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Schu's panel and trim system.

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  • Schu's panel and trim system.

    In another thread I hijacked and posted a picture of my panel, so I'll put more information here.

    Trim system:

    I always thought that the Bearhawk Trim system was a little too sensitive and I didn't care how it servoed specially when flying at aft CGs. I also wanted electric trim because it's pretty neat. Many build a tray in the back and have a Ray Allen servo drive the trim torque tube in the H-stab, but there are many on the forum that recommend against that because the trim system is so powerful that runway trim can be very dangerous, and one person even mentioned losing a close friend to a run away trim crash.

    My solution is to put the trim servos directly in the elevator. This solves a number of problems. No more servoing trim system, I have two servos in case one fails, and the trim system can be made however sensitive I want by simply speeding up or slowing down the servos. I have built upon this idea and am in the middle of developing a custom trim controller that will control the servos as well as made a backup system that when selected doesn't pass go or collect $200 it immediately puts 12VDC on the servos. My trim controller has the ability to know the position of both servos because of the linear resistor built into the servos. This gives me the ability to monitor if one of the servos failed and there is a disagreement in reported position and it also gives me a 3rd button on my stick to drive both servos to neutral. Another feature is the overhead trim wheel is retained, but there is no mechanical linkage, it's just a rotary encoder that tells the controller to move the trim.

    Given that I installed a garmin G3X with auto pilot servos, I can have the trim servo output from that operate the trim controller which means that the autopilot can trim the airplane which is nice because the little servos don't need to fight with the stick, and AP cancel will hand me a trimmed airplane.

    I needed a way for the trim controller to tell me if there is an issue, so I'm using a discrete input on the engine monitor to detect trim fault (simply pulling a pin low) and then raise a master warning and "trim fault"

    Panel:

    The panel was cnc laser cut at sendcutsend.com out of .063 aluminum and has everything perfectly lined up. Because I have a cad drawing of the panel I was able to have aerographics make me a vinyl sticker with the labeling which I applied to the panel.

    You may notice that there aren't that many breakers. This is because my design philosophy is to only use breakers for things I would reasonably want to troubleshoot in flight, everything else is in a fuse which is on the bottom of the panel where the brake line under the horizontal tube is.

    My airplane has two completely independent electrical systems. No bus ties, no diodes, there is a main system with 60A alternator and EXT900 battery and an aux system with 8A gear driven alternator and a small ETX104 battery. My critical avionics and electric ignition have dual (diode or'd) inputs. This means that whatever system has the higher voltage is the one that is used. Simply turning the voltage regulator down on the smaller alternator is enough to make this all work. This also means I have multiple wires and fuses powering anything critical and a short on one system can't cause an outage on the other.

    I'm explaining the electrical system because it ties into the switch layout. The switches on the left side are things I typically only operate during startup/shutdown and switches in the middle I may operate on the ground or in flight.

    Startup Sequence:

    You may notice that the order of switches are the order of use. Master on connects the main and starter contactor to the main battery and powers the main bus. Aux on connects the aux bus to the aux battery which powers on my critical avionics while they are completely isolated and allows me to see oil pressure and temps. Ignition 1 and 2 connects my ignition system to the main bus. Now we start with the start switch. Then we turn on the aux alternator which starts charging the secondary battery, then the avionics master which swings all of the avionics over to the main bus, then we have ignition test which shuts off the top or bottom ignition system.

    This proves that the aux bus works, provides instrumentation at startup, and isolates electronics until alternators are stable. Shutdown sequence is the opposite except you pull lean instead of start.

    The only real exception here is the boost pump, which I placed next to the throttle to ensure it's easy to reach.

    Here are pictures of the servo blisters and mounts along with the panel and other systems.
    Last edited by schu; 12-31-2022, 04:53 PM.

  • #2
    I have a question regarding your decision to integrate your trim system into the G3X. As I understand it the G3X will trim to reduce load on the autopilot servos. I'm curious if the trim will be continuously hunting. Obviously the trim units will see more use from this.
    I worry about this after dealing with a bonanza that had auto pitch controll for the electric prop. The owner advised me not to use the auto trim as the constant hunting wore out motors. Requiring frequent replacements.
    I'm just curious if this should be a concern. And thanks for sharing.

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    • #3
      I guess you'll need a slightly heavier counterbalance, with the servo inside the elevator instead of inside the stabiliser. Do you think the whole assembly weighs much?

      Very nice panel.
      Once you're up and flying and operating the controls "unconsciously", you may like some coloured heat shrink on those switches might help you find the right switch quickly and easily, without consciously thinking about which one is the right one. Just thinking out loud - obviously it's a very personal choice!

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