For those of you who intend to construct the elliptical tail surfaces for the Z-21, I recommend this simple solution for achieving the suggested increase in area in the upper hemisphere of approximately 10%, equivalent to about 2" in overall height. The vertical tail surfaces on Rupert's aeroplane were based on the standard Z-1 S vertical tail, cut down in height to suit the shallower sternpost height of the Z-21. This is not the best solution and results in a very slender ellipse in side elevation, and also requires a slimming of the finpost at the lower end to accommodate the slender sternpost of the basic Z-21.
I recommend the following, which will result in an identical (ie. deeper) fin and rudder to that of the unmodified Z-1S and R
Using the Z-1 S fin rudder drgs. add 2" in depth to the forward vertical fin member, ie. 2" lower at the bottom, and build an additional base rib at this location. Note this is an additional rib and will not affect the existing 'base rib' which should remain in its original position as drawn. Skin with 1.0 mm plywood between the 'new' base rib and the 'old' base rib, each side of the fin. Include the 'nose' profile of the new base rib to follow the tailplane leading edge profile, as drawn. Move the 1/4" dia. attachment bolt for the finpost down 3/4" from its position on the Stummeflitzer sternpost, to suit the location for the Z-21, and adjust the internal blocks and bracketry to suit.
Retain the finpost and rudder post dimensions and widths as drawn on the Stummel sheets. This is all that's necessary other than to make a slightly bigger root block at the base of the forward vertical in the fin, to move the forward fin fitting forward to connect with the tailplane spar fitting.
I attach a picture of the deeper fin and rudder shape as standard on the Stummels, and a modified photograph of a Stummelfin to demonstrate the above diagramatically.
Regards,
Lynn |
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