REFLECTOR: Cabin Heating

[Ronnie Brown]

With very low cooling air temperatures going to the engine and cylinders, I
would think the need for oil cooling to be very low.

220 degrees oil temperature is probably not a problem during cold weather
operations.  Talk to a good engine man (Don George if you bought your engine
from him).  I know my Cessna 172 manual suggested blocking off the air to
the oil cooler in cold operations to keep the oil temperature up.  If the
rear oil cooler isn't providing enough cooling, I'd say the oil cooler isn't
doing its job - needs more air flow??

If my heater flapper is mostly open, I get some warm air and my oil temp
runs 180-185 during 35-40 degree ambient.  Closing the flapper to force air
through the cabin and block the oil cooler exit runs my oil temp up to 205 -
210 and I get lots of cabin heat.  I still need to work on air leaks - I
haven't sealed my canard cover and my cold air vents are leaking. By the
way, I do not have a rear cooler - don't need one.  My CHT's are below 380
on climb and 350-360 in cruise in the summer.  Less when LOP.

Ronnie Brown
173 Elite RG - 200 HP Lyc

Ronnie

----- Original Message -----
From: "John Dibble" <aminetech@bluefrog.com>
To: <reflector@tvbf.org>
Sent: Tuesday, January 27, 2004 11:53 AM
Subject: Re: REFLECTOR: Cabin Heating


| Chuck,
| The rate of heat transfer is proportional to the (average) temperature
| difference between the air and the oil.  So increasing the temperature
| of the exiting air will definitely reduce cooling of the oil considerably.
|
| John
|
| 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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