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1. 05:35 AM - Re: DC Wiring Diagrams for SPA Panther LS (jsajpf)
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| Subject: | Re: DC Wiring Diagrams for SPA Panther LS |
Rick,
Does the aircraft pitch trim system include a manual trim wheel or lever, or is
the sole means of pitch trim the electric system?
The electric trim circuit lacks a combination "arm" and "command" input (think
of the split trim switch on many GA type certificated aircraft). Only a "command"
input is shown. I think this single input is common in E/AB airplanes but
I personally do not favor it.
I think your relay circuit for pitch trim (rather than direct switching of motor
current with a momentary switch) provides a measure of protection against uncommanded
or runaway pitch trim, in that an opposite direction command at the
switch will change the state of the motor legs, at least stopping further trim
movement while the switch is held.
I think a cutout switch to remove power from the motor circuit is advisable, located
such that a free hand can get get to it, perhaps while on its way to the
manual trim control (mine will be next to the manual trim wheel). Removal of
power from the existing circuit would require the pilot to locate and open the
trim circuit breaker while also fighting the trim forces, and countering the
uncommanded trim in some way (e.g. restrain the manual trim control or holding
opposite direction trim command with the switch).
Does the trim servo connect to the trim system in a way that allows the servo input
to be manually overriden; meaning a slip feature that would allow holding
the manual trim input against servo motion? Perhaps the servo itself has this
feature?
These system safety measures may all be unnecessary on the class of airplane you're
building. I advise you to consider what sort of trim induced control forces
you might expect at the speeds and configuration combinations of the airplane,
and then look to see how quickly the electric system might get you into trouble;
rate of trim, range of trim, etc. The airplane I will build is noted
for trim sensitivity at cruise speeds so I'll have at least two trim speeds (slow
for flaps up, faster for flaps down). There are systems that allow continuously
variable speeds as well, typically based on airspeed.
I've seen some all-electric trim systems incorporate a direction reversal switch
that would allow a measure of control redundancy should a single direction fail.
Well done on the wiring diagrams!
John
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=500724#500724
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