Engine Cooling - why not....

"GTH" schrieb im Newsbeitrag
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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

"oilsardine" wrote in message
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"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
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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.

Outlet would be about one feet in front of the cowl/windshield intersection.

wrote

my reading of that drawing indicates morgans has a point about higher
pressure where the cooling air wants to exit, thus potentially
reducing flow.

Yep. I can't emphasize enough that the OP needs to abandon his current
thinking about cooling exits, in the position he suggests. He WILL end up
having to re-do them, at the penalty of much work and re-work, and *that* is
not what *I* would want to be doing, with a brand new plane.

Ever notice where the inlet for your car's dashboard interior vents are, you
know, the ones that will blow a pretty healthy air flow even with the fan
off and the windows rolled up?

On 99.9% of the cars, it is those little slots in the sheet metal, right in
front of the windshield. Lots of high-high pressure, there. NOT where you
want an outlet for cooling air. Doing it that way, it could almost have
reverse flow, or almost totally stagnant flow. Not good for cooling an
already hot running motor.
--
Jim in NC

oilsardine wrote:

"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...


Won't matter at all if

The air in the cowl is below outside ambient pressure.

You can suck air through - you can not blow it through.



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.



Most likely, it the cooling systems like this can be made to work at
all, cooling will be sensative to airspeed and angle of attach.

NOT a good idea.

Look, your sketch shows the local low pressure area at the bottom of the
cowl. Do you have a really valid reason for wanting to go backwards?

I've found Peter Garrison's web site on Melmoth 2; here's the section
on cooling:

http://www.melmoth2.com/texts/Cooling%20flow.htm

I was wrong about the outlets facing almost forward; they looked that
way in a very poor photo which was all I had to go on, but Garrison
has written that people nevertheless keep asking him why his cowling
has three inlets and no outlets. It's interesting that even though
the 360's as-cast fins are better suited to updraft cooling than those
on a VW Garrison had to do a lot of fiddling with baffles and cowl
flaps to get the system to work pretty well, and he's still not sure
that there's a drag advantage in it. A final bit of weirdness: the
system cools better in climb than in cruise mode, probably because the
suction at the top front of the nose is stronger at higher angles of
attack.

As usual from Garrison, there are a lot of technical details and very
well explained. I'm glad I found the site; I'm going to study it
closely.

I forgot to mention that photos of Melmoth 2's cooling system are not
in the "Cooling" section; they're in "Pictures" and "Progress":

http://www.melmoth2.com/texts/Pictures.htm

http://www.melmoth2.com/texts/Progress.htm

A lot of scrolling will be required in "Progress"...