Hi Jay,

Yes, the "flat plate" refers to an automotive-like placement of the
radiator.

I suspect that the skin radiator might need a much larger area than a
honeycomb type heat exchanger in a duct since the stagnant boundary layer on
a cowling would limit heat transfer to the free-stream flow. The area
available on a cowling might not be enough either.

I would be very suspicious of calculations comparing the heat transfer
efficiency of skin vs. honeycomb radiators. This is an area were
experimental data is needed.

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
om...
Hi Bill,

Thanks for joining the fray.

At first I was also thinking the wing location for the radiator made a
lot of sense, but then thinking about the complexity of installation
caused me to reconsider. And along the way I found that the turbulent
characteristic of air adds greatly to its heat transfer
characteristics. Since turbulence drops exponentally with distance,
putting the heat transfer surface on the cowl near to the propeller
made more and more sense. That location allows people to go with the
"firewall forward" type of thinking and keep radiator hoses short.

As far as the aerodynamic effects, I hadn't figured there would be too
much effect because of the amount of heat added to this huge volume of
air. I guess it would make the air slightly less dense around the
fusalage and back dispating as the boundary air mixes with more of the
air mass.

p.s. What you were refering to a "flat plate" is really the
traditional blow through type radiator see on autos and other low
speed vehicles. Right?


"Bill Daniels" wrote in message
...
The skin radiator was been tried on the Schneider Cup seaplane racers in
the
1930's and it worked, at least for that purpose. It probably worked
much
better than the flat plate alternative seen on other aircraft from that
era.
It might not have as much advantage over a highly efficient ducted
radiator
like the P-51 used.

Skin radiators weren't really tried on military aircraft in WWII, at
least
as far as I know, probably out of concern they would be very vulnerable
to
enemy fire. After the war, people interested in performance were into
jets
and not too interested in some weird pre-war radiator design even though
it
might work fine.

Then there is a question of the effect of heating the boundary layer.
Some
say that it will thicken and separate if the wing skin is heated. On
the
other hand, some say it will have a turbulator effect and energize the
boundary layer. The Schneider Cup racers did not have laminar flow
airfoils
so any effects, good or bad, might not have been noticed.

I have read a bit of work on "Hot Wing" aerodynamics and the results
were
inconclusive as far as effects on the extent of laminar flow on the wing
but
seemed to suggest a reduction in L/D which would be expected if the
heating
disturbed the boundary layer.

It's possible, even likely, that a skin radiator would work best for
cooling
and have the least negative effects on laminar flow if the surface
chosen
were already subject to turbulent flow. The wing leading edge behind
the
prop comes to mind.

Bill Daniels