Matt,
Yes, the oil cooler is 3/8" thicker than the glycol
exchanger. Also,
maybe more significant, is that the fin count is much higher for
the oil
cooler, resulting in higher drag/pressure drop across it. I had
considered adding a dedicated exit duct for the oil cooler, but
didn't
want to pay the drag penalty. That's when I decided to try the
oil-to-water exchanger. The beauty with that solution is that
it didn't
cost me any additional cooling drag. I feel that if I could
fit a
slightly larger glycol exchanger in place of what I'm running
now, that
I could eliminate the oil/air exchanger altogether. I even flew
with
50% of the oil/air exchanger blocked off. It was pretty close
with the
current glycol exchanger, but not quite enough to fly in Texas
in the
summertime. So, I left the oil/air exchanger in place and don't
have
any more cooling problems. That's a real good feeling.
Mark S.
Mark,
So you're not interested in the cooling redundancy that Paul has
suggested as a good idea - using oil-air and glycol-air
exchangers at
the same time? I still think that would be the direction I'd
go. In
fact, I'd make that a requirement, as I think it's something
that could
make for a more favorable outcome should the airplane suffer from a
single component failure..
Maybe it's just anecdotal, but the vaunted P-51 Mustang has a
separate
oil-air cooler, as I believe do the other Merlin powered aircraft
(Spitfires, Hurricanes, etc). I think the P-40 (Allison
powered) was
the same way.
The Mustang had an induction air to glycol supercharger
intercooler, but
this ran with a separate cooling loop from the engine - and had
its own
coolant pump and air-glycol exchanger. This allowed putting the
intercooler where the directness/compactness/packaging is
important. It
wouldn't be practical to have a duct feeding an air-air intercooler
between the stages of the supercharger (on a Merlin).
Please keep in mind, I don't have a rotary powered airplane, nor a
liquid cooled airplane, nor even an airplane I built myself, so
take my
ideas with a grain of salt.. :)
I also commend you for putting together an airplane that's running
well. I admire the accomplishment.
Regards,
Matt-
Matt,
I do have a glycol-air and an oil-air exchanger, but also an oil-glycol
exchanger. I don't see where removing the oil-glycol exchanger is going
to improve the time I have to get on the ground should the glycol system
spring a leak. I may explore the possibility of building a dedicated
exit duct for the oil-air exchanger though... in my spare time. If that
works out, then I'll consider removing the oil-glycol exchanger.
Mark S.
Mark,
I'm not necessarily proposing that you remove the oil-glycol exchanger.
I just got the impression you were moving towards removing the oil-air
cooler if you could get the temps where you wanted them without it.. I
believe you said, "My only regret is that there isn't enough excess
cooling capacity that would allow me to remove the oil/air exchanger
completely."
Having both the oil-air and oil-glycol exchangers doesn't bother me.
Going without an oil-air exchanger bothers me. If you lose a bunch of
glycol you won't be directly cooling the metal in the engine,
_nor_ will
you be cooling the oil that keeps the bearings and rotors happy. If you
have an oil-air exchanger, losing glycol supply doesn't directly impact
your ability to supply cool oil to the bearings and rotors, and so I
think that means the engine will run longer.
Regards,
Matt-
What's with the Glycol/air cooler nomenclature? It is WATER gents. Water
is the best cooling medium there is for heat transfer. The only reason
we use
glycol at all is to bump up the boiling point. If you have an adaquate
system,
that is pressurized to prevent boilover at altitude You need only a
lubricity additive.
Car racers frequently use only a lubricty additive and rust preventitive
in distilled water.
If you plane is hangared in the midwest, I can see glycol as it is
normally used in cars
as a anti-freeze agent, but never more than 50-50. Why lose heat
transfer capability
when our biggest problem is having radiators big enough? Just wondering.
Bill Jepson
Bill,
Very correct on the water. Many racing sanctions also ban coolant as it
contaminates the track when a radiator gets hit (we would never do that!).
The lube/corrosion inhibitor we used is RedLine Water Wetter. We ran back to
back tests on a USAC paved sprint car and had 15 deg F cooler running with
water wetter. Don't know the chemistry of what they are doing, but it does
make water transfer heat better. Allowed us to use a smaller radiator to
reduce nose weight.
Probably worth looking into for our rotary stuff as well. It may help some
of the guys with marginal cooling.
Larry
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