X-Virus-Scanned: clean according to Sophos on Logan.com X-PolluStop-Diagnostic: (direct reply)\eX-PolluStop-Score: 0.00\eX-PolluStop: Scanned with Niversoft PolluStop 2.1 RC1, http://www.niversoft.com/pollustop Return-Path: Received: from fed1rmmtao09.cox.net ([68.230.241.30] verified) by logan.com (CommuniGate Pro SMTP 4.3c4) with ESMTP id 860093 for flyrotary@lancaironline.net; Thu, 07 Apr 2005 00:29:45 -0400 Received-SPF: none receiver=logan.com; client-ip=68.230.241.30; envelope-from=ALVentures@cox.net Received: from BigAl ([68.7.14.39]) by fed1rmmtao09.cox.net (InterMail vM.6.01.04.00 201-2131-118-20041027) with ESMTP id <20050407042855.TVSE19936.fed1rmmtao09.cox.net@BigAl> for ; Thu, 7 Apr 2005 00:28:55 -0400 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: rule of thumb and RV-3 sizes- Date: Wed, 6 Apr 2005 21:29:10 -0700 Message-ID: <000001c53b2a$585751f0$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C53AEF.ABF879F0" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C53AEF.ABF879F0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable ..cut Note: the exhaust area requirement is greater than the inlet = combination of oil and coolant due to the now considerable hotter air temperature. = Rule of thumb: Coolant air inlet opening for 200 HP coolant cooled engine ~60 = sq. in., oil inlet opening ~30 sq. in. equals a total opening of 90 sq. in. = A good place to start with exhaust opening is 1.4 times the inlets or 126 = sq. in. Close the exit area down with cowl flaps to as little as 80% of the inlet combination at cruise conditions! =20 ...cut =20 I do understand that an air-cooled installation is a different animal, = but by the end of the day ( or at the cowl exit...for that matter) = everything is air cooled. The interesting thing is that both run a intake/exit ratio = of 78%, the intake (I think you meant 'exhaust) being bigger - just about confirming the above statement! =20 Schmidtbauer mentiones the " rule of thumb" - exit about 150% of inlet. =20 I think for our purposes, the 1.5 ratio is more applicable than 1.28. It = can be lower IF you have well shaped entrance and exit ducting. Typically = we focus on entry ducting, and then have rapid expansion at the exit from = the core - sudden expansion pressure loss; losing all momentum and then, = usually a rather sudden acceleration out a fairly small opening. Definitely = less than optimum. =20 I don't think there is a great difference on the amout of cooling = necessary, as the efficiency of both engines are fairly close. So some heat goes = out the exhaust and the rest has to be cooled. For sure you need different ducting, but the amount of heat energy should be about the same and you = want to get rid of it with the least drag, either way. =20 You're right. The biggest difference is the higher rejection temp, and larger delta T of the air on the air-cooled engines allows for a lower = air flow rate. =20 Al ------=_NextPart_000_0001_01C53AEF.ABF879F0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Message
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Note:  the exhaust area requirement is greater = than the inlet combination of oil and coolant due to the now considerable hotter = air temperature.  Rule of thumb:  Coolant air inlet opening for = 200 HP coolant cooled engine ~60 sq. in., oil inlet opening ~30 sq. in. equals a total = opening of 90 sq. in.  A good place to start with exhaust opening is 1.4 = times the inlets or 126 sq. in.  Close the exit area down with cowl flaps to = as little as 80% of the inlet combination at cruise = conditions!

 

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I do understand that an air-cooled installation is a different animal, but by = the end of the day ( or at the cowl exit...for that matter) everything is = air cooled. The interesting thing is that both run a intake/exit ratio of = 78%, the intake (I think you meant ‘exhaust) being bigger = - just about confirming the above statement!

 

Schmidtbauer mentiones the " = rule of thumb" - exit about 150% of inlet.

 

I think for our purposes, the 1.5 = ratio is more applicable than 1.28. It can be lower IF you have well shaped = entrance and exit ducting.  Typically we focus on entry ducting, and then = have rapid expansion at the exit from the core – sudden expansion = pressure loss; losing all momentum and then, usually a rather sudden acceleration = out a fairly small opening.  Definitely less than = optimum.

 

I don't think there is a great difference on the amout of cooling necessary, as = the efficiency of both engines are fairly close. So some heat goes out the = exhaust and the rest has to be cooled. For sure you need different ducting, = but the amount of heat energy should be about the same and you want to get = rid of it with the least drag, either way.

 

You’re right.  The = biggest difference is the higher rejection temp, and larger delta T of the air = on the air-cooled engines allows for a lower air flow rate.

 

Al

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