A few points:
1. Wingtip vortices are an issue during the approach and landing phase do to the fact that aircraft on approach are sequenced closer together and the higher angle of attack at the wing root along with all the high lift devices combine to create the issue.
2. Winglets are not lift adding devices. They are drag reducing devices which inexorably increases lift by comparison to aircraft that do not have them.
3. I completely agree on the point that 'large aircraft' are utilizing the advantages of aircraft equipped with winglets in part to accommodate airport
restrictions... However historically if an aircraft is built that airlines want, airports will concede and adapt - As they always have as planes have gotten larger.. Most recently the 380 is the example of reference.
4. Agreed, this is a sailing forum... However even the notion of adding a winglet (or any vortex degenerating device) to the top of a sail is totally useless from an aerodynamics standpoint... Most simply explained for a winglet like device to be effective it has to be a certain percentage of the chord of the airfoil. Since sails
come to a virtual point at the top of a mast it would reduce the width of the "winglet" to the width of the sail at its peak... Essentially making it useless... And yes, hard to get to, and an unnecessary waste of weight in the exact place you wouldn't want any extra...
5. Lastly, most of the light aircraft and experimental aircraft (note: I'm excluding the light sport category bc I know absolutely nothing about it) that had winglet-ish devices were added for stability along the vertical axis of most aircraft... While I'm completely open to the idea that by designing the aircraft this way there were invariably some drag/lift ratio benefits i would imagine it was a secondary benefit... Think SuperEZ in the way of experimental... Winglets.. Kinda. And no empennage or rudder
to speak of... Er go stability
6. The only operator I know of that was operating the -400 without winglets was JAL... And that was just weird looking. I have colleagues that are in the -4 and the -8 now and even they're not crazy about the "weird" Japanese versions... Of course that's pure opinion..
Lastly... Since you are apparently dialed in... Why didn't they ever put winglets on the 777? That one always bothered me -
Sent from my iPhone using Cruisers Sailing Forum