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in Figure 2-7.
Pitch angle is the angle the WSC wing root chord (center
of wing) makes with the Earth’s horizontal plane. Many
pilots confuse the pitch angle, which is easily seen and felt,
with the angle of attack (AOA) which is not as perceptible.
For example, if fl ying in a glide with the engine idle and
the nose lowered, the pitch angle can be below the horizon.
Another example would be fl ying at full power climb with
the nose raised, resulting in the pitch angle being well above
the horizon. [Figure 2-8] Pitch angles are covered in greater
detail in chapter 6.
Deck angle is the angle of the cart’s wheel axles to the landing
surfaces, as in the powered parachute (PPC) deck angle.
Relative wind is the direction of the airfl ow with respect to
the wing; it is parallel to and opposite the WSC fl ightpath.
Relative wind may be affected by movement of the WSC
through the air, as well as by all forms of unstable, disturbed
air such as wind shear, thermals, and turbulence. When a
2-5
Figure 2-8. Pitch angle examples of nose high (top) and nose low
(bottom).
High Speed Cruise Speed (trim) Low Speed (near stall)
Control bar pulled in No control bar pressure Control bar pushed out
18°
Angle of Attack
10°
Angle of Attack
3°
Angle of Attack
Relative Wind
Flightpath
Relative Wind
Flightpath
Relative Wind
Flightpath
Figure 2-9. Angle of attack effect on speeds, relative wind, and flightpath for level flight.
WSC is fl ying through undisturbed air, the relative wind is
parallel to and opposite the fl ightpath. [Figure 2-7]
AOA is the angle between the relative wind and the wing
chord line. Because of the wing twist, the AOA is greatest
at the wing root and decreases along the wing span to the
tips. This is an important concept covered in the stability
section of this chapter. For changing speeds during gliding,
level fl ight, and climbs, AOA is the primary control for speed
changes. Lower angles of attack produce higher speeds, and
higher angles of attack result in slower speeds.
The pilot changes the AOA by moving the control
bar forward for high angles of attack and slow speeds
as shown in Figure 2-7 (top) for high angle of incidence and
Figure 2-8 (top) for high pitch angle. Low angles of attack for
fast speeds are shown in Figure 2-7 (bottom) for low angle of
incidence and Figure 2-8 (bottom) for low pitch angle.
Most of the time, the pilot is fl ying at the cruise AOA,
which is the trim position of the control bar, and the pilot is
neither pushing out nor pulling in on the control bar. This
trim position is the AOA and speed the aircraft fl ies if the
pilot is fl ying straight and releases the control bar in calm
air. [Figure 2-9, middle]
Planform is the shape or form of a wing as viewed from
above. The WSC wing comes in a number of planforms
ranging from the larger and slower wings to the smaller and
faster wings.
Aspect ratio is the wingspan divided by the average chord
line. A WSC aircraft with a common 200 square foot training
wing (about a 35 foot wingspan), and with a typical mean
chord line of 7 feet, would have an average aspect ratio of 5.
This relatively low aspect ratio is less effi cient at producing
lift. A higher performance wing with 140 square feet, a 35
foot wing span, and an average 5 foot average chord would
have an aspect ratio of 7. The WSC wing is similar to airplane
wings in that the aspect ratio differs with the specifi c design
2-6
Slow Trainer—Low Aspect Ratio
Fast Cross-Country—High Aspect Ratio
Figure 2-10. Wing planforms showing the slow trainer with a low
aspect ratio and the fast cross-country with a high aspect ratio.
Foam or mylar maintains the airfoil
shape up to the high point.
Rigid ribs called battens
maintain the airfoil shape.
Figure 2-11. Rigid airfoil preformed ribs called battens and leading
edge stiffener maintain the rigid airfoil shape.
mission for the aircraft. For the same wing area and similar
design, the lower aspect ratio wings produce less lift and
more drag; higher aspect ratio wings produce more lift, less
drag, and may require more pilot effort to fl y, depending on
the design. [Figure 2-10]
Wing loading is a term associated with total weight being
carried by the wing in relation to the size of the wing. It is the
amount of load each square foot of the wing must support.
Wing loading is found by dividing the total weight of the
aircraft, in pounds, by the total area of the wing, in square
feet. For example, the wing loading would be 5.0 pounds per
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Weight-Shift Control Aircraft Flying Handbook(17)
