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Refl ex cables—most wings with a king post use cables to
hold the trailing edge up at unusually low or negative angles
of attack. These refl ex cables are secured to the top of the
king post and attach to several positions on the trailing edge
where the battens are located. Different manufacturers have
different positions where these are attached, depending on
the design of the wing. Refl ex cables also provide additional
refl ex at high speeds because the drag of the wires pulls up
the trailing edge, creating more refl ex at these higher speeds.
[Figure 3-16]
Washout struts—tubes near the tips that keep the tip trailing
edge up during very low or negative angles of attack. They
can be inside or outside the double surface of a wing. The
refl ex cables may not go to the wingtip, so washout struts
are used to hold up the trailing edge at the tip at very low
and negative angles of attack. [Figure 3-17]
Sprogs—for wings using struts with no king post, sprogs
are used to keep the inboard trailing edge up in place of the
refl ex cables. A wire attached to the top of the leading edge
holds the sprog up in place. [Figure 3-18]
Pitch Control System
The pitch control system is a simple hinge on the keel at the
hang point that allows the pilot to push the control bar out and
3-9
Far Back View
Top View
Figure 3-20. Shifting weight to the right pulls the keel to the right
(or lets the crossbar shift to the left) and increases twist on the right
side for roll control.
Strap attached to crossbar
that goes around wing keel,
limiting its travel side to side.
Figure 3-21. Crossbar travel limiter.
Figure 3-19. Hang point wing attachment.
Trim Systems
There are a number of trim systems to relieve the control
pressures for pilots to fl y at different “hands off” trim speeds.
Ground adjustable trim allows the pilot to adjust the trim
speed of the wing on the ground and remain at one speed
during fl ight, while fl ight adjustable trim systems can change
the trim speed in fl ight.
Ground Adjustable Trim Systems
The most common ground adjustable trim system, and typical
of most aircraft, is moving the wing attachment hang point
forward for faster trim speeds and aft for slower trim speeds.
Each manufacturer has different hardware, but the basics of
sliding the carriage wing hang point forward and backward
on the keel is similar for all. As an example, moving the
hang point at the furthest aft position to the furthest forward
position could speed the wing up 20 knots. This in turn
moves the control bar position back to a new “hands off”
trim speed.
pull the control bar in to control pitch. This wing attachment
is different for each manufacturer, but all designs have this
hang point wing attachment so the control bar is always
perpendicular to the longitudinal axis of the aircraft. This
raising and lowering of the nose is the pitch control system
for the WSC aircraft. [Figures 2-7 and 3-19]
Roll Control System
Control bar movement from side to side controls the roll about
the longitudinal axis. The wing attachment hang point allows
the carriage to roll around the wing keel. Thus, it can also be
looked at from the carriage point of view, when the control
bar is moved side to side, the wing rotates around the wing
keel relative to the carriage. [Figures 2-31 and 3-19]
It would fi rst appear that moving the control bar to one side,
thus shifting weight to the opposite side, could alone bank
the aircraft. It is true that shifting weight to the right would
naturally bank the aircraft to the right and put it into a right
hand turn. However, the weight alone is not enough to provide
adequate roll control for practical fl ight.
As weight is moved to one side, the keel is pulled closer to
that side’s leading edge. The actual keel movement is limited
to only 1 to 2 inches each side of center. However, this limited
keel movement is suffi cient to warp the wing, changing the
twist side to side (as discussed earlier in the aerodynamics
section) to roll the aircraft [Figure 2-24] by changing the
lift side to side. Simply, the shifting of weight from side to
side pulls the keel toward the leading edge on that side and
warps the wing to roll the aircraft.
Besides the keel shifting relative to the leading edges and
crossbar, overall roll control is adjusted by the designers to
fi t the mission of the wing through sail material/stiffness,
leading edge stiffness/fl exibility, amount of twist, amount
of travel the keel is allowed, airfoil shape, and the planform
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Weight-Shift Control Aircraft Flying Handbook(31)
