X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from lrcmmta07-srv.windstream.net ([166.102.165.79] verified) by logan.com (CommuniGate Pro SMTP 5.3c4) with ESMTP id 4040384 for flyrotary@lancaironline.net; Thu, 24 Dec 2009 16:59:27 -0500 Received-SPF: pass receiver=logan.com; client-ip=166.102.165.79; envelope-from=montyr2157@windstream.net Return-Path: X-WS-COS: WSOB804 X-Cloudmark-Category: Undefined:Undefined X-Cloudmark-Analysis: v=1.1 cv=fQSbGZYPoo58QFQf7/DywxCkD3theYl8m2mUN13YeBU= c=1 sm=0 a=AkRM4UhNubgA:10 a=Ie3aRxaihoU2Oq8a_tQA:9 a=szFSX1OihQ3GrAQiLC8A:7 a=oJLlthGOD4w1KmklpApnGUESiwUA:4 a=acPYtHRp5LOOEKEv:21 a=kqVKPOhLPVXDlSb-:21 a=UretUmmEAAAA:8 a=Ia-xEzejAAAA:8 a=X2TizB4Il0R4h7--wpgA:9 a=OsbT5tnnmBX9PnwLugsA:7 a=FW4H-3nKvBeQWOwnwbdEIFu0u0UA:4 a=iVkDmfvjeKcA:10 a=EzXvWhQp4_cA:10 a=SPQdiUhDLCbww1sYP4FffA==:117 X-Cloudmark-Score: 0 Authentication-Results: lrcmmta07 smtp.user=montyr2157; auth=pass (LOGIN) Received: from [98.20.255.193] ([98.20.255.193:60106] helo=newbox) by lrcmmta07 (envelope-from ) (ecelerity 2.2.2.45 r()) with ESMTPA id 9F/5C-23468-C14E33B4; Thu, 24 Dec 2009 15:58:52 -0600 Message-ID: From: "MONTY ROBERTS" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Meredith Effect - Spitfire Date: Thu, 24 Dec 2009 15:58:51 -0600 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_013F_01CA84B1.FCE0CFF0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5843 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 This is a multi-part message in MIME format. ------=_NextPart_000_013F_01CA84B1.FCE0CFF0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Tracy, Probably not accurate for most airplanes. There are so many variables = involved. I would think in an optimized system the exit temps will be = higher for an air cooled engine. Most of the air cooled engines we're = familiar with have very low energy density compared to the WW2 radials. = I mean look at one of those corncob engines that pumps out multiple = thousands of HP sometime. I always wondered how in the HELL they managed = to cool those things. One way was they put a lot of fuel and also water = through them at max power. But even at cruise power there just isn't = that much in the way of airflow area and fins there. The main barrel of = the cylinder gets some cooling from the intake charge and the oil, so = it's not that hot.The main hot spot is going to be around the exhaust = valve and there you are definitely limited by the amount of fins you can = put on the thing. I'd bet the sodium cooled valves and lots of oil = directed at that area is the only way it works. That's where liquid = cooling has a decided advantage. My guess is in the typical light = aircraft there is too much air passing over the cylinders so the exit = air is not that hot once the airstreams mix again. Plus you still have = to cool the oil. Most installations are far from optimal. Practicality = dictates always. If you really optimized it and restricted the airflow = where it wasn't doing that much good I would bet you could get closer to = the 2X number(at least for the engine minus oil). Look at the cooling = inlets on some of the formula one aircraft. Airplanes where people are = really paying attention to the details have very small inlets. It really = used to bother me why all the rotary installations had to have such = great big inlets to cool properly compared to the fast guys at Reno = pumping out gobs more power. One day the DeltaT thing smacked me upside = the head.....DUH!!! Then there is also the ADI fluid. ;-) =20 The great thing about liquid cooling is it lets you smooth out all the = hot spots and move them somewhere else....but nothings free. A well executed liquid cooling system will beat a poorly executed air = cooled setup...no doubt. But nobody's going to build a waste heat 200 = mph ram jet, no matter how hard they try. Congrats on getting the new ride in the air BTHW ;-) I've been following = with great delight, just no time to comment. I should be cleaning up the = shop right now.....but I'm goofing off a little today. Monty P.S. I'm going to have to go back and read up on Ed's Delta = trick.....He's making the rest of us look bad again....;-) ----- Original Message -----=20 From: Tracy Crook=20 To: Rotary motors in aircraft=20 Sent: Thursday, December 24, 2009 3:23 PM Subject: [FlyRotary] Re: Meredith Effect - Spitfire I'm wondering if that figure for airflow is true (2x airflow for water = cooled vs air cooled). All the measurements I have seen (not many) = indicate that the exit air temperature on a Lyc installation is not = significantly different than on our water cooled engines. The total = heat per HP is not that different so my assumption is that the CFM = requirement is not much different. =20 The only advantage the air cooled engine's higher Dt gives you is that = it requires far fewer square inches of surface area to transfer a given = number of BTU with a given number of CFM. Our advantage is that we = can add surface area a LOT more easily than an air cooled can. You can = only put so many fins on a cylinder head. But I may be missing something. Other thoughts? Tracy=20 ------=_NextPart_000_013F_01CA84B1.FCE0CFF0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Tracy,
 
Probably not accurate for most = airplanes. There are=20 so many variables involved. I would think in an optimized system the = exit temps=20 will be higher for an air cooled engine. Most of the air cooled engines = we're=20 familiar with have very low energy density compared to the WW2 radials. = I mean=20 look at one of those corncob engines that pumps out multiple thousands = of HP=20 sometime. I always wondered how in the HELL they managed to cool those = things.=20 One way was they put a lot of fuel and also water through them at max = power. But=20 even at cruise power there just isn't that much in the way of airflow = area and=20 fins there. The main barrel of the cylinder gets some cooling from the = intake=20 charge and the oil, so it's not that hot.The main hot spot is going = to be=20 around the exhaust valve and there you are definitely limited by the = amount of=20 fins you can put on the thing. I'd bet the sodium cooled valves and lots = of oil=20 directed at that area is the only way it works. That's where liquid = cooling=20 has a decided advantage.  My guess is in the typical light aircraft = there=20 is too much air passing over the cylinders so the exit air is not that = hot once=20 the airstreams mix again. Plus you still have to cool the = oil. Most=20 installations are far from optimal. Practicality dictates = always. If you=20 really optimized it and restricted the airflow where it wasn't doing = that much=20 good I would bet you could get closer to the 2X number(at least for the = engine=20 minus oil). Look at the cooling inlets on some of the formula one = aircraft.=20 Airplanes where people are really paying attention to the details = have very=20 small inlets. It really used to bother me why all the rotary = installations had=20 to have such great big inlets to cool properly compared to the fast guys = at Reno pumping out gobs more power. One day the DeltaT = thing=20 smacked me upside the head.....DUH!!! Then there is also the=20 ADI fluid. ;-)  
 
The great thing about liquid cooling is = it lets you=20 smooth out all the hot spots and move them somewhere else....but = nothings=20 free.
 
A well executed liquid cooling system = will beat a=20 poorly executed air cooled setup...no doubt. But nobody's going to build = a waste=20 heat 200 mph ram jet, no matter how hard they = try.
 
Congrats on getting the new ride in the = air BTHW=20 ;-) I've been following with great delight, just no time to comment. I = should be=20 cleaning up the shop right now.....but I'm goofing off a little=20 today.
 
Monty
 
P.S. I'm going to have to go back and = read up on=20 Ed's Delta trick.....He's making the rest of us look bad=20 again....;-)
----- Original Message -----
From:=20 Tracy=20 Crook
Sent: Thursday, December 24, = 2009 3:23=20 PM
Subject: [FlyRotary] Re: = Meredith Effect=20 - Spitfire

I'm wondering if that figure for airflow = is true=20 (2x airflow for water cooled vs air cooled).   All the = measurements=20 I have seen (not many) indicate that the exit air temperature on a Lyc = installation is not significantly different than on our water cooled = engines.=20   The total heat per HP is not that different so my assumption is = that=20 the CFM requirement is not much different. 

The only = advantage=20 the air cooled engine's higher Dt gives you is that it requires far = fewer=20 square inches of surface area to transfer a given number of BTU with a = given=20 number of CFM.    Our advantage is that we can add surface = area a=20 LOT more easily than an air cooled can.  You can only put so many = fins on=20 a cylinder head.

But I may be missing something.  Other=20 thoughts?

Tracy
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