/So say your coming in to land and give a little up trim
/as you slow... You lift your finger off of the trim switch
/but you keep hearing the tone.... You know you have
/trouble instantly.... Pull the trim C/B and the emergency
/is over....
I had real heartburn over most of the warning and/or
emergency proceedures wrapped around trim systems.
It seems that the bigger the airplane, the worse it
gets. But I really object to the idea that a pilot
is expected to take his eyes from the runway ahead,
panel in front and start searching for a breaker to
pull . . . see guys, that's why I HIDE 'EM! If you
don't put them in the cockpit, then you have to do a
BETTER job of handling the situation.
/Maybe we could get Bob N. to design us an nice system that
/would provide a tone that would not make us crazy and
/help warn us of possible uncommanded trim motion....
My favorite trim control system for little airplanes
replaces the single, two-pole, double-throw, spring-
loaded, center-off switch with two single pole mechanisms.
In some of the King-Air size airplanes, the pilot's
thumb has to actuate two, side-by-side switches
simultaneously. You have to jam or break TWO switches
to get uncommanded motion. It's also very easy to
check in pre-flight. An alternative, is to add a second,
push button in series with trim power. You have to squeeze
the button to apply power and operate the trim switch
simultaneously to get motion. With either of these two
methods, the reactiion to undesired trim response
requires nothing more than to reverse the action in
your fingers that originally precipitated the fault.
You don't have to look anywhere or do anything except
RELAX.
Some of my designs where autopilots are part of the
equipment, I include a master disconnect system for
ALL electically driven flight surfaces. A latching
relay in series with dc power to all electric flight
controls is wired in series with a normally-
closed, wheel master disconnect button. In this case, any
uncommanded operation of flight surfaces is reacted
to in the most natural of responses . . . grab the
wheel. This is where the pilot works to (1) override
the uncommanded motion of flight controls and (2)
disconnects all potential offending devices . . .
again without so much as a glance from his most important
duty of being a pilot.
This same system has another feature. If electrical system
power goes down for any reason, the relay drops out and
makes sure that all electrically driven flght surfaces
remain disabled when power returns. Many autopilots have this
feature built in . . . . no sense presenting multiple
surprises to the pilot when power comes back on.
It doesn't have to be complicated.
Regards,
Bob . . .
AeroElectric Connection
////
(o o)
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