Engine Cooling - why not....

[oilsardine[_2_]]

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

[oilsardine[_2_]]

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

[GTH]

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

[[email protected]]

>
> 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

[oilsardine[_2_]]

"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[_2_]]

> 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.

[GTH]

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

>
>

[Morgans[_2_]]

"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

[oilsardine[_2_]]

"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.

[quietguy]

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.

[[email protected]]

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

[Morgans[_2_]]

> 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

[[email protected]]

> 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

[cavelamb himself[_4_]]

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.

[cavelamb himself[_4_]]

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?

[cavelamb himself[_4_]]

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?

[quietguy]

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.

[quietguy]

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"...

[[email protected]]

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

[oilsardine[_2_]]

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"...

[Bill Daniels]

> 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