This is what I had hoped to do also except to have the
front edge of the NACA moveable so that when I needed it I could
drop it down and get a lot more air. This has already been proven
to a limited extent by Vance Atkinson on his Cozy. He put a small
linear actuator on the leading edge of his NACA and saw a
noticable difference in cooling. Once the engine had cooled and
stabilized after a climb he retrims it to the normal position.
This way you don't have to stair step in a climb the way Tracy
does. I will have to see if Vance has any hard data. In his
configuration it has +/- 1" of travel, I am talking about
dropping it down a whopping 3" with side seals to prevent loss of
air. At that point it is no longer a NACA but a scoop. I am just
waiting for John to fly his Cozy to confirm whether there is
enough cooling in his design once he gets to altitude and things
stabilize after climb.
...Chrissi
I assume Vance Atkinson has an air cooled air craft
engine with less pressure
drop or resistance to air flow than a radiator.
Paul Lamar
Yes, he has a Lycoming. You might take a look at the
airpath of a plans built Cozy. Not what I would call freeflowing
by any means. Sure it is not as bad as a radiator but everything
possible has been done to compartmentalize and baffle the engine.
The cylinders are each wrapped with alumnimun sheet with an
opening top and bottom, all the air has to flow up through those
slots. The air also has to make several abrupt turns. I would
guess that John's plenum with radiator, cooler and intercooler
has more open area than a plans built Cozy and a much freeer exit
path once past the coolers. Cozies are fraught with cooling
issues because the air really does not want to go where they are
putting it. The Long-EZ archives are full of schemes for trying
to improve cooling no matter what kind of scoop.
...Chrissi
New to the list. This pertains to carnard pushers. Would
vortex generators upstream help airflow into the intake ports?
Carl Murakami
Velocity 13B wannabe
I don't think so. Even with a zero boundary layer thickness a NACA duct
is not recommended for feeding heat exchangers. It is best suited for
things that suck like jet engines. Ironically it is not even used for
those.
Paul Lamar
Actually, Paul, vortex generators HAVE been tried and, after some
experimentation, found to be very effective. I forget who did this, but its
on his web page somewhere. I believe the guy used two or three just behind
the landing brake and increased his airflow quite dramatically. As for
overall effectiveness of NACA's, they're cooling over a thousand canards
flying today. Admittedly canards don't cool real well, but that takes us
back to Chrissi's original point - take a look at the baffling in the plans
Cozy. Straight through a rad, then out might well be less resistance. I plan
to find out. I'm puzzled by your comment about zero boundary layer - isn't
the NACA designed to take the boundary layer into the cowl with minimum
drag?
How many people have downloaded the NACA paper? Raise your hand.
Measure the fin spacing on an air cooled engine. Measure the
fin spacing on a radiator. Which configuration will flow
more air at low pressure?
Yes the NACA duct will work better (when it works at all)
with a zero boundary layer thickness. Yes vortex generators re energize
the boundary layer.
Here is what I think happens. As the pressure builds up in front the
the rad fed by a NACA duct it causes external diffusion and the airflow
is diverted away from the NACA duct opening. At this point the boundary
thickness has nothing to do with it.
Instead of spending hours on speculation and quoting anecdotal evidence
on how Tom, Dick and Harry improved the cooling of their air cooled engine
powered Cozy, build a NACA/Rad test set up and measure the flow and pressures.
Use a pick up truck.
Having said that here is another anecdote for you. Someone got the
bright idea of shaving the scoop off a P51 Reno racer and replaced
it with a NACA duct. Guess what?
Paul Lamar
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