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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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