According to the RK Zero instructions, the pushrods for rudder and elevator are connected with yellow tubing, instead of black shrink tubing. Do I shrink the yellow tubing too? Why yellow in one place, and black in the other?

From : Don Stackhouse

No, they're not connected with yellow tubing, they go THROUGH yellow tubing. The yellow tubing acts as support bearings for the pushrod to slide in (which is why you need to be very careful not to get glue inside the yellow tubing!). The yellow tubing supports the pushrod so it doesn't flex and buckle.

Where there needs to be a connection or an adjustment between two pieces of wire, such as between the wire servo coupler and a pushrod, or between the front and back sections of the rudder pushrod, we use the black heat-shrink tubing. Overlap the wires by about 1/2" with a 1/2" long piece of shrink tubing around the joint, then shrink the black tubing to make the connection. It will still be possible to slide the wires inside the tubing to make adjustments, but there should be enough friction in the joint to safely fly it. Fly it once, then land and set the ailerons and elevator so the plane flies level at cruise power (usually about the 30% to 40% throttle position on the A6M2). Center the rudder after adjusting the ailerons for each of these test flights.

Now, fly it again and do some turns in both directions, noting whether the nose tends to hang to the outside of the turn in turns in one direction, and points to the inside of the turn in the other direction. Land and adjust the rudder as necessary till the plane turns the same in both directions.

Once the plane is trimmed to fly level with the stick centered, and has the yaw (rudder) trim set so that it turns the same in both directions, lock the adjustments by wicking a tiny drop of thin cyanoacrylate into each of the black heat-shrink tubing sleeves.

If at some time in the future you need to change one of the adjustments, just get two pairs of small pliers, grab the wires on both ends of the shrink tube sleeve, and twist the wires (that is, rotate them around their axis, do not try to bend a kink into them). You will feel a little pop as the glue joint inside the black tubing breaks loose. Make the adjustment, test fly it (the broken C/A joint will usually still have enough friction to allow this), and then lock it down again by wicking in a fresh drop of thin C/A. Once again, be careful not to get any C/A inside the yellow tubes, it would lock up your controls!

The final adjustment is the tailwheel. The tailwheel on the A6M Zero is connected directly to the rudder, so to adjust the tailwheel you simply bend/twist the strut as required (on some of the other RK Series models the tailwheel has its own pushrod, which is strapped to the side of the rudder pushrod by a black tubing sleeve). Adjust the tailwheel so the model tracks straight when it rolls on the ground.

Don Stackhouse
DJ Aerotech