I made the cowl flap torque tube out of 5/16 OD thick walled 4130 tube; in the center it was tapped and a coupler nut was made which uses two cotter pins to help transfer the load from one side to the other. I wanted to be able to split the torque tube for maintenance options in the future. The torque tube is supported by two 5/16 ID 4130 tubes welded into the exhaust hanger brackets. They have lube holes drilled into them. Two inch lugs convert the rotary motion of the torque tube into the linear opening and closing of the cowl flap. Pressed in oilite bushings are used to decrease friction and wear. Another lug will need to be welded on, but I plan on using a bellcrank higher up on the firewall and additional linkage but I'll wait till the other components are laid out prior to deciding on its location.
