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 4040407 for flyrotary@lancaironline.net; Thu, 24 Dec 2009 17:18:12 -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=o2QoyYduAAAA:8 a=5kgCHx-JAAAA:8 a=Ia-xEzejAAAA:8 a=7g1VtSJxAAAA:8 a=oCcaPWc0AAAA:8 a=4yH030NR_AjppKWV3ygA:9 a=UbPYnUkVYHjrahvZJPsA:7 a=fy-CEOUpnQ-E_tviQZKkERTyLPwA:4 a=5zrLeAV0Z70A:10 a=TlnOPt13aEMA:10 a=BPCOYmGL8QAA:10 a=EzXvWhQp4_cA:10 a=NpRM0PAM3H5fi6dV:21 a=eNVL-6SZFSrWbunf:21 a=UretUmmEAAAA:8 a=CMaN91O936NpzWYJhjwA:9 a=8IDGFl6vQkUtB0cot1EA:7 a=WYsHTx_kohHqPg3x_a4j7ANHDGkA:4 a=d-1ze5jHbJEA:10 a=iVkDmfvjeKcA:10 a=SPQdiUhDLCbww1sYP4FffA==:117 X-Cloudmark-Score: 0 Authentication-Results: lrcmmta07 smtp.user=montyr2157; auth=pass (LOGIN) Received: from [98.20.255.193] ([98.20.255.193:60146] helo=newbox) by lrcmmta07 (envelope-from ) (ecelerity 2.2.2.45 r()) with ESMTPA id 6F/1E-23468-188E33B4; Thu, 24 Dec 2009 16:17:37 -0600 Message-ID: <82041170E3BA4A3EBA1B78AC452804FB@newbox> From: "MONTY ROBERTS" To: "Rotary motors in aircraft" References: Subject: Meredith Effect - Spitfire Date: Thu, 24 Dec 2009 16:17:37 -0600 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_015E_01CA84B4.9B7C8850" 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_015E_01CA84B4.9B7C8850 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Tracy I also forgot to mention that you aren't quite right about the less = surface area thing. Although less surface area is needed the, convection = coefficient along with the surface temp dictates surface area required. = That can be influenced by turbulence, fluid velocity, surface condition = etc. The mass flow of air required is unfortunately directly governed by the = temperature difference. No way around that one. It is simply a function = of the specific heat of air, temp difference, and the amount of heat = rejected. Monty =20 ----- 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 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 -------------------------------------------------------------------------= ----- No virus found in this incoming message. Checked by AVG - www.avg.com=20 Version: 8.5.430 / Virus Database: 270.14.119/2585 - Release Date: = 12/24/09 08:11:00 ------=_NextPart_000_015E_01CA84B4.9B7C8850 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Tracy
 
I also forgot to mention that you = aren't quite=20 right about the less surface area thing. Although less surface area is = needed=20 the, convection coefficient along with the surface temp dictates surface = area=20 required. That can be influenced by turbulence, fluid velocity, surface=20 condition etc.
 
The mass flow of air required is = unfortunately=20 directly governed by the temperature difference. No way around that one. = It is=20 simply a function of the specific heat of air, temp = difference,=20 and the amount of heat rejected.
 
Monty  
----- 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 (2x = airflow=20 for water cooled vs air cooled).   All the measurements I = have seen=20 (not many) indicate that the exit air temperature on a Lyc = installation is not=20 significantly different than on our water cooled engines.   The = total=20 heat per HP is not that different so my assumption is that the CFM = requirement=20 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=20 surface area to transfer a given number of BTU with a given number of=20 CFM.    Our advantage is that we can add surface area a LOT = more=20 easily than an air cooled can.  You can only put so many fins on = a=20 cylinder head.

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

Tracy

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

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

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

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

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

Thermo = is as=20 Thermo does.

Monty

----- Original Message ----- From: = "Thomas=20 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 try that again


-----Original=20 Message-----
From: Rotary 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:  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


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


No virus found in this incoming message.
Checked by AVG = -=20 www.avg.com
Version: 8.5.430 / Virus Database: 270.14.119/2585 - = Release=20 Date: 12/24/09 08:11:00
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