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

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.

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

In quantitative terms, I've no idea. At a guess, it appeared to be
about 25%.

The main reason for this is that the cooling air expands as it picks
up heat. The casting draft takes this into account with the
passageways being progressively larger on the 'down-wind' direction.
Reverse the direction of the air-flow, you end up trying to force the
heated air into a passageway that is steadily decreasing in cross-
section.

I went through this phase yearz & years ago, was surprised when it
didn't work as well up vs down, went back to doing it the other way.
Every few years I read about another instant expert who thinks they've
discovered the Silver Bullet, citing all sorts of benefits. Best I
can say is try it both ways... then think for yourself.

-R.S.Hoover

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

--------------------------------------------------------------------------------------------------------

In quantitative terms, I've no idea. At a guess, it appeared to be
about 25%.

The main reason for this is that the cooling air expands as it picks
up heat. The casting draft takes this into account with the
passageways being progressively larger on the 'down-wind' direction.
Reverse the direction of the air-flow, you end up trying to force the
heated air into a passageway that is steadily decreasing in cross-
section.

I went through this phase yearz & years ago, was surprised when it
didn't work as well up vs down, went back to doing it the other way.
Every few years I read about another instant expert who thinks they've
discovered the Silver Bullet, citing all sorts of benefits. Best I
can say is try it both ways... then think for yourself.

-R.S.Hoover


Or, take a small file and open the passages up.

wrote in message
...

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

In quantitative terms, I've no idea. At a guess, it appeared to be
about 25%.

The main reason for this is that the cooling air expands as it picks
up heat. The casting draft takes this into account with the
passageways being progressively larger on the 'down-wind' direction.
Reverse the direction of the air-flow, you end up trying to force the
heated air into a passageway that is steadily decreasing in cross-
section.

I went through this phase yearz & years ago, was surprised when it
didn't work as well up vs down, went back to doing it the other way.
Every few years I read about another instant expert who thinks they've
discovered the Silver Bullet, citing all sorts of benefits. Best I
can say is try it both ways... then think for yourself.

-R.S.Hoover


Indeed the breakthrough that led to the development of high power air cooled
engines for WWII aircraft was advances in cooling fin design. The ability
to cast and machine extremely fine fins combined with high octane fuel
allowed Allied aircraft to develop far more HP per pound than Axis aircraft
engines. Fins aren't trivial.

Bill Daniels

"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.

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