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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?
-----
Original Message -----
Sent: Friday, March 10, 2006
1:25 AM
Subject:
[FlyRotary] Re: NACA's, Cooling and Sport Aviation Mag..
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.
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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