Surface radiators for water cooled engines

"Barnyard BOb --" wrote in message
...

I'd put forth the idea that the worst
case environment for an aircraft is always better than the worst case
for an automobile. Does anyone disagree on this point?

Yeah, I do. Many cars typically don't operate at 80% of rated power
for
long
periods.

Worst case environment for an automobile is sitting in stop and go
traffic
on hot sunny day for long periods of time.

Nope.
Popular misconception at best.

Most cars have absolutely no
trouble staying cool while screaming down the highway at full throttle.

Wrong again....
Most cars screaming down the highway get tickets or crash
long before they sustain 80% for long periods. Lots of variables,
but... speeds at 80% power could readily be exceeding 100 mph.


Barnyard BOb --


Right. The worst possible overheating, IMHO, is with a vehicle with an
automatic transmission, pulling a trailer up a grade that requires the
driver to keep WOT for an extended period of time. Add to that, a hot summer
day, running the AC.


You have engine load, additional transmission waste heat, lower road speed,
hot air, and even warmer air going across the radiator because of the AC
unit. Most any vehicle will overheat after an extended time, without
additional cooling, such as a transmission cooler.
--
Jim in NC

"Jay" wrote in message om...

I'm not sure its fair to compare a 10" 1/4 HP electric fan to a 150HP
propeller.

That 150HP propeller is developing some useful thrust as well. For efficiency
the last thing you want is a large amount of it impinging on some flat plate.
That 1/4HP fan is shrouded and delivers almost all of it's flow directly to the cooling fins
of the radiator.

Wrong again....
Most cars screaming down the highway get tickets or crash
long before they sustain 80% for long periods. Lots of variables,
but... speeds at 80% power could readily be exceeding 100 mph.


Barnyard BOb --



Yeah, my car screams down the road at 70+ with the engine turning a whole 2800
rpm. Hardly more than about 40% power in most cases.


Bob Reed
www.kisbuild.r-a-reed-assoc.com (KIS Builders Site)
KIS Cruiser in progress...Slow but steady progress....

"Ladies and Gentlemen, take my advice,
pull down your pants and Slide on the Ice!"
(M.A.S.H. Sidney Freedman)

In article ,
(Jay) writes:


I'm not sure its fair to compare a 10" 1/4 HP electric fan to a 150HP
propeller.



Depends on how much of the output from each actually has contact with the
cooling surface. That 10" 1/4 hp fan is placed directly next to the radiator
and the output is forced through and past the cooling surfaces at a constant
and predictable velocity. The vast majority of the output from that 150 hp
propeller will not even be close to the cooling surface and its velocity will
varry considerably.

Bob Reed
www.kisbuild.r-a-reed-assoc.com (KIS Builders Site)
KIS Cruiser in progress...Slow but steady progress....

"Ladies and Gentlemen, take my advice,
pull down your pants and Slide on the Ice!"
(M.A.S.H. Sidney Freedman)

Barnyard BOb -- wrote in message
Most cars have absolutely no
trouble staying cool while screaming down the highway at full throttle.

Wrong again....
Most cars screaming down the highway get tickets or crash
long before they sustain 80% for long periods. Lots of variables,
but... speeds at 80% power could readily be exceeding 100 mph.


Barnyard BOb --

Driving up a long grade in an automobile or a climb out after takeoff
in an aircraft are doing pretty much the same work with the same range
engine. Difference is the airspeed past the cowl/hood is WAY higher
and more turbulent in the aircraft.

But I'd have to agree with you BOb that 80% rated power in a car is
easily over 100MPH on level ground in many of the sportier cars.

No doubt an aircraft engine lives more of its life at higher power
levels. But this is more a case of reliability, not cooling system
sizing as the worst case cooling scenario is worse in the car
environment.

(Jay) wrote:

Most cars have absolutely no
trouble staying cool while screaming down the highway at full throttle.

Wrong again....
Most cars screaming down the highway get tickets or crash
long before they sustain 80% for long periods. Lots of variables,
but... speeds at 80% power could readily be exceeding 100 mph.


Barnyard BOb --

Driving up a long grade in an automobile or a climb out after takeoff
in an aircraft are doing pretty much the same work with the same range
engine. Difference is the airspeed past the cowl/hood is WAY higher
and more turbulent in the aircraft.

But I'd have to agree with you BOb that 80% rated power in a car is
easily over 100MPH on level ground in many of the sportier cars.

No doubt an aircraft engine lives more of its life at higher power
levels. But this is more a case of reliability, not cooling system
sizing as the worst case cooling scenario is worse in the car
environment.
++++++++++++++++++++++++++++++++++

All this talk is going nowhere.... fast.
Are you going to fish or just keep cutting bait?


Barnyard BOb --

Its true that the larger proportion of the air from the propeller
never goes onto the cowl, but it's still a lot.

A surface radiator isn't necessarily a flat plane, what shape is the
cowl on the airplane you fly? And the air stream is directed onto the
cowl at an angle as is necessary to flair around the engine/cowling.
The cowl would look similar to the current cowls except it would be
more stream lined and have no large holes to duct in air. And of
course in big red letters "HOT SURFACE- DO NOT TOUCH"

"Ron Natalie" wrote in message om...
"Jay" wrote in message om...

I'm not sure its fair to compare a 10" 1/4 HP electric fan to a 150HP
propeller.

That 150HP propeller is developing some useful thrust as well. For efficiency
the last thing you want is a large amount of it impinging on some flat plate.
That 1/4HP fan is shrouded and delivers almost all of it's flow directly to the cooling fins
of the radiator.

You're going to have drag anyway as the air goes around the cowl,
might as well use it to do something useful. So in this case, the
cooling causes no ADDITIONAL drag, right?

I'm NOT saying to use a blow through radiator like a car has, these
are only efficient (defined as heat transfer per unit drag) at low air
speeds. At the airspeeds a couple feet behind the propeller on climb
out, most of those fins are down at ambient, transfering no heat,
doing nothin' but causing drag.

I'm thinking that the bottom surface of the cowl area would be an idea
location:
1) Its out of the way during normal engine service.
2) Doesn't complicate removal of the top of the cowl
3) Periods of high load tend to be coincident with periods of high
AOA, so this puts more air over the surface when you need it.
4) Looks like a lot of common cowls have a relatively flat spot down
there maybe 2'x2'.

You might argue that the heat transfer for that area isn't sufficient,
and I think the analysis needs to be done, but not by a direct
comparison of area from an automobile finned type radiator. The
conditions are just too different to make that meaningful. A bottom
up calculation that includes heat transfer effects of turbulent air,
heat transfer properties of materials (likely Aluminum), waste heat
from engine, etc.


Regards

"Ron Natalie" wrote in message om...
"Jay" wrote in message om...

Every amount of air that you want to use to cool is effectively drag.
Are you claiming your design is going to work without changing the
shape of the cowling? I don't think you're going to get anywhere near
the heat transfer you need. You were talking about car radiators.
I can tell you that plastering a car radiator horizontal on top of the
cowl is not going to cool very well.

Jay wrote:

You might argue that the heat transfer for that area isn't sufficient,
and I think the analysis needs to be done, but not by a direct
comparison of area from an automobile finned type radiator. The
conditions are just too different to make that meaningful. A bottom
up calculation that includes heat transfer effects of turbulent air,
heat transfer properties of materials (likely Aluminum), waste heat
from engine, etc.

So do it. Take a couple of 2'x2' sheat of .035 aluminum and a few
strips of 3/8" flat aluminum. Lay the flat strips on one piece of sheet
so that it forms sides and an interior maze that the water will have
to flow through. Drill, caulk and rivet it together. Add a spout for
the water to go in and come out with temp probes at each one. Add a
couple of T joints to the plumbing of your wife's car (don't let her
catch you at it) and bolt the thing to the hood in a way that will
shield one side (the one that will be inside the cowl) and also simulate
the AOA of the cowl bottom on climbout.

Drive around a while at 60 to 70mph and then report back here with what
you find out.


--
----Because I can----
http://www.ernest.isa-geek.org/
------------------------

Earlier, (Jay) wrote:

You're going to have drag anyway as the air goes around the cowl,
might as well use it to do something useful. So in this case, the
cooling causes no ADDITIONAL drag, right?...

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.

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.

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...

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.

Thanks, and best regards to all

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