REFLECTOR: Cabin Heating

[Jim Sower]

It sounds like most of what we need is already in place.  My 173FG has the front oil
cooler in a plenum.  The input to the plenum is the NACA in the nose, and it exhausts
out the bottom of the plenum.  I have a 2" duct out the back of the plenum going to
the cabin foot warmers (could be larger and go to more places).  As it stands now,
only the (tiny bit of) exhaust from the oil cooler that doesn't go overboard goes into
the heat system.  I aim going to make a flapper valve that can cover either the outlet
to the cabin completely or the overboard opening completely or anything in between.

If it's really cold, I'll block the overboard vent and the only air that passes
through the oil cooler will be whatever the outlet to the cabin will permit.  Air flow
will be much reduced and therefore much hotter.  If I don't need that much heat, I can
crack the overboard vent which will increase flow through the cooler but reduce flow
into the cabin (the rest going over the side).  I can keep venting the overboard vent
more and more until I have the cabin vent blocked and all the air the cooler will pass
going over the side.  One flapper valve, a plenum that's already there, no additional
oil coolers.  I may have to make a new plenum so the flapper will fit between the
cooler and cabin outlet bulkhead and be big enough to cover the overboard vent, but
that's not rocket science.

Limiting air flow to the hot air I need should make for enough delta-T to heat the
cabin, and increasing air flow as my heating requirements go down will tend to match
increased oil cooling requirements.

Just a theory ... Jim S.

Dave Black wrote:

> Scott,
>
> > I think if you had the nose oil radiator and an inside one for cabin
> > heating you could easily run them in series, much easier plumbing.
> >
> > Then close off the cabin heat outlets on the oil cooler duct.  If your oil
> > is too cool just close the flap(that used to direct the air into the cabin)
> > a bit thus reducing the flow through the radiator and raising the oil
> > temps, good for the engine and for the passengers too.
>
> You may be on to something! It would be stone simple plumbing. And I believe
> it would be a huge improvement over the standard nose cooler only
> installation.
>
> I see two drawbacks:
>
> 1) The total length of the oil line. The longer the line, the more 'congealed
> oil plug' effect you have in cold weather. But now that I think of it, with
> this system, there'd be absolutely no need to leave the original cooler in the
> nose. Rather, it should be relocated to the engine compartment. Hence the
> total plumbing could be MUCH shorter than the standard system.
>
> 2) The cabin heater would always be hot, even in summer. However I'm certain
> that with some clever design, most of the unwanted heat from the cabin heater
> during the summer can be contained, blocked from entering the cabin, or ported
> overboard. Heck, if the unwanted heat can be eliminated efficiently, the cabin
> heater could even be used during summer as an auxiliary oil cooler. There are
> certainly times when that would be a good thing.
>
> All-in-all, I believe two coolers in series with no valves is a big
> improvement over the standard system. Certainly it'd be a very simple to
> plumb, and cabin temperature control becomes a matter of controlling a blower
> motor and flapper(s).
>
> I guess a flapper valve located in the cabin floor could direct hot air either
> back into the cabin or overboard. It needs to work quite effectively to keep
> the cabin from getting hot in summer. But I'll bet it could be done. On the
> other hand, putting a bypass valve around the cabin heater would keep the heat
> out too.
>
> Hmmm...
>
> Dave Black
> Shortwing RG