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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 flight, 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 flying 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 flies if the pilot is flying 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 efficient 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 

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