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 [201.225.225.168] (HELO cwpanama.net) by logan.com (CommuniGate Pro SMTP 5.1.7) with ESMTP id 1872042 for flyrotary@lancaironline.net; Tue, 27 Feb 2007 13:53:39 -0500 Received-SPF: none receiver=logan.com; client-ip=201.225.225.168; envelope-from=rijakits@cwpanama.net Received: from [201.224.94.164] (HELO usuario5ebe209) by frontend2.cwpanama.net (CommuniGate Pro SMTP 4.2.10) with SMTP id 102922453 for flyrotary@lancaironline.net; Tue, 27 Feb 2007 14:17:09 -0500 Message-ID: <006801c75aa0$6d302f10$a45ee0c9@usuario5ebe209> From: "Thomas y Reina Jakits" 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 13:52:26 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0065_01C75A76.83B81AB0" 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_0065_01C75A76.83B81AB0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Hmm, if I remember right from reading what I have from K&N - if you do not = have the optimal lenght available you start to cut it from the intake - = take radiator and apply the optimum duct, measure from the radiator = towards the intake whatever distance you have available and cut the duct = there.... Dave, are you a Navy-flyer or a medic?? :) Thomas ----- Original Message -----=20 From: Ed Anderson=20 To: Rotary motors in aircraft=20 Sent: Tuesday, February 27, 2007 1:34 PM Subject: [FlyRotary] Re: Pinched ducts was : [FlyRotary] Re: cowl = openings for water radiators Hummm, Dave, perhaps my understanding of what it takes to keep the = boundary layer attached to the duct wall is flawed. =20 From what I believe I understood regarding airflow in a duct is that = the pressure recovery both aids and hinders the boundary layer's = attachment to the duct wall. The pressure build up (area of slower = molecules) tend to push and keep the boundary layer pushed against the = wall of the duct as it curves out - at the same time it is slowing down = the boundary layer. So its the point of separation is (at least in = part) contingent on how much speed the boundary layer has enabling it to = push how far into the pressure recovery area - before it ultimately = separates. The further the better is my understanding. My understanding is that in a duct - it is the recovery pressure = which builds in the expansion area just before the core. This "high" = pressure area will "push" back on the boundary layer causing it slow = and eventually to separate from the wall. . However, if you keep the = boundary layer speed up it pushes further into the pressure recovery = area following the duct curve before the "back pressure" slows it enough = to cause it to separate. =20 Also the speed of a molecule in all random directions is much, much = higher than the component imparted by the airspeed - about 1100 ft/sec = at sea level as I recall compared to about 40 ft/sec in the duct. So my = interpretation is that (at least in a duct) its the back pressure of the = recovered pressure that causes the separation - not necessary the curve = of the duct alone although that certainly contributes to the pressure = recovery. That being said,its clear that the three factors (duct = curve, expansion area and separation) really go hand in hand. The = greater the curve the more pressure recovery occurs and the greater the = tendency for separation. The higher the velocity of the boundary layer = the further it can penetrate into the higher pressure area before being = slowed and separation occurs. =20 There is NO doubt that having a longer duct would improve the = situation. However given I only had 3 -6" my take was that speeding up = the air (and boundary layer energy) would ensure it penetrated deeper = into the bell shape before the pressure recovery caused separation. = But, as I have often stated - I could be completely wrong about what I = think I understand. You are after-all the Navy flyer and I know they cram a lot of areo = into Navy pilot's heads. Me- I'm a electrical engineer, so what I know = about aerodynamics is what I have read (and think I understand). But, regardless these pinched ducts have provided the best cooling = with the smallest opening that I have achieved - so, Dave, if you stay = quite it may not learn the truth {:>) Ed ----- Original Message -----=20 From: David Leonard=20 To: Rotary motors in aircraft=20 Sent: Tuesday, February 27, 2007 11:46 AM Subject: [FlyRotary] Re: Pinched ducts was : [FlyRotary] Re: cowl = openings for water radiators Ed, Good discussion about streamline ducts. No doubt that they are = superior although I have a slightly different take on what quality makes = them work best. I also agree that it is wall separation that we are = trying to avoid.=20 But IMHO the important way to get there is "avoiding sharp turns." = I think of the air molecules as little race cars coming in the duct. = The less turning they do, the better. If they need to turn, the radius = of the turn needs to be as large as possible. And just as important, = the turn radius is distributed so that more of the turn is done after = the air has started to slow down (near the face of the radiator). In = other words, the turn radius is a function of speed. Just like with a = car, don't turn it much before slowing down or it will separate.=20 With that in mind, see why the "conventional duct" is so terrible. = There is a single sharp turn right at the end of the straight-a-way. = Separation occurs there and the whole plenum becomes turbulent. With the bell shaped duct (K&N), it is easy to see why we need = length. The longer the duct, the larger the turn radius can be = throughout the whole distance. =20 Given our limited space however, there will undoubtedly be a point = where the necessary turn radius becomes too small for the speed of the = air and it separates. But at least get the air to expand as much as = possible before that happens.=20 With your restriction in the neck you are setting yourself back = before you start the necessary expansion. You have created less = distance over which to average the turning radius, you have increased = the speed - meaning the air can tolerate less of a turning radius before = separating (lower velocities are known to maintain laminar flow much = better than high velocity), and you have increased the total amount of = expansion the streamlines need to undergo (narrower starting point). So = my guess is a rather dismal effect on cooling compared to what you could = have.=20 BUT, since your cooling is still adequate I am sure you have made a = very nice overall drag reduction. There is no way a conventional duct = with that amount of area would work well. In other works, while I am = very skeptical that the restriction actually helped cooling, big kudos = to you for absolutely minimizing drag and duct area while maintaining = sufficient cooling.=20 In fact, seeing as how you have proven that it works I am = considering doing that for my oil and intercooler ducts as they are = currently getting more air than they need... =20 JMHO --=20 David Leonard Turbo Rotary RV-6 N4VY My websites at: http://members.aol.com/_ht_a/rotaryroster/index.html http://members.aol.com/_ht_a/vp4skydoc/index.html http://leonardiniraq.blogspot.com=20 =20 On 2/26/07, Ed Anderson wrote:=20 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).=20 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.=20 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.=20 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?=20 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 {:>).=20 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 =20 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 =20 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.=20 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 =20 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.=20 -------------------------------------------------------------------- -- 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_0065_01C75A76.83B81AB0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Hmm,
 
if I remember right from reading = what I have=20 from K&N - if you do not have the optimal lenght available you start = to cut=20 it from the intake - take radiator and apply the optimum duct, measure = from the=20 radiator towards the intake whatever distance you have available and cut = the=20 duct there....
 
Dave,
are you a Navy-flyer or a medic?? = :)
 
Thomas
----- Original Message -----
From:=20 Ed=20 Anderson
Sent: Tuesday, February 27, = 2007 1:34=20 PM
Subject: [FlyRotary] Re: = Pinched ducts=20 was : [FlyRotary] Re: cowl openings for water radiators

Hummm, Dave, perhaps my understanding of what = it takes=20 to keep the boundary layer attached to the duct wall is=20 flawed.  
 
From what I believe I = understood regarding=20 airflow in a duct is that the pressure recovery both aids and = hinders the=20 boundary layer's attachment to the duct = wall.  The pressure=20 build up (area of slower molecules) tend to push and keep = the boundary=20 layer pushed against the wall of the duct as it curves out - at = the same=20 time it is slowing down the boundary layer.  So its the = point of=20 separation is (at least in part) contingent on how much speed the = boundary layer has enabling it to push how far into the pressure = recovery area=20 - before it ultimately separates.  The further the better is my=20 understanding.
 
  My understanding is that in a duct = - it is=20 the recovery pressure  which  builds in the expansion area = just=20  before the core.  This "high" pressure area  will = "push" back=20 on the boundary layer causing it slow and eventually  to separate = from=20 the wall.  .  However, if you keep the boundary layer speed = up it=20 pushes further into the pressure recovery area following the duct = curve before=20 the "back pressure" slows it enough to cause it to separate. =20
 
Also  the speed of a molecule in all = random=20 directions is much, much higher than the component imparted by the = airspeed -=20 about 1100 ft/sec at sea level as I recall compared to about 40 ft/sec = in the=20 duct.  So my interpretation is that (at least in a duct) its the = back=20 pressure of the recovered pressure that causes the separation - not = necessary=20 the curve of the duct alone although that certainly contributes to the = pressure recovery.  That being said,its clear that  the = three=20 factors  (duct curve, expansion area and separation)=20   really go hand in hand.  The greater the curve the = more=20 pressure recovery occurs and the greater the tendency for=20 separation.   The higher the velocity of the boundary layer = the=20 further it can penetrate into the higher pressure area before being = slowed and=20 separation occurs. 
 
There is NO doubt that having a longer duct = would=20 improve the situation.  However given I only had 3 -6" = my take=20  was that speeding up the air (and boundary layer energy) would = ensure it=20 penetrated deeper into the bell shape before the pressure recovery = caused=20 separation.  But, as I have often stated - I could be completely = wrong=20 about what I think I understand.
 
  You are after-all the Navy flyer and I = know they=20 cram a lot of areo into Navy pilot's heads.  Me- I'm a electrical = engineer, so what  I know about aerodynamics is what I have read = (and=20 think I understand).
 
But, regardless these pinched ducts = have provided=20 the  best cooling with the smallest opening that I have achieved = - so,=20 Dave,  if you stay quite it may not learn the truth = {:>)
 
 
 
Ed
 
 
----- Original Message -----
From:=20 David=20 Leonard
To: Rotary motors in = aircraft=20
Sent: Tuesday, February 27, = 2007 11:46=20 AM
Subject: [FlyRotary] Re: = Pinched ducts=20 was : [FlyRotary] Re: cowl openings for water radiators

Ed,
 
Good discussion about streamline ducts.  No doubt that = they are=20 superior although I have a slightly different take on what quality = makes=20 them work best.  I also agree that it is wall separation that = we are=20 trying to avoid.
 
But IMHO the important way to get there is "avoiding sharp=20 turns."   I think of the air molecules as little race cars = coming=20 in the duct.  The less turning they do, the better.  If = they need=20 to turn, the radius of the turn needs to be as large as = possible.  And=20 just as important, the turn radius is distributed so that more of = the turn=20 is done after the air has started to slow down (near the face of the = radiator).  In other words, the turn radius is a function of=20 speed.  Just like with a car, don't turn it much before slowing = down or=20 it will separate.
 
With that in mind, see why the "conventional duct" is so=20 terrible.  There is a single sharp turn right at the end of the = straight-a-way.  Separation occurs there and the whole plenum = becomes=20 turbulent.
 
With the bell shaped duct (K&N), it is easy to see why we = need=20 length.  The longer the duct, the larger the turn radius can=20 be throughout the whole distance. 
 
Given our limited space however, there will undoubtedly be a = point=20 where the necessary turn radius becomes too small for the speed of = the air=20 and it separates.  But at least get the air to expand as much = as=20 possible before that happens.
 
With your restriction in the neck you are setting yourself back = before=20 you start the necessary expansion.   You have created less = distance over which to average the turning radius, you have = increased the=20 speed - meaning the air can tolerate less of a turning radius = before=20 separating (lower velocities are known to maintain laminar flow much = better=20 than high velocity), and you have increased the total amount of=20 expansion the streamlines need to undergo (narrower = starting=20 point).  So my guess is a rather dismal effect on = cooling=20 compared to what you could have.
 
BUT, since your cooling is still adequate I am sure you have = made a=20 very nice overall drag reduction. There is no way a = conventional=20 duct with that amount of area would work well.  In other works, = while I=20 am very skeptical that the restriction actually helped = cooling, big=20 kudos to you for absolutely minimizing drag and duct area while=20 maintaining sufficient cooling.
 
In fact, seeing as how you have proven that it works I am = considering=20 doing that for my oil and intercooler ducts as they are currently = getting=20 more air than they need...
 
JMHO

--
David Leonard

Turbo Rotary RV-6 N4VY
My = websites=20 at:
http://memb= ers.aol.com/_ht_a/rotaryroster/index.html
http://members= .aol.com/_ht_a/vp4skydoc/index.html
http://leonardiniraq.blogspot.= com=20
 
On 2/26/07, Ed=20 Anderson <eanderson@carolina.rr.com&g= t;=20 wrote:=20
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=20 reportedly had the best pressure recovery (84% or thereabouts) = around for=20 a subsonic duct that they had found.  It was called a = "StreamLine=20 Duct" (See attached graph - the graph a of the top graph shows the = shape=20 of the duct (or at least 1/2 around the center line - sorry for = the poor=20 quality).  
 
 After quite a bit of studying and = thinking=20 about what I had read about cooling ducts, it finally became clear = to me=20 that the perhaps top thing that is clearly detrimental to good = cooling is=20 having flow separation in the duct.   Most of the old = drawings=20 of a cooling duct shape followed a sinusoidal shape - rapid = expansion=20 right after the opening.  It turns out that "traditional" = shape is=20 probably one of the worst shapes for a cooling duct (the story why = is too=20 long to get into 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=20 pressure is recovered by the expansion of the duct, the build up = of the=20 very pressure recover we want -  starts to hinder the = boundary layer=20 flow near the wall of the duct.  It slows it down and causes = it to=20 lose energy and attachment to the duct wall.  At a certain = point the=20 flow separates and starts to tumble/rotate and depending where = (near the=20 duct entrance or near the core) the flow separates, determines how = much of=20 the core area is adversely affected.  So if the boundary = layer's=20 energy level (air speed of its molecules) is maintained at a high = level=20 separation is less likely.
 
So ideally, you would like to prevent any = separation=20 during pressure recovery.  The Streamline Duct is the so = called=20 "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=20 "bell" shape just before the core.  The long non-expanding = part of=20 the duct maintains the energy (air flow) of the boundary layer and = separation does not occur until well into the "bell" shape=20 expansion. 
 
 In fact, it happens way up in the = corner of=20 the bell/core interface and affects a very small area of the=20 core.
For full effectiveness the "Streamline = duct" from=20 K&W needs a length of 12-17".  Well, that's way more = distance=20 than I had.  So I got to thinking that if keeping the speed = of the=20 air molecules near the duct wall helps prevent boundary layer = separation=20 and the cooling killing eddy of turbulent air -  what could I = do with=20 my short 3 - 6" (no jokes you guys).  We all know from = Bernoulli that=20 if an area is squeezed down that the velocity of the air flow = increases -=20 right? 
 
So I decided to try to maintain or = increase the=20 energy of the air by pitching down the neck just before it goes = into the=20 bell shape expansions in hopes that the increased energy will help = the=20 boundary layer stay adhered to the duct wall until well into the = corner of=20 the bell shape.  So that's the story of the pinched = ducts. =20 There is no question in my mind that this is not as effective as = if I=20 could have had the 16" to build the duct - but, in this hobby, you = work=20 with what you've got - right?
 
Does it work?  Who knows - but I seem = to fly=20 with less opening area than most folks and have no cooling=20 problems.  So that's my 0.02 on the topic - see told you, you = would=20 regret asking {:>).
 
Ed
 
 
----- Original Message ----- =
From: John = Downing=20
To: Rotary motors in=20 aircraft
Sent: Monday, February = 26, 2007=20 8:53 PM
Subject: [FlyRotary] Re: = cowl=20 openings for water radiators

 
Ed, is there some particular = reason that=20 you necked the inlet down small, then enlarged it again.  = Thankyou=20 for the pictures.  JohnD
----- Original Message ----- =
From: Ed = Anderson=20
To: Rotary motors=20 in aircraft
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=20 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=20 each opening with a good diffuser/duct.  Attached are = some photos=20 of my current ducts.  The openings are 18 sq inches = each.  I=20 have had one opening down to as little as 10 square inches - = but that=20 was a bit marginal - so opened it back up.  I have a = generous=20 exit area for the hot air including a larger 4" x 12" bottom = opening=20 as well as louvers on each side of the cowl.  So you = mileage=20 could vary - but Tracy has essentially the same size opening = as well=20 as several others.
 
Ed
----- Original Message ----- =
From: John = Downing=20
To: Rotary=20 motors in 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=20 3/4' round holes which are 17.6 sq. inches on each = side.  My=20 radiators are quite close to the opening and I plan on = making the=20 diffusers trumpet shaped, will the openings be large enough = if I can=20 stay over 20 sq. inches on each side with a decent trumpet=20 shape.  JohnD      =20 hushpowere II on order - hope to start in 2 weeks if = weather=20 cooperates.

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