according to this photo and caption, these cool looking winglets increase efficiancy all around and pay for themselves.
If these are so great, why don’t all new wide body jets have them? They can’t cost so much as to be a deal breaker, can they?
If it’s good enough for luxair and Aeromexico , why ain’t it good enough for the good old USA?
Burt Rutan’s being doing similar things with aircraft for decades. Supposedly, when he was fresh out of college he got a job at an aircraft manufacturer as an engineer, but quit when he realized that they weren’t open to new ideas.
There’s probably a jillion or so reasons why they’re not in use on US jets: bureaucratic inertia, FAA regs, customers aren’t demanding them, etc., etc. I remember reading ages ago in Popular Science about how someone had figured out that if you made the wing on a jet a ring, you’d get all kinds of fuel economy and safety benefits from it, but so far, I’ve yet to see a single jet with one of those wings.
I think Southwest is also going for the retrofit. A modification like that won’t be cheap. If you have a plane nearing the end of its useful service life you need to look long and hard at the cost/benefit aspect.
I hadn’t heard about this. Is it a horizontal ring or a vertical ring?
Me either. However, I remember in grade school the teacher had my son make a ring out of paper and it flew just beautifully. A whole lot better than any paper airplane you ever saw. It flew with the ring vertical.
Vertical ring. A quick google turns up this site complete with Photoshopped images!
I don’t design the things I just fly 'em, but…
Airliners use the wings to store fuel. If you fill that nonplanar wing up with fuel you are going to have serious control issues. All that weight sitting so far above the fuselage = much larger elevator surfaces required. Also, can you even build a structure like that that wieghs as much as a current wing but (in the MD-90 pictured) carry 40,000 lbs of fuel? What about control surfaces? They would have to be curved as well, and provide as much roll authority as the current ailerons that sit way out on the end of the wings.
Just my initial thoughts on the thing…I’m sure some engineers will point out the errors of my ways!
As to the winglets on US airlines,
Southwest is getting them on new 737-700s, as is ATA with their -800s.
As MonkeyMensch pointed out if an airplane is close to the end of it’s service life the mod won’t be worth it. The legacy carriers in the US (AA, United, Delta, Northwest, Continental, USAir) are still hurting financially and need every available dime for daily operations.
I think the winglets look great, and I’d love to see them on more airplanes.
I can’t remember the details of the article, but here’s a variation on the design which appears to not have some of the problems that you mentioned.
Here’s a NASA paper on the subject. Googling “nonplanar wings” turns up the highest number of relevant hits (“ring wing” kicks out a bunch nonrelated stuff, and “ring wing plane” gets nothing), but most of the results are .PDF files, so I won’t link to them.
Now THOSE look more workable! Thanks for the links!
Winglets improve efficiency at high speed and high lift profiles by reducing drag. They move the wing tip vortices caused by the air below the wing meeting the air above the wing further out. The vortices interfere less with the airflow out there.
But, there always has to be a pay off, right? They weigh more and because they are way out on the end of the wing, the wing has to be strengthened to cope with the extra load stress, which in turn costs more weight. At low speed-low lift, when the vortex strength and airflow velocity is lower, the winglets have less of an effect. In fact, in this situation they increase form drag.
So, they are only cost effective over longer distances and when long climbs are required. For that reason, airlines that intend to use the aircraft for short hops choose not to use winglets. Also, the new Boeing 777 was designed from scratch using new computer aided design equipment. This method produced a much more efficient wing shape which made any aerodynamic improvements from winglets negligible when balanced against the excess weight and wing stress.
http://www.b737.org.uk/winglets.htm
http://airtransportbiz.free.fr/Technique/Thewinglet.html http://www.boeing.com/commercial/737family/winglets/index.html http://oea.larc.nasa.gov/PAIS/Concept2Reality/winglets.html
Watching a fully-loaded 777 takeoff you can see some serious wing flex.
As cabdude pointed out, it makes winglets uneccessary. Heck, in this photo the wing is starting to take on that “ring” shape!
cabdude is right, but there’s more. The winglets don’t just relocate tip vortices, the relocation weakens them as well. The tip vortex, which you can see sometimes as a “white tornado” in humid air, is caused by air flowing from the wing underside around the tip to the lower-pressure top side. That flow in turn reduces pressure under the wingtip, reducing its lift and making it largely dead weight (but making it possible to make lighter than the lifting area of the wing). The vortex represents pure inefficiency - a fair amount of power goes into churning air, not lifting the airplane. To compensate, you either have to make the wing larger (a common tradeoff) or add winglets (another common tradeoff).
The winglet tends to separate the low- and high-pressure regions, inhibiting the vortex from forming in the first place. Although there is still some delta-P at the winglet’s tip, it’s much lower and the vortex is therefore weaker, with less energy loss. Boeing’s blended designs reduce turbulence due to interference between the horizontal and vertical surfaces, something like wing root fairings at the fuselage do, but they weigh and cost more than a retrofit design would. Nothing comes free.