The Mustang's cooling system (an external combustion ramjet) is probably
about as good as it is going to get utilizing radiators for heat exchangers,
because the thrust produced by a ramjet is very dependent on internal
efficiencies (drag). A radiator is a very high drag ramjet heat source
(combustor) because of its large surface area, and relatively poor
aerodynamics. The net thrust of a ramjet type cooling system could be
increased if a more efficient (lower drag) method is found to transfer the
heat to the internal airflow.

I agree with Corky's statement that effective cooling is more important (the
Mustang's was inadequate for prolonged ground operation) than a few miles
per hour in cruise for slower aircraft. However, for aircraft cruising
above 150-175 MPH, I believe cooling drag is certainly high enough to be of
interest to any designer.

RJ

"Corky Scott" wrote in message
...
On Tue, 15 Jul 2003 11:54:37 -0600, "Bill Daniels"
wrote:



Another area where I would like to see some experimental data is the
"Radiator Ramjet" (just to pick a controversial term) where the radiator
is
in a tube and the heated air exits the rear of the tube at a higher
velocity
than the cool air entering the front of the tube, theoretically producing
a
small amount of thrust that offsets the drag of the radiator.

Bill Daniels
"Jay" wrote in message
. com...
Hi Bill,

You don't need experiental data for this Bill, you just described the
P-51 Mustang cooling system.

However, even with three heat exchangers putting out heat into the
exhaust air and a 1400 horsepower engine producing the heat, the
Mustang never actually managed to get a net thrust out of the system.
In addition, the point where the cooling system was ***ALMOST***
equalling drag was a very specific speed and altitude. I forget the
exact height but it was above 20,000 feet and the speed was over 300
mph. Only under those circumstances did the power being generated and
the speed being flown produce the necessary heat to accelerate the
exhaust air flow to nearly cancel out cooling drag. By the way, most
of the cooling systems did this to some fashion, but the Mustang was
the first to actually design the cooling system to really benefit from
it. This concept was researched and written up by a British
aerodynamicist by the name of Meridith, and the produced thrust became
known as the "Meridith Effect".

North American designed the Mustang's system using the best
aerodynamicists available at the time and with virtually unlimited
resources to manufacture the kind of heat exchangers that would work
in this environment.

By the end of WWII, almost all research into liquid cooled systems
came to a halt as jet powered aircraft became the future for military
aircraft.

I'm not an aerodynamics engineer, just a home builder. But my
impression is that most relatively slow homebuilt or GA airplanes do
not produce the heat needed to really accelerate the exhaust flow to
make much out of the Meridith Effect. After all, we're always leaning
out and cruising at reduced power settings. We have big wings, for
the most part, and a lot of drag. Something really slippery like a
Long EZ or Vari EZ or Glassair or Lancair might be fast enough to
benefit, but getting the cooling system designed and fitted within the
tiny wetted area of the fuselage might be nearly impossible.

From my personal point of view, it's far more important to make sure
the cooling system does the job all day and every day and on the
ground too than to agonize over a few mph, real or imaginary.

Corky Scott