THAT WAS A TEST.... (yeah...THATs the ticket!)..... That was only a TEST. If an ACTUAL example had existed then I would have posted a picture..... and caught my error. Doh!Joe Moilanen wrote:Wouldn't "positive" castor mean (king-pin/bolt head AFT) instead of FWD? The bolt would angle forward at it's bottom end if the castor was positive?GAHorn wrote:The “steerable” tailwheels’ steerability depends on several factors, not to exclude:
1- Weight & Bal ...the amount of weight on the tailwheel can vary quite a bit, not only from plane to plane but from flight to flight.
2- Tailwheel MainSpring-Angle: The caster affects the ability of the tailwheel to rotate or steer because a “positive” caster (king-pin/bolt head FWD) will require the tailwheel to actually LIFT the weight upon the tail landing gear. The “free-space” of reduced-effort is a narrow band, ...It is so much easier to remain within the narrow-angle, the wheel constantly “searches” for that band....and that allows “shimmy”. Negative caster (king-pin/bolt head AFT) will allow better rudder-only steering because it does not require the tailwheel to lift the weight of the airplane to deflect from side-to-side. This forces the wheel to remain within the detents ...so the steering mechanism remains engaged. This keep the turntable/friction-discs clutched...and reduces the tendency to “shimmy”. This might seem counter-intuitive ....nonetheless, incorrect caster is what primarily causes “shimmy”.
The on-line video (produced by one of the tailwheel mfr reps) of how to adjust the tailwheel steering by raising the tailwheel off the ground in the hangar.... is simply wrong, sad to say. They should know better, but it’s an example of how misunderstood this subject is.
Joe
4518C
YES!.. POSITIVE CASTER is when a line is drawn thru the pivot and the bottom of the line is FORWARD of the contact (footprint) of the wheel. I mistakenly used the King-bolt NUT when describing the geometry. THANK YOU JOE! For catching my mistake. I will edit my earlier post to draw proper attention to the issue. Here’s a “pic” of Positive/Neutral/Negative CASTER: