REFLECTOR: Franklin Coolong Plumum

[MikeWatsonSpg at cs.com]

As anyone who flies with a Franklin knows, long taxi and hot days
produces CHT temperatures approaching maximum before takeoff.
Shutting down the engine in the run up area is not an option at some
airports, and restarting after fifteen or twenty minutes is a b...h.

The plenum as supplied by velocity, consist of two arm pit scoops
which feeds a wide box covering the entire upper portion of the engine.

The box is very difficult to seal, especially around and under the starter
gear housing and on the rear (facing prop) of #5 and #6 cylinders.

While taxing or holding, the heat of the entire engine is trapped within
the plenum, the prop does not seem to have any effect in pulling any
meaningful amount of air through at taxi or hold RPM.

Those flying with roof nacca scoops may get a chimney effect which allows
the heat to rise out the top. (just a guess).

My thoughts to relieve the problem is to make two separate plenums,
each fed from it's own armpit scoop. They would cover only the large
section of the cylinder head fins providing a tighter fit on left, right
and rear edges. 

This would eliminate the heat from the base of the cylinders and the center
section of the engine from accumulation in the plenum when not in flight.
The only drawback I see is if something got stuck in one arm pit scoop,
one would loose all cooling on that bank of cylinders.

Has anyone tried this, any thoughts??

Mike W.
 
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