Engine Cooling - why not....

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

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.

oilsardine wrote:

"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.





Number one rule to keep firmly in mind.

You can push air about as well as you can push string.

I think you need to go look at some sucessful pusher installations.

You won't find any using dir duct tubing.

Wonder why?

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"...

On Dec 28, 7:59 pm, cavelamb himself wrote:

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

I hate to tell you this but a brand new VW head, straight out of the
box from the plant at Puebla, Mexico, requires about two man-hours of
skilled work with rifflers & files just to get rid of the existing
casting flash and chamfer the as-machined edges. Failure to perform
this minor amount of detailing -- another of those 'unimportant'
little details -- can reduce the thermal efficiency of the head by as
much as 50%. Then you need to address the fact that for the last ten
years or so the Puebla plant has NOT included the required air-dams
that fit between the chambers on the underside of the heads.

Once you have a pair of heads that will cool to the original VW spec
you'll find you improve their heat-transfer in two very significant
ways. The first is to use thermal barrier coatings to reduce the
amount of heat going into the heads, the second is to blast the fins
with COARSE media and to then treat them so as to preserve the
'infinite' surfaces created by the blasting, and to increase their
thermal emissivity (by about 7%) with another coating (TechLine's
'TLTD').

Plus a few dozen other things, none of which are found on the typical
Aero-vee nor Great Planes head.

But as for simply increasing the size of the cooling air passageways,
proceed with caution. Most guys who think bigger is better end up
cutting into the exhaust valve guides, resulting in the eventual
failure of the guide (and ruining the head) -- a few have even cut
into the exhaust port itself After making all the mistakes you can
think of, my approach is to try and make the heat-transfer process
more efficient, typically by increasing the surface area of the
existing channels then doing what I can to improve the velocity of the
cooling-air flow through them by paying the keenest possible attention
to pressure differentials and distribution.

This sort of thing is rarely as intuitive as 'bigger is better.'
Fortunately, an engine doesn't know how to lie; it will always tell
you when you get it right.

-R.S.Hoover

thanks, Guys for guiding me (back) to the right direction ;-)) Don't like to
experiment the rest of my life with cooling issues. This Melmoth reading -
excellent stuff.


"quietguy" schrieb im Newsbeitrag
...
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"...