[NSRCA-discussion] Weather Vane

[tocdon at netscape.net]

The physical effect of weather vaning, as best explained in a vertical upline (most profound and easily seen example).

Measure the distance front of the aircraft to the center of gravity,?subtract the difference from that point to the center of side area lift (fuselage side lift), times velocity squared,?divided by the co-tangent of the angle from vertical upline (this can be calulated by the second differential equation at airspeed "a", for the horizontal component of velocity"b", during a verical up-line of length "c"- which approaches zero in a perfectly wind corrected crab angle- at least at any given instant)?This is used to?calculate?side- intertial force at each discrete point in time "t"?(otherwise the same lift-inertial phenomenon we feel during the dreaded?"downwind turn").? So the corrective input becomes a parabolic arc (charted on a graph with the rudder input being the vertical axis and?inverse of velocity on the horizontal axis) for the rudder stick to counteract the lift (minus x-axis (side force)?gravitational pull as the aircraft slows), such as that at the top of a stall turn, just before the pivot.

In other words, differing rudder inputs are needed?to maintain the correct crab angle during each maneuver.? Some planes that have a center of lift far behind the center of gravity, requiring more rudder correction to keep the plane from weather vaning too much.? Thats why you see some weather-vaning pattern designs moving the canopy forward, to bring the two closer together (but ideally not at the same point) and therefore make the plane feel as though it is?self-correcting in a cross wind.

All the above is referenced with respect to where?the judges (are)?firmly planted.

All the best,

Don





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