I'm not sure if there is an optimal dihedral
angle for sink rate, but the more angle the
unit has, the quicker it will transition and
start rotation, especially if the unit is heavi-
er than the rocket body. Try to make the
three blade angles the same, but if they are
a degree or two off, it doesn't seem to cause
major problems, unlike balance and pitch
differences.
While holding the central shaft side-
ways, make sure the blades are balanced.
Gravity will orient heavier blades down
to indicate which blades need to be light-
ened. You can sand the upper surface of the
blades to make fine adjustments, but you
may also have to add weight to the lighter
ones. This is also a good time to treat the
end grain of the blade tips with CA or ep-
oxy to prevent damage from the ejection
charge, since this process may unevenly
add weight. When the blades are balanced
the hub will not rotate on its own, no mat-
24 JANUARY/FEBRUARY 2020 SPORT ROCKETRY
Photo 10.
Secure Kevlar line around
engine and tape motor
and line in place.
Photo 9.
Kevlar shock line needs to
be straight with no twisting.
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