We did a tour of Duncan Aviation years ago and I remember the person giving the tour talking about the person that engineered the wing flairs at the end of the wings. If I recall to have them on your plane you had to spend six figures (I think??) to use them but the fuel savings out weighed the cost. I’m sure there’s a Freeper that has a better idea of cost.
Winglets.
..who described the circulation vortex generated by the wing tip tabs and the exact shape of the airfoil for optimum lift in level flight.
And based on Admiral Lord Nelson's battle plan in 1805 at Trafalgar...established the mathematical formulation of Warfare (Aircraft in Warfare published in 1916)
I didn’t work on those but have worked on winglets for other aircraft. They make a big difference in efficiently. Easily pay for themselves. It is an expensive project as an add on. Besides the usual design, testing, analysis, and manufacturing you have what is called a “supplemental type certificate” to allow them to be used on the aircraft in question. All huge expenses.