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dive situation. As shown in Figure 2-29, the root area of the
wing has refl ex which creates a positive pitching moment
for the root chord to rotate the nose up towards a level fl ying
attitude. At the same time, the tips are at a negative AOA
producing lift in the opposite direction as usual, creating a
moment to bring the nose/root chord up to a positive AOA
to start producing lift and raising the nose to a normal fl ight
condition. The negative lift or downward force as produced
at the tips and root as shown provide a positive moment to
raise the nose back to a normal fl ying attitude.
2-16
Dihedral from wing flex
Anhedral built into frame
Figure 2-30. Wing front view example showing anhedral in the
middle of the wing and dihedral at the outboard section of the wing
because of leading edge flex.
Relative Wind
Flightpath
Trailing edge at center
of wing held up by
reflex lines.
Reflex lines used
to hold up the
trailing edge
Aerodynamic force at tips
Wing root at negative AOA
producing no lift
Trailing edge of tips
held up with washout
struts at negative
angle of attack
Tip moment arm -LT
Reflex force moment arm
Reflex in
airfoil creates
force near
trailing edge
of root area
Positive moment
caused by
aerodynamic
force at tips
plus reflex in
airfoil at root
-LR
Relative Wind
Reflex
Figure 2-29. Emergency vertical dive recovery for a WSC wing.
Refl ex also provides a stable pitch up moment for an airfoil
when it is fl ying at normal fl ight angles of attack. The greater
the refl ex, the greater the nose up moment of the airfoil. This
is used in some WSC airfoil designs and also for trim control
as discussed in Chapter 3.
Carriage Moments
The wing design is the main contributing factor for pitch
stability and moments, but the carriage design can also
infl uence the pitching moment of the WSC aircraft. For
example, at very high speeds in a dive, a streamlined carriage
would have less drag and, therefore, a greater nose-up moment
because of less drag. The design of the carriage parts can have
an effect on aerodynamic forces on the carriage, resulting in
different moments for different carriage designs.
The drag of the wing in combination with the drag of the
carriage at various airspeeds provides a number of pitching
moments, which are tested by the manufacturer—a reason
the carriage is matched to the wing for compatibility. Each
manufacturer designs the carriage to match the wing and takes
into account these unique factors.
Pitch Moments Summary
Overall, the amount of sweep, twist, specifi c airfoil design
from root to the tip, and the carriage design determine the
pitching moments of the WSC aircraft. Some have small
pitching moments, some have greater pitching moments.
Each WSC model is different with a balance of these
aerodynamic parameters to accomplish the specifi c mission
for each unique carriage and wing combination.
Roll Stability and Moments
As described in the Pilot’s Handbook of Aeronautical
Knowledge, more dihedral or less anhedral in a WSC wing
creates more roll stability. More roll stability might be helpful
for a training wing or a fast wing made for long cross-country
straight fl ight, but most pilots want a balance between roll
stability and the ability to make quicker turns and a sport
car feel for banking/turning. Therefore, a balance between
the stability and the instability is achieved through anhedral
plus other important wing design features such as nose angle,
twist, and airfoil shape from root to tip.
An aerodynamic characteristic of swept wings is an “effective
dihedral” based on the sweep of the wing and angle of attack.
The combination of the physical anhedral in the wing and the
effective dihedral due to wing sweep provides the balance of
stability and rolling moments for a particular wing design.
The design of the wing can have actual dihedral or anhedral in
the wing. Even with anhedral designed in the inboard section
of the wing, the outboard sections of the wing could have
some dihedral because of the fl ex in the outboard leading
edges. As the wing is loaded up from additional weight or
during a turn, the tips fl ex up more creating more dihedral
and a roll stabilizing effect when loaded. [Figure 2-30]
Generally, it is thought that the wing remains level and the
weight shifts to the side to initiate a turn. Another way to
look at how the WSC wing rolls is to examine the carriage
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Weight-Shift Control Aircraft Flying Handbook(24)
