X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from poplet2.per.eftel.com ([203.24.100.45] verified) by logan.com (CommuniGate Pro SMTP 5.3c4) with ESMTP id 4040475 for flyrotary@lancaironline.net; Thu, 24 Dec 2009 20:17:44 -0500 Received-SPF: none receiver=logan.com; client-ip=203.24.100.45; envelope-from=lendich@aanet.com.au Received: from sv1-1.aanet.com.au (mail.aanet.com.au [203.24.100.34]) by poplet2.per.eftel.com (Postfix) with ESMTP id A7FF4173982 for ; Fri, 25 Dec 2009 09:17:02 +0800 (WST) Received: from ownerf1fc517b8 (203.171.92.134.static.rev.aanet.com.au [203.171.92.134]) by sv1-1.aanet.com.au (Postfix) with SMTP id 8B90FBEC0AD for ; Fri, 25 Dec 2009 09:10:47 +0800 (WST) Message-ID: <44EC3B909BB74BAD9CAB7B49D4AE086A@ownerf1fc517b8> From: "George Lendich" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Meredith Effect - Spitfire Date: Fri, 25 Dec 2009 11:10:47 +1000 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0031_01CA8552.E9180B40" 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 X-Antivirus: avast! (VPS 091225-0, 12/25/2009), Outbound message X-Antivirus-Status: Clean This is a multi-part message in MIME format. ------=_NextPart_000_0031_01CA8552.E9180B40 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Tracy, I'm no expert, but I do follow cooling issues with great interest and = keep notes on previous attempts and successful outcomes. From these = notes I conclude that with different core fin densities and size one = core likely to steal from the other core from the available air = available. As you described in your own trials, so it's logical to have = separate air for each core. It's also logical to know that higher deltaT in air cooled engines = require smaller inlets - trade off is larger tolerances etc. I'm at a loss to understand similar exit air with the larger delta T, = given similar conditions. Seems unlikely to me. Finally 2 x times the cooling of air cooled engines does seem a rather = large difference, unless we are talking 1.5 cu" times the HP and 3 = cu"times the HP . I do believe even 1.5 is a very low number. So I will = settle for 2 times the HP for air cooled and perhaps with exceptional = efficiency 2.5 times the hp for water cooled. I believe that anything under that limit will result in marginal = performance in high HP and exceptionally hot days. As Lynn said there is = no such thing as excess cooling and that's true, however the penalty is = excess drag. So I'm happy to be given new 'rules of thumb' in the = event your results are different. Being conservative I will probably = stick to the '3 times' rule of thumb - but I in no way put a mocker on = your attempts nor ridicule your endeavours. George (down under) 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 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 =3D 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 ------=_NextPart_000_0031_01CA8552.E9180B40 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Tracy,
I'm no expert, but I do follow cooling = issues with=20 great interest and keep notes on previous attempts and successful = outcomes. From=20 these notes I conclude that with different core fin densities  and = size one=20 core likely to steal from the other core from the available air = available.=20 As you described in your own trials, so it's logical to have separate = air for=20 each core.
 
It's also logical to know that higher = deltaT in air=20 cooled engines require smaller inlets - trade off is larger tolerances=20 etc.
 
I'm at a loss to understand similar = exit air with=20 the larger delta T, given similar conditions. Seems unlikely to=20 me.
 
Finally 2 x times the cooling of air = cooled engines=20 does seem a rather large difference, unless we are talking 1.5 cu" = times=20 the HP  and 3 cu"times  the HP . I do believe even 1.5 is a very low number. So I will settle = for 2=20 times the HP for air cooled and perhaps with exceptional efficiency 2.5 = times=20 the hp for water cooled.
 
I believe that anything under that = limit will=20 result in marginal performance in high HP and exceptionally hot days. As = Lynn=20 said there is no such thing as excess cooling and that's true, however = the=20 penalty is excess drag.  So I'm happy to be given new 'rules of=20 thumb'  in the event your results are different. Being conservative = I will=20 probably stick to the '3  times' rule of thumb - but I in no way = put a=20 mocker on your attempts nor ridicule your endeavours.
George (down under)
I'm=20 wondering if that figure for airflow is true (2x airflow for water = cooled vs=20 air cooled).   All the measurements I have seen (not many) = indicate=20 that the exit air temperature on a Lyc installation is not = significantly=20 different than on our water cooled engines.   The total heat per = HP is=20 not that different so my assumption is that the CFM requirement is not = much=20 different. 

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

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

Tracy

On Thu, Dec 24, 2009 at 3:38 PM, MONTY = ROBERTS <montyr2157@windstream.net&g= t;=20 wrote:
Thomas,

Though=20 the Meredith effect is possible in theory if you actually run the = numbers=20 you find that the only time it would produce any thrust is at power = levels=20 in excess of 1000 hp and flight speeds over 400 mph. Even then the = effect is=20 very small and any gain you might get from it will be decimal dust = compared=20 to the drag from ingesting extra air. A liquid cooled engine will = require=20 ingesting roughly 2X the cooling air compared to an air cooled = engine for=20 the same power level. There is no way to make up for that 200 degree = extra=20 temp differential you get from an air cooled engine. You can't fool = Qdot =3D=20 mdotCpDeltaT. Liquid cooling has numerous advantages. Drag reduction = is not=20 one of them. The "cooling thrust" Myth is a Myth.

At our = speeds and=20 power levels you will be wasting your time chasing Mr. Meredith. = That does=20 not mean you shouldn't do a good job on the diffuser and the nozzle = to=20 minimize drag, but you can forget about any thrust. This is true = even if you=20 dump all the heat from the exhaust into the exit air so don't = bother. Just=20 point the exhaust aft.

In a piston engine fighter there are = tactical=20 advantages to having a slender nose that you can see around. Liquid = cooling=20 allows this. It also allows greater power density in the engine = because you=20 can have heat transfer through sub cooled boiling at the hot spots = in the=20 cooling jacket. It also allows a lower frontal area from a drag = standpoint,=20 but you pay by having to reject heat at 200 deg or so less than an=20 air-cooled engine. That is perhaps an acceptable trade off. In = practice I am=20 not sure that the big radial aircraft were not superior to the = mustangs etc.=20 There is more frontal area with a radial, but there is also more = useable=20 internal volume and the cooling drag is less. More internal fuel = means more=20 stores and more/larger ammo in the wings. Plus better resistance to = battle=20 damage. Sea Fury vs. Mustang? The Sky Raider was in use as late as = Vietnam.=20  Anyway it's all hangar flyin' at this point.

None of = that=20 applies to us. There are so many real world practical constraints=20 (packaging, size, and weight) to a working cooling system that = trying to get=20 the "optimum" is just not feasible. This is doubly so since the gain = you are=20 going to be chasing does not exist. There is not enough heat = rejection at=20 our power levels, and there is not enough ram pressure to recover at = our=20 speeds.

Thermo is as Thermo does.

Monty

----- = Original=20 Message ----- From: "Thomas Mann" <tmann@n200lz.com>
To: "Rotary motors in = aircraft"=20 <flyrotary@lancaironline.net>
Sent: = Wednesday,=20 December 23, 2009 11:55 AM
Subject: [FlyRotary] Re: Meredith = Effect -=20 Spitfire


Let's=20 try that again


-----Original Message-----
From: = Rotary=20 motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of = Thomas=20 Mann
Sent: Wednesday, December 23, 2009 11:50 AM
To: Rotary = motors=20 in aircraft
Subject: [FlyRotary] Meredith Effect - = Spitfire

I=20 thought I would share this bit of info I ran into regarding the=20 Meredith
Effect associated with the belly type scoop as was = used on the=20 P-51 and
Spitfire.

Enjoy.

T=20 = Mann





--------------------------------= ------------------------------------------------


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Homepage:=20  http://www.flyrotary.com/
Archive and = UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.htm= l



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No=20 virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 8.5.430=20 / Virus Database: 270.14.117/2583 - Release Date: 12/23/09 = 08:28:00


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Homepage:  http://www.flyrotary.com/
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