Electric Trim Switch Question

[jmbueller]

I've recently sold my 7 and purchased a 4 that I'm doing some upgrades to. I fly with a pilot friend fairly often, and am adding a push to talk button in the rear. I was toying with the idea of adding an elevator trim switch back there too. Neither of these things will be on the stick (probably put them near the rear throttle control), as I want to keep that very easily removable.

My question is what is involved in adding the duplicate trim switch? I don't want the front and rear to interfere with each other. Ideally, I'd like a selector switch to choose which seat gets to use their trim switch.

Any advice would be appreciated.

 

[BobTurner]

I've recently sold my 7 and purchased a 4 that I'm doing some upgrades to. I fly with a pilot friend fairly often, and am adding a push to talk button in the rear. I was toying with the idea of adding an elevator trim switch back there too. Neither of these things will be on the stick (probably put them near the rear throttle control), as I want to keep that very easily removable.

My question is what is involved in adding the duplicate trim switch? I don't want the front and rear to interfere with each other. Ideally, I'd like a selector switch to choose which seat gets to use their trim switch.

Any advice would be appreciated.

It is an excellent idea to add a selector switch. Should aft and front seat simultaneously select trim up for one and trim down for the other, you’ll pop the CB. I also know of a passenger who rested a book on a trim switch, resulting in an abnormally high nose up. While you’re at it, note the current required for the trim motor and the current capacity of the switch(es). You may need to add relays to carry the load.

 

[JDA_BTR]

I wired the copilot stick with all the same switches as the pilot stick. I ran the common ground wire for all of them to a switch on the panel to enable/disable the copilot stick. Works perfectly. Depending on your setup you might want some clever diode arrangements or relays, but for me with the G3X systems it was simple.

 

[AlpineYoda]

I have four way trim on a hat switch on each of my sticks - no fancy diodes or anything. I'm just trusting that only one person at a time will have a hand on a stick, and therefore only one person at a time will have a thumb on the hat. I guess it is possible that someone could bump the switch exactly when the other person is flying and trimming, but that's a heck of a coincidence. If your trim switch is mounted elsewhere, the question is why would someone else touch it? If it is mounted in a place easy to hit by accident, that might be a bad idea in the first place. A second pilot who is the pilot flying could bump it and not know it, if it is that easy to do so, and put the plane dangerously out of trim. With a selector switch, you could be unable to quickly correct the error, once it is identified. On the other hand, if it is somewhere that only the pilot flying will touch it, like my hat switch, the chances that the other person trims in the opposite direction are very low.

If you use a diode, imagine that the other person somehow hits the trim switch wherever you located it and runs it to full limit (a human induced runaway trim). Their action would trigger the diode and lock you out from running it in the other direction until they took pressure off the switch that they may not know they are pressing. If a CB trips when the switch is pressed in opposite directions, at least that cuts out the runaway trim before it goes all the way to the limit.

How many times do you trim during a flight? I set mine for takeoff during runup, then a few quick bursts at different cruise speeds (I just flick mine when it needs it - a quarter second bump), then a longer trim (half a second?) as I slow to pattern speeds. That's about it. Maybe 5-10 seconds total run time during a complete flight. Do you need to add complexity (and points of failure) in switches and diodes for 5-10 seconds of potential conflict?

 

[Mich48041]

This circuit uses no relays. The pilot can not reverse what the copilot is doing, but the pilot can stop the trim motor by pressing his own opposite direction switch.

 

[Tankerpilot75]

I recommend you install the Pat Hatch trim relay board with a “coolie hat” trim switch on new Tosten military style stick grips. Running the wires down through the stick and using either a dsub pin or molex connection at the base of the stick so you can remove it when you want. The trim relay board will prevent the rear pilot from canceling out your trim movement and vise-versa.

https://phaviation.com/products/product-category/the-ultimate-trb-hub/. This control hub is great and facilitates a lot of functions.

I installed this when I converted from manual to electric trim and have loved it ever since. On my sticks I’ve got PPT, Trim (elevator and aileron), comm 1&2 swap (CP side), freq swap (both sides), flaps (pilot side only), transponder ident, and A/P engage/disengage. Just about everything I need on the grips!