X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao12.cox.net ([68.230.241.27] verified) by logan.com (CommuniGate Pro SMTP 5.0.8) with ESMTP id 1031057 for flyrotary@lancaironline.net; Sat, 11 Mar 2006 20:16:43 -0500 Received-SPF: none receiver=logan.com; client-ip=68.230.241.27; envelope-from=ALVentures@cox.net Received: from BigAl ([68.7.14.39]) by fed1rmmtao12.cox.net (InterMail vM.6.01.05.02 201-2131-123-102-20050715) with ESMTP id <20060312011206.SGLB17437.fed1rmmtao12.cox.net@BigAl> for ; Sat, 11 Mar 2006 20:12:06 -0500 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: NACA's, Cooling and Sport Aviation Mag.. Date: Sat, 11 Mar 2006 17:15:56 -0800 Message-ID: <000001c64572$84c180a0$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C6452F.769E40A0" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C6452F.769E40A0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable I guess I'm missing something here; but I don't see that the ASI reading inside the cowling tells you about the pressure recovery, or the = pressure drop across the cooling fins of the airplane. If I blocked the exit = from the cowl, and the inlet is facing into the airstream, I'd expect the ASI would read (essentially) the same as that from the pitot tube. IOW, if = the flow is being significantly affected by exit conditions (area, exit = ducting, or the pressure at the exit) then it tells you neither about potential pressure recovery of the inlet, nor the relative pressure drop of = radiator vs. cooling fins. What it tells you is. . ; well, the pressure inside = the cowling above the engine. =20 No? =20 Al =20 =20 =20 Subject: [FlyRotary] Re: NACA's, Cooling and Sport Aviation Mag.. =20 Just a comment on one often repeated point: "There is less pressure differential [on an aircooled engine] than with a radiator". This = factor is a major one in the decisions/arguments made regarding cooling of = aircraft engines. =20 The problem is that I have seen absolutely no empirical evidence to = support it and some which refutes it. For example, some Lycoming powered RV = flyers locate a backup airspeed indicator pickup inside the cooling plenum over = the cooling fins. They report that it reads within a few MPH of the primary = ASI fed from the pitot tube. This indicates that almost full dynamic = pressure is being recovered from the airstream and that pressure differential is = at least as much as seen on radiator installations.=20 =20 Bottom line is that reduced backpressure is NOT one of the advantages of = an aircooled engine. At least that is the working premise I go on when = making cooling decisions on my airplane. If I'm wrong, I'd like to know. = Anyone have data supporting/refuting this? =20 Tracy ----- Original Message -----=20 From: WRJJRS@aol.com=20 To: Rotary motors in aircraft =20 Sent: Friday, March 10, 2006 1:25 AM Subject: [FlyRotary] Re: NACA's, Cooling and Sport Aviation Mag.. =20 Group, The problem with submerged inlets, and Buly is correct to mention that = means flush with the surface, is that they do not handle back pressure well. = Ed A posted the original NACA data and their conclusion was that submerged = inlets don't work well with RADIATORS. The comments PL has been making are only = to re-publish the data. If you do a smoke tunnel test on submerged inlets = you will find that once enough pressure is built up they will "flip" and = hardly take in any air at all. The actual NACA ducts also have the carefully designed lips, or rounded edges to train the boundry layer into the = inlet. The full profile defined by the NACA is rarely used. Most of the inlets = we see are some attempt at looking like a NACA inlet, without the trouble = of actually BEING a NACA inlet. We used to call this "eyeball engineering." Aircooled engines do work better with NACA inlets as there is less = pressure differential than with a radiator. This doesn't mean they will never = work, just that the NACA didn't recomend their use with a radiator/heat = exchanger. Bill Jepson =20 =20 In a message dated 3/9/2006 8:24:30 PM Pacific Standard Time, atlasyts@bellsouth.net writes: John, would you stop calling it a NACA scoop. Remove the big raised =20 lip and make it flat. Than come and report to us. Your inlet is half =20 submerged and half raised scoop. NACA is a flush with the surface =20 SUBMERGED inlet. Buly On Mar 9, 2006, at 10:44 PM, John Slade wrote: > Dave, > My only cooling intake is the plans Cozy IV NACA. > Cooling has never been a problem. > Regards, > John > > David Staten wrote: >> At the risk of invoking PL's name, anyone else read this months =20 >> Sport Aviation mag from EAA, and notice an article on cooling that =20 >> seems to indicate that NACA's are acceptable and adequate for =20 >> aircraft cooling needs? I have no idea regarding the authors =20 >> credentials, and I no longer monitor PL's "newsletter".. I was =20 >> curious more than anything else... Pauls reaction, others =20 >> reactions, etc. >> >> Translation.. yes.. I'm stirring the pot/Trolling... I figure if =20 >> we are using NACA's on the Velocity, that makes us somewhat of a =20 >> NACA supporter.. >> >> Dave =20 ------=_NextPart_000_0001_01C6452F.769E40A0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

I guess I’m missing = something here; but I don’t see that the ASI reading inside the cowling tells you = about the pressure recovery, or the pressure drop across the cooling fins of = the airplane.  If I blocked the exit from the cowl, and the inlet is = facing into the airstream, I’d expect the ASI would read (essentially) = the same as that from the pitot tube.  IOW, if the flow is being = significantly affected by exit conditions (area, exit ducting, or the pressure at the = exit) then it tells you neither about potential pressure recovery of the = inlet, nor the relative pressure drop of radiator vs. cooling fins.  What it = tells you is. . ; well, the pressure inside the cowling above the = engine.

 

No?

 

Al

 

 

 

Subject: [FlyRotary] Re: NACA's, Cooling and Sport Aviation Mag..

 

Just a comment on one often repeated point:  "There is less pressure differential [on an aircooled engine] than with a = radiator".   This factor is a major one in the decisions/arguments made regarding = cooling of aircraft engines.

 

The problem is that I have seen absolutely no empirical evidence to support = it and some which refutes it.  For example,  some Lycoming powered RV flyers locate a backup airspeed indicator pickup inside the cooling = plenum over the cooling fins.  They report that it reads within a few MPH = of the primary ASI fed from the pitot tube.  This indicates that almost = full dynamic pressure is being recovered from the airstream and that pressure differential is at least as much as seen on radiator = installations. 

 

Bottom line is that reduced backpressure is NOT one of the advantages of an = aircooled engine.  At least that is the working premise I go on when making = cooling decisions on my airplane.  If I'm wrong, I'd like to know.  = Anyone have data supporting/refuting this?

 

Tracy

=

----- Original Message -----

Sent: Friday, March = 10, 2006 1:25 AM

Subject: [FlyRotary] Re: NACA's, Cooling and Sport Aviation = Mag..

 

Group,

The problem with submerged inlets, and Buly is correct to mention that means = flush with the surface, is that they do not handle back pressure well. Ed A = posted the original NACA data and their conclusion was that submerged inlets = don't work well with RADIATORS. The comments PL has been making are only to re-publish the data. If you do a smoke tunnel test on submerged inlets = you will find that once enough pressure is built up they will "flip" = and hardly take in any air at all. The actual NACA ducts also have the = carefully designed lips, or rounded edges to train the boundry layer into the = inlet. The full profile defined by the NACA is rarely used. Most of the inlets we = see are some attempt at looking like a NACA inlet, without the trouble of = actually BEING a NACA inlet. We used to call this "eyeball = engineering." Aircooled engines do work better with NACA inlets as there is less = pressure differential than with a radiator. This doesn't mean they will never = work, just that the NACA didn't recomend their use with a radiator/heat = exchanger.

Bill Jepson

 

 

In a message dated 3/9/2006 8:24:30 PM Pacific Standard Time, = atlasyts@bellsouth.net writes:

John, would you stop calling it a NACA scoop. Remove the big raised 
lip and make it flat. Than come and report to us. Your inlet is = half 
submerged and half raised scoop. NACA is a flush with the surface  =
SUBMERGED inlet.
Buly


On Mar 9, 2006, at 10:44 PM, John Slade wrote:

> Dave,
> My only cooling intake is the plans Cozy IV NACA.
> Cooling has never been a problem.
> Regards,
> John
>
> David Staten wrote:
>> 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

 

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