X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from ispmxmta06-srv.alltel.net ([166.102.165.167] verified) by logan.com (CommuniGate Pro SMTP 5.0.8) with ESMTP id 1029173 for flyrotary@lancaironline.net; Fri, 10 Mar 2006 00:46:08 -0500 Received-SPF: pass receiver=logan.com; client-ip=166.102.165.167; envelope-from=montyr2157@alltel.net Received: from Thorstwin ([162.40.138.192]) by ispmxmta06-srv.alltel.net with SMTP id <20060310054520.QDLB27467.ispmxmta06-srv.alltel.net@Thorstwin> for ; Thu, 9 Mar 2006 23:45:20 -0600 Message-ID: <000501c64405$d9ca8010$01fea8c0@Thorstwin> From: "M Roberts" To: Subject: flyrotary_Web_Archive Date: Thu, 9 Mar 2006 23:45:33 -0600 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0002_01C643D3.8EAF4750" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0002_01C643D3.8EAF4750 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable At the risk of invoking PL's name, anyone else read this months Sport = Aviation mag from EAA, and notice an article on cooling that seems to = indicate that NACA's are acceptable and adequate for aircraft cooling = needs? I have no idea regarding the authors credentials, and I no longer = monitor PL's "newsletter".. I was curious more than anything else... = Pauls reaction, others reactions, etc. Translation.. yes.. I'm stirring the pot/Trolling... I figure if we are = using NACA's on the Velocity, that makes us somewhat of a NACA = supporter.. Dave, ZZZZZZZZZIIIIIIINNNNNNGGGGGGGG Hit the drag and set the hook!!! I took = the bait. NACA submerged inlets will work just fine. Some people have a favorite = quote from the very preliminary first report (NACA-ACR-5I20, 14NOV1945) = on these inlets: "Submerged inlets do not appear to have desirable pressure recovery = characteristics for use in supplying air to oil coolers, radiators, or = carburetors of conventional reciprocating engines. The required = diffusion of the air and the range of inlet-velocity ratios is too great = to give desirable characteristics at all flight conditions." Now if you read nothing else on this subject and never did any actual = building or testing and totally ignored all the instances where these = inlets work just fine you would conclude that they would never work. You = would, however, be totally, completely and utterly wrong. Some people fail to cite their sources or subsequent papers and prefer = to copyright the work of others while twisting the facts to fit their = (very wrong) view of the world. The later and much more thorough investigation on these inlets was = released 13JAN48 (NACA-RM-A7I30)Two of the original authors wrote this = paper as a continuation of the work. This paper is very good and highly recommended. It actually gives the = design variables and relevant data required to properly design an = efficient, low drag flush inlet.=20 Quoting directly from this paper on page 18 under the heading:=20 Possible Applications For NACA Submerged Inlets "Other applications could include some ducting systems involving cooling = and carburetor air. If this type of entrance could be substituted for = the protruding scoop-type of inlet, the aerodynamic neatness of the = aircraft would be greatly enhanced." There are several gotchas with a flush inlet.=20 1.) you must not have a thick boundary layer RELATIVE TO THE SIZE OF THE = SCOOP. 2.) you must have the appropriate mass flow ratio and pressure recovery = ratio chosen for your application. This is difficult to do over a large = range with radiators. If you insist on making the cooling system design = with a Mack truck sized radiator using design criteria suitable for = fully laden WWII bombers operating out of North Africa in the middle of = summer at Vy, you will be unable to come up with a flush inlet design = that will work. However, if you design for cruise and our application, = you will be able to make a very nice low drag installation. 3.) You need an appropriate diffuser after the inlet. This is one = problem I have with this paper. They used a very long, gradual diffuser. = Which is probably not a good idea with the flush inlet. The two vortices = make for a very turbulent flow field. This means you will have a lot of = losses from mixing in a long diffuser duct. A short multi segment 7 deg = type or perhaps a shorter K&W streamline diffuser will probably be a lot = better. It's hard to say what the effect of the turbulence on the = streamline diffuser would be. It would take some testing to find out = whether the guide vanes in the shorter 7 deg diffuser would be better or = worse than the K&W streamline type. I do think shorter is better. The = turbulence should help to minimize seperation. Trying to stretch out the = process is just going to make a lot of losses. I would suggest that the combination of a thick boundary layer and a = less than optimal diffuser make this study CONSERVATIVE.... The relative = results are still useful, however. 4.) the lip must be a very thick airfoil shape. Most people totally = screw the pooch here. They also make the ducts way too short and way too = steep. Then they put little bitty inlets in a thick boundary layer, or a = low pressure region.=20 Guess what? if you do all these things that the paper says not to do-it = won't work. Some people take that to mean they will never work, ever, = anywhere, period.=20 Data never lies, but liars always use data, and a few quotes out of = context for good measure. Monty =20 ------=_NextPart_000_0002_01C643D3.8EAF4750 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
At the risk of invoking = PL's name,=20 anyone else read this months Sport Aviation mag from EAA, and notice an = article=20 on cooling that seems to indicate that NACA's are acceptable and = adequate for=20 aircraft cooling needs? I have no idea regarding the authors = credentials, and I=20 no longer monitor PL's "newsletter".. I was curious more than anything = else...=20 Pauls reaction, others reactions, etc.

Translation.. yes.. I'm = stirring=20 the pot/Trolling... I figure if we are using NACA's on the Velocity, = that makes=20 us somewhat of a NACA supporter..
 
Dave,
 
 
ZZZZZZZZZIIIIIIINNNNNNGGGGGGGG Hit the drag and set the hook!!! = I took=20 the bait.
 
NACA submerged=20 inlets will work just fine. Some people have a favorite quote = from the=20 very preliminary first report (NACA-ACR-5I20,=20 14NOV1945) on these inlets:
 
"Submerged inlets do not=20 appear to have desirable pressure recovery=20 characteristics for use in supplying air to oil coolers, radiators, or=20 carburetors of conventional reciprocating engines. The = required=20 diffusion of the air and the range of inlet-velocity ratios is too great = to give=20 desirable characteristics at all flight=20 conditions."
 
Now if you read nothing else on this = subject and=20 never did any actual building or testing and totally ignored all = the=20 instances where these inlets work just fine you would conclude that they = would=20 never work. You would, however, be totally, completely and utterly=20 wrong.
 
Some people fail to cite their sources = or=20 subsequent papers and prefer to copyright the work of others while = twisting the=20 facts to fit their (very wrong) view of the world.
 
The later and much more thorough = investigation on=20 these inlets was released 13JAN48 (NACA-RM-A7I30)Two of the = original=20 authors wrote this paper as a continuation of the work.
 
This paper is very good and highly = recommended. It=20 actually gives the design variables and relevant data required to = properly=20 design an efficient, low drag flush inlet.
 
Quoting directly from this paper on page = 18 under=20 the heading:
 
Possible Applications For NACA Submerged = Inlets
 
"Other applications could include some = ducting=20 systems involving cooling and carburetor air. If this type of entrance = could be=20 substituted for the protruding scoop-type of inlet, the aerodynamic = neatness of=20 the aircraft would be greatly enhanced."
 
There are several gotchas with a flush = inlet.=20
 
1.) you must not have a = thick boundary=20 layer RELATIVE TO THE SIZE OF THE = SCOOP.
 
2.) you must have the appropriate mass = flow ratio=20 and pressure recovery ratio chosen for your application. This is = difficult to do=20 over a large range with radiators. If you insist on making the cooling = system=20 design with a Mack truck sized radiator using design criteria suitable = for fully=20 laden WWII bombers operating out of North Africa in the middle of summer = at Vy,=20 you will be unable to come up with a flush inlet design that = will=20 work. However, if you design for cruise and our application, you will be = able to=20 make a very nice low drag installation.
 
3.) You need an = appropriate diffuser after=20 the inlet. This is one problem I have with this paper. They used a very = long,=20 gradual diffuser. Which is probably not a good idea with the flush = inlet. The=20 two vortices make for a very turbulent flow field. This means you = will=20 have a lot of losses from mixing in a long diffuser duct. A short = multi=20 segment 7 deg type or perhaps a shorter K&W streamline diffuser will = probably be a lot better. It's hard to say what the effect of the = turbulence on=20 the streamline diffuser would be. It would take some testing to = find out=20 whether the guide vanes in the shorter 7 deg diffuser would be = better or=20 worse than the K&W streamline type. I do think shorter is better. = The=20 turbulence should help to minimize seperation. Trying to stretch out the = process=20 is just going to make a lot of losses.
 
I would suggest that the combination of = a thick=20 boundary layer and a less than optimal diffuser make this study = CONSERVATIVE....=20 The relative results are still useful, however.
 
4.) the lip must be a very thick airfoil = shape.=20 Most people totally screw the pooch here. They also make the ducts way = too short=20 and way too steep. Then they put little bitty inlets in a = thick=20 boundary layer, or a low pressure region.
 
Guess what? if you do all these things = that the=20 paper says not to do-it won't work. Some people take that to mean they = will=20 never work, ever, anywhere, period.
 
Data never lies, but liars always use = data, and=20 a few quotes out of context for good measure.
 
 
Monty
 
 
 
 
 

 ------=_NextPart_000_0002_01C643D3.8EAF4750--