KAUST From United States, joined Jun 2009, 16 posts, RR: 6 Posted (4 years 8 months 3 weeks 5 days 22 hours ago) and read 1932 times:
Greetings!
The thread in the civil aviation forum of the CO 757 with winglets made me wonder, would winglets on the 757 change it's dreaded wake turbulence any?
I know that it is somewhere the ire of planes taking off/landing behind it, any chance of a change in waiting times now?
Thanks -
KAUST
"Houston, this is Apollo 8. We are now in Lunar orbit."
Quoting 2H4 (reply 5):
Think the upcoming winglets on 757's will alleviate that wake turbulence, or is it mainly a result of the trailing edge flap configuration?
Keep in mind that a large portion of winglet operation is the production of thrust through a forward vectoring of the resultant freestream-vortex flow at the wingtips, an effect which doesn't relate directly to wake turbulence strength at all. The reduction of vortex strength is the other (sometimes smaller) part of winglet operation, which does affect wake strength, but it is probably not major enough to significantly reduce the 757's wake turbulence strength. Having said that, the main source of the 757's disproportionately strong wake is indeed its general wing-flap geometry (as Klaus correctly stated), anyway, so with that in mind winglets would have an even smaller overall effect on the wake strength.
Whether the 757's wake really is so grossly out of proportion to its size and weight is another much-debated question...
2H4 From United States, joined Oct 2004, 8118 posts, RR: 65 Reply 3, posted (4 years 8 months 3 weeks 5 days 21 hours ago) and read 1858 times:
AIRLINERS.NET CREW DATABASE EDITOR
No sweat, man. I'd like to hear some more opinions, particularly from the wizards of Tech-Ops......as opposed to the armchair CEOs we know and love from Civil Aviation.
Quoting KAUST (Reply 2): (Side note): Who is Aeroweenie?
AeroWeanie is an aerodynamic badass. Basically, if you were to combine Neo from the Matrix with an Aerodynamics Professor, he's what you'd end up with. He's engineered some extreme aerodynamic modifications to airliners, and has been involved in the design of Boeing winglets.
AeroWeanie From United States, joined Dec 2004, 1527 posts, RR: 54 Reply 4, posted (4 years 8 months 3 weeks 5 days 20 hours ago) and read 1852 times:
Thanks for the kudos!
I'm curious to see what happens regarding the wake turbulence. Winglets should disperse the tip vortex. However, I'm not sure that the tip vortex is the problem. It might be a wake shed off tip of the flap or something like that. If you look at a wake imaging photo of the wake behind an airliner, there are a lot of big vortices being shed at various locations on the span. I'll scan in such a photo when I get to work tomorrow and post it here.
2H4 From United States, joined Oct 2004, 8118 posts, RR: 65 Reply 5, posted (4 years 8 months 3 weeks 5 days 20 hours ago) and read 1849 times:
AIRLINERS.NET CREW DATABASE EDITOR
Quoting AeroWeanie (Reply 4): It might be a wake shed off tip of the flap or something like that.
Thanks, AeroWeanie!
I'm sure this has already been explored, but what about a "winglet" of sorts for the edges of the flap to reduce wake shed/wake turbulence?
I'm picturing a very thin fence mounted to the edge(s) of the flap that would fit between the flap and the neighboring control surface. When the flap is retracted, the "flap fence" could simply jut out into the relative wind like a wing fence.
Has this already been explored? If so, what factors make it ineffective?
QantasA332 From Australia, joined Dec 2003, 1500 posts, RR: 50 Reply 7, posted (4 years 8 months 3 weeks 5 days 15 hours ago) and read 1801 times:
Thanks for the very kind words, 2H4!
Here's a good illustration of the very central role of wing-flap geometry in the net vortex production of aircraft (and, ultimately, in the wake strength) - the two main visible vortices in the photo are indeed flap-generated and not coming off the wingtips at all:
Also note the small vortices orginating from the horizontal stabilizer tips. As you may have guessed, and for obvious reasons, they're actually rotating in the opposite direction to their corresponding-side wingtip vortices. Pretty neat!
AeroWeanie From United States, joined Dec 2004, 1527 posts, RR: 54 Reply 8, posted (4 years 8 months 3 weeks 5 days 8 hours ago) and read 1738 times:
Here is the wake imaging photo of the wake behind a 737-300 in the wind tunnel. This picture was made by having a series of lights on the back of a total pressure probe. As different values of total pressure where measured, different color lights would come on. This gives the contours of total pressure. In the wake, there will be a total pressure deficit and the vortices will be seen quite clearly.
In this picture, you can see (from right to left), the boundary layer on the fuselage, a big vortex coming off the inboard edge of the inboard flap, several vortices being shed by engine and the edges of the thrust gate, a big vortex at the inboard edge of the outboard flap, more vortices from the outboard flap, another big one from the outboard edge of the outboard flap and finally, a smaller at the tip.
I should note that this picture is from the late Jim Crowder's paper "Wake Imaging System Applications at the Boeing Aerodynamics Laboratory", SAE paper 851895, October 1985.
AeroWeanie From United States, joined Dec 2004, 1527 posts, RR: 54 Reply 11, posted (4 years 8 months 3 weeks 4 days 20 hours ago) and read 1610 times:
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