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How many servos have been damaged by the excesive side forces put on them by the tailwheels of our larger and heavier 1/4 scale aircraft? Here is a solution to the problem. While developing my 1/4 scale Stearman PT-17, I found I wanted more scale realism as I progressed through the design stages. One of the weaker areas, I felt, was the tailwheel control mechanism. As I studied the tailwheel mechanism as illustrated in the maintenance manual for the full scale aircraft, I decided to try and simulate the full scale action.
After much head scratching and cutting and trying, I hit on it. It is very simple and very effective, and can be built without the need of an elaborate machine shop. The control cables are installed in the usual way allowing for the pivoting of the assembly during the shock travel. The control horn is soldered to a wheel collar that has a shallow dimple drilled in it. This assembly is then slid on to the tailwheel post against another wheel collar that is locked to the post by its set screw. This collar has a couple of allen type set screws in it, which are adjusted to mate with the dimple in the horn assembly. Tension is applied to the mating pieces by a spring and another collar above the control horn on the wailwheel post. The shock absorber spring tension is also adjusted by repositioning a wheel collar, after the model is completed.
Maximum rudder throw is required to maintain ground
control as the steering mechanism unlocks on occasional sharp turns.
I have been using this set up, modified to suit my SR9, and it is to me,
a very delightful experience in ground handling control. It forces you
to use the rudder very much like on the real thing. The accompanying
drawing is from my Stearman plans showing how to make it. It is also
available from R&L Enterprises, 2055 Baseline Road, Roseville, CA
95678 for $35.00 P/PD. As time permits, all of my 1/4 scale designs
will be updated to this concept.