N135TD, an XS mono-wheel with 912S, has about 110 hours on it now. We
have had problems with the muffler coming off the header pipes, due to
retaining springs losing their tension (temper?).
Suspecting excess heat as the problem, we installed thermocouples in
the several places inside the upper and lower cowl, connected to our
engine monitoring gauges. These gauges log the cowl temps plus all
engine parameters once every ten seconds. After each flight, all data is
downloaded to a laptop for evaluation.
Our initial test flight showed lower cowl temps peaking at 400 F,
sustained temps of 375 F, with an OAT of about 35 F. It is quite likely
then that on a hot day our cowl temps are up to 450 F. We have found
droplets of nylon tie wrap in the lower cowl, which melt at about 450 F,
I'm told. Our upper cowl temps run cool at about 70-80 F. Lower cowl
temps can vary by up to 150 deg F, depending on fairly small changes in
pitch and yaw, with cruise attitude and power and a yaw (even a slight
one) to the right causing the worst temps (ram air entering the exhaust
opening in the left side of the cowl seems the culprit).
We have made a number of mods to the cowl to try to bring the lower
cowl temps down, with about 12 test flights on different configurations
so far. We have managed to drop the peak temps to about 280 F, with
sustained temps of about 275 (OAT of about 40 F). This particular
configuration has two reverse scoops at the bottom of the cowl and a
2.25" cooling hole in the upper part of the radiator duct. We have yet
to perform cruise performance tests to see how much the additional drag
has hurt us.
Has anyone else noticed excess heat in the lower cowl?
Any suggestions on what mods to the cowl will get rid of this heat?
Terry Seaver
A135 / N135TD
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