Return-Path: Received: from [216.52.245.18] (HELO ispwestemail1.mdeinc.com) by logan.com (CommuniGate Pro SMTP 4.2b3) with ESMTP id 88371 for flyrotary@lancaironline.net; Mon, 24 May 2004 23:01:14 -0400 Received: from 7n7z201 (unverified [67.136.146.26]) by ispwestemail1.mdeinc.com (Vircom SMTPRS 3.1.300.2) with SMTP id for ; Mon, 24 May 2004 20:01:12 -0700 Message-ID: <160501c44204$83972680$c8918843@7n7z201> From: "William" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Two problems solved, 2 more pop up... Date: Mon, 24 May 2004 22:00:58 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1409 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1409 You have to look at how heat is transferred *both ways*. Aluminum *is* a good reflector, especially in the infrared where the exhaust heat is radiating. When an object is out in the sun, it is being bathed in visible light in addition to some infrared. The temperature that a body or paint goes to in the sun is a function of how much it absorbs, reflects, and emits. For normal paints and aluminum, the relationship Absorptance = Emittance = (1 - reflectivity) holds, for any given wavelength. Aluminum has a reflectance of about 0.8 to 0.9, meaning that 10% is absorbed, but it also means that its emmisivity is only ~.1 also, so that energy that gets absorbed is not reemitted until it gets hot. White paint, on the other hand has a reflectance of 0.9, however the paint is bound together with an organic binder that has an emittance close to 0.9 to 0.95 in the infrared. So the white paint can get rid of the heat deposited from the visible spectrum faster than aluminum, but will "appear" black (i.e. absorb and emit well) in the infrared. Bill Schertz KIS Cruiser # 4045 ----- Original Message ----- From: "David Carter" To: "Rotary motors in aircraft" Sent: Sunday, May 23, 2004 11:48 PM Subject: [FlyRotary] Re: Two problems solved, 2 more pop up... > I've noticed that shiney polished aluminum airplanes are quite hot in the > sun, whereas white and light cream colored painted exteriors are quite cool. > I used to think and "aluminum" finish would be best for reflecting heat, but > I no longer think that. I think the same situation would prevail inside the > cowl. > > David > > ----- Original Message ----- > From: "Chad Robinson" > To: "Rotary motors in aircraft" > Sent: Sunday, May 23, 2004 9:25 PM > Subject: [FlyRotary] Re: Two problems solved, 2 more pop up... > > > Given that the primary goal is reflecting radiated heat (rather than > "real" > > thermal insulation) what's wrong with a coat or two of shiny silver paint? > > It's not as good as polished aluminum but it's decent, and high on the > > reflective scale. Sherwin Williams (and others) sells a product called > > "Silver-Brite" that is marketed as "heat reflective" and "dry heat > resistant > > to 700degF". I haven't tested its adherence to epoxy so it might need a > primer > > coat to help it stick better (it's designed for metal) but that's not a > > painful step. In any event, it would sure be a lot easier to apply than > either > > foil OR fiberfrax, especially to an oddly-shaped cowl. > > > > Unless real thermal insulation properties are necesary? > > > > Regards, > > Chad > > > > >> Homepage: http://www.flyrotary.com/ > >> Archive: http://lancaironline.net/lists/flyrotary/List.html