Trim Killer Switch

[Tom Maxwell]

I didn't want hi-jack a previous thread so I am starting this one with regards to trim killer switches. The previous post talked about using closed loop servos systems to position the trim tab and a concern came up about a run-a-way condition. Mr. Adamson indicates he installed a "Trim Killer" switch to disable the servos circuits in the the event of a run-a-way condition.

My question is, has anyone ever had the need to kill a trim circuit because of a run-a-way condition? My other question is, whether or not it is even practical to attempt to kill the servo circuits in the event of a run-a-way condition?

My thinking is that unless the servo is unimagineably slow, before a run-a-way condition can be noticed, diagnosed, and then acted upon, the trim tab is going to be at its mechanical stop anyway. So a kill switch may help prevent an overheat condition (presumably a fuse or breaker will do the same thing) but my feeble mind is thinking that counting on a killer switch to stop the tab before it reaches a stop will probably be futile.

Has anyone tested this or had to depend on a killer switch in a real life situation?

[Ironflight]

Actually Tom, the elevator trim servo is unimaginably slow.....If you are hand flying, I am pretty sure you'd notice the out-of-trim condition long before it got to the hard stop. That said, I Do have a very effective kill switch - it's called the circuit breaker, and it even has a red ring around it so I can find it in a hurry.

Paul

[L.Adamson]

My trim killer switch, actually labled "trim disable" serves several functions. Power goes from the fuse buss, directly to the switch, and then to a sperate aileron & elevator panel mounted circuit breaker.

The trim servos are not that fast; even without being speed regulated. I think you'd feel a runaway trim condition quicker than a servo going stop to stop. But.... I have not actually tried. The switch is surrounded in red, and quick and easy to get to. The circuit breakers are on the right side of the 6A's panel, and a servo could easily make it to the stop, by the time you read what was what on the different breakers, and pulled them.

The second function of the trim disable switch, is if I don't like what a pilot in the right seat is doing with my trim.

And last, my panel reminds me of a T-37 trainer, but much better looking! Just a whole lot of guages, knobs & switches to make us look smart. In fact, I get lots of comments on how good it looks, but I'd prefer "glass" these days, instead of the six pac.

IMO, since my plane is fully set up for a right side pilot, including brakes, I believe that right sider would appreciate full trim functions also. I spent quite a few hours in the right side of a 9A. I had no right side brakes, and it was somewhat inconvienent.

L.Adamson

[Vern]

Because I used fuse blocks behind the panel i.a.w. Electric Bob, I put a kill switch on the panel for both trim and autopilot since I cannot pull a cb as with many other aircraft.

On my 6A, a runaway trim would be very controllable in flight.

[mgomez]

While I'm not yet at this stage, my schematics show this:

A button on the Infinity Aerospace joystick, at the base of the stick, will disconnect the A/P and the trim. That way, if the airplane does anything untoward, one button will kill whatever it is. The fact that it's on the stick grip is deliberate: my hand will jump to the stick of its own volition if I notice the airplane doing anything odd.