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Angier writes:
<< Before machining the bushings, I simply substituted the .063 stainless
pins for the 1/4" bolts on the bench and observed the same result.
Now, if the elevator is 100% mass balanced and the hinge is located on the
spar centerline, my twisted logic would lead me to think that one could
place the elevator in any position from in trail to 90deg up or down and
it would stay in that position. Doesn't seem to work that way though. What
do you think? >>
I think you need to use 1/4" bolts instead of the 0.063 pins. The reason
is that the center of rotation is the center of the pin (not the center of
the bearing). When the elevator is horizontal the center of rotation is
0.0925 above the center of the bearing. As the elevator rotates, the center
of rotation moves forward and aft as a function of the cosine of the angle,
making the assembly unstable. Imagine a big steel hoop with two rings 180
degrees apart. Now hang the hoop on a small bar. The assembly will want to
hang with the weights at the 12:00 and 6:00 positions because moment arm
of the 6:00 weight is now longer than the moment arm of the 12:00 weight.
Marv writes:
<<Once you've achieved a level of balance that logic
says is right, I'd go ahead and overbalance the counterweights by an ounce
or so. >>
Good advice!
<< The final result is going to be determined by the amount of filler,
primer and paint that will ultimately be applied and you're probably going
to have to adjust the end result slightly after all the finishing is completed.>>
You MUST recheck the balance after paint and finish.
<< If you really want to be anal about it, I suspect the proper
way to balance the elevators is to actually balance the entire "pitch control
system", as the addition of the pushrods, bobweight, control sticks, trim
system, and all their associated hardware are actually going to enter into
the picture when all is said and done.>>
True only to the extent that vertical accelerations of the tail should not
cause the elevator to deflect opposite the direction of acceleration (an
upward movement should NOT cause the elevator to deflect down, causing more
upward movement).
Regards
Brent Regan
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