Wing tip fences and winglets

[jhurditch]

I have a query regarding the difference between the utilization of winglet devices on jet aircraft. It is my understanding that winglets help prevent the flow of high pressure air from underneath the wing from jumping around the wing tip into the low pressure air on top of the wing reducing wing tip vortices. I am wondering why Airbus would use a wing tip fence which extends both above and below the wing whilst Boeing uses a winglet which only extends above the wing. Is there a more effective design?

[extreme P]

Airbus A320 flies with Aviation Partners blended winglets - FlightBlogger - Aviation News, Commentary and Analysis (http://www.flightglobal.com/blogs/flightblogger/2008/12/airbus-a320-flies-with-aviatio.html)

Based on this one might think yes.

[Tyres O'Flaherty]

Probably correct, but it's economics that rules.

Those straight up & down fences were probably much cheaper to add, ( remember its a cost benefit analysis that rules what is done ) than those carefully formed & aerodynamically analysed blended winglets.

They didn't go on there until it was worthwhile adding them in pounds shillings and pence

[jhurditch]

It seems supprising they would not incorporate blended winglets into the A380

[Mechta]

When I was on a contract at Airbus a few years ago, I went to a lecture on wing design given to the Filton branch of the RAeS.

Winglets, in all their forms, were a significant part of the lecture, and the bit I was previously unaware of, was how they were used to control wing bending and loads on the wing root. A well designed winglet can reduce the bending load on the root, despite generating more lift in the outboard part of the wing. Early Whitcomb winglets may have increased bending loads on the wing to the extent that the weight of the extra structure cancelled out the performance benefits.

As has been noted previously, Airbus are now offering Whitcomb style winglets on the A320, so unless it is just for marketing reasons (customers won't buy the planes without them?), they must now offer greater benefits.

Winglets can also be used to control the torsional loads in a wing; as on, for example, the QinetiQ Zephyr 7 UAV, with its 'Klingon Battlecruiser' wingtip. In this instance the large span (22.5m) and ultra-lightweight structure (50kg AUW) necessitated a tip design which reduced the tendency for the tip to tuck under.

[Jetstream Rider]

It seems supprising they would not incorporate blended winglets into the A380

Airbus were constrained by an 80m "box" into which to fit the A380, that might have something to do with it. Having the last 5 m ish as winglet might have been less efficient than having wing all the way to the edge of the box. There is a lot to think about in wing design, but I wouldn't be surprised if the span limitation was the reason for not having them.

[Mechta]

It seems supprising they would not incorporate blended winglets into the A380

Jhurditch, I think its far more likely that Airbus have held back on offering winglets at this stage, as the A380 is currently in a class of its own. They don't need to offer winglets to sell them. In a few years time, when orders start slacking, they can offer winglets as a very obvious differentiator between 'old' and 'new' A380s (think of the 747-300 and 747-400), to get the original launch customers reaching for their chequebooks again, so their fleets will continue to look 'modern'.

Having the last 5 m ish as winglet might have been less efficient than having wing all the way to the edge of the box

Jetstream Rider, I can't see how a wing extending to the edge of the 80m box without a winglet is going to be more efficient that a wing with a winglet of which the tip also reaches the edge of the box. If it were the case you wouldn't see them on 15 metre sailplanes.

[code0]

Wing fences were developed way back in 1930s by a German designer to overcome stalling problem of Messerschmitt Bf 109B (not to confuse with wing tip fences). i guess later, post war, when the civil aircraft companies started their production they looked into the matter of reducing the wing tip vortices that caused lot of drag/more fuel cost by having "wing tip fences".

Blended wing tip is a little new concept if you compare to wing tip fences. I think when it comes to reducing induced drag at cruise, so many things apply than just fitting a winglet. Airbus A320, 330, 340 are designed before than 737NG series. I personally think the pre-structural audit decision of fixing winglets (after launching the product) made the Airbus to continue with the fenced tip and Boeing to have the blended tip.

And the latest solution from Boeing is to have "Ranked tips" which does not curve upward or downward but extends the tip chord with a higher sweep angle than of the main wing. you could notice this in Boeing 777-300ER and 787 and 747-8i.

Boeing test their wingtip technologies with a US company which now consult for Airbus as well.

To answer your question, simply having different winglets is a matter of available technology and financially viable decision.

NOTE : Ideas, Opinions, Thought are just to help the question quoted.

Code0