Trim System (3)

3 hours

Now that the tail is coming together I felt like seeing how this pitch trim system is supposed to work.  With the Y-tail, it would be complicated to use trim tabs, so the system uses two springs instead to just apply pressure to the elevator pushrod.  One spring is fixed, and pulls the stick forward, and the other one is adjustable and pulls the stick aft.

The aft spring is attached to the pushrod using this bracket and two hose clamps. 

I spent about 45 minutes making this thing, then realized it was supposed to be 1/8" thick, and I had used 1/4" aluminum.  I threw it away and re-made it out of 1/8" bar stock, which went a lot faster than the first one.

The other end of the aft spring attaches to the horizontal member just behind the seat (which I can't remember the name for... aft fuselage cross-tie?).  The plans show the end of the spring hooked through the top of this C-channel, but when I put the spring there it rubbed on the flap drive tube.

Instead of that, I decided to mount the forward end of the spring to the larger member just forward of that.  It has this extra duplicate hole next to the hole for the elevator pushrod that doesn't do anything, so that seemed like a good spot.

However, the force of the spring tension flexed the sheet metal a little bit there, which I didn't like, so I made a quick little reinforcement plate and riveted it in place.  I think this will do it.

At the forward end, there's another spring attached to the stick that pulls it the opposite direction.  This red bracket mounts to the back side of the instrument panel with a knob on the front.  Turning the knob clockwise shortens a cable, which increases the tension on the forward spring and effectively gives you nose-up trim.

This is full nose-down:

This is full nose-up.  The instructions say that you should be able to trim the ruddervators full up on the ground with the trim system, but this is as far as mine goes.  I will need to shorten this spring or buy a shorter one to increase the tension.  I'll work on that some more later!