Late model Boeings - why no winglets?

[Mr Proachpoint]

Saw a B777 on approach the other day and wondered why the much heralded innovation of winglets wasn't carried on beyond the B744 and the late model B737/BBJ series. Is there such a thing as a wing that doesn't benefit from these additions?
When you study the theory behind them, they do make a lot of sense.

Any ideas?

MAPt

[SeveralMillionPounds]

This might explain (excerpt from a FAQ site I found):

If winglets are so great, why Why don't all airplanes have them? In the case of the Boeing 777, an airplane with exceptionally long range, the wings grew so long that folding wingtips were offered to get into tight airport gates. Dave Akiyama, manager of aerodynamics engineering in Boeing product development, points out that designing winglets can be tricky because they have a tendency to flutter. And so the computer came up with a Boeing 777 wing design that did away the winglets and fly just as efficiently.

"Bearing in mind I'm not an aerodynamicist", as they say..

More here
http://www.geocities.com/khlim777_my/

[fixa24]

winglets were a "customer option" on the b737*8, so i'm assuming it is the same for all a/c....

[Groaner]

Blended winglets (the smooth curvy ones) are designed and sold by Aviation Partners, who Boeing have a shareholding in. They have some patented design stuff on the winglets. They sell them to airlines both as customer-furnished equipment which Boeing then installs on the production aircraft, or as retrofits for later installation.

They've only so far done blended winglets for -700s and -800s, and are trying to get the -300's certified.

I heard they are looking at other types (MD-80s), and then maybe widebodies.

Apparently the blended winglets are a lot better than "normal" wing-ends, and somewhat better than "kinky" winglets (in fuel efficiency, maintenance savings due to reduced engine thrust, and in obstacle-limited or short airfields). So we might see them on 777s yet, but probably not for a long time. Maybe 767-300s first.

[HotDog]

It's called Raked wingtips. The raked tip is more efficient in reducing tip vortice drag and is lighter than winglets.

[avioniker]

BTW
The -300 STC is approved and there are more than a couple of planes running winglets as we speak...:D

[ft]

If you are free to design a new wing, and span is not a limitation, adding the same weight as a bit of extra wing span is more efficient than adding winglets.

However, winglets are relatively easy to add to an existing wing design.

Further, winglets make a neat place to display the company logotype... :rolleyes:

Cheers,
Fred

[Mr Proachpoint]

I saw a documentary in NZ recently that blew the trumpet of the B747 from day one to the B744. The Boeing lot are a pretty proud bunch of lads and ladesses but the one that came through as the proudest was the 'Winglet Guy'. He was one of the many thousands of people who assemble the 747-400 and his only job was to bash in the close tolerance pins that secure the winglets. He had a munting big hammer and a munting big smile. His point was that he had the one job that made the B744 stand out from all the others.

I reckon that even if they used (not saved) a tonne of gas on each transoceanic leg, who cares? They make a wing look very pretty. I suspect that Joe Pax has no idea what is behind them but likes the look of them nontheless.

MAPt

[747FOCAL]

HotDog,

Raked tips are no better than winglets. Boeing engineers just like them better because they came up with the idea. But......in true Boeing fashion, it takes forever to get good ideas on airplanes. I have a 707 marketing pitch that shows the 707 with raked wingtips. The pitch is about 50 years old.:p

[HotDog]

Yes Focal, I'm well aware of the fact that raked wingtips have been around a long time. Conventional wisdom seems to think they are more efficient than winglets.

<Raked wingtips have been around for about 50 years but it seems modern wing design has only adapted this philosophy in relatively recent years.
The fore runner of modern raked wingtips was called the Hoerner wing tip, in common use on STOL wing designs.
With a conventional rounded or square wingtip, the vortex is centered around the wingtip. If the wingtip is cut at 45 degrees , with a small radius at the bottom and a relatively sharp top corner, the high pressure secondary air flow travels around the rounded bottom but can't go around the sharp corner and is thus pushed outward.
The performance of the wing depends on the distance from the right to left tip vortices (the effective wingspan) and not the actual measured geometric span. Raked wingtips provide the longest effective span for a given geometric span or a given wing weight.
The raked tip is more efficient in reducing tip vortice drag and is lighter than winglets.>

[E1453]

The winglet should be something the enginneers use to fix a problem without having to redesign it all over.

In all cases in commercial aviation, winglets appeared to solve weight problems, so the basic wing design could be preserved, wich saves a lot of money.

examples: MD-11: they couldn't stretch the DC-10's wing enough to suport the increased weight of the MD-11 over the DC-10 (remender, the original DC-10-10 wing had already been stretched to build the DC-10-30)

A340: Airbus was expecting to use new Super Fan engines from IAE, wich did not came to life, so they were stuck with less powerfull CFM engines. To improve performance, probably 2nd segment performance, they added the winglets

B747-400: same thing. New version, more range = more weight + same wing = winglets

ERJ-145XR: new version, longer range = winglets

[747FOCAL]

Hotdog,

Hats off. I was more poking fun at the manufacturers for not implementing sooner. Though the difference is small, raked tips appear to be more efficient.

:)

[used2flyboeing]

Bent winglets are good - but they are really onthere for sex appeal .. The Boeing raked winglets are really quite interesting - their profile on the bullnose is rather blunt - some exotic engineering from stodgy old boeing I'll bet .. They also fit into ancient airport parking stalls better ..

[FJJP]

But then there is the question of wing bending relief. However, I would guess that airlines don't intend to keep the ac long enough for root fatigue to become an economic issue. Why spend money on pretty winglets when you don't have to? Let the next owner worry about fatigue problems...