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and the wing moment from the carriage point of view. For
example, the CG hangs far below a wing weighing ⅛ of
the carriage weight. When the control bar is moved to the
side, creating a moment about the carriage/wing hang point,
the carriage stays vertical and the wing rotates around the
carriage. Therefore, there are two rolling moments that both
contribute to the WSC rolling into a bank:
• The pilot creating the force on the control bar rotating
the wing about the wing/carriage hang point.
2-17
Smaller area
creating loss of drag
Larger area
creating more drag
Yawed to the left, the wing
automatically rotates
into the relative wind
Relative Wind
Flightpath
Figure 2-32. Yaw correction about the vertical axis.
CG
Arm
Pilot input roll moments
Pilot input force
Resultant roll moments about CG
Figure 2-31. Pilot induced moments about wing/carriage hang point
and resultant CG rolling moment.
Figure 2-33. Keel pockets and horizontal stabilizers are additional
tools designers use for yaw stability on the wing.
• Shifting weight to one side of the wing, thus warping
the wing to aerodynamically change the lift on each
side, as in airplane roll control. [Figure 2-31]
Carriage Moments
Carriage weight and resultant CG are the main factors that
contribute toward increasing the roll moment for the carriage.
Carriage aerodynamic forces are not typically a factor for
rolling moments.
Roll Stability Summary
Overall, roll stability and moments are a manufacturer/
make/model balance between dihedral/anhedral, wing twist,
nose angle, airfoil shape from root to tip, and leading edge
stiffness. Some designs are stable, others neutral, and others
can be designed to be slightly unstable for quick side-to-side
rolling.
Yaw Stability and Moments
There is no signifi cant turning about the vertical axis because
the WSC wing is designed to fl y directly into the relative
wind. Any sideways skidding or yaw is automatically
corrected to fl y straight with the swept wing design. An
airplane uses the vertical tail to stabilize it to fl y directly into
the relative wind like a dart. The unique design of the WSC
aircraft performs the same function through the swept wing
design, but also the wing twist and airfoil shape from root to
tip assists in the correction about the vertical axis. A simple
way to understand the yaw stability is to see that any yawing
motion is reduced simply through the increased area of the
wing as it rotates about its vertical axis. [Figure 2-32]
There is a slight amount of adverse yaw similar to an airplane
that can be noticed when a roll is fi rst initiated. The amount
varies with the specifi c manufacturer’s design and make/
model. In addition, the wing can yaw side to side to some
degree, with some different manufacturer’s make/model
more than others. The higher performance wings with less
twist and a greater nose angle are noted for less yaw stability
to gain performance. These wings also require more pilot
input and skill to minimize yaw instability through pitch
input. An addition to the wing planform, twist, and airfoil
shapes to minimize yaw, some wings utilize horizontal
stabilizers similar to these in airplanes and others use tip fi ns.
[Figure 2-33] Generally, the WSC wing is yaw stable with
minor variations that are different for each wing and can be
controlled by pilot input, if needed.
Carriage Moments
The wing is a signifi cant factor in the design of yaw stability,
but the carriage can be a large factor also. If the area in front
of the CG is greater than the area in back of the CG, and
the wing yaws to the side, then the front would have more
2-18
Thrust line below the center of gravity
Thrust line above the center of gravity
CG Thrust line
CG
Thrust line
Figure 2-35. Thrust line moments.
Figure 2-34. Wheel fins for carriage yaw stability.
drag and create a moment to yaw the WSC aircraft further
from the straight fl ight. Therefore, fi ns are sometimes put
on the carriage as needed so the carriage also has a yawing
aerodynamic force to track the WSC aircraft directly into the
wind. [Figure 2-34]
Since the carriage has such a large effect on yaw stability,
the carriage is matched to the wing for overall compatibility.
Each manufacturer designs the carriage to match the wing and
takes into account these unique factors of each design.
Yaw Stability Summary
These factors make the WSC aircraft track directly into
the relative wind and eliminate the need for a rudder to
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Weight-Shift Control Aircraft Flying Handbook(25)
