DOWNTURNED WING TIPS

Tips that turn downwards, as shown in Fig. 6.6d, have frequently been used on sailplanes. These should not be confused with the upswept Homer tip described above. Their purpose is mainly to protect the wing tip and ailerons from damaging contact with the ground.

Aerodynamically, the downtumed tip may have some good effect, tending to confine the high pressure air and restrict its movement round to the upper side, the opposite of the Homer tip. In an exaggerated form, if the camber of the wing is carried round all the way, the result resembles the lower part of a Whitcomb winglet (Fig. 6.8). As before, there may be some benefits for aileron control and tip stalling, although little is known of this.

In the highly competitive sailplane market, fashion sometimes seems to be quite influential. There is a tendency for manufacturers and designers to introduce changes if there is even a small amount of experimental evidence to support them. The changes draw attention to their products. They stress the latest research findings, hoping thereby to make more sales to leading pilots. (These outstanding pilots usually win the competitions anyway, even when flying aircraft of slightly inferior performance.) Research goes on. Further changes, again with some scientific support, may follow after a few years. In terms of practical experience in flight, it is very difficult to show that any particular type of wing tip has a large advantage. This is the case with full sized aircraft. It is even more so with models.