REFLECTOR: Franklin Coolong Plumum

John Dibble aminetech at bluefrog.com
Tue Jul 19 18:23:54 CDT 2005


Mike,
I believe I have what you described on my SRGE/Franklin.  Separate
armpit scoops and plenums that just cover the cylinders.  In summer at
cruise my CHTs run 110-130 C, depending on altitude/OAT.  When taxiing,
if the engine was started cold, CHTs and oil temp are not a problem.  If
the engine was warm before starting I do as much as I can before
starting, like talk with delivery, check controls.  Keeping the throttle
at minimum helps.  Also I do my run up (at 1100 rpm) while taxiing.  Oil
temp is my biggest problem on extended taxi.  I have a fan in the duct
line.  It will hold the temp, but if I forget to turn the fan on and let
the temp get hot, it won't cool it down, just hold it from getting
hotter.

John

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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