X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from qw-out-2122.google.com ([74.125.92.25] verified) by logan.com (CommuniGate Pro SMTP 5.3c4) with ESMTP id 4040328 for flyrotary@lancaironline.net; Thu, 24 Dec 2009 16:23:43 -0500 Received-SPF: pass receiver=logan.com; client-ip=74.125.92.25; envelope-from=rwstracy@gmail.com Received: by qw-out-2122.google.com with SMTP id 9so1665097qwb.25 for ; Thu, 24 Dec 2009 13:23:09 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:sender:received:in-reply-to :references:date:x-google-sender-auth:message-id:subject:from:to :content-type; bh=xU9KJAiPenfb6ke6K+Qh7FDGrlxtP9DDhgjyyfYmFaE=; b=J8uncb15LFZfTsU+Iw4e5y2kw+qm2RFLmTwKK+1AIBYN2oWNVrxzZfKqEcZfuD1F/k oTpqzv6KNEfUinXEppyeF6X6Ez0KfweZyZEa+dxtLq+40tF5TPnoDZPvRlot2tW+cE0u stNUkkrNBBPwcRfN1tJQfthQy8s8tqQLs5RyE= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:content-type; b=KyOmyAnfbBEURZwQN01JCDkb3U9PB/Qz6vVlf8lerxncWCRBSE38MLNvQb18gQ3CI6 i0el8Fm6wppKnvliVQlqwDOqP9ZUrcuVLRyhJ24mg2mVVn7JCRJQsvoGCNAwRYpYNDSo prg2YoaZfUckrp3PwwfXRihBO6f05CyXMT6T4= MIME-Version: 1.0 Sender: rwstracy@gmail.com Received: by 10.224.29.203 with SMTP id r11mr6089384qac.110.1261689789120; Thu, 24 Dec 2009 13:23:09 -0800 (PST) In-Reply-To: References: Date: Thu, 24 Dec 2009 16:23:09 -0500 X-Google-Sender-Auth: 0f18f118d6d729e4 Message-ID: <1b4b137c0912241323p3bf292d4vb497aaf8b005245a@mail.gmail.com> Subject: Re: [FlyRotary] Re: Meredith Effect - Spitfire From: Tracy Crook To: Rotary motors in aircraft Content-Type: multipart/alternative; boundary=000feaef4470b28179047b800b6a --000feaef4470b28179047b800b6a Content-Type: text/plain; charset=ISO-8859-1 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. 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 On Thu, Dec 24, 2009 at 3:38 PM, MONTY ROBERTS wrote: > Thomas, > > Though the Meredith effect is possible in theory if you actually run the > numbers you find that the only time it would produce any thrust is at power > levels in excess of 1000 hp and flight speeds over 400 mph. Even then the > effect is very small and any gain you might get from it will be decimal dust > compared to the drag from ingesting extra air. A liquid cooled engine will > require ingesting roughly 2X the cooling air compared to an air cooled > engine for the same power level. There is no way to make up for that 200 > degree extra temp differential you get from an air cooled engine. You can't > fool Qdot = mdotCpDeltaT. Liquid cooling has numerous advantages. Drag > reduction is not one of them. The "cooling thrust" Myth is a Myth. > > At our speeds and power levels you will be wasting your time chasing Mr. > Meredith. That does not mean you shouldn't do a good job on the diffuser and > the nozzle to minimize drag, but you can forget about any thrust. This is > true even if you dump all the heat from the exhaust into the exit air so > don't bother. Just point the exhaust aft. > > In a piston engine fighter there are tactical advantages to having a > slender nose that you can see around. Liquid cooling allows this. It also > allows greater power density in the engine because you can have heat > transfer through sub cooled boiling at the hot spots in the cooling jacket. > It also allows a lower frontal area from a drag standpoint, but you pay by > having to reject heat at 200 deg or so less than an air-cooled engine. That > is perhaps an acceptable trade off. In practice I am not sure that the big > radial aircraft were not superior to the mustangs etc. There is more frontal > area with a radial, but there is also more useable internal volume and the > cooling drag is less. More internal fuel means more stores and more/larger > ammo in the wings. Plus better resistance to battle damage. Sea Fury vs. > Mustang? The Sky Raider was in use as late as Vietnam. Anyway it's all > hangar flyin' at this point. > > None of that applies to us. There are so many real world practical > constraints (packaging, size, and weight) to a working cooling system that > trying to get the "optimum" is just not feasible. This is doubly so since > the gain you are going to be chasing does not exist. There is not enough > heat rejection at our power levels, and there is not enough ram pressure to > recover at our speeds. > > Thermo is as Thermo does. > > Monty > > ----- Original Message ----- From: "Thomas Mann" > To: "Rotary motors in aircraft" > Sent: Wednesday, December 23, 2009 11:55 AM > Subject: [FlyRotary] Re: Meredith Effect - Spitfire > > > Let's try that again >> >> >> -----Original Message----- >> From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On >> Behalf Of Thomas Mann >> Sent: Wednesday, December 23, 2009 11:50 AM >> To: Rotary motors in aircraft >> Subject: [FlyRotary] Meredith Effect - Spitfire >> >> I thought I would share this bit of info I ran into regarding the Meredith >> Effect associated with the belly type scoop as was used on the P-51 and >> Spitfire. >> >> Enjoy. >> >> T Mann >> >> >> >> > > > -------------------------------------------------------------------------------- > > > -- >> Homepage: http://www.flyrotary.com/ >> Archive and UnSub: >> http://mail.lancaironline.net:81/lists/flyrotary/List.html >> >> > > > -------------------------------------------------------------------------------- > > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 8.5.430 / Virus Database: 270.14.117/2583 - Release Date: 12/23/09 > 08:28:00 > > > -- > Homepage: http://www.flyrotary.com/ > Archive and UnSub: > http://mail.lancaironline.net:81/lists/flyrotary/List.html > --000feaef4470b28179047b800b6a Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable I'm wondering if that figure for airflow is true (2x airflow for water = cooled vs air cooled).=A0=A0 All the measurements I have seen (not many) in= dicate that the exit air temperature on a Lyc installation is not significa= ntly different than on our water cooled engines. =A0 The total heat per HP = is not that different so my assumption is that the CFM requirement is not m= uch different.=A0

The only advantage the air cooled engine's higher Dt gives you is t= hat it requires far fewer square inches of surface area to transfer a given= number of BTU with a given number of CFM.=A0 =A0 Our advantage is that we = can add surface area a LOT more easily than an air cooled can.=A0 You can o= nly put so many fins on a cylinder head.

But I may be missing something.=A0 Other thoughts?

Tracy
On Thu, Dec 24, 2009 at 3:38 PM, MONTY ROBERTS = <montyr21= 57@windstream.net> wrote:
Thomas,

Though the Meredith effect is possible in theory if you actually run the nu= mbers you find that the only time it would produce any thrust is at power l= evels in excess of 1000 hp and flight speeds over 400 mph. Even then the ef= fect is very small and any gain you might get from it will be decimal dust = compared to the drag from ingesting extra air. A liquid cooled engine will = require ingesting roughly 2X the cooling air compared to an air cooled engi= ne for the same power level. There is no way to make up for that 200 degree= extra temp differential you get from an air cooled engine. You can't f= ool Qdot =3D mdotCpDeltaT. Liquid cooling has numerous advantages. Drag red= uction is not one of them. The "cooling thrust" Myth is a Myth.
At our speeds and power levels you will be wasting your time chasing Mr. Me= redith. That does not mean you shouldn't do a good job on the diffuser = and the nozzle to minimize drag, but you can forget about any thrust. This = is true even if you dump all the heat from the exhaust into the exit air so= don't bother. Just point the exhaust aft.

In a piston engine fighter there are tactical advantages to having a slende= r nose that you can see around. Liquid cooling allows this. It also allows = greater power density in the engine because you can have heat transfer thro= ugh sub cooled boiling at the hot spots in the cooling jacket. It also allo= ws a lower frontal area from a drag standpoint, but you pay by having to re= ject heat at 200 deg or so less than an air-cooled engine. That is perhaps = an acceptable trade off. In practice I am not sure that the big radial airc= raft were not superior to the mustangs etc. There is more frontal area with= a radial, but there is also more useable internal volume and the cooling d= rag is less. More internal fuel means more stores and more/larger ammo in t= he wings. Plus better resistance to battle damage. Sea Fury vs. Mustang? Th= e Sky Raider was in use as late as Vietnam. =A0Anyway it's all hangar f= lyin' at this point.

None of that applies to us. There are so many real world practical constrai= nts (packaging, size, and weight) to a working cooling system that trying t= o get the "optimum" is just not feasible. This is doubly so since= the gain you are going to be chasing does not exist. There is not enough h= eat rejection at our power levels, and there is not enough ram pressure to = recover at our speeds.

Thermo is as Thermo does.

Monty

----- Original Message ----- From: "Thomas Mann" <tmann@n200lz.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, December 23, 2009 11:55 AM
Subject: [FlyRotary] Re: Meredith Effect - Spitfire


Let's try that again


-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Thomas Mann
Sent: Wednesday, December 23, 2009 11:50 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Meredith Effect - Spitfire

I thought I would share this bit of info I ran into regarding the Meredith<= br> Effect associated with the belly type scoop as was used on the P-51 and
Spitfire.

Enjoy.

T Mann





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No virus found in this incoming message.
Checked by AVG - www.avg.c= om
Version: 8.5.430 / Virus Database: 270.14.117/2583 - Release Date: 12/23/09= 08:28:00


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Homepage: =A0http:/= /www.flyrotary.com/
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