SAWE Report - Cal Poly San Luis Obispo

This leads us to believe that the area required maintaining static stability is not the driving factor
in the size of the horizontal. Control power required to rotate the aircraft, dynamic
considerations, and high angle of attack recovery will most likely drive this size.
A similar study was conducted on the vertical stabilizer to see what area would required for
varying cant angles to maintain 0.001 (1/degree) lateral weathercock stability. This is illustrated
in Figure 10.3.
Figure 10.3 - Vertical Area Required for Static Stability with Cant Angle
From Figure 6.3 it can be seen that at 30°, 165 ft 2 of vertical area is required to maintain 0.001
(1/degree) of lateral weathercock stability. Although the 30° cant angle on the verticals was
initially selected to match the bottom fuselage facets for RCS considerations, lowering that angle
to 20° would allow other advantages. Shallower cant angles are easier to manufacture, require
less structure, weigh less, and have less coupling with pitch modes. For these reasons, the impact
on RCS was investigated for the 20° cant angle as well as the pitch coupling term for rudder
deflection, C
δ
.
m r
The RCS code was run on two aircraft configurations. The same wing, fuselage, and horizontal
were modeled with the vertical planforms mounted at both 20° and 30°. The results of that study
are shown as Figure 10.4.
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