Aero drag - increased frontal area?
Actually, this has been puzzling me - when retrofitted to sailplanes, winglets have typically shown a benefit at low airspeeds, higher angles of attack (predictably), but show a performance deficit in the higher end of the speed range, due, as I understand, to increased aero drag.
So,
1) why are they so prolifigate on airliners? (which don't generally fly too slowly)
2) Why are they getting so long - virgin blue's 737's are sporting very tall ones - where's the benefit in the huge height?
Cheers!