Return-Path: Received: from [65.33.85.197] (account ) by logan.com (CommuniGate Pro WebUser 4.1b1) with HTTP id 2081953 for ; Fri, 21 Mar 2003 01:18:39 -0500 From: "Marvin Kaye" Subject: Re: [FlyRotary] Thick or Thin? The debate continues To: flyrotary X-Mailer: CommuniGate Pro WebUser Interface v.4.1b1 Date: Fri, 21 Mar 2003 01:18:39 -0500 Message-ID: In-Reply-To: <000001c2ef69$69aaf010$27f90844@Leonards> MIME-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format="flowed" Content-Transfer-Encoding: 8bit Posted for "David Leonard" : Ok, I'll submit an opposing viewpoint. Though I point out that from the beginning I am proved wrong by the real experience of NASCAR. I will also agree that if there needs to be a choice between efficient rad and efficient airplane - choose the efficient airplane! I think the key to the argument for a thin rad lies in the fact that parasitic drag is a function of the velocity SQUARED. Implying to me that passing air quickly through a rad pays a disproportionately higher drag penalty than passing a slightly larger amount of air slowly. Comparing 2 rads of the same volume; one thick, one thin: if we are going to, say, pass 10 cubic feet of air through in 5 seconds, it will need to be going faster in the thicker rad (with proportionately less surface area)- as already mentioned. As you point out above the thicker rad will allow each packet to get hotter because it will be spending more time crossing the thicker rad (so less air is needed). But this is offset somewhat by the fact that the slower speed in the thin rad allows each packet to gain more heat per inch and spend almost as much time in the rad. Paul once illustrated it best for me when he said the ideal would be to take a 'small' packet of fast air and use an efficient diffuser to expand the cross section and slow it down (now higher pressure), pass it slowly and efficiently through the rad. Yes, most energy is now lost, but obviously not ALL of it (otherwise it would never leave the cowl), and use an efficient diffuser to go back to small cross section and high speed. The other key point then becomes "efficient diffuser." IMHO, the happy medium is to use the broadest rad that will fit without disturbing the profile of the aircraft - and still leaves room for efficient diffusers (whatever that is) (7 degree rule and all I suppose). David Leonard The Rotary Roster: http://members.aol.com/_ht_a/rotaryroster/index.html