REFLECTOR: Cabin Heating

[John Dibble]

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
>