and occurs at a higher speed. [Figure 5-15] With ballast, it
would be more difficult to work small, weak thermals. The
best glide ratio is the same, but it occurs at a higher speed. In
addition, the sink rate at higher speeds is lower with ballast.
From the polar, then, ballast should be used under stronger
thermal conditions for better speed between thermals. Note
that the stall speed is higher with ballast as well.
Flaps with a negative setting as opposed to a 0 degree setting
during cruise also reduce the sink rate at higher speeds, as
shown in the polar. [Figure 5-16] Therefore, when cruising at
or above 70 knots, a –8° flap setting would be advantageous
for this glider. The polar with flaps set at –8° does not extend
to speeds lower than 70 knots since the negative flap setting
loses its advantage there.
Wingtip extensions also alter the polar, as shown in
Figure 5-17. The illustration shows that the additional
3 meters of wingspan is advantageous at all speeds. In
some gliders, the low-speed performance is better with the
tip extensions, while high-speed performance is slightly
diminished by comparison.