Rob, just to carry on the line ---- There are so many ways to skin the
cat.
I love the Walnut wheeled, Reichel geared, spring driven pitch trim
system in my 320. I know how many tangential pushes to give it to retrim
after flight regime changes. I can measure the humidity by the resistance
in moving the wheel (higher humidity, walnut swells, higher resistance). I
love to caress the fine natural finish of the walnut for each trim
adjustment and it looks nice, too. Oh, I can always override the
springs should I runaway trim it with a forearm muscle tic or mental lapse (ever
more frequent these days).
The rudder and aileron trims are tabless, internal servo operated,
spring driven systems (similar to the aileron spring cartridge in the modern
Cirrus) and runaway trim means overcoming some wee spring after I have swallowed
a backup can of organically grown spinach.
I am intrigued to read about the complex systems used to forestall
electrical gremlins causing flight control problems - How about carrying
pre-calibrated bungees to be attached to eyelets on the stick to overcome
runaway trim (as listed on the emergency checklist). They could be
color coded - red for right, lilac for left, umber for up, etc.
Grayhawk
Rob, this might not make it to the LML since I am in mail
server limbo. If it doesn't show up there, perhaps you could re-post
it if you are not embarassed.
In a message dated 6/27/2008 6:31:41 P.M. Central Daylight Time,
rwolf99@aol.com writes:
I read
the description of a pitch trim that failed to opeate. But the logical
step from the nuisance "it doesn't move when I want it to" to the
hazardous "it moves when I don't want it to" isn't quite so logical.
Failing one way just isn't as likely as failing the other way.
1)
Why would the motor fail to run? It's either not getting any power, or
the motor is broken. This can happen due to a wire connection failue
("broken wire") anywhere in the chain from the power bus to the ground.
Count the connections -- there could be as many as a dozen or more. A
pin-socket connector has three junctions -- the wire to the pin, the pin to
the socket, and the socket to the wire. The junction between the wire
and the switch is another, and so forth. A continuity break anywhere in
the loop will cause the trim to not operate.
2) Why would the
motor run uncommanded? Either the switch has failed (mechanically broken
so that the contacts touch) or it is welded shut. There's really no
other way for it to happen. We don't really put enough power through the
switch to weld it, so it's really only a physically broken switch that would
cause it. Yeah, it can happen, but I wouldn't lose sleep over it.
Check it during the preflight and the likelihood of it failing in the next
hour is pretty small.
- Rob Wolf