Eraser...
you are right about the a-320 family, but i was not considering them as winglets, i mean, to be fair, they are something quite different to what the b737 & 747 and a340 have.
this is exactly my point, the weight and size of the 'winglets' that airbus use on the a320 family is far less than that of the b737's, and are obviously deemed to do as good a job, so why the huge things on the b737?