Low Speed (near stall) Cruise Speed (trim) High Speed 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. Figure 2-8.  Pitch angle examples of nose high (top) and nose low  (bottom). 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  2-5