"Exponential" differential via mechanics
David J. Gall
Bob,
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Larry Hamm's suggestion is good but it requires significant angular displacement of the belcrank to get any substantial differential. Consider this alternative: Make your tailcone belcrank in the shape of the letter 'K' with the angled legs pointing forward. The rudder pedal cables connect to the angled legs, but the rudder and tailwheel cables connect to the straight leg. This gives a differential since the angular displacement of the belcrank is increased for any given linear displacement of the cable the more the angled belcrank leg moves forward in its arc [dtheta/dx goes as 1/cos(theta)]. Similarly, move the cable attachment points on the rudder pedals aft of the plane of the rudder pedal pivot so that as the rudder pedal is pressed forward, the attachment point arm becomes more perpendicular to the line of travel of the cable. Either of these geometries will induce a differential movement in the belcrank; both together will give even more differential. The resulting angular differential can be amplified or reduced by varying the ratio between the length of the angled legs of the belcrank and the effective lengths of the rudder pedal arms (and the desired throw of the pedals forward of neutral). The ratio of the length of the angled legs of the belcrank to the straight legs and, finally, to the length of the rudder and tailwheel belhorns will control the total angle of the rudder and tailwheel deflections with rudder pedal displacement. David J. Gall P.S. Larry's suggestion does not have to be fabricated as an oval or ellipse; a simple diamond or even a rectangle will work.
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