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