Engine Cooling - why not....

Hi,
did a lot of research and thinking about my engine cooling/cowling lately.
It's a conventional VW-Dub powered pusher. There's quite a lot of space
below the engine an very few on top. I want to do a tightly cowled engine
(only the heads and barrels enclosed, not the complete engine under
pressure). Yes - I know the 'traditional' method is feeding the air under
pressure on top and sucking out below. But in my case things would be much
easier (and streamlined) if I would feed the pressureized air from below and
let the hot stuff exit through the top cover of the cowling. It will be an
aluminun cowling, so heat is not such an issue. Any don'ts except an
oil-spilled windscreen in case of engine failure (even then all oil hoses,
cooler, pushrod tubes will be -outside- of the pressurized chamber). Your
suggestions/opinions are highly appreciated.
Happy New Year to All

sorry, of course no pusher, prop is at the front end ;-)

oilsardine a écrit :
But in my case things would be much
easier (and streamlined) if I would feed the pressureized air from below and
let the hot stuff exit through the top cover of the cowling. It will be an
aluminun cowling, so heat is not such an issue.

Assume you mean tractor engine.
"Reverse" cooling has already been done. It can work, but the air is
pre-warmed when passing the exhaust pipes before reaching the cylinders
and heads. See for instance the Eze family.

NACA and NASA studies (Miley) have shown that this method generates a
little more drag than an equally engineered "normal" cooling.

So, unless you look for ultimate performance, you can do as you want.
BTW, where will the exhaust discharge ?

Best regards,
--
Gilles
http://contrails.free.fr

NACA and NASA studies (Miley) have shown that this method generates a
little more drag than an equally engineered "normal" cooling.
----------------------------------------------------

Also, the draft of the VW's head castings show that the direction of
the cooling-air flow was taken into account when creating the
demountable, permanent molds. Just another of the 'unimportant'
details that tend to get overlooked (or deliberately ignored) when
converting the VW for flight.

-R.S.Hoover

"GTH" schrieb im Newsbeitrag
...
....
So, unless you look for ultimate performance, you can do as you want.
BTW, where will the exhaust discharge ?

the exhaust will discharge down/aft. This may not pose an problem, because I
will use 114mm diameter air duct routing the pressurized air from
nose-bowl's inlet to the cylinder shroud. So hot and cold air will not be
mixed.

schrieb im Newsbeitrag
...


NACA and NASA studies (Miley) have shown that this method generates a
little more drag than an equally engineered "normal" cooling.
----------------------------------------------------

Also, the draft of the VW's head castings show that the direction of
the cooling-air flow was taken into account when creating the
demountable, permanent molds. Just another of the 'unimportant'
details that tend to get overlooked (or deliberately ignored) when
converting the VW for flight.

-R.S.Hoover



good point, Veeduber. Wonder how much this effect/penalty is.

oilsardine a écrit :

the exhaust will discharge down/aft. This may not pose an problem, because I
will use 114mm diameter air duct routing the pressurized air from
nose-bowl's inlet to the cylinder shroud. So hot and cold air will not be
mixed.

So you will discharge cooling air up, and exhaust/engine compartment air
down ?

Best regards,
--
Gilles
http://contrails.free.fr

"oilsardine" wrote in message
...

"GTH" schrieb im Newsbeitrag
...
...
So, unless you look for ultimate performance, you can do as you want.
BTW, where will the exhaust discharge ?

the exhaust will discharge down/aft. This may not pose an problem, because
I will use 114mm diameter air duct routing the pressurized air from
nose-bowl's inlet to the cylinder shroud. So hot and cold air will not be
mixed.

I would not think that that is a large enough diameter tubes for engine
cooling. Someone may have used that size and had it work OK, but I would be
surprised. I would think that you would need double that, or one tube for
each cylinder.

If you had that size intake, and no tubes, but instead an open plenum
pressurizing one side of the cylinders, you would have much less drag, and
more airflow, than the air slowing down going through the tubes.

Also, most "Updraft" cooling engines do not do well on single engine
airplanes, because the windshield is relatively close behind the engine, and
that makes the whole top of the engine cowl an area of positive pressure.
With positive pressure on the outlet, the air will have a very hard time
getting out, and you will have a hot engine. At the very minimum, the
outlets would need to be on the side of the cowl, ala Thorpe T-18. I think
even those have some of the air exiting the bottom, in the area of low
pressure. I'm sure someone will correct that if it is wrong.
--
Jim in NC

"Morgans" schrieb im Newsbeitrag
...
....
I would not think that that is a large enough diameter tubes for engine
cooling. Someone may have used that size and had it work OK, but I would
be surprised. I would think that you would need double that, or one tube
for each cylinder.

sorry, yes, one tube per side. This would be the same what Sonex recommends
for the AeroVee

If you had that size intake, and no tubes, but instead an open plenum
pressurizing one side of the cylinders, you would have much less drag, and
more airflow, than the air slowing down going through the tubes.

yes, but on the other hand would then have much more air leaks. All those
wires tubes going through the baffling...

Also, most "Updraft" cooling engines do not do well on single engine
airplanes, because the windshield is relatively close behind the engine,
and that makes the whole top of the engine cowl an area of positive
pressure.

Outlet would be about one feet in front of the cowl/windshield intersection.
The cowl blends almost straight into the windscreen. There should be
negative or zero pressure on the exit side and poitive pressure on the
scoop.
You may have aloog on this sketch:
http://www.ph21.de/guest/updraft-cooling.JPG

However question is how close is this to the pressure situation of my bird.

In Sports Car Club of America Formula Vee racing (my other expensive
hobby) a few guys have tried updraft cooling on the blueprinted 1200cc
motors we use, which put out about 60 bhp, have no cooling fans and
are run at full throttle (except for brief braking) at average speeds
in the 80-90 mph range; we also run in drafting packs which put a lot
of hot air into every motor except the one in front. Nobody has stuck
with it; they say that the cooling drag is not reduced measurably (if
at all) and the heads run about 20-30 deg F hotter than with downdraft
cooling.

Your figure shows a low-pressure area on top of the nose. This is
substantiated by the placement of the cooling outlets on Peter
Garrison's updraft-cooled Melmoth II; they're so far forward and so
close to facing forward that everyone mistakes them for inlets. Also
note the high-pressure area under the nose in the figure; the only
reason this changes to low pressure behind the cowling is the "chin"
at the cowl's bottom rear. This is not a natural feature; it has to
be induced with aerodynamic trickery at some cost in drag.