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Yes, it tells you the pressure above the cooling fins of the engine (almost
full dynamic pressure). Yes I am making the assumption that the pressure
below the engine (other side of the cooling fins) is the same as the backside of
the radiator. Is that not reasonable? The cooling exit is
the same in both examples. Note that the pressure above the
engine was almost full dynamic pressure WITHOUT the exit being blocked.
Therefore my conclusion that the pressure differential is NOT lower on the
aircooled engine.
Am I missing your point Al?
Tracy
----- Original Message -----
Sent: Saturday, March 11, 2006 8:15
PM
Subject: [FlyRotary] Re: NACA's, Cooling
and Sport Aviation Mag..
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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