A technical question for those with the knowledge on this forum. Can anyone explain why some BA planes have large winglets, some small winglets, some no winglets and some with winglets both above and below the wing tip. Travelled from T5 earlier this week on an A320 which had huge winglets. Looking at the other planes on the taxi out. The 777 did not appear to have winglets. The 747 had winglets smaller than the A320 and the A380 and what I think was a A321 had winglets both above and below the wing. Can anyone explain the differences and benefits of the variety of winglets available and also not having winglets Or is it just a manufacturers thing?