Winglets!?

[Dave]

Ok, so if Winglets make wings better and more efficient, why are they not on the Boeing 777?

Also, why are they small on a/c such as Airbus A320 and A380, but stupidly massive on Boeing 737?

Thanks.

[Alty]

The 777 had a wingspan length constraints of 200 ft. maximum (it ended up at 199'11"), which was probably based on airline input (presumably to fit 747 Classic gates). Some airlines also wanted folding wingtips to fit DC-10 gates, but no one ordered that option in the end.

Traditional thinking is that if you can get away with it, additional span is superior to a winglet. A winglet also adds structural complexity because it adds a bending moment. Then there is weight cost to consider. Boeing and Airbus will do exhaustive trade studies on things like this, and for the 777 the winglets did not earn their way on. But also remember that the early 90's computing technology was not what it was a decade later.

The 747-400 winglets do have a small cruise benefit, but it only shows up for mod and long haul flights (hence the 747 Domestic for Japan does not have winglets or the -400 wing extensions). These were designed empirically (with wind tunnel trials). Once influence for them making their way on the -400 was the looks - the airlines saw the mockups and liked them for their logos and distinction from the 747 Classic. The MD-11 winglets were no doubt influenced by the 747-400, were likely also empirically designed, looked cool, and were integrated into a tip extension design added to the DC-10 wing.

The 737 winglets are not "stupid" because they are large, and in fact some airlines like them for their distinctive look. They are the result of more advanced understanding of their function, as well as much-dvanced computational techniques (CFD). The promo materials for the Aviation Partners winglets also suggest a benefit for lower speed operations (takeoff, climb) which can be huge for noise abatement reasons. For an already-designed wing, the 737-ish design may make sense.

When you have a clean slate to work with, you might choose additional span as it is more structurally efficient. If you can meet the airplane performance criteria, why bother with complex and costly winglets. This probably holds for the A380. The 787 does not have winglets, but raked (swept back) wingtips like used on the 767-400. Again, there decisions were probably the result of trade-studies among the various options. As for Airbus, the 320 "winglets" look to be little more than tip fences that reduce the spanwise flow at the tip (one of the general winglet benefits), that also happen to add some level of distinction versus the older 737's.

There are probably some people out there (the Aviation Partners principals - at least some of whom are ex-Boeing) who think that all new airplanes should have a similar large winglet design instead of the raked wingtip. Who knows which is better, but if the AP was so great for a clean-sheet wing, Boeing probably would have included it. Airbus wouldn't be allowd to "use" the AP design because AP has some sort of agreement in place with Boeing.

[Beertender]

Hi Dave,

here is an article with a full explanation on winglet design:

http://www.flightinternational.com/Articles/2000/07/26/68669/Style+or+substance%2c+winglets+are+part+of+modern+aviation+. html

Cheers
Beertender

Dave,

The hyperlink does not seem to work, let me see.....
okay, here it is:

DATE:26/07/00
SOURCE:Flight Daily News

Style or substance, winglets are part of modern aviation
Graham Warwick

Some are small, some are big, Airbus¹s are a different shape and some Boeings have them and some don¹t. Ever wondered why?We¹re talking about winglets, of course, and the answer is a combination of style and substance.

Winglets were first developed in the 1960s by NASA aerodynamicist Dr Richard Whitcomb. He had the idea of putting cambered and twisted endplates on a wing to improve its efficiency without increasing its span. Whitcomb also developed the "Coke bottle" area ruling that allows fighters to go supersonic and the supercritical aerofoil that allows transports to fly efficiently at high subsonic speeds.

Winglets reduce the component of drag that is generated by lift, but increasing wing span can achieve the same effect, so designers have a choice to make. Boeing used winglets on the 747-400 because its wing couldn¹t get any longer and still fit airport gates. Learjet first used them to make its business jets look more modern, starting an enduring fashion.

Boeing decided winglets did not offer any advantage on its all-new 777, and for the stretched 767-400ER making its debut here at the show it developed a unique raked wingtip. This increased efficiency without incurring the weight penalty of strengthening the wing to take winglets.

Boeing is leaning toward raked tips for the stretched 747X, but is still evaluating winglets. Under a joint venture with Aviation Partners, Boeing is flight testing 4.4m-tall blended winglets on a 747-200F. These are bigger versions of the winglets fitted to the Boeing Business Jet here at the show and now offered on Next Generation 737s.Seattle-based Aviation Partners says the smoothly curved transition from wing to winglet makes its design more efficient. More than 100 Gulfstream II owners have already retrofitted their aircraft with blended winglets, which will be available next year for Hawker business jets. Dassault Falcons could follow.

Beginning next year, the Aviation Partners Boeing joint venture plans to offer blended winglets for retrofit to "classic" 737s and 747s.Airbus, meanwhile, has added "wingtip devices" to its A3XX large airliner. First seen on the A310 and fitted across the A320-family aircraft, these dart-like devices don¹t improve wing efficiency quite as much as winglets, but behave more predictably "off design", Airbus argues.

Bombardier, starting with the Challenger, has now adopted winglets across its entire range of business and regional jets, and Embraer has revealed that its new ERJ-170/190 regional jet will have blended winglets - similar to those on the airborne early warning version of its ERJ-145.No-one seems immune from the lure of winglets, even nature. Three decades after Whitcomb invented winglets, scientists discovered that flying squirrels raise the tips of their "wings" as they glide from tree to tree. Unfortunately, there are no squirrels in the flying display to demonstrate.

(found on Flightinternational.com )

Cheers
BT