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for faster speeds for the same thrust. The leading edge is the
forward edge of the airfoil, and the rear edge of the airfoil
is called the trailing edge. The chord line is an imaginary
straight line drawn from the leading edge to the trailing edge.
The WSC airfoil typically uses a different camber with the
airfoil high point farther forward than the airplane airfoil,
creating a more stable airfoil. [Figure 2-2]
The WSC wing is a unique design of airfoils that differ
throughout the wing span. Looking at a top view of the wing,
in the center is the wing root and on each end is the wingtip.
Wing chord is any section of the wing parallel to the wing
root. [Figures 2-3 and 2-4] The wingtip chord is the chord
where the trailing edge is furthest to the rear of the wing. This
can be inboard of the tip (as shown) and can vary depending
on the specifi c wing design. The nose angle is the angle made
by the leading edges, typically ranging from 120° to 130°.
Sweep is the angle measured between the quarter chord line
(line of 25 percent chords) and a line perpendicular to the
root chord. [Figure 2-3]
2-3
Rear View
Leading Edge
Wing Span
Wing Tip
Wing Root Tip Chord
Anhedral Angle
(Dihedral would be the
wing angled up)
Trailing Edge
Figure 2-5. Rear view of a WSC wing and aerodynamic terms.
CG
CG
Side View
Flightpath
Wing Root
Tip Chord
Wing Root
Figure 2-4. Side view of a WSC wing and aerodynamic terms.
Looking at the rear view of the wing, anhedral is the angle
the wings make angling down and dihedral is the angle the
wings make angling up. [Figure 2-5] Dihedral is the positive
angle formed between the lateral axis of an airplane and a line
which passes through the center of the wing. Anhedral is the
similar negative angle. Wings with sweep have an “effective
dihedral” characteristic that counteracts the physical anhedral
to develop the required roll stability for the particular make/
model design objective. This is explained in the Pilot’s
Handbook of Aeronautical Knowledge in much greater detail
for further reference. Unlike airplanes which typically have
signifi cant dihedral as viewed from the front or back for
roll stability, WSC wings typically have a slight amount of
anhedral as shown in Figure 2-5 and effective dihedral which
is a characteristic of the swept wing design.
Wing twist is the decrease in chord angle from the root
to the tip chord, common to all WSC wings and ranging
from 5° to 15°. This wing twist is also called washout as
the wing decreases its angle of attack from root to tip. The
term billow was originally used for the early Rogallo wings
as the additional material in degrees that was added to the
airframe to create the airfoil. It is still used today to defi ne the
amount of twist or washout in the wing. The WSC may not
have twist/washout when sitting on the ground, and must be
fl ying and developing lift to display the proper aerodynamic
twist characteristic of WSC wings. [Figure 2-6]
The longitudinal axis is an imaginary line about which the
aircraft rolls around its center of gravity (CG); it is also
called the roll axis. The longitudinal axis is not necessarily a
fi xed line through the carriage because the roll axis changes
for different fl ight confi gurations, but can be approximated
by the middle of the propeller shaft for a properly designed
WSC aircraft and is typically parallel with the fl ightpath of
the aircraft as shown in Figure 2-7. Angle of incidence is
the angle formed by the root chord line of the wing and the
longitudinal axis of the WSC aircraft.
2-4
Wing twists from root to tips
Relative
Wind
Relative
Wind
Relative
Wind
AOA high at Root
AOA lower at midpoint
AOA low at tip
Chord Line
Chord Line
Chord Line
Figure 2-6. Wing twist shown for a WSC wing in flight.
Relative Wind
Flightpath
Relative Wind
Flightpath
Longitudinal Axis
Longitudinal Axis
CG
CG
Low Angle of Incidence
High Angle of Incidence
Control Bar Out—Slow Flight
Control Bar In—Fast Flight
Root Chord of Wing
Control Bar
Control Bar
Root Chord of Wing
Carriage Hang Point
Carriage Hang Point
Figure 2-7. Angle of incidence.
Unlike that of an airplane, the WSC angle of incidence has a
signifi cant change in fl ight because the carriage is attached to
the wing, which allows the wing to rotate around the carriage
hang point on the wing and is controlled by the pilot as shown
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Weight-Shift Control Aircraft Flying Handbook(16)
