KonaB777 From , joined Dec 1969, posts, RR:
Reply 1, posted (15 years 2 weeks 6 days 23 hours ago) and read 2329 times:
What winglets do is break up wingtip vortices, which cause drag. This trick helps increase the range by like 5% or something. The 747-400D flies much much shorter flights, so the "range extending" winglets aren't really needed, as their only purpose on the -400D is adding weight.
Mit From United States of America, joined Dec 2000, 166 posts, RR: 0
Reply 2, posted (15 years 2 weeks 6 days 23 hours ago) and read 2325 times:
Yes. The weight penalty of the winglets is only offset on longer flights. (They're deceptively large -- over six feet tall!) The plan of most 747 domestic operators is to use the planes until they have relatively low hours and high cycles. At that point, they can have the winglets added and put into international service where they will accumulate lots of hours but not many cycles.