X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from [65.54.250.88] (HELO hotmail.com) by logan.com (CommuniGate Pro SMTP 5.0.8) with ESMTP id 1037455 for flyrotary@lancaironline.net; Fri, 17 Mar 2006 14:01:05 -0500 Received-SPF: pass receiver=logan.com; client-ip=65.54.250.88; envelope-from=lors01@msn.com Received: from mail pickup service by hotmail.com with Microsoft SMTPSVC; Fri, 17 Mar 2006 11:00:20 -0800 Message-ID: Received: from 4.174.4.45 by BAY115-DAV16.phx.gbl with DAV; Fri, 17 Mar 2006 19:00:16 +0000 X-Originating-IP: [4.174.4.45] X-Originating-Email: [lors01@msn.com] X-Sender: lors01@msn.com From: "Tracy Crook" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: NACA's, Cooling and Sport Aviation Mag.. Date: Fri, 17 Mar 2006 14:00:10 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_011B_01C649CB.1B1B23B0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: MSN 9 X-MimeOLE: Produced By MSN MimeOLE V9.10.0011.1703 Seal-Send-Time: Fri, 17 Mar 2006 14:00:10 -0500 X-OriginalArrivalTime: 17 Mar 2006 19:00:20.0742 (UTC) FILETIME=[09D53260:01C649F5] This is a multi-part message in MIME format. ------=_NextPart_000_011B_01C649CB.1B1B23B0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Subject: [FlyRotary] Re: NACA's, Cooling and Sport Aviation Mag.. Yes, it tells you the pressure above the cooling fins of the engine = (almost full dynamic pressure). Yes I am making the assumption that the = pressure below the engine (other side of the cooling fins) is the same = as the backside of the radiator. Is that not reasonable? The cooling = exit is the same in both examples. Note that the pressure above the = engine was almost full dynamic pressure WITHOUT the exit being blocked. = Therefore my conclusion that the pressure differential is NOT lower on = the aircooled engine. Am I missing your point Al? Tracy I guess my point was that there isn't enough information to draw the = conclusion. But if the exits are the same, and the pressure in front of = the radiator is the same as that above the cooling fins; then the = pressure drops should be about the same. But of course it varies from = one installation to another, rad thickness, fin density, etc. In any case; I agree with your premise - I have seen no data that = definitively supports the conclusion of lower pressure drop for cooling = the air cooled engine. Should one also infer then, that the flow rate = required is also about the same - that the higher fin temp does not give = a higher delta T to the cooling air? Al A : Yes, I do believe that the higher fin temps do not result in = higher delta T to cooling air (supported by some exit air temp readings = on Lyc. installations) The reason is that there are fewer 'collisions' = between each air molecule and fins than with fins in a rad (especially a = thick one). The average air velocity is higher in the Lyc than a rad. = If you slowed the air in the Lyc to the same speed as in a rad, it would = not cool the engine for two reasons. Not enough turbulence (required = for good heat transfer) and not enough CFM even if there were enough = turbulence. =20 You have probably noticed the fins on the really high performance = radial engine heads from WWII era. They have an incredible fin density = (similar to a radiator). In the case of the cylinder barrel fin = assemblies (a separate part that is clamped to the cylinders) they look = VERY similar to radiator fins, including turbulators between the fins = which accomplish the same thing as the louvers in radiator fins. These = air cooled engines probably DID have higher delta T temps than our = liquid cooled roraries. If you just scaled up a Lycoming O - 360 = cylinder assembly and tried to get the HP/CI that the super charged = radials did, they would burn up in very short order. Tracy ------=_NextPart_000_011B_01C649CB.1B1B23B0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Subject: [FlyRotary] Re: NACA's, Cooling and Sport Aviation=20 Mag..

 

Yes,=20 it tells you the pressure above the cooling fins of the engine (almost = full=20 dynamic pressure).  Yes I am making the assumption that the = pressure=20 below the engine (other side of the cooling fins) is the same as the = backside=20 of the radiator.  Is that not reasonable?   The = cooling=20 exit is the same in both examples.    Note that the = pressure=20 above the engine was almost full dynamic pressure WITHOUT the exit = being=20 blocked.  Therefore my conclusion that the pressure differential = is NOT=20 lower on the aircooled engine.

 

Am I=20 missing your point Al?

 

Tracy

I guess = my point=20 was that there isn=92t enough information to draw the = conclusion.  But if=20 the exits are the same, and the pressure in front of the radiator is = the same=20 as that above the cooling fins; then the pressure drops should be = about the=20 same.  But of course it varies from one installation to another, = rad=20 thickness, fin density, etc.

 

In any = case; I=20 agree with your premise =96 I have seen no data that definitively = supports the=20 conclusion of lower pressure drop for cooling the air cooled = engine. =20 Should one also infer then, that the flow rate required is also about = the same=20 =96 that the higher fin temp does not give a higher delta T to the = cooling=20 air?

 

Al

 

A : =20 Yes, I do believe that the higher fin temps do not result in higher = delta T to=20 cooling air (supported by some exit air temp readings on Lyc.=20 installations)  The reason is that there are fewer 'collisions' = between=20 each air molecule and fins than with fins in a rad (especially a = thick=20 one).  The average air velocity is higher in the Lyc than a = rad.  If=20 you slowed the air in the Lyc to the same speed as in a rad, it would = not cool=20 the engine for two reasons.  Not enough turbulence (required for = good=20 heat transfer) and not enough CFM even if there were enough=20 turbulence. 

 

You=20 have probably noticed the fins on the really high performance radial = engine=20 heads from WWII era.  They have an incredible fin density = (similar=20 to a radiator).  In the case of the cylinder barrel fin = assemblies (a=20 separate part that is clamped to the cylinders) they look VERY similar = to=20 radiator fins, including turbulators between the fins which accomplish = the=20 same thing as the louvers in radiator fins.   These air = cooled=20 engines probably DID have higher delta T temps than our liquid cooled=20 roraries.  If you just scaled up a Lycoming O - 360 cylinder = assembly and=20 tried to get the HP/CI that the super charged radials  did, they = would=20 burn up in very short order.

 

Tracy

 

 

 

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