SonexBuilders.net

Hi all,

I am building a subsonex with the aeroconversions trim system and trying to integrate the automatic pitch trim control of my autopilot in. I had a few ideas for how to do this but was wondering if anyone had integrated an electric trim system with the aeroconversions trim system (or had a better trim system for the Y tail).

I was thinking of either using a stepper motor to drive the actual aeroconversions knob shaft from behind (so it could be overridden) or mounting the spring to a plate that could be moved by an RAC electric trim shaft (although I'm not sure they have enough throw).

Thoughts? Suggestions?

Thanks!
Tommy.

Tommy,
I've never heard of someone electrically driving an Aeroconversions trim but I think some similar home-rolled solutions have been done. No reason it wouldn't work.

I didn't want to take up panel space with the big red knob so I elected to use a linear actuator with a 4 inch throw under my seat instead. The springs are still installed on the stick as called out in the plans. I installed an extra helper spring for up trim. Some calibration is required of spring tension. Flight testing will determine that. The cable was cut and routed from the stick attach point to the actuator mounted side to side under the passenger side of the seat. so far it hasn't failed. I have a momentary switch on my panel for trim mainly for cost savings but a hat switch on the stick is certainly a better idea. Linear actuators are common place and easily found on the internet. Get the strongest load capacity for the money you want to spend. Keep weight fit and form in mind when shopping. The 4 inch throw seems to work fine for me.

any build pictures of that setup?

Tommy, I'm working on doing that now and have some parts coming this week. I'll post some pics as I get it worked out.

Ed Grasso

lakespookie wrote:any build pictures of that setup?

This is the only picture I could find and probably doesn't include the detail you were looking for. You can see the short loop of the outer sheath of the control cable. Bare cable routed to stick and attach point of linear actuator. Cable is held rigidly taut by force of springs. Actuator is mounted to rear spar carry through. Pull cable to neutral trim/stick center with actuator in center position and attach. I can pull my seat back off if you want a better picture of the actuator

I swapped out the mechanical trim system for RayAllen servos (aileron and elevator) built into the control surfaces. They are controlled by a hat switch on my control stick.

There is another outfit (name escapes me) that does a similar thing but uses RC type servos to an A/P.

This YouTube shows one way to do it. https://www.youtube.com/watch?v=c5y7g0naF-s
I copied this in my Waiex. Put actuator in different location, principle the same.

I like the idea of using a ray allen in the seat pan loacation if you can easily remove the seat pan that would be great otherwise no worries. you gave me a basic idea of how to do it.

That video was great thanks everyone.

Fore those looking for a quick way to calculate the necessary reduction pivot to hook a linear actuator up to a ray allen position sensor for a trim system like the one in the video and described here this tool is very handy https://www.omnicalculator.com/math/arc-length

you can either pick a fixed angle for example 90 degrees and then use the cord length to know how far from your pivot you need to make the pivot bar and and then pick the displacement cord length to know where to set your ray allen position sensor attachment point.

Or you can use the cord length of the actuator + the desired length of your pivot arm to determing the angle that is needed for that throw, just make sure its under like 160 degrees so you dont go past the rotational limit. and then input the smaller cord length for the position sensor to determine position.

Personally i think option one is better because it results in a more well defined sweep range at the expense of length of the pivot, although if you are constrained by space option 2 will allow you to make for a shorter length of pivot at the cost of more angle, but you wont have to guess at the cord length conversions. i would also pad the chord length so you never exceed the length of throw of the position sensor