5 ms·

Licensed to dispatch planes or not, everything you've said about fluid dynamics is wrong. You first seem to have confused "winglets" with "vortex generators." I

Licensed to dispatch planes or not, everything you've said about fluid dynamics is wrong. You first seem to have confused "winglets" with "vortex generators." I think. The only winglike thing that messes with the viscous boundary layer is a VG. Second, winglets have nothing to do with a "mixing boundary;" They do what they do, even in completely inviscid flow, where there is no boundary layer. Third, whether an air mass has to "accelerate" has nothing to do with efficiency. For example, air is adiabatically compressed as it meets the stagnation point on a wing, or en masse as it enters a subsonic diffuser (jet intake). The former is a consequence of fluid flow in general, and the latter is by design. Both are completely isentropic and lead to no total pressure losses in the flow. Finally, it's meaningless to say that wings "can be designed to have...arbitrary amounts of lift," and plainly incorrect to say that drag is the "secret sauce." (Aeroelastic flutter? Wing mass? Control moments? Moment coefficients?) Reducing induced drag is done in exactly two ways. You either increase the span or put a winglet on so you can effectively increase the span while still being able to park the plane. Nobody thinks they can do brain surgery, but everybody is a fluid dynamicist.

theoh 8y ago
This reply is so gratuitous. It would have been enough to say that wing extensions in general (winglets and the 777x ones included) serve to improve the overall efficiency/performance of the wing (so they might not be generating any lift at all, if it's even possible to analyze them in isolation). It's fine to make the point that we're all unqualified to discuss this because we aren't fluid dynamicists. But dumping a load of technical language on us that you don't expect us to understand is a rude, non-productive, and self-aggrandizing way to do that.
- AceyMan 8y ago
  I sought only to say how the upside could be something other than lift increase (in the absence of any white papers from Boeing or the like) and provided some loosely framed concepts that support that possibility. I would address the GPs nit-picky points, but the tone is so snarky it's not worth my effort. I may not be a fluid dynamicist, but neither am I a pedantic putz. (subtext: chill out, dude.)
  - theoh 8y ago
    To amplify the sentiment a little bit: the guy who invented winglets did so based on physical intuition, not calculation. https://en.wikipedia.org/wiki/Richard_T._Whitcomb https://en.wikipedia.org/wiki/Richard_T._Whitcomb He was such an intuitionist that AFAICS he apparently spent some of his last years on perpetual motion machines (i.e. some kind of quantum zero-point energy device.) The idea that it's not OK to have spirited discussions about this, that the science should dictate who is right and who is wrong, is just inadequate to the problem. The design space for aircraft is huge, and almost any conceivable practical technique or configuration is going to be conventional, based on experience.

theoh 8y ago

This reply is so gratuitous. It would have been enough to say that wing extensions in general (winglets and the 777x ones included) serve to improve the overall efficiency/performance of the wing (so they might not be generating any lift at all, if it's even possible to analyze them in isolation). It's fine to make the point that we're all unqualified to discuss this because we aren't fluid dynamicists. But dumping a load of technical language on us that you don't expect us to understand is a rude, non-productive, and self-aggrandizing way to do that.

AceyMan 8y ago
I sought only to say how the upside could be something other than lift increase (in the absence of any white papers from Boeing or the like) and provided some loosely framed concepts that support that possibility. I would address the GPs nit-picky points, but the tone is so snarky it's not worth my effort. I may not be a fluid dynamicist, but neither am I a pedantic putz. (subtext: chill out, dude.)
- theoh 8y ago
  To amplify the sentiment a little bit: the guy who invented winglets did so based on physical intuition, not calculation. https://en.wikipedia.org/wiki/Richard_T._Whitcomb https://en.wikipedia.org/wiki/Richard_T._Whitcomb He was such an intuitionist that AFAICS he apparently spent some of his last years on perpetual motion machines (i.e. some kind of quantum zero-point energy device.) The idea that it's not OK to have spirited discussions about this, that the science should dictate who is right and who is wrong, is just inadequate to the problem. The design space for aircraft is huge, and almost any conceivable practical technique or configuration is going to be conventional, based on experience.