X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from web81307.mail.mud.yahoo.com ([68.142.199.123] verified) by logan.com (CommuniGate Pro SMTP 5.2c1) with SMTP id 2499977 for flyrotary@lancaironline.net; Wed, 21 Nov 2007 18:17:39 -0500 Received-SPF: none receiver=logan.com; client-ip=68.142.199.123; envelope-from=ron2369@sbcglobal.net Received: (qmail 31320 invoked by uid 60001); 21 Nov 2007 23:17:02 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=sbcglobal.net; h=X-YMail-OSG:Received:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type:Content-Transfer-Encoding:Message-ID; b=qdmfdJMa4Xrd4fj3RN5ZYFXGszUDK5/uJ7c1B2ymd07ylTOsVi0HMGjfD5wJ//37FS+rmYyionGzZ2vdG7uiJjf7Wayt/lgnB9mUP3RqP4cNuaQchPoI1V2e0KfH8ubWnXcSY8Nqtg8BLjxi2u4tJVEwTDDk4T23tOMeguzhhCA=; X-YMail-OSG: KhvdWnoVM1m5B05EMzIVD0s2cDWHeAgqZsXwbDQ_ Received: from [192.146.217.215] by web81307.mail.mud.yahoo.com via HTTP; Wed, 21 Nov 2007 15:17:02 PST Date: Wed, 21 Nov 2007 15:17:02 -0800 (PST) From: Ron Springer Subject: Re: [FlyRotary] Re: Naca Report on Radiator Thickness To: Rotary motors in aircraft In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Message-ID: <708765.29834.qm@web81307.mail.mud.yahoo.com> > > The drag increase of 58% sounds way too low. You > > increased surface area by 300%. Unless mass flow > > decreased a lot (it didn't) or drag coefficient > > dropped a lot (it shouldn't), then this can't be > > right. > > Well, there is no change in frontal area between the > radiators, so the old 1/2pV^2*A drag factor remains > essentially the same for all - discounting the > small 5% decrease in mass flow which would (by > itself) help decrease the frontal drag some. So the > question is would the increase in skin friction be > proportional to the increased internal surface area > ( I would presume it is)? And if it is? Then what > is the absolute amount of drag per square inch based > on. Is the internal core drag a small part or a > large part of the overall core drag.???? I know - > it probably depends........ {:>) Ed, This is a very good point. I am thinking flat plate drag equations and infinitesimally thin fins. That is not true. The drag is probably dominated by the stagnation of air on the frontal area of the fins and anything else that produces frontal area. That frontal drag will probably dominate the internal skin friction drag. So, even though the internal skin friction drag should go up 260% for the thicker case (see other email), the frontal drag will be only be slightly reduced due to the lower mass flow. The net effect could very well be only a 58% increase as your equations show. I've been schooled! Thanks, Ron