Figure 2-2. Angle of incidence.  Figure 2-3. Angle of trim and center of pressure in gliding  flight.  Planform  is the shape or form of a wing as viewed  from above. The PPC wing comes in two wing plan- forms: rectangular, and elliptical. [Figure 2-5] The el- liptical planform leading and trailing edges are curved  to form an elliptical shape when viewed from the top  or bottom. These two shapes have unique flying char - acteristics. Rectangular wings typically produce more  drag, are lower-performance, and do not move fore  and aft, relative to the cart, as quickly as elliptical  wings. These characteristics are more obvious when  the wing is inflating, during pitch changes, and when  flying in turbulence. Rectangular wings are therefore  more stable and require less effort to fly. Elliptical  wings are higher-performance and more efficient due  to less drag. Elliptical wings react more quickly with  changing conditions and require greater pilot experi- ence and skill during inflation, in turbulent air, and  with abrupt throttle changes.  Aspect ratio  is the wingspan divided by the average  chord line. A PPC with a common 500-square foot  rectangular wing (about a 38-foot wingspan) and with  a typical mean chord line of 13 feet, would have an  average aspect ratio of about 3. This relatively low  aspect ratio is less efficient at producing lift. An ellip - tical wing with the same 500 square feet and a 45-foot  wing span and an 11-foot average chord would have  an aspect ratio of about 4. The PPC wing is similar to  airplane wings in that the aspect ratio will differ with  the specific design mission for the aircraft. Generally,  rectangular wings have lower aspect ratios and lower  efficiency than the higher aspect ratio and higher effi - ciency elliptical wings. Generally, a high aspect ratio  wing, compared to a low aspect ratio wing, produces  higher lift at lower angles of attack with less induced  drag. [Figure 2-6]. 2-2