Winglets
For another authoritative explanation of modern wing design(with quite a bit on winglets) try:
Wing Aerodynamics and the Science of Compromise. Jeff Jupp RAeS Lanchester Lecture 10 May 2001. I have heard Jeff described as the father of the A340 wing! His lecture explains clearly what factors are involved in modern wing design. He also makes it clear that although elliptical loading is the theoretical optimum for a wing of given span it is most emphatically not the optimum for a wing of given weight. |
Owain Glyndwr
"Elliptical". As in: Spitfire? Does this refer to plan, section, chord, or Station? I'm lost. Lyman |
Elliptical, as in lift distribution. How you achieve that is up to the designer, Spitfire wing is the 'easy' way but not the only way.
Onglide is able to do the comprehensive answer, but then he dioes make his living as an aero consultant. |
Lyman
"Elliptical". As in: Spitfire? Does this refer to plan, section, chord, or Station? [local lift coefficient (at any spanwise station) times local chord]/ [wing lift coefficient times mean aerodynamic chord] plotted against spanwise station as a decimal fraction of semispan. Aerodynamicists obtain the span loading they desire by combinations of planform (local chord) local AoA variations (wing twist) and wing camber (no lift angle) Sorry if you are lost! |
Once lost, now found. Good Scout!
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The only questions remaining in my mind are -
Why do the 777-200LR & 777-300ER have raked wingtips rather than winglets? And how does the raked wingtip provide any benefit? Is it similar to a delta in that the wing ends at a point rather being squared off? |
The raked wingtip is precisely a winglet rotated coplanar to the wing.
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OG: Great explanation mate.
Regarding retrofits to early designs, am I right in thinking that their wings were typically more highly outboard loaded than current practice (to minimise wave drag with their early transonic aerofoils)? So these wings have stronger tip vortices to work with and lift distributions that start closer to the non-planar ideal. A question remains: Once you realise you have your 6% strength margin to spend on a wingtip modification, what are the considerations that would lead you to add a winglet rather than merely extending the span? |
Would it have to do with newer and lighter materials available, also advanced modelling to suss risk/benefit in development instead of on wing test programs?
OG mentioned gate width and taxiway clearance re: added span? |
what are the considerations that would lead you to add a winglet rather than merely extending the span? |
OG,
Interesting post... I am currently working with the real-time wake turbulence measurements, so I understand the roll-up, creation, advection, and decay of the vorticies, and the effect of winglets and sharklets quite well. (crunching data on hundreds of multi-variant arrivals, incl A380) Would be interesting to converse on these matters, especially in regards to wingtip vorticies. |
So these wings have stronger tip vortices to work with The vortex is a rollup combination from the bottom surface of the wing structure, (for lack of a better example, a boat plane in the water) coupled with the rollup from the top surface of the wing. Just as a boat planing through the water, the surface area in contact, the shape of that surface, and the directional flow as a resultant of that surface, are what create the vortex. The winglet or sharklet, tend to reduce the drag associated with the outer portion of the wing, where the camber and length are at their greatest discontinuity, winglets/sharklets reducing the turbulent airflow in the last portion of the wing, ie cavitation, thus reducing drag. Winglets/Sharklets, in reducing the cavitation, in smoothing the airflow, will tend to optimize the particular wing for its particular vortex creation. This is not necessarily a bad thing, and each configuration must be looked at distinctly. Just as the angle of attack differs with conditions and aircraft loading, so does the resultant vortex. (Leave out the weight, focus on the aircraft config at load) Current designs of winglets/sharklets rely on a certain configuration... this is similar to fixing flaps at a certain configuration... hardly optimized flight. |
FlightPathOBN
How close are we to articulating Winglets, and are they indicated? |
Lyman,
I would suppose that given the wingflex of the 787, that may be a resultant. If the wing was designed for the aircraft, then the winglet would be moot, but perhaps the resultant wingspan may be too great, hence a turn-up to artificially lengthen the wing. In reality, we are looking at a blend from Bernoulli to Newton. |
these wings have stronger tip vortices to work with |
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The 777W has 'Raked" wingtips, basically horizontal winglets, which, because of their tapered shape, serve the same basic purpose as the traditional winglet
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yes, with the wingflex on the 777, that would be the only option...
think if the 787 had vertical winglets like a 737... http://operationsbasednavigation.com...mb-476x237.jpg |
I can imagine a reason for having the winglets pointing up, (avoidance of the runway surface perhaps) but would they be more effective if they pointed down? ie containing the higher pressure.
I have a propeller on my paramotor with the 'winglets' pointing to the higher pressure side of the blade. |
Downward pointing winglets would, I think, create more zero lift drag in the form of interference drag (where there are sharp angles between surfaces)...
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Jan 2012. Airbus files patent for flexible downward pointing winglet...
Airbus Files Patent For Downward-Facing Winglet at Flightstory.net - Aviation Blog, News & Stories http://www.flightstory.net/wp-conten...-2-613x700.jpg |
QinetiQ's Zephyr 7 UAV used downward facing wingtips, although from what I recall, these were to reduce torsional twisting in the wing. It was explained to me how, but I can't remember. :confused:
http://images.xpert-zone.com/images/oooueu.jpg |
Why no 777 winglets......
To counteract this effect, the wing needs to be strengthened. On an Airbus A330, some 440 pounds of reinforcement had to be added. Tamarack Active Winglets Offer Weight-saving Aerodynamic Improvements | Aviation International News |
new Poseidon...
http://sphotos-a.xx.fbcdn.net/hphoto...01380765_n.jpg |
Look who didnt read this thread!
JetBlue Airways (JBLU) has agreed to purchase 110 ship-sets of retrofit Sharklets from leading aircraft manufacturer – Airbus. http://finance.yahoo.com/news/jetblu...w_default=true |
A350 XWB...interesting configuration of winglets...
http://image-store.slidesharecdn.com...0-original.jpg |
FlightPath,
It looks weird because of the perspective of the photo. Here is another photo taken of the same airplane. http://i.imgur.com/uuqth6O.jpg You can see the right winglet is nicely tilted upwards and not "curled-over" like your photo makes it look like. The left winglet explains the discrepancy between your photo and mine - the winglet is actually curved backwards towards the tail. It seems logical that this would help reduce induced drag as the winglet is affecting the air for a longer time, reducing the intensity of the wingtip vortex. It'd be interested in some aerodynamic analysis of this but I doubt Airbus will be revealing any of that data! |
As an aside to the discussion on winglets, why does the B777 have such pronounced dihedral?
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not sure on the 777..
I am curious why the brand new P-8, which is a 737-800 built with 737-900ER wings, looks like that... |
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