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My fault for not defining the 'probe'. It was more or less a
static port at the rear of the plenum, not a pitot probe. A pitot type
probe was placed in the inlet as an experiment in one case and it
measured around 100 mph at cruise speeds (~180?).
Tracy
----- Original Message -----
Sent: Saturday, March 11, 2006 11:00
AM
Subject: [FlyRotary] Re: NACA's, Cooling
and Sport Aviation Mag..
Tracy, I'm not certain what the airspeed
probe in the cowling is really telling you , except that the velocity (dynamic
pressure) of the air stream as measured by the probe is near that of
the outside air.
It would seem to me that it depends
on how the airspeed indicator is oriented. If it is pointing into the
airstream coming through the cowl duct then the airspeed probe itself is a
stagnation point (regardless of what's happening around it). If on the
other hand, if the airspeed probe is oriented perpendicular to the airflow and
is being used more as a static port then I would agree that indicates the
pressure build up is close to that of a radiator core stagnation.
If we look at Q = Mv(Th-Ta)*cp. We know we
have higher temp cylinder heads with a Lycoming than with our
core. That being the case, it would seem that you might not need
the same mass flow to conduct away the same Q. However, while the
cylinder head temps are higher, the$64 question is whether the
heated departing air temp increased any more (or less) than it would through a
core. It seems pretty clear that regardless of whether cylinder head or
core that slowing the air down (within limits) provides more time for heat
transfer to the air and should result in better cooling in either case.
But, it may be that given the higher temps of the cylinder head that you
may not require as much pressure recovery to cool as with a core. Just
some speculative thinking.
New Hangar is due to arrive
tomorrow!
Ed
----- Original Message -----
Sent: Saturday, March 11, 2006 10:14
AM
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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