REFLECTOR: Franklin Coolong Plumum

michalk michalk at awpi.com
Tue Jul 19 14:10:04 CDT 2005


Yes.  That's how I made mine.  Not flying yet, but it's a very nice 
tight fit.  I have a right angle aluminum with slotted holes for 
grommets that hold the spark plug and CHT wires.

A foam plug was made on the engine, and then the plenum was glassed in 
place, also laying up onto the aluminum angle.


MikeWatsonSpg at cs.com wrote:
> 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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