Fairly recently I see many planes with upturned wing-tips–it looks like about a one-foot extension on each wing pointing up at about a 90-degree angle. I’d like to know what that’s about, and if it’s really fairly new. If they’ve ‘always’ been like that, I’ll eat my hat. :eek:
They’re commonly called winglets. The first big passenger jet to have them was Boeing’s 747-400 in 1985.
Oh, and as for their purpose:
I think that they appearing on planes about 20 years ago. Plane are expensive items that last 20 or 30 years, so it takes a while for most planes to have them. I would guess that around 1/2 of the jets I see at the airports have them now.
They reduce wingtip vorticies which give better fuel economy by reducing drag.
Many thanks for the cites/sites for interesting reading.
The winglets are a substitute for longer wings, which accomplish the same effects mentioned above (i.e. improving the lift-to-drag ratio). They give performance almost as good as making the wings longer by the length of the winglets. They reduce the overall width of the plane, which has certain advantages, one of which is the ability to fit into a standard gate at an airport.
P.S. Contrary to popular opinion, vortices are not a bad thing. Without vortices, there would be no lift. It is all about optimizing the vortices to give the lift, but avoid drag to the extent possible.
Here is a citation for my previous post. I learned this from John Denker’s fabulous tutorial on the physics of flight:
Prior threads on point. In the older threads you can see the tone of both the Q & A is that these are something pretty new:
From 2004: Boeings' blended winglets - Factual Questions - Straight Dope Message Board
From 2005: Boing! Boing! Boeing! Airliner related questions - Factual Questions - Straight Dope Message Board
From 2006: Why do the wings of jets curve up at the end now? - Factual Questions - Straight Dope Message Board
My assumptions: the velocity and weight of the aircraft have a direct bearing on the effectiveness of the winglet.
Right or wrong or somewhere in the middle?
ETA: Mighty fine link there, JWT Kottekoe.
I’d turn that around. Any given winglet is designed to fit the wing it’s attached to. And speeds & wing loading are a key factor in winglet design. Some wings can benefit more than others.
One of the main advantages to winglets is that you get 80-ish% of the improvement you’d get by simply extending the wing, but without the need to beef up the rest of the structure to handle even more lift even farther out on that long skinny lever arm. So in terms of incremental performance per incremental weight gain, they’re a very good trade.
They’re also one of the few mods you can make to an in-production wing without needing to go back & rework a lot of upstream structure. Which makes them cost effective for the manufacturer to sell & the operator to buy.
Winglet’s benefits accrue mostly in cruise. So a wing whose mission involves very little cruise (e.g. fighter or crop duster or trainer) will not see a mission benefit from adding them. Converesly, any long range transport will benefit, be it a small bizjet or an A380, and regardless of whether it’s fast or slow.
Would winglets have worked on (say) a DC3? Funny how they are a new innovation.
That would depend on the winglet. This will certainly be true of winglets designed for airliners, as cruise is where they spend most of their flight time.
But because a big part of a winglet’s job is to mitigate induced drag, it’s possible to design some that work well for aircraft that fly heavy and slow (when induced drag is most significant). An example would be the Bombardier 415 “waterbomber”.
Not all that new. Burt Rutan used them on the VariEze composite homebuilt, which first flew in 1975.
Excellent question! 
I also wonder, at what speeds do the addition of winglets become advantageous?
Do they offer the same benefits/advantages to slower, propeller driven aircraft?
Damn, you’re quick, Xema! 
I’m curious about how the winglets affect the wing in ground effect. My understanding is that the wing tip vortices play a role in the WiG effect, so it seems to me that reducing them would also reduce the WiG effect. Right?
Though the first aircraft to use them on a production model was the Learjet 28
(which I’ve seen is mentioned in your link, but it’s a fact I happen to know so I’m stating it anyways! :smack::))
First aircraft, or first passenger aircraft?
The Heinkel He 162 had winglets, which can be seen here. Unlike many modern implementations these faced downwards, presumably (?) because the aircraft is already high-winged; the orientation of the winglet has an effect on the direction of the lift generated by it, as well, but given the size of the winglets on, say, a modern 737 I presume their upward-facing direction is as much to avoid giving ground traffic something to hit as anything else. I don’t know how well the physics of winglets were understood then, though, and I don’t know why specifically they were included on the 162.
To a meaningful extent both winglets and flying in ground effect are doing the same thing: reducing the energy of the wingtip vortices. Thus an aircraft with winglets should expect less relative benefit from ground effect than one without.
They are quite useful on sailplanes, which frequently spend most of thier flight under 100 kt.
Interesting! I hadn’t thought about sailplanes. Thanks Kevbo!