REFLECTOR: Franklin Coolong Plumum

[Jim Sower]

I've seen a couple of Long-EZs that had "enclosed" prop extensions 
(fairing from the flywheel to the prop hub) that had fins fastened to 
the fairing.  Amounted to what looked like a 10 or 12 1.5" x 2" turbine 
blades, set at about 45 deg pitch just inside the cowl.  Don't have any 
details, but the guys said it improved cooling for ground operations.
Sounds like it would work pretty good ... Jim S.

John Dibble wrote:

> 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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