GlasairProject.com Elevator Trim Modification

New Style Elevator Trim Wheel:

When it came time to install the elevator control parts and think about a trim system, I found the GI design to be a source of complaints from pilots. I decided to install a newer style trim wheel. I wasn't sure how I was going to attach this assembly to the elevator, so I researched all the manual and electric trim systems built for the Glasair. I found that they all relied on the same connection points at the elevator counter weight arm.

I also discovered what I believe to be a problem that should be addressed as it relates to the GI elevator. These trim systems use springs to keep tension on the cables. This tension is focused on pulling the elevator counterweight arm forward with as much as 70lbs. of tension. I also read that a lot of GI owners had experienced a high rate of elevator hinge wear. This all made perfect sense to me, so I set out to design a system that would retain the spring tension, but focus on something more durable than the elevator hinges.

The design I finally settled on uses a modified elevator control belcrank at the point where the front and rear elevator control rods connect. I built a new control belcrank with two additional holes just below the rear control rod mounting hole. This is where I connected the springs from the trim system. The spring that exits the rear of the control tunnel proceeds parallel to and just below the upper control rod to a pulley in the floor just ahead of the rear bulkhead. At that point the cable makes a full reversal and ends up in the center console attached to the trim wheel. The spring that connected to the front of the control horn is connected to a cable that goes directly into the trim wheel.

This design only places tension on the control belcrank when the stick is moved against the springs. To keep the springs from pulling their mounting bolts out of the aluminum belcrank, I used two stainless steel connecting plates linking the two screws on the inside of the belcrank. These plates come pre-made from Aircraft Spruce (p/n 05-02072)