Return-Path: Received: from [65.54.169.76] (HELO hotmail.com) by logan.com (CommuniGate Pro SMTP 4.1.5) with ESMTP id 2645880 for flyrotary@lancaironline.net; Tue, 21 Oct 2003 18:47:37 -0400 Received: from mail pickup service by hotmail.com with Microsoft SMTPSVC; Tue, 21 Oct 2003 15:47:36 -0700 Received: from 65.137.51.34 by bay3-dav46.bay3.hotmail.com with DAV; Tue, 21 Oct 2003 22:47:36 +0000 X-Originating-IP: [65.137.51.34] X-Originating-Email: [lors01@msn.com] Reply-To: "Tracy Crook" From: "Tracy Crook" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: temps behind radiator? Date: Tue, 21 Oct 2003 18:50:14 -0400 Organization: Real World Solutions Inc. MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_00E6_01C39804.29B62580" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1158 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 Message-ID: X-OriginalArrivalTime: 21 Oct 2003 22:47:36.0617 (UTC) FILETIME=[52C21990:01C39825] This is a multi-part message in MIME format. ------=_NextPart_000_00E6_01C39804.29B62580 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Message There's not really much we can do about oil flow rate, short of not = restricting it. Does the oil typically flow at double the rate of the = coolant in the stock configuration? I've never really thought about = that, but I can't see how it could. =20 If the oil doesn't flow that much faster than water, and it has half = the heat rejection of water, then do we need to size the oil cooler the = same as the radiator? I've been amazed at how little radiator I need, = compared to how hard it is to cool the oil, so this is starting to make = sense. =20 Don't forget that the amount of heat rejected to the oil is about 40% = of what goes into the water. The specific heat of oil is actually about = 70% that of a 50/50 mix of water/glycol (.6 vs .84 in metric) My dyno = test showed the flow rate of water just a bit more than double that of = the oil if you have a thermostat in the coolant circuit (triple without = the thermostat). Now you put in the factor of typically allowing the = oil about 20 F higher the coolant, and you have the air flow right, it = works out that the heat transfer area (core volume, if you wish) of the = oil cooler can be just a bit less than half the radiator. And Mazda had = things figured correctly. This, of course, assumes that you have the same incoming air temp to = both. Putting the oil cooler behind the radiator throws a big wrench = into optimizing the cooling systems; and is a bad idea from the git-go. = Heat rejected is pretty much proportional to the temp difference between = the air and the coolant/or oil. But if that's your only configuration = option, and the air temp increase through the rad is, say, 35F; and you = want to climb out on a 90F day, you can expect to need an oil cooler = core volume of roughly 1 =BD times normal; or about =BE the size of the = rad. This is rough estimating and assumes equal effectiveness of rad and = cooler; but you get the idea. Al All Good points except that the oil cooler behind the rad *does* get = maximum use out of every CFM of cooling air which is the ideal situation = in aircraft. If it takes a bigger oil cooler, then so be it. Ever take = a look at that 11" stack of heat exchangers in a P51? That is the = biggest reason the plane could escort bombers all the way to & from = Germany. =20 Sorry, I'm going to bore everyone again with my favorite saying on = this subject - "Remember, we are trying to build efficient *airplanes*, = not efficient radiators." Tracy ------=_NextPart_000_00E6_01C39804.29B62580 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Message
 
There's not = really=20 much we can do about oil flow rate, short of not restricting it.  = Does=20 the oil typically flow at double the rate of the coolant in the stock=20 configuration?  I've never really thought about that, but I can't = see how=20 it could. 

 

If the=20 oil doesn't flow that much faster than water, and it has half the heat = rejection of water, then do we need to size the oil cooler the same as = the=20 radiator?  I've been amazed at how little radiator I need, = compared to=20 how hard it is to cool the oil, so this is starting to make = sense. =20

 

 

Don=92t = forget that=20 the amount of heat rejected to the oil is about 40% of what goes into = the=20 water.  The specific heat of oil is actually about 70% that of a = 50/50=20 mix of water/glycol (.6 vs .84 in metric) My dyno test showed the flow = rate of=20 water just a bit more than double that of the oil if you have a = thermostat in=20 the coolant circuit (triple without the thermostat).  Now you put = in the=20 factor of typically allowing the oil about 20 F higher the coolant, = and you=20 have the air flow right, it works out that the heat transfer area = (core=20 volume, if you wish) of the oil cooler can be just a bit less than = half the=20 radiator.  And Mazda had things figured = correctly.

 

This, of = course,=20 assumes that you have the same incoming air temp to both.  = Putting the=20 oil cooler behind the radiator throws a big wrench into optimizing the = cooling=20 systems; and is a bad idea from the git-go.  Heat rejected is = pretty much=20 proportional to the temp difference between the air and the coolant/or = oil.=20 But if that=92s your only configuration option, and the air temp = increase=20 through the rad is, say, 35F; and you want to climb out on a 90F day, = you can=20 expect to need an oil cooler core volume of roughly 1 =BD times = normal; or about=20 =BE the size of the rad.

 

This is = rough=20 estimating and assumes equal effectiveness of rad and cooler; but you = get the=20 idea.

 

Al

 

All Good = points=20 except that the oil cooler behind the rad *does* get maximum use out = of every=20 CFM of cooling air which is the ideal situation in aircraft.  If = it takes=20 a bigger oil cooler, then so be it.  Ever take a look at that 11" = stack=20 of heat exchangers in a P51?   That is the biggest reason = the plane=20 could escort bombers all the way to & from Germany.  =20

 

Sorry, = I'm going to=20 bore everyone again with my favorite saying on this subject - = "Remember, we=20 are trying to build efficient *airplanes*, not efficient=20 radiators."

 

Tracy

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