SonexBuilders.net

I am thinking about an alternative to the Sonex Dial-a-Trim for pitch trim in my Xenos. It is the "pull on the spring attached to the elevator pushrod" type trim. I guess this is the standard set up for the XNS and YX. I am thinking of using a vernier cable which has 3-3/8" travel. Big movements can be made by pushing in the center button and small movements done by turning the knob. Has anybody tried this? Is there some obvious reason why this would not work? I am somewhat concerned about the bend radius of the vernier cable. There are used vernier cables available so the low cost, small mount space, and ability to make fast, big movements along with fine adjustments seems attractive.

Rick Caldwell
Xenos 0057

Have you considered leverage? The Sonex has light stick forces, but I imagine the trim spring needs to apply around 10lbs of force. When you push the button, that force will be released instantly, probably causing sudden pitch changes before you can react. You might find that you can only use the vernier mode, but then might wish the knob were bigger like the dial-a-trim, especially if the turn ratio is less.

I made a trim wheel much like a Cessna. I would post a picture but I'm getting a message that the pic is too wide by 31 pixels!!!
BV

Pitch Trim Cable

On both my RV-6 and RV-7 I used the standard Van's manual vernier trim cable. It works very well. The RV's are quite sensitive to very small trim adjustments and so the "turning of the trim knob" worked excellent for slight trim corrections at cruise. Van's recommends removing the center push button so as not to induce drastic trim changes. I never removed my push button but I never used it either.........that would be a much too aggressive change of trim "in flight".

In regard to the 180 degree bend in the cabin to reverse direction......it was not a problem with friction although this is a high quality cable. If you wish to go to this "Van's trim system" I would highly recommend you buy a "Van's RV-6 or 7" trim cable from Van's...we know it works. As I recall it was 167" long.

Gordon.......Onex.....Hummel 2400

Gordon,

Do you think that would work on a Waiex? They don't typically have trim tabs and instead pull directly on the elevator pushrod. I expect the forces will be much higher than controlling a tab. I imagine the dial-a-trim exists because standard controls cannot handle the forces.

Trim Cable ......Pitch

Chris.........I am not familiar with the Waiex control system. If it is like the other Sonex and Onex airplanes the Sonex trim knob feeds tension in either direction to the elevator push rod. A vernier cable from Aircraft Spruce of the proper length would do the same thing.........the Van's trim cable would be MUCH too long for that application. The Van's cable is meant to go all the way back to the elevator trim tab......about 167" as I recall.

Of note......Van's uses a "double spring tension system" .......similar to the Sonex elevator pitch control......for aileron trim. The springs are much smaller and a short lever is mounted between the seats to trim for fuel used from either wing tank during flight. It is simple, cheap and works very well.

Gordon........Onex........Hummel 2400