REFLECTOR: Cabin Heating
Jim Sower
reflector@tvbf.org
Tue, 27 Jan 2004 21:29:06 -0600
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<... It was unexpected (in my mind) that the front oil cooler carried that large a
fraction of the cooling load ...>
I'm amazed. I had no idea. I have an IO-360 and Cozys with O-360 seem to work OK
with only one of the two coolers I'm using. Go figure.:-( Now, I've only got about a
2" diam duct coming out of the plenum to the cabin and that sounds about like what
gave you your overtemps. Maybe if I didn't completely seal the overboard vent? At
the very least, your experience tells me to be very careful and don't let expectations
get out of hand. Bummer.
A more benign system (less failure modes, no high pressure lines in cabin area, etc.-
albeit more complex) occurred to me last night: Run about 4' of (copper?) tubing back
and forth through the lower engine pan and exit at a point where oil level is about 5
qt. Plumb these through an electric pump to a smallish heat exchanger in the cockpit.
Use low viscosity oil for heat. Leaks in the engine dilute the oil some - no damage
and can be fixed with an oil change. Leaks elsewhere stop immediately when you turn
off he pump. Low pressure system renders leaks anywhere an order of magnitude less
likely.
Another possibility would be to "T" off of the oil line to the cooler into your
heating system through a small orifice and thence back to the pan. Since the oil pump
produces several times more volume than the engine consumes at cruise, a relative
trickle should (key word here) not be missed. Again, low pressure system, etc. Or
perhaps capture some of the oil that gets vented back to the pan from the pump and
route that to the heater core.
High pressure plumbing in the cabin just spook me .... Jim S.
Chuck Jensen wrote:
> Since every configuration is different, yours may vary but I tried some of
> your proposed fixes with less than stellar results. My cabin air is fed from
> a flapper that opens and taps air flow downstream plenum of the front oil
> cooler and ducts it to the cabin. It was obvious, due to the massive
> airflow thru the oil cooler, the outlet discharge air was heated just a few
> degrees. Figuring that by slowing the air flow, the increased residence
> time would allow sufficient heating of the air, I cut some squares of a
> cloth bag filter and put 4 layers over the cooler inlet and plugged the
> plenum outlet. The only air allowed to pass was what I feed to the cabin.
> My plan was to rely on the rear oil cooler to maintain engine oil temps.
>
> On the test flight at OAT 5C, the cabin heat was nice and toasty; a big
> improvements (and a high "smug" factor). Then the oil temps started to
> climb, and climb. Finally topping out at 220C (181C is normal) and elevated
> CHTs at reduced cruise. End of experiment. Removed the outlet plug and 2
> of the 4 cloth layers on the inlet and went back to freezing at 0C OAT. It
> was unexpected (in my mind) that the front oil cooler carried that large a
> fraction of the cooling load. I expected to be able to block off the front
> cooler and still maintain adequate oil temperatures. Not. There just doesn't
> seem to be a happy medium.
>
> Bottom line; I'm going to try a second oil cooler, in series with the front
> cooler, that's dedicated solely to cabin heat.
>
> Chuck
>
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<... It was unexpected (in my mind) that the front oil cooler carried
that large a fraction of the cooling load ...>
<br>I'm amazed. I had no idea. I have an IO-360 and Cozys with
O-360 seem to work OK with only one of the two coolers I'm using.
Go figure.:-( Now, I've only got about a 2" diam duct coming out
of the plenum to the cabin and that sounds about like what gave you your
overtemps. Maybe if I didn't <i>completely</i> seal the overboard
vent? At the very least, your experience tells me to be very careful
and don't let expectations get out of hand. Bummer.
<p>A more benign system (less failure modes, no high pressure lines in
cabin area, etc.- albeit more complex) occurred to me last night:
Run about 4' of (copper?) tubing back and forth through the lower engine
pan and exit at a point where oil level is about 5 qt. Plumb these through
an electric pump to a smallish heat exchanger in the cockpit. Use
low viscosity oil for heat. Leaks in the engine dilute the oil some
- no damage and can be fixed with an oil change. Leaks elsewhere
stop immediately when you turn off he pump. Low pressure system renders
leaks anywhere an order of magnitude less likely.
<p>Another possibility would be to "T" off of the oil line to the cooler
into your heating system through a small orifice and thence back to the
pan. Since the oil pump produces several times more volume than the
engine consumes at cruise, a relative trickle should (key word here) not
be missed. Again, low pressure system, etc. Or perhaps capture
some of the oil that gets vented back to the pan from the pump and route
that to the heater core.
<p>High pressure plumbing in the cabin just spook me .... Jim S.
<p>Chuck Jensen wrote:
<blockquote TYPE=CITE>Since every configuration is different, yours may
vary but I tried some of
<br>your proposed fixes with less than stellar results. My cabin air is
fed from
<br>a flapper that opens and taps air flow downstream plenum of the front
oil
<br>cooler and ducts it to the cabin. It was obvious, due to the
massive
<br>airflow thru the oil cooler, the outlet discharge air was heated just
a few
<br>degrees. Figuring that by slowing the air flow, the increased
residence
<br>time would allow sufficient heating of the air, I cut some squares
of a
<br>cloth bag filter and put 4 layers over the cooler inlet and plugged
the
<br>plenum outlet. The only air allowed to pass was what I feed to
the cabin.
<br>My plan was to rely on the rear oil cooler to maintain engine oil temps.
<p>On the test flight at OAT 5C, the cabin heat was nice and toasty; a
big
<br>improvements (and a high "smug" factor). Then the oil temps started
to
<br>climb, and climb. Finally topping out at 220C (181C is normal)
and elevated
<br>CHTs at reduced cruise. End of experiment. Removed the
outlet plug and 2
<br>of the 4 cloth layers on the inlet and went back to freezing at 0C
OAT. It
<br>was unexpected (in my mind) that the front oil cooler carried that
large a
<br>fraction of the cooling load. I expected to be able to block
off the front
<br>cooler and still maintain adequate oil temperatures. Not. There just
doesn't
<br>seem to be a happy medium.
<p>Bottom line; I'm going to try a second oil cooler, in series with the
front
<br>cooler, that's dedicated solely to cabin heat.
<p>Chuck
<br> </blockquote>
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