Dassault 7X winglets
It is my understanding the Dassault 7X when introduced had no winglets. Marcel Dassault is rolling over in his grave as a result of his strong beliefs in proper airfoil design.
You would think that when they installed winglets you could simply compare performances and fuel burn with and without them. However, when the winglets were installed on the 7X the wing span was increased as well as a couple of hundred pounds of structure to beef up the wing structure was added at the same time. It is like trying to compare oranges to apples.
Much of the added range may simply have come from a higher wing aspect ratio and how much improvement is due to the winglet is difficult to measure. in spite of many aircraft being equipped with winglets today, I remain skeptical to the level of improvement due to a new winglets as advertised at the NBAA convention of being responsible for more than a 9% fuel savings. The effort of Boeing to achieve a 20% fuel savings by the design of the 787 which has no winglets adds to my argument. Just my opinion...