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-03.southeast.rr.com ([24.25.9.102] verified) by logan.com (CommuniGate Pro SMTP 5.1.7) with ESMTP id 1872092 for flyrotary@lancaironline.net; Tue, 27 Feb 2007 14:21:28 -0500 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 l1RJKNlP005851 for ; Tue, 27 Feb 2007 14:20:24 -0500 (EST) Message-ID: <000b01c75aa4$5a6cbac0$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 14:20:33 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0008_01C75A7A.70F23560" 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_0008_01C75A7A.70F23560 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable I agree, Thomas - if you are forced to truncate the "streamline duct" = you want to start at the core and go toward the inlet. However, I = decided that to see if pinching the duct before the bell shape would = work since I have such a short distance. In fact, when I calculated out the opening by simply extending the = streamline duct coordinate out 3-6" from the core - the opening was = 60-75% (I forget exactly) the size of my core. I decided that would up = the cooling drag quite a bit - so decided to try the pinched shape which = restricts the size of the opening to near that of the streamline duct = but then tries to compensate for the short length by speeding up the = boundary layer for great penetration toward the core. Again, my cooling = is fine and I can top out at 200 mph in my draggy RV-6A, so I think the = drag is down a bit.=20 But, again that is just my theorizing about why I choose to pinch the = curve. Ed ----- Original Message -----=20 From: Thomas y Reina Jakits=20 To: Rotary motors in aircraft=20 Sent: Tuesday, February 27, 2007 1:52 PM Subject: [FlyRotary] Re: Pinched ducts was : [FlyRotary] Re: cowl = openings for water radiators 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_0008_01C75A7A.70F23560 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
I agree, Thomas - if you are forced to = truncate the=20 "streamline duct" you want to start at the core and go toward the=20 inlet.   However, I decided that to see if pinching the duct = before=20 the bell shape would work since I have such a short = distance.
 
  In fact, when I calculated out the = opening by=20 simply extending the streamline duct coordinate out 3-6" from the core - = the=20 opening was 60-75% (I forget exactly) the size of my core.  I = decided that=20 would up the cooling drag quite a bit - so decided to try the pinched = shape=20 which restricts the size of the opening to near that of the streamline = duct but=20 then tries to compensate for the short length by speeding up the = boundary layer=20 for great penetration toward the core.  Again, my cooling is fine = and I can=20 top out at 200 mph in my draggy RV-6A, so I think the drag is down a=20 bit. 
 
But, again that is just my theorizing about why = I choose=20 to pinch the curve.
 
Ed
 
----- Original Message -----
From:=20 Thomas y=20 Reina Jakits
Sent: Tuesday, February 27, = 2007 1:52=20 PM
Subject: [FlyRotary] Re: = Pinched ducts=20 was : [FlyRotary] Re: cowl openings for water radiators

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=20 cut it from the intake - take radiator and apply the optimum duct, = measure=20 from the radiator towards the intake whatever distance you have = available and=20 cut the duct there....
 
Dave,
are you a Navy-flyer or a medic?? = :)
 
Thomas
----- Original Message -----
From:=20 Ed Anderson
To: Rotary motors in = aircraft=20
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=20 the boundary layer's attachment to the duct=20 wall.  The pressure build up (area of slower = molecules) tend=20 to push and keep the boundary layer pushed against the = wall of the=20 duct as it curves out - at the same time it is slowing down the = boundary=20 layer.  So its the point of separation is (at least = in part)=20 contingent on how much speed the boundary layer has enabling it to = push how=20 far into the pressure recovery area - before it ultimately = separates. =20 The further the better is my 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"=20 back on the boundary layer causing it slow and eventually  to = separate=20 from the wall.  .  However, if you keep the boundary layer = speed=20 up it pushes further into the pressure recovery area following the = duct=20 curve before the "back pressure" slows it enough to cause it to=20 separate. 
 
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=20 the duct.  So my interpretation is that (at least in a duct) = its the=20 back pressure of the recovered pressure that causes the separation - = not=20 necessary the curve of the duct alone although that certainly = contributes to=20 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=20 and 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=20 it 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=20 they cram a lot of areo into Navy pilot's heads.  Me- I'm a = electrical=20 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=20 {:>)
 
 
 
Ed
 
 
----- Original Message ----- =
From:=20 David=20 Leonard
To: Rotary motors in = aircraft=20
Sent: Tuesday, February 27, = 2007=20 11:46 AM
Subject: [FlyRotary] Re: = Pinched=20 ducts 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=20 coming in the duct.  The less turning they do, the = better.  If=20 they need to turn, the radius of the turn needs to be as large as=20 possible.  And just as important, the turn radius is = distributed so=20 that more of the turn is done after the air has started to slow = down (near=20 the face of the radiator).  In other words, the turn radius = is a=20 function of speed.  Just like with a car, don't turn it much = before=20 slowing down or 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=20 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=20 before you start the necessary expansion.   You have = created=20 less distance over which to average the turning radius, you have = increased=20 the speed - meaning the air can tolerate less of a turning = radius=20 before separating (lower velocities are known to maintain laminar = flow=20 much better than high velocity), and you have increased the total = amount=20 of 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=20 I 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=20 to 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=20 liquid cooled engines written back in the hey day of high speed = mustangs=20 lightenings, spitfires, etc. Sort of the liquid cooling=20 bible.   Chapter 12 (the one of most interest to us) = showed a=20 duct that reportedly had the best pressure recovery (84% or = thereabouts)=20 around for a subsonic duct that they had found.  It was = called a=20 "StreamLine Duct" (See attached graph - the graph a of the top = graph=20 shows the shape of the duct (or at least 1/2 around the center = line -=20 sorry for the poor 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=20 is having flow separation in the duct.   Most of the = old=20 drawings of a cooling duct shape followed a sinusoidal shape - = rapid=20 expansion right after the opening.  It turns out that = "traditional"=20 shape is probably one of the worst shapes for a cooling duct = (the story=20 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=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=20 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=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=20 layer flow near the wall of the duct.  It slows it down and = causes=20 it to lose energy and attachment to the duct wall.  At a = certain=20 point the flow separates and starts to tumble/rotate and = depending where=20 (near the duct entrance or near the core) the flow separates, = determines=20 how much of the core area is adversely affected.  So if the = boundary layer's energy level (air speed of its molecules) is = maintained=20 at a high level separation is less likely.
 
So ideally, you would like to prevent = any=20 separation during pressure recovery.  The Streamline Duct = is the so=20 called "Trumpet" duct or "Bell" duct .  After the opening, = there is=20 a long section of non-expanding duct followed by a rapid = expansion into=20 the "bell" shape just before the core.  The long = non-expanding part=20 of the duct maintains the energy (air flow) of the boundary = layer and=20 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=20 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=20 flow increases - 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=20 of 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=20 in 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 for the pictures.  JohnD
----- Original Message ----- =
From: Ed = Anderson=20
To: Rotary=20 motors 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=20 distance on the radiators.  You should do Ok with 20 sq = inch on=20 each opening with a good diffuser/duct.  Attached are = some=20 photos of my current ducts.  The openings are 18 sq = inches=20 each.  I have had one opening down to as little as 10 = square=20 inches - but that was a bit marginal - so opened it back = up.  I=20 have a generous exit area for the hot air including a larger = 4" x=20 12" bottom opening as well as louvers on each side of the=20 cowl.  So you mileage could vary - but Tracy has = essentially=20 the same size opening as well as several others. =
 
Ed
----- Original Message = -----
From: John Downing=20
To: Rotary=20 motors in aircraft
Sent: Monday, = February 26,=20 2007 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=20 sq in. on each side.  Sam James for the 160 Lycoming = is using=20 4 3/4' round holes which are 17.6 sq. inches on each = side. =20 My radiators are quite close to the opening and I plan on = making=20 the diffusers trumpet shaped, will the openings be large = enough if=20 I can 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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