X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 04 May 2006 10:49:30 -0400 Message-ID: X-Original-Return-Path: Received: from smtp114.sbc.mail.mud.yahoo.com ([68.142.198.213] verified) by logan.com (CommuniGate Pro SMTP 5.0.9) with SMTP id 1091396 for lml@lancaironline.net; Thu, 04 May 2006 03:11:51 -0400 Received-SPF: none receiver=logan.com; client-ip=68.142.198.213; envelope-from=elippse@sbcglobal.net Received: (qmail 63678 invoked from network); 4 May 2006 07:11:05 -0000 Received: from unknown (HELO Computerroom) (elippse@sbcglobal.net@71.157.178.134 with login) by smtp114.sbc.mail.mud.yahoo.com with SMTP; 4 May 2006 07:11:05 -0000 X-Original-Message-ID: <000501c66f49$f086f530$86b29d47@Computerroom> From: "Paul Lipps" X-Original-To: "Marv Kaye" Subject: oil cooler NACA inlet & prop size X-Original-Date: Thu, 4 May 2006 00:11:14 -0700 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0002_01C66F0F.420D5380" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2869 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2869 This is a multi-part message in MIME format. ------=_NextPart_000_0002_01C66F0F.420D5380 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable If you don't know the characteristics of the NACA curved-divergent = inlet for its proper design, I would advise you to instead use a = stagnation/pitot inlet, that is, one which projects out from the cowling = pointing forward and with a streamlined aft body. See Hoerner's "Fluid = Dynamic Drag" for some inlet shapes and their drag coefficients. You = might also want to look at the NACA parallel-wall submerged duct which = has a square outlet that is much easier to interface to a round duct. It = also has better pressure-recovery characteristics than the = curved-divergent inlet at duct velocities greater than half of the = free-stream velocity. Look at your oil-cooler's spec sheet from the = manufacturer, pick the cooling flow from the middle of the graph of = heat-rejection vs flow, size the inlet for that flow at cruise, then add = 25% to the area. Say the center of your spec sheet graph shows 300 cfm/ = 5cfs, and your cruise speed is 230 mph. Then your inlet area is 5 * 144 = / (230 * 22/15) =3D 2.13 square inches. Increase that by 25% to get 2.67 = sq. in. 1 5/8 " square, 2 5/16" X 1 3/16" rectangle or 1 7/8" diameter = round, all with nice, rounded lips. Then provide a diverging duct from = that inlet to the oil cooler to slow the flow and increase the pressure, = and then a converging duct from the cooler to the cowl outlet, pointed = toward the rear, with an outlet area of about 3-3.5 sq in to get the = flow back up to freestream velocity.=20 A three blade prop can be considerably reduced in diameter relative = to a two blade of the same mass-flow characteristic, so you might want = to go that route. Each blade sweeps an area based on the diameter, so a = three blade would sweep the same area at a reduced diameter. Carried to = the extreme, a 59" three-blade would intercept the same area and mass as = a 72" two-blade. A three-blade would also give you better static and = climb thrust, as well as a bigger hole in your bank account. But what = the Hell, it's only money! My three-blade is only 63" diameter, and has = very good climb and cruise efficiency! ------=_NextPart_000_0002_01C66F0F.420D5380 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

If you don't know the = characteristics=20 of the NACA curved-divergent inlet for its proper design, I would advise = you to=20 instead use a stagnation/pitot inlet, that is, one which projects out = from the=20 cowling pointing forward and with a streamlined aft body. See = Hoerner's=20 "Fluid Dynamic Drag" for some inlet shapes and their drag = coefficients. You=20 might also want to look at the NACA parallel-wall submerged duct which = has a=20 square outlet that is much easier to interface to a round duct. It also = has=20 better pressure-recovery characteristics than the curved-divergent = inlet at=20 duct velocities greater than half of the free-stream velocity. Look = at your=20 oil-cooler's spec sheet from the manufacturer, pick the cooling flow = from the=20 middle of the graph of heat-rejection vs flow, size the inlet for = that flow=20 at cruise, then add 25% to the area. Say the center of your spec = sheet=20 graph shows 300 cfm/ 5cfs, and your cruise speed is 230 mph. Then your = inlet=20 area is 5 * 144 / (230 * 22/15) =3D 2.13 square inches. = Increase that by=20 25% to get 2.67 sq. in. 1 5/8 " square, 2 5/16" X 1 3/16" = rectangle or 1=20 7/8" diameter round, all with nice, rounded lips. Then = provide a=20 diverging duct from that inlet to the oil cooler to slow the flow and = increase=20 the pressure, and then a converging duct from the cooler to the cowl = outlet,=20 pointed toward the rear, with an outlet area of about 3-3.5 sq in to get = the=20 flow back up to freestream velocity.

A three blade prop can be = considerably=20 reduced in diameter relative to a two blade of the same mass-flow=20 characteristic, so you might want to go that route. Each blade sweeps an = area=20 based on the diameter, so a three blade would sweep the same area at=20 a reduced diameter. Carried to the extreme, a 59" three-blade would = intercept the same area and mass as a 72" two-blade. A = three-blade=20 would also give you better static and climb thrust, as well as a bigger = hole in=20 your bank account. But what the Hell, it's only money! My = three-blade is=20 only 63" diameter, and has very good climb and=20 cruise efficiency!

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