ft
Winglets also increase the
effective wingspan and reduce the wingtip vortex. They are also bolted to the wing and you can MEL them at an approx. 2.5% performance penalty, however, they are heavier than raked wing tips. You are correct about the Hoerner wingtip, the raked wingtip concept is a derivative of that design.
If you wish to delve into this deeper, try:
http://www.desktopaero.com/appliedae...nonplanar.html
Cheers,HD