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to overcome that unnecessary drag. The energy that produces the vortices is wasted energy. The object of glider design is to convert all of the energy into useful lift and the necessary thrust. Any wasted energy translates into poorer performance. [Figure 3-12]  Glider designers attempt to reduce drag by increasing the aspect ratio of the glider. The greater the aspect ratio of the wing is, the lower the induced drag is. Wingtip devices, or winglets, are also used to improve the efficiency of the glider. There are several types of wingtip devices and, though they function in different manners, the intended effect is always to reduce the aircraft’s drag by altering the airflow near the wingtips. Such devices increase the effective aspect ratio of a wing, without materially increasing the wingspan. 

## Total Drag 

Total drag on a glider is the sum of parasite and induced drag. The total drag curve represents these combined forces and is plotted against airspeed. [Figure 3-13] 

L/D$_{MAX}$ is the point at which the lift-to-drag ratio is greatest. At this speed, the total lift capacity of the glider, when compared to the total drag of the glider, is most favorable. In calm air, this is the airspeed used to obtain maximum glide distance. 

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## Wing Planform 

The shape, or planform, of the wings also has an effect on the amount of lift and drag produced. The four most common wing planforms used on gliders are elliptical, rectangular, tapered, and swept forward. [Figure 3-14] 

## Elliptical Wing 

An elliptical wing is a wing planform shape that minimizes induced drag. Elliptical taper shortens the chord near the wingtips in such a way that all parts of the wing experience equivalent downwash, and lift at the wing tips is essentially 

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