X-CGP-ClamAV-Result: CLEAN X-VirusScanner: Niversoft's CGPClamav Helper v1.23.0 (ClamAV engine v0.103.0) X-Junk-Score: 20 [X] X-KAS-Score: 20 [X] From: "Finn Lassen finn.lassen@verizon.net" Received: from sonic315-20.consmr.mail.ne1.yahoo.com ([66.163.190.146] verified) by logan.com (CommuniGate Pro SMTP 6.3.5) with ESMTPS id 155910 for flyrotary@lancaironline.net; Wed, 21 Jul 2021 13:39:26 -0400 Received-SPF: pass receiver=logan.com; client-ip=66.163.190.146; envelope-from=finn.lassen@verizon.net DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=verizon.net; s=a2048; t=1626889149; bh=vqSz95QACRNOrcs1AfBOArbVXzAWjOGTphlU94yl0vs=; h=Subject:To:References:From:Date:In-Reply-To:From:Subject:Reply-To; b=mRY9bbeuRjFyNu8DOeLNO19hrGc3GPFByniFLL42sH56VUAyW0ASMPPSWibJVZZNc+JP1r+FlbGIcZWQ/79dCUDNfhxo59s3sWp8Mm4HYUBI0hHe3cmi7CTUfMc8OCm18Zzkom4DkYhJstMQypCdPoyIOhE98nwrT+GpuzWKuoqLZGXyRWuPWbaYmp20D8+cld0oAZz0U+p57u5aAHaaLMh29nUlriG6OppDkEat3yOW9+TOofFmzyBn3K0dmjAavkFCJCcJdmg+NG7tmdtxCcUo+HSpYbtZ0oH83U2bTvGym9RE13bvcH4sUOYUeGSYNAili/Eg/inkpKz0fWIaYQ== X-SONIC-DKIM-SIGN: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yahoo.com; s=s2048; t=1626889149; bh=pmESAKNRsOrE9Vk/Owe3LqevzJvM7Wvy9LmststRPa/=; h=X-Sonic-MF:Subject:To:From:Date:From:Subject; b=bf98meMD0/Ojv68LntC9WpbcTv2Kvr2YB3ajJcimAJQsycjlpvClF3CM5Mlq1CWHtWVV6qKX1MBpyZ9bbd0NRgV7TO26oU2aW6lKFCF3z9OAGIgnWs+uj/PozJlk3AGZNPhfciY7mZ6bmpQypql2EkAQKq+4ZO9nCkeUH50r6JHcHaPdwO62foB7JCgpZGbOVA3sE056bye5N3+g3fjaMTqxjInWf4bEmRpfaTMDBYlfBTSkPR/lENdC7xrg1ZaoBD4Az6N3ObF2LxAjydY4N0aRuJ4/CQgi8jp539XoQMFHJhwZGLDwWo6sYmV4UFLAmZq5K+13Qn3pnZvHT5clZw== X-YMail-OSG: Re4cMsUVM1mPswfX70ERpxzZWdbnD3YS8ZhmW6Xkwi0xYCGYVIThWouoFf3MQUc 7mB0J2SGoP8njrg76UBGRcDyOffIzyhemYrv.DwyydGQXNu6cdYfneI2gv6Fnew2A8tGE2ogci5q 73H93nm2V3E2Cn9MptcN0Abd_sV5naK.A7jC2dpFNKA8sNKwHWrlcFhxBmd0MwKFXbkFyILWshfp LvRFam4UlEwu.gtP00qMKl0EiYFbPaCK.TaUoJkJCByPlAY4EzymfogYneWiujpOalNre9m_OI41 7ERm3ae8Uxc3ratnF1w2h5vBNKK2C7KNwUCKcDvSe1Z0RK4M65sjD6Jc8DTYOSF8yo3zGJ2HewIE MW9JoTsJ8VxWUMc623bdB2Gs7qLl0QYOnFoP2AUY_3_HVt58BRhvVcb6e2eOXSYbzmziZtGY11LH ztkEbDHQUJOsAmyRBxyI78fzSvobNyy_C8oMU40pfgDFb7KgIc_rmXfaSTKO3Cjxfli2MH5.qJax s3WqsrjjN3uPJwZuCtuTRNFSTf.BBxAx59H.4fMWmyXXHsdbEPuOZU.R6vMrM4s0k2BDdxfKqAw6 mDcpkSpIeUQg_froNjIRIa3rPIkQ1mvh2vHhoiBsVr.VmuiM8ktn9AGAdiMzB0F_6mZtp72UCike _b1YeUIhbYvOW2V5K7oPOMrs0S0X26MFvZ9Db42Z6EKIrQiePAmYEkACeSZ6VdhKcpjB9ai4Eyb8 MWr0K0Jd3Nt4gAKaA3cOQod58RzFvX_DLTCVXovNxgga4PtyAr_5pJlvmAB_isavJP.eTTrP3MYy 9SiMWti7FTpCXe08CwFOlmkXYr0ozs1EDw68HfRAVML7DI271utx0kEB8HnpbGTgcXl0zHy4ddJO YRKXbzpy9RefRkePtzZlBn_tbTj8iWej2g5yM..alE6Ef0IWzBXXtXFdBA4QyzVljAbtBpE3AWo1 Cdg5SO1h9GwZV2szJX2WKYaFHIq_wJWwu5XZ3ft2QOnsoa0gUmBAYgncZ12Pz6DvtJmIRrif1D5G 8UinvlEA5jGI4wOCQWTGXWFvfVIlu3lKQw2f2y9Ysiy_9n2G9fpJqklxa3Z2aUcEHDEfvNSHR85Q ah6zYD0EQWIF52_pwjfyvz2xt1X2jcjCK00_WmRla1BUXAacPW13rL_Va2W4yj13ts1_BnGWvpOl sRSx._tNXhbAnQiJ0.rEDSPLFT6cF8xJ8Oi1RGBI6Vu0yihLd9VSopl9.sIkTSPSmnHQ.Yh4MVU1 lgzwVZilAgqyuSg9vf22BasPrYzqCzmKT6qlr2CO5Ku1F1xODJCYNGD6i9tKOWwBIKUGlm4XYIBC Eb3bww2nCBpx5st.0hAqSjYVQTF1xtwgPdrRHVsfYPIclH7vq1hgI7sJDokqs1tkaP3EBjLa7bI2 r4vlFkQ35tZhzo1_dq9mGJsS4xTw0drBG0gcTwGjLs3XU5BoJ_Bb469kD1YXumrpowoypUCdf26A bsESXisDqWVcphGCpaKHvzO1eQ6cCth4nMf6d0mXIM2v0Fk43YNyObbVVEbfunt3K3sPPiHbjnfw vEYJq0NHhvLjQiD_J0pgMwJ1W8CqDl.Vgsa1YhEvcZNYXtfmqJsdTOCHXJ6PQQGjido7qnhhNv8t uSZPn2SpB6Ji0dlloohhdvYcSzytY6g1asBZE.9xfJ9bcN3TGOppj.0jVjTwZEQAenmP9LSFxMXK UZvjoWSZ5po54A04hMCSrI3StphYTFsgMWMwWTakiWmc0s2zeXzcghkw8eqMPujy9O.CQnv93Y25 43dGNv03YINnE.ScAiaw5kU8SHGrpJ5OWqTyZmSO8qJiPzxwr2dZ9r_2qtGRqnPlfDcFYAU_dFEj WR2ELRs00GQIlsZiyRaMN4bW09RzpMyhhcuheC_qCakxYgqQmCfOYfxcUJKTcY2uWa_xcICOTt87 pE5U3DS1VpCA6NCjED6eME6B64Fya3oH9j2EKlmtY_c_6c52klu1HDvVgzuluEacY__2lWT_ofKg 54TAOVUm3PMQTNM_GbGWHvzaoj90zr8BTXoyMKJBVDBU88fxyk5LGbFnl_zSPzCp5BbUwAC2E0gj PZpopOggoWY82dZhXYquek3PFZTBfMKQcgWZi1DsVV6igGgbKScOVVHaQWmo7ubFu0IVcazwj.Ts o.cgaTv.KiDtOBSCTEoDOEwN_kqKMhHJeEPg1OKl5rQqNDA1WWW8W4vI2TES2i16j5JPDhZwxBX7 EYrD.hF9yyEL7QygbGHD3u3AbeadB5obTmX4RVDjWm9EwLYokvDZ8eIPAG3oYY2pzCOhvUDQ9FHS _2QlNIa94UllUhAZ9GDPLtSeBisDD4tqWlJ6a5cmOcyP9_.fOBzZL6M9qUr8Wn7YurPksmd6obCu g3J2S9P4dtXCsMJZOF1c7XKv1IdA3kDWqeEIqeGvODZHIrRy2JKxk2A46nxNAbPAkYhNZ8A-- X-Sonic-MF: Received: from sonic.gate.mail.ne1.yahoo.com by sonic315.consmr.mail.ne1.yahoo.com with HTTP; Wed, 21 Jul 2021 17:39:09 +0000 Received: by kubenode512.mail-prod1.omega.bf1.yahoo.com (VZM Hermes SMTP Server) with ESMTPA ID cffbc549b07734c8618318cc1ca17b06; Wed, 21 Jul 2021 17:39:04 +0000 (UTC) Subject: Re: [FlyRotary] Re: Inlet cooling article To: Rotary motors in aircraft References: Message-ID: Date: Wed, 21 Jul 2021 13:39:00 -0400 User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/alternative; boundary="------------31993BC2744763772D105AE8" Content-Language: en-US X-Antivirus: Avast (VPS 210721-4, 07/21/2021), Outbound message X-Antivirus-Status: Clean X-Mailer: WebService/1.1.18469 mail.backend.jedi.jws.acl:role.jedi.acl.token.atz.jws.hermes.aol Content-Length: 57168 This is a multi-part message in MIME format. --------------31993BC2744763772D105AE8 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit I think the keyword here is drag. Yes, if you could hang a thin radiator in the air, with enough area to provide adequate cooling, that would not slow down the air as it passes through it, you would not need any ducting, diffusers or plenums. Unfortunately in the real world we run into things like a wide range of airspeed, angle of attack of the radiator and turbulence (=drag) caused by air passing over cooling fins. Not that I know what I'm doing. Still trying to get small radiators (2 cu in/HP) to work. One thing I have learned is the difficulty in making two rads and an oil cooler share limited air exit area. Point being that if you want to limit cooling drag, both entry and exit air flow and paths become critical. And for those starting down this road, start with bigger than optimum rads if you have room for them (and can tolerate the weight increase). It's a lot easier to throttle air flow (e.g. exit flap) than tying to optimize everything to get small rads to work. And yes, one radiator would make life much, much simpler, if you have room for it! Finn On 7/21/2021 11:54 AM, Ernest Christley echristley@att.net wrote: > I'm just a computer programmer, not an aerodynamicist, but I think the > whole converting speed to pressure thing is a red-herring that causes > more confusion than it solves. > > What you're after is flow through the entire heat exchanger.  Building > big plenums so that the you can stop the air and then accelerate it is > one way to get there, but where else in aviation do we attempt to stop > the air so that we can start it again? > > The first radiators just hung out in the airstream and had terrible > performance.  The problem was that they created so much turbulence > that air went around them instead of through, and some parts of the > radiator didn't get used at all.  As airplanes got faster, that > turbulence would occur even between fins, obstructing the flow, and > making some parts of the radiator unused.  The point that K&W was > making, at least by my reading, was that the air needed to be slowed > to be smooth through the WHOLE heat exchanger. > > The ducting I have on top of my Corvair engine doesn't look like any > others I've seen. Bascially, all I have is a sheet of aluminum that > taper down as it goes back. I do not have a "plenum" of any sort, and > I do not try to slow the air down.  I just make sure that it smoothly > spreads out and moves through all the cylinders. When first flying, I > was concerned about the CHTs being too low. . . that the cooling might > be TOO good, because they stay below 250*F. > > I guess my message is that you're not looking for "pressure > recovery".  That is just one means to reach the end, which is to make > sure that ALL of the radiator is radiating. > > I could very well be completely off base. > > On Wednesday, July 21, 2021, 11:30:45 AM EDT, Marc Wiese > cardmarc@charter.net wrote: > > > As I recall the K&N curves, the duct/plenum is supposed to decrease > the speed approaching the radiator (or fins), thusly increasing the > pressure, which does the cooling. Not speed, pressure differential. > After the fins, the deal is to regain the speed and have an adequate > size smooth hot air exit. > So a couple of inches of H2O pressure drop across the fins? > The P51 arrangement seems to be about the best? Or wing root LE like > the Hurricane/Mosquito? > M > > Sent from my iPhone > >> On Jul 21, 2021, at 10:12 AM, Finn Lassen finn.lassen@verizon.net >> wrote: >> >>  >> Seems what we're missing is a curve that's the product of these curves. >> >> In other words some kind of bell or parabolic curve with top where >> you have max cooling/drag. >> >> Obviously you can push fluid (and air) through a radiator at a >> furious rate, but the drag will go up. >> >> So for both fluid and air rates there must be an optimum spot. >> >> Finn >> >> On 7/21/2021 8:42 AM, Stephen Izett stephen.izett@gmail.com >> wrote: >>> This graph from Mocal might be helpful. It's for their oil coolers >>> but the trends may be transferable to water exchangers. >>> The solid line is Pressure Drop. >>> The two dotted lines tell the story of two different oil flow >>> rates/tube. >>> >>> >>> >>> m/sec 5 10 15 20 25 >>> kmh 18 36 54 72 90 >>> mph 11.2 22.4 33.6 44.8 55.9 >>> >>> >>> Increasing the air flow 5 fold from 11 to 56 mph only increases the >>> heat transfer: >>> 2 fold with an oil flow of 0.02 L/sec/ tube and 2.3 fold by doubling >>> the oil flow rate per tube to 0.04 L/sec/tube >>> While pressure drop increased 13 fold. >>> >>> So, diminishing returns from increasing airflow or fluid flow. >>> >>> Steve Izett >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>>> On 21 Jul 2021, at 2:48 pm, 12348ung@gmail.com >>>> >>> > wrote: >>>> >>>> Charlie, >>>> No, no reference, just what I have read and also talking to Rad >>>> manufacturers such as BWR in Brisbane.  You can check it out by >>>> passing your hand through a naked flame.  Quickly and there is no >>>> heat transfer.  Pass slowly and you will see what the argument is. >>>>   As I said the truth is there somewhere and as Lyn so aptly puts >>>> it  “I could well be wrong”.. >>>> Neil. >>>> *From:*Rotary motors in aircraft >>> > >>>> *Sent:*Wednesday, July 21, 2021 12:25 PM >>>> *To:*Rotary motors in aircraft >>> > >>>> *Subject:*[FlyRotary] Re: Fwd: Inlet cooling article >>>> Hi Neil, >>>> >>>> Do you have a reference for that? Slowing a medium down so it has >>>> time to absorb the heat seems to conflict with physics as I've been >>>> led to understand it. >>>> >>>> Charlie >>>> >>>> On 7/20/2021 5:01 PM,12348ung@gmail.com >>>> wrote: >>>> >>>> Charlie, >>>> Much wisdom out there, you just have to find the truth! Max >>>> cooling is apparently 30 MPH, so Any faster and it does not >>>> pick up heat before going past.  Look at big trucks, that grill >>>> is not only for looks, they slow the air to get max cooling.  >>>> If too slow they have a quite large fan that kicks in to drag >>>> air through  at 30 MPH not 100! >>>> As you say, what do I know – I have seen too many that do not >>>> work – without any degree. >>>> Neil. >>>> *From:*Rotary motors in aircraft >>>> >>>> *Sent:*Wednesday, July 21, 2021 7:07 AM >>>> *To:*Rotary motors in aircraft >>>> >>>> *Subject:*[FlyRotary] Re: Fwd: Inlet cooling article >>>> On 7/20/2021 3:26 PM, Marc Wiesecardmarc@charter.net >>>> wrote: >>>> >>>> Comments? >>>> >>>> *Subject:**Inlet cooling article* >>>> >>>> https://www.kitplanes.com/down-to-earth-40/ >>>> >>>> Sent from my iPhone >>>> >>>> I remember the Laboda article about enlarging their cooling >>>> inlets, but not many of the details. >>>> This: >>>> The plenum receives air through two circular air intake ducts >>>> behind the propeller and squeezes it, Bernoulli-style, so that >>>> the air accelerates across the cylinders and between their >>>> fins, carrying the heat back, down and out an outflow "gate" at >>>> the back and bottom of the engine area, forward of the firewall. >>>> >>>> Is contrary to everything I've ever read about cooling >>>> efficiently. Faster relative flow will always have higher drag, >>>> all else being equal. Accelerating the air even faster than >>>> freestream just sounds crazy. My understanding is that there's >>>> a balancing act between having the room in an a/c to 'recover' >>>> (increase) differential pressure across the heat exchanger >>>> (engine fins, in this case), and causing too much drag from the >>>> air going through the fins too fast (there's aerodynamic drag >>>> in the heat exchanger, just like over the a/c itself). It's >>>> surprising to me that James made the plenum the way he did. The >>>> rest sounds like putting bandaids on stuff. The next-to-last >>>> image, of the final inlet, shows what appears to be a *much* >>>> smaller plenum inlet than the cowl ring in front of it, and a >>>> rather sharp edged lip where the plenum starts. It looks like >>>> the air would accelerate until it hits that sharp lip, and >>>> immediately go turbulent, which will kill any pressure recovery >>>> and actually slow flow into the cylinder fins. >>>> >>>> Most Lyc plenums I've seen (even the ones James made for the 4 >>>> cyl engines) have significant volume above the cylinders with >>>> smoothly expanding ducts feeding the plenum. That allows the >>>> air to slow in an organized fashion, which increases >>>> *pressure*, which is what actually makes the air move through >>>> the fins. >>>> >>>> But what do I know; I have an Economics degree.... >>>> >>>> Charlie >>>> >>>> >>>> Virus-free.www.avast.com >>>> >>>> >>> >> --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus --------------31993BC2744763772D105AE8 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: 8bit
I think the keyword here is drag.

Yes, if you could hang a thin radiator in the air, with enough area to provide adequate cooling, that would not slow down the air as it passes through it, you would not need any ducting, diffusers or plenums.

Unfortunately in the real world we run into things like a wide range of airspeed, angle of attack of the radiator and turbulence (=drag) caused by air passing over cooling fins.

Not that I know what I'm doing. Still trying to get small radiators (2 cu in/HP) to work. One thing I have learned is the difficulty in making two rads and an oil cooler share limited air exit area. Point being that if you want to limit cooling drag, both entry and exit air flow and paths become critical. And for those starting down this road, start with bigger than optimum rads if you have room for them (and can tolerate the weight increase). It's a lot easier to throttle air flow (e.g. exit flap) than tying to optimize everything to get small rads to work. And yes, one radiator would make life much, much simpler, if you have room for it!

Finn

On 7/21/2021 11:54 AM, Ernest Christley echristley@att.net wrote:
I'm just a computer programmer, not an aerodynamicist, but I think the whole converting speed to pressure thing is a red-herring that causes more confusion than it solves.

What you're after is flow through the entire heat exchanger.  Building big plenums so that the you can stop the air and then accelerate it is one way to get there, but where else in aviation do we attempt to stop the air so that we can start it again?

The first radiators just hung out in the airstream and had terrible performance.  The problem was that they created so much turbulence that air went around them instead of through, and some parts of the radiator didn't get used at all.  As airplanes got faster, that turbulence would occur even between fins, obstructing the flow, and making some parts of the radiator unused.  The point that K&W was making, at least by my reading, was that the air needed to be slowed to be smooth through the WHOLE heat exchanger.

The ducting I have on top of my Corvair engine doesn't look like any others I've seen. Bascially, all I have is a sheet of aluminum that taper down as it goes back. I do not have a "plenum" of any sort, and I do not try to slow the air down.  I just make sure that it smoothly spreads out and moves through all the cylinders.  When first flying, I was concerned about the CHTs being too low. . . that the cooling might be TOO good, because they stay below 250*F.

I guess my message is that you're not looking for "pressure recovery".  That is just one means to reach the end, which is to make sure that ALL of the radiator is radiating.

I could very well be completely off base.

On Wednesday, July 21, 2021, 11:30:45 AM EDT, Marc Wiese cardmarc@charter.net <flyrotary@lancaironline.net> wrote:


As I recall the K&N curves, the duct/plenum is supposed to decrease the speed approaching the radiator (or fins), thusly increasing the pressure, which does the cooling. Not speed, pressure differential. After the fins, the deal is to regain the speed and have an adequate size smooth hot air exit. 
So a couple of inches of H2O pressure drop across the fins?
The P51 arrangement seems to be about the best? Or wing root LE like the Hurricane/Mosquito?
M

Sent from my iPhone

On Jul 21, 2021, at 10:12 AM, Finn Lassen finn.lassen@verizon.net <flyrotary@lancaironline.net> wrote:


Seems what we're missing is a curve that's the product of these curves.

In other words some kind of bell or parabolic curve with top where you have max cooling/drag.

Obviously you can push fluid (and air) through a radiator at a furious rate, but the drag will go up.

So for both fluid and air rates there must be an optimum spot.

Finn

On 7/21/2021 8:42 AM, Stephen Izett stephen.izett@gmail.com wrote:
This graph from Mocal might be helpful. It's for their oil coolers but the trends may be transferable to water exchangers.
The solid line is Pressure Drop.
The two dotted lines tell the story of two different oil flow rates/tube.

<Screen Shot 2021-07-21 at 7.58.40 pm.png>

m/sec 5 10 15 20 25
kmh 18 36 54 72 90
mph 11.2 22.4 33.6 44.8 55.9

Increasing the air flow 5 fold from 11 to 56 mph only increases the heat transfer:
2 fold with an oil flow of 0.02 L/sec/ tube and 2.3 fold by doubling the oil flow rate per tube to 0.04 L/sec/tube
While pressure drop increased 13 fold.

So, diminishing returns from increasing airflow or fluid flow.

Steve Izett















On 21 Jul 2021, at 2:48 pm, 12348ung@gmail.com <flyrotary@lancaironline.net> wrote:

Charlie,
                     No, no reference, just what I have read and also talking to Rad manufacturers such as BWR in Brisbane.  You can check it out by passing your hand through a naked flame.  Quickly and there is no heat transfer.  Pass slowly and you will see what the argument is.   As I said the truth is there somewhere and as Lyn so aptly puts it  “I could well be wrong”..  
Neil.
 
From: Rotary motors in aircraft <flyrotary@lancaironline.net> 
Sent: Wednesday, July 21, 2021 12:25 PM
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: [FlyRotary] Re: Fwd: Inlet cooling article
 
Hi Neil,

Do you have a reference for that? Slowing a medium down so it has time to absorb the heat seems to conflict with physics as I've been led to understand it.

Charlie

On 7/20/2021 5:01 PM, 12348ung@gmail.com wrote:
Charlie,
                   Much wisdom out there, you just have to find the truth!   Max cooling is apparently 30 MPH, so Any faster and it does not pick up heat before going past.  Look at big trucks, that grill is not only for looks, they slow the air to get max cooling.  If too slow they have a quite large fan that kicks in to drag air through  at 30 MPH not 100!
                As you say, what do I know – I have seen too many that do not work – without any degree.
Neil.
 
From: Rotary motors in aircraft <flyrotary@lancaironline.net> 
Sent: Wednesday, July 21, 2021 7:07 AM
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: [FlyRotary] Re: Fwd: Inlet cooling article
 
On 7/20/2021 3:26 PM, Marc Wiese cardmarc@charter.net wrote:
Comments?
 

Subject: Inlet cooling article

 https://www.kitplanes.com/down-to-earth-40/

Sent from my iPhone
I remember the Laboda article about enlarging their cooling inlets, but not many of the details.
This:
The plenum receives air through two circular air intake ducts behind the propeller and squeezes it, Bernoulli-style, so that the air accelerates across the cylinders and between their fins, carrying the heat back, down and out an outflow "gate" at the back and bottom of the engine area, forward of the firewall.

Is contrary to everything I've ever read about cooling efficiently. Faster relative flow will always have higher drag, all else being equal. Accelerating the air even faster than freestream just sounds crazy. My understanding is that there's a balancing act between having the room in an a/c to 'recover' (increase) differential pressure across the heat exchanger (engine fins, in this case), and causing too much drag from the air going through the fins too fast (there's aerodynamic drag in the heat exchanger, just like over the a/c itself). It's surprising to me that James made the plenum the way he did. The rest sounds like putting bandaids on stuff. The next-to-last image, of the final inlet, shows what appears to be a *much* smaller plenum inlet than the cowl ring in front of it, and a rather sharp edged lip where the plenum starts. It looks like the air would accelerate until it hits that sharp lip, and immediately go turbulent, which will kill any pressure recovery and actually slow flow into the cylinder fins. 

Most Lyc plenums I've seen (even the ones James made for the 4 cyl engines) have significant volume above the cylinders with smoothly expanding ducts feeding the plenum. That allows the air to slow in an organized fashion, which increases *pressure*, which is what actually makes the air move through the fins.

But what do I know; I have an Economics degree....

Charlie
 
Virus-free. www.avast.com



--------------31993BC2744763772D105AE8--