Surface radiators for water cooled engines

OK, Bob and Jay, chill out. You're both cool engineers and have a lot to
contribute. Lets just rattle the idea around a bit and see what comes out.

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

"Jay" wrote in message
om...
(Bob Kuykendall) wrote in message
If you think you have a good idea, then fine, try it. Make a
prototype, test it under representative conditions, and publish your
results. If the results bear out your assertions, you will be hailed
as an insightful genius. If there are competitive advantages to your
idea, you can expect to see swift application of it to a wide variety
of heat exchange situations.

I think its too soon make that step, I'm not sure what the proportions
need to be.

Anyhow, yammering about your idea here on Usenet accomplishes less
than zero, since it takes up time that you could otherwise be using to
implement and test your idea. From the fact that you persist in
arguing about it in this forum, I can only conclude that you are more
interested in the argument that in the idea under discussion.

"Listen, I'm not here for an argument..." (Python)
I didn't come to the newsgroup to as advice. The idea was to have a 2
way discussion, I guess you could call that yammering. Sometimes in
the early stages of a development you just brain storm and bounce
ideas off different people's heads. Its a fun excercise for people
who like to think and interact. Its true, the CNC isn't chewing
aluminum and there aren't any flames yet, so it isn't quiet as
exciting, but until you think you've got the theory understood, you're
wasting time and material trying to construct something that will
likely take an inordinate amount of experimentation to optimize.
Thats the difference between an engineer and a tech I guess.

And that's a shame, since your surface radiator idea would be pretty
easy to prototype. All you need is an old pickup truck, an old car
hood, a bunch of copper tubing, a bunch of cheap plumber's solder, and
a propane torch. Oh, and a driver's license...

You need a propeller and cowl as well. The success of the idea may
hinge on the turbulence in the prop wash which decays very quickly as
you get further from the prop blade.

I mean, I think it's a dead-end idea, but I'm prepared to be
demonstrated wrong. But if you persist in just telling folks that
they're wrong without a shred of either empirical evidence or
engineering support, you're gonna stay pigeonholed in a lot of folks'
chucklehead files.

In a discussion its okay to disagree with someone as long as you can
supply a reason. The other person, can then attempt to address that
issue. This goes on and on until you've either come to the same
conclusion or some fundamental point on which there is a disagreement
which must be settled by experimental data or a more detailed off-line
analysis.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com

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 ...
OK, Bob and Jay, chill out. You're both cool engineers and have a lot to
contribute. Lets just rattle the idea around a bit and see what comes out.

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

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

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

"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.

Yeah, North American did well with the Mustang given that it was just old
"slide rule" engineers one generation ahead of me working on it. I imagine
the kids these days using Computational Fluid Dynamics programs and modern
materials could improve on the Meridith Effect - maybe a lot.

I don't want to get too far form the original posters idea on skin
radiators. That idea is worth some experiments too.

Bill Daniels

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