Photo Description

Building a KIS Cruiser

Flap Modification


Bill Schertz, Dec, 2002

Individual Adjustment

After trial mounting the flaps on the wings, and adjusting them, I found that there was a discrepancy in the "zero" position. I.e. when the right flap is aligned with the jig, the left flap is slightly down.

I made two new nylon blocks with a maximum offset, and this still did not bring them into alignment as much as I would like. I was resigned to making a new torque tube, but last week we had a presentation by one of the chapter members who just finished an RV-8. He commented that he had to make a slight adjustment on one flap in order to correct a wing-heavy turning tendency. This solidified my resolve to modify the flap system to allow individual adjustment of the flaps, to help make the final plane fly straight without an add-on wedgie as done on Bill Grote’s Cruiser.

I removed the flap torque tube from the plane, and rechecked it on a flat surface. Sure enough, there is a slight misalignment – I would have sworn that I did it correctly a couple of years ago when making the torque tube, but here was the proof, somehow I had managed to get a slight offset. The offset was not enough to account for all the misalignment, by carefully using a vernier caliper, I determined that there are some tolerances to the thickness of the molded skins, that can either contribute to or subtract from any misalignment in the torque tube. In my case they added to the problem.

This is a photo of the "stock" flap torque tube, with the system designed for no independent adjustment. I found that there was room to move the bearing block to the right by ½", then slide the input arm to the right by ½" also.
This then allowed a second control arm to be positioned to the left of the original, and a second bearing block to be installed in the tunnel. The left bearing block does not wholly rest inside the tunnel, but it does sit under the seat. At this point the torque tube has NOT been cut, so the outside bearing blocks and continuous torque tube are used to align the inside bearing blocks.
Here I have removed the torque tube, and cut it in half, and installed a second input arm. The split arms will now allow individual adjustment of the flaps to correct any minor inbalances in the system.
Close up of the two arms, shown with only one of the two required bolts in place.
Next I have to modify the push rod to have two rod ends on it. I will post those pictures when done, however I am still rummaging for a short bit of ¾" x .035 tubing. More when it is done.