Bungee Trim

What I did instead of fitting an aileron trim tab was to attach a lever to the spar between my knees which runs 2 nylon cords via small pulleys at either side then through the spar lightening holes and back to the bottom of the control yoke where the elevator cable attaches. There is 6" of light bungee cord on either side of the attachment point, slightly stretched. By moving the lever either one way or the other slight tension is applied to one bungee by stretching it and at the same time slackens the other side by an equal amount ( see attached rough drawing) This applies side force to the control yoke which means you can adjust the side forces to balance out any "heavy feel" right or left . The lever is pivoted at the bottom and on an arc up near the top, a series of indentation allow for a nodule ( in this case the tail of a rivet through the lever) to click into one of the indentations. It took an afternoon to make and cost around $5 to make. I hope you can make sense of the above and my toenail dipped in tar drawing. It was easy to make and really works well. If one side did break the lever can be moved to remove any tension on the other side, foolproof. The lever was made from the same steel strips sent with the wheel fairing (ZAC sent me 2 sets ) and bent slightly to have pressure against the arch with the dimple holes. I also added a couple of fiber washers on either side of the spar where it pivots to ensure it didn't scratch the spar. You may also have noticed that the point where the cable is attached to the lever is above the pivot point instead of below. This is so when moving the lever to the right it leans the yoke to the right and visa versa. The actual point of attachment on the lever is not critical, the higher up the lever, the further you have to move the lever to trim. Where I have it drawn is about where I have it and I rarely move the lever more than a couple of inches.

I bent the top of the lever out a bit so it falls easily to hand and because of the spar cap it is not even seen and I have never moved it accidentally. Incidentally, the tension I put on the short pieces of bungee was very small and the cord I used as cable is only marine nylon about 4mm. The pulleys are just small aluminum type. The 2 6" pieces of bungee attach to the point right at the bottom of the Yoke where the elevator cable attaches. The nylon cables attach to the bungee, not the point where the elevator attaches to the yoke. The nylon cable goes from there via the pulleys and back to the lever. With both sides going to the lever you are tensioning one a little while reducing tension on the other which halves the tension required when the yoke is centered. Increasing the tension will reduce the feel of the yoke. Make up a mock setup out of scrap on the workbench and you will see what I mean.

Baz

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