Oil coolers

Somehow, in 6 years of flying, I missed the fact that not all light piston
airplanes have oil coolers. Why is this so? What factor determines when an
O-320, for instance, must have an oil cooler? ISTR that the oil does a large
percentage of the cooling in aircraft piston engines. How does the engine
get rid of this heat without an oil cooler?
--
Dan
C172RG at BFM

"mikem" wrote:
Oil doesn't do "coolling" per se;

When an "oil cooler" is added to an engine, it simply increases the
total surface area of the engine assembly that the cooling airflow can
interact with.

These two statements don't quite jibe, do they?

The oil cooler removes heat from the engine and the medium that conveys heat
to the cooler is oil. I don't see any difference between that and how water
cools a water-cooled engine.
--
Dan
C172RG at BFM

On Fri, 8 Aug 2003 19:19:30 -0500, "Dan Luke"
wrote:

"mikem" wrote:
Oil doesn't do "coolling" per se;

What I tried to convey is that the oil doesnt cool the engine; Oil is
used to reduce temperature gradients inside the engine. "Cooling"
takes place where the airflow comes in contact with metal...

When an "oil cooler" is added to an engine, it simply increases the
total surface area of the engine assembly that the cooling airflow can
interact with.

You started the thread by acting surprised that not all aircraft
engines have oil coolers. I tried to point out that aircraft engines
have such large external surface areas, that if appropriately cowled,
they can get rid of heat without an external oil cooler.

Adding an oil cooler has more to do with automatically regulating
engine oil temperature for water vapor boil off and constaining sizes
of cowling openings for streamlining (ala LoPriesti) than out of pure
heat-transfer necessity.

The oil cooler removes heat from the engine and the medium that conveys heat
to the cooler is oil. I don't see any difference between that and how water
cools a water-cooled engine.

In those cases where a cooler has been designed in to acheive those
other criteria, niether do I, and I said so...

MikeM

Don't underestimate the amount of heat the oil removes from the engine...
It is critical... Without it's help pistons would burn up within minutes,
valve springs would overheat, etc...High powered engines often have a an oil
spray directed to the bottom of the piston... The oil cooler is needed where
the oil pan, case, prop hub, and tappet covers, cannot radiate the heat load
adequately...
Denny

Oil doesn't do "coolling" per se;

Ask a performance boater about a "Drive Shower". Oil cools well there too.
Doesn't make it necessary or even helpful in all cases though. Mikes post
makes sense too.
Wayne


"Dennis O'Connor" wrote in message
...
Don't underestimate the amount of heat the oil removes from the engine...
It is critical... Without it's help pistons would burn up within minutes,
valve springs would overheat, etc...High powered engines often have a an
oil
spray directed to the bottom of the piston... The oil cooler is needed
where
the oil pan, case, prop hub, and tappet covers, cannot radiate the heat
load
adequately...
Denny

Oil doesn't do "coolling" per se;

"mikem" wrote:
You started the thread by acting surprised that not all aircraft
engines have oil coolers. I tried to point out that aircraft engines
have such large external surface areas, that if appropriately
cowled,
they can get rid of heat without an external oil cooler.

Where are you getting this from? I don't mean to sound insulting, but
this seems dubious. Appropriately cowled? All the light piston
aircraft I am familiar with are cowled the same: a forced air plenum
above the cylinders creates a differential pressure across the
cylinders and heat is conveyed out of the cowling by the resulting
airflow. In some installations, an oil cooler is installed to use this
same d. p. for additional cooling.

Adding an oil cooler has more to do with automatically regulating
engine oil temperature for water vapor boil off...

So in hot weather it's not needed?

...and constaining sizes
of cowling openings for streamlining (ala LoPriesti) than out of
pure
heat-transfer necessity.

On a Cessna 172?

The oil cooler removes heat from the engine and the medium that
conveys heat
to the cooler is oil. I don't see any difference between that and
how water
cools a water-cooled engine.

In those cases where a cooler has been designed in to acheive those
other criteria, niether do I, and I said so...

Well, you started out by saying that oil doesn't do cooling.
--
Dan
C172RG at BFM

On Mon, 11 Aug 2003 15:04:58 -0400, "Dennis O'Connor"
wrote:

Don't underestimate the amount of heat the oil removes from the engine...
It is critical... Without it's help pistons would burn up within minutes,
valve springs would overheat, etc...High powered engines often have a an oil
spray directed to the bottom of the piston...

Yes, but spraying oil on the underside of the pistons does nothing to
remove that heat from the engine! The oil just carries the heat from
the piston into the oil pan. The piston/cylinder is cooler than it
would be without the oil spray, but the oil/lower end of the engine is
now much hotter. This is why I said that oil just reduces temperature
gradients. Getting the heat out of the lower end is another matter
entirely.

How does the heat get carried away from the engine's lower end? If the
engine has no oil cooler, then the temperature of the lower
end/crankcase/oil pan will stabilize when the heat being carried away
by the airflow through the cowling just matches the heat being
produced inside the engine (convection). Heat loss from the engine due
to radiation does a very small part of the total heat flow.

The oil cooler is needed where
the oil pan, case, prop hub, and tappet covers, cannot radiate the heat load
adequately...

I prefer to think that this is just a choice made by the designer.
Clearly in high performance engines/aircraft, it is advantageous to
"concentrate" some of the heat transfer from the engine to the cooling
airflow into one spot, which we call an "oil cooler". As I have
already pointed out, this makes possible automatic regulation of oil
temperature, and LoPresti-small opening cowling. However, there are
many aircraft flying without oil coolers, so a cooler is not
mandantory

The reason I got into this thread in the first place it to try to
dispell the OWT that you cited above: "Don't underestimate the amount
of heat the oil removes from the engine.". If an aircraft has no oil
cooler, then the amount of heat removed from the engine by the oil is
ZERO! (Unless you have a BIG leak).

MikeM

Well, you're experience is somewhat limitted then.

Granted.

The Navions (and
some others for sure) come with a large intake on the bottom of the
cowl and blow air UP on to the cylinders.

The principle is the same: a pressure differential is created across
the cylinders.

Other planes just blow air
horizontally accross the engine with no vertical separation,

What airplanes?

some just
have the cylinders stuck out in the airstream.

Yes, like a radial in a Stearman, for instance.
--
Dan
C172RG at BFM

"mikem" wrote:
The reason I got into this thread in the first place it to try to
dispell the OWT that you cited above: "Don't underestimate the
amount
of heat the oil removes from the engine.". If an aircraft has no oil
cooler, then the amount of heat removed from the engine by the oil
is
ZERO! (Unless you have a BIG leak).

You are just splitting hairs. No, oil is not dumped out of my
airplane's engine taking excess heat with it. Neither is water dumped
out of my car's engine, yet the car engine is still a "water cooled"
design.
--
Dan
C172RG at BFM

On Tue, 12 Aug 2003 16:30:14 -0500, "Dan Luke"
wrote:

You are just splitting hairs. No, oil is not dumped out of my
airplane's engine taking excess heat with it. Neither is water dumped
out of my car's engine, yet the car engine is still a "water cooled"
design.


But there are not many cars without a radiator, either! (except
dragsters). I haven't seen a "water cooled" car for more than fifty
years. Nowadays, they use a witches brew of Silicates to carry heat
from the block to the radiator. The cooling takes place when air blows
through the radiator...

MikeM