X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from [24.25.9.103] (HELO ms-smtp-04-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 5.0.4) with ESMTP id 882221 for flyrotary@lancaironline.net; Wed, 14 Dec 2005 16:20:56 -0500 Received-SPF: pass receiver=logan.com; client-ip=24.25.9.103; envelope-from=eanderson@carolina.rr.com Received: from edward2 (cpe-024-074-025-165.carolina.res.rr.com [24.74.25.165]) by ms-smtp-04-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id jBELJu1u007751 for ; Wed, 14 Dec 2005 16:19:56 -0500 (EST) Message-ID: <000701c600f4$2520bac0$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Cowl Exit Date: Wed, 14 Dec 2005 16:20:01 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0004_01C600CA.3C059370" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0004_01C600CA.3C059370 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable John, It really depends on how much power/heat you are going to be = producing. However, if you have --say 24 sq inch for each of three = openings (two for GM cores and one for oil cooler) then you have a total = of 72 sq inches for cooling air to come into the cowl. Now you are = going to heat the air which will naturally cause it to expand in volume, = and based on your opening size 4.25*11.25 =3D 47.8 sq inches for this = expanded air to get out. Your exit area is way too small in my = opinion.=20 A "rule of thumb" for exit area that I have seen is no less than 1.2 = ratio of exit to intake. I have seen that ratio up to 1.7. so that = would indicate you would need 1.2*72 =3D 86 to 1.7*72 =3D 122 sq inches. = Personally, I would lean toward the 122 myself. Here is a rule of thumb I just got off the internet You will hear rules of thumb that the exit openings, because the air is = heated and thus presents more volume than the original intake air, = should be 2.5 times the area of the intake opening. With good extraction = of this heated air, allowed by the fact that it is exhausted into a low = pressure area, the exit cross section can be as small as the intake in = some cases. In others larger, but I have never seen this exit area have = to exceed about 1.5 to twice the area of intake.=20 From a different source Exit area totals 66.7 square inches which comes = to about a 1 to 1.5 ratio inlet to exit area. Notice no indication that anything less than intake area would do the = job. I used the solid pink foam from a lumberyard (had to glue several planks = together). I taped it with duct tape to prevent the foam from = dissolving when I put on the epoxy - work fine for me. Ed A ----- Original Message -----=20 From: John Downing=20 To: Rotary motors in aircraft=20 Sent: Wednesday, December 14, 2005 3:17 PM Subject: [FlyRotary] Cowl Exit Looking back thru my notes, I seen a posting that Buly's plane needed = 126 inch of outlet air to make the cooling system work. Is this amount = necessary for tractor installations? At present I have an opening 4 - = 1/4" x 11 - 1/4", with the exhaust to exit short of the opening to help = siphon out the cowling heat. I really don't want to get everything = buttoned up and find out it isn't going to cool. What are you fellows = using on your RV's. Thankyou in advance. JohnD I need to get some = foam for remolding the cowl, what can I get at the lumber yard that will = sand and work well? ------=_NextPart_000_0004_01C600CA.3C059370 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
John,   It = really=20 depends on how  much power/heat you are going to be = producing. =20 However, if you have --say 24 sq inch for each of three openings (two = for GM=20 cores and one for oil cooler) then you have a total of 72 sq inches = for=20 cooling air to come into the cowl.  Now you are going to heat the = air which=20 will naturally cause it to expand in volume, and based on your opening = size=20 4.25*11.25 =3D 47.8 sq inches for this expanded air to get = out.   Your=20 exit  area is way too small in  my opinion. 
 
  A "rule of thumb" for exit area that I = have seen is=20 no less than 1.2 ratio of exit to intake.  I have seen that ratio = up to=20 1.7. so that would indicate you would need 1.2*72 =3D 86 to 1.7*72 =3D = 122 sq=20 inches.  Personally, I would lean toward the 122 = myself.
 
Here is a rule of thumb I just got off the=20 internet
 
You will hear rules of thumb that the exit openings, because = the air is=20 heated and thus presents more volume than the original intake air, = should be 2.5=20 times the area of the intake opening. With good extraction of this = heated air,=20 allowed by the fact that it is exhausted into a low pressure area, the = exit=20 cross section can be as small as the intake in = some=20 cases. In others larger, but I have never = seen this=20 exit area have to exceed about 1.5 to twice the area of = intake.=20
 
From a different source  = Exit area totals 66.7 square inches which = comes to=20 about a 1 to 1.5 ratio inlet to exit area.
 
Notice no indication that anything less than = intake area=20 would do the job.
 
 
I used the solid pink foam from a lumberyard = (had to glue=20 several planks together).  I taped it with duct tape to prevent the = foam=20 from dissolving when I put on the epoxy - work fine for me.
 
Ed A
----- Original Message -----
From:=20 John=20 Downing
Sent: Wednesday, December 14, = 2005 3:17=20 PM
Subject: [FlyRotary] Cowl = Exit

Looking back thru my notes, I seen a = posting that=20 Buly's plane needed 126 inch of outlet air to make the cooling system=20 work.  Is this amount necessary for tractor installations?  = At=20 present I have an opening 4 - 1/4" x 11 - 1/4", with the exhaust to = exit short=20 of the opening to help siphon out the cowling heat.  I really = don't want=20 to get everything buttoned up and find out it isn't going to = cool.  What=20 are you fellows using on your RV's.  Thankyou in advance. =20 JohnD   I need to get some foam for remolding the cowl, what = can I=20 get at the lumber yard that will sand and work=20 well?
------=_NextPart_000_0004_01C600CA.3C059370--