Mostly, but there are many aerodynamic tricks to turn the "Karman Vortices" (Proper scientific name of the wingtip wake vortices) energy into something more useful. Winglets are like sails in the vortex, they actually produce thrust! (As well as an outword pull...) Boeing likes the "raked wingtips" as those harness the lift and by having a larger wingspan, less vortex is produced (without as much stress on the "host wing.") A "longer wing" has less wasted energy too, until the weight penalty of the wing offsets the aerodynamic benefit.
Its more accurate to say "Heavy plane=Big wake"
|Quoting A350 (Reply 21):|
I fail to understand how so large differences between wind tunnel experiments and reality can occur. Sure, the wind tunnel experiment is a scaled down model, but I'm convinced they have done a decent work at it. Perhaps the WhaleJet will end up with winglets as ugly as those of the 737NG
Me too! I am an expert on CFD modeling of turbulence. Ok, my specialty is combustors, but I fail to see how this was missed! Was their gridding wrong? Or did airbus use a K-E derived turbulence model (which overpredicts dissipation and hence would understate the vortices). For the claims they made, I expected Airbus to have employed the computationally expensive eddy simulation technique... Apparently not!
Also, with wind tunnels there is a huge scaling issue. Smaller turbulence dissipates *much* faster than larger turbulence. Tenikas and Lumly (sp?) wrote the definitive introduction text on the subject. Let's put it this way, most fluid engineers complete their careers without ever understanding turbulence. Most would scale wind tunnel results wrong. Because of the much greater effective viscosity in a wind tunnel, they are a poor device for estimating wake vortex propagation. CFD should have been the more accurate tool.
True. The only fix I see is to grow the winglets.
|Quoting Astuteman (Reply 43):|
Hence the HUGE wings.... (Interestingly, A engineers wanted to make the wings even bigger - now we know why
Actually, they wanted larger wings for fuel efficiency. There have been other discussions on A.net about this. However, larger wings would have mitigated the vortices.
|Quoting ContnlEliteCMH (Reply 52):|
Fluid mechanics is definitely a black art, despite what some on this board postulate, that computational fluid dynamics is mature enough that you shouldn't even need physical testing. But wind tunnel testing is a well-established method. There are millions of wind tunnel hours in the books.
CFD is very mature. But, it still takes someone who knows gridding (model setup), turbulence models, and most importantly error analysis! Oh, but think of it as a black art, that raises my salary!
(Alas, now I only teach others CFD, I've been promoted beyond a user...)
|Quoting Mariner (Reply 122):|
My question remains unanswered: can these numbers change without - as some are suggesting above - changes to the aircraft itself?
No. Something is going to have to be done with the wingtips. Well, or you could take 200,000lbm out of the aircraft... To say the least, the MTOW increases aren't helping this issue.
Look, I apologize for the long technical post. If you would like to know more, please contact me and I'll try to explain in terms you'll understand.