Re: Boeing Deception: 777X Wing Actually Elongated 787 Wing
Posted: Wed Sep 12, 2018 3:21 pm
OK, I buy the argument that increasing the aspect ratio can decrease the induced drag.
But what about the tip vortices? If a wing is simply stretched but has the same form and lifting profile at the tip, it’s going to generate much the same vortices at the tip
The claim that winglet orientation is immaterial and that a horizontal winglet prevents air bleeding from bottom to top as effectively as a vertical one needs a bit of justification. From the (admittedly simplistic) “damming air from getting round the corner” point of view, it would seem so much easier for the flow to make the single +180 deg rotation from bottom to top around the tip (and initiate a vortex) instead of the +90, +180, -90 path needed to get round a vertical winglet (or the -90, +180, +180, -90 for a wingtip fence).
Furthermore, if you do have a vertical winglet, why would you give it a “lifting” profile?
If you do, the winglet itself will generate its own tip vortices, and the pressure differential created would assist the main vortex generation by helping move the air round the wingtip from bottom to top. Surely a winglet ought to have a neutral profile and AOA, so that it would generate no pressure differential, less drag, and no tip vortices of its own, and would constitute a buffer zone of “dead air” hindering the flow of air from bottom to top of the main wing.
But what about the tip vortices? If a wing is simply stretched but has the same form and lifting profile at the tip, it’s going to generate much the same vortices at the tip
The claim that winglet orientation is immaterial and that a horizontal winglet prevents air bleeding from bottom to top as effectively as a vertical one needs a bit of justification. From the (admittedly simplistic) “damming air from getting round the corner” point of view, it would seem so much easier for the flow to make the single +180 deg rotation from bottom to top around the tip (and initiate a vortex) instead of the +90, +180, -90 path needed to get round a vertical winglet (or the -90, +180, +180, -90 for a wingtip fence).
Furthermore, if you do have a vertical winglet, why would you give it a “lifting” profile?
If you do, the winglet itself will generate its own tip vortices, and the pressure differential created would assist the main vortex generation by helping move the air round the wingtip from bottom to top. Surely a winglet ought to have a neutral profile and AOA, so that it would generate no pressure differential, less drag, and no tip vortices of its own, and would constitute a buffer zone of “dead air” hindering the flow of air from bottom to top of the main wing.