winglets
 

Greetings for all!

This may be the most asked question or not! but why Boeing 777's do not have have wingtip devices? but 737s winglet program caught like a fire for NGs. I know the latest are designed with ranked but not as popular as NG's original or retrofitted 6 feet winglet. Any ideas?

PS: as the reason behind the wingtip devices is to reduce the induced drag and especially long haul flights, The aeroplane which can virtually connect two cities in the world as they say doe not have any. this itches my head!

Winglets offer the best advantage if the wing design is a little long in the tooth. With modern wings winglets are much less likely to be worth their weight and cost.

Of course a really modern design that has been cocked up - especially in the tip area - could also show some payback.

Boeing 747-400 being a good case!

Or the A320 for instance *cough cough cough? - oh wait, excuse me, those are sharklets, obviously something completely different :D

STBYRUD
 

My point exactly. Since the A320 first flew in Feb 87 I would suspect the aerodynamics goes back to perhaps 1982. Thirty years is a long time ago in the aero business.

Hope your cough gets better soon.

Golly Brian. That is outside my pay grade. I have read that the most modern concepts for wing tip design try very hard to deal with the issues that winglets address regarding flow round the tip. Just look at the 787 for example.

However I do know a bloke who is s hot on such matters so I will try and contact him.

I am relying on old knowledge here, so go easy. Retro fit winglets add a substantial amount of weight when installed on older wings (especially at the wing root), so their cost benefit diminishes. Newer wings have smoother transition zones, reduced tip chord length, and flex more, something winglets addressed in the olden days.

Ah, progress.

Aspect ratio for one I would guess, and modern CAD design. The triple seven wing chord at the tip is quite narrow and is also quite thin. Winglets although have given way to the raked wingtips on more modern designs.

winglets add a substantial amount of weight

.. and can be expected to have an adverse effect on wing fatigue properties due to the additional loads.

How large is their effect on fuel savings? I remember someone saying that the bigger reason is that PAX love winglets and it improves their perceived quality of the fleet. True or BS?

Winglets do several things, sutch as lengthining the wing from an aerodynamic standpoint. Wing flex and rake are more effective as you see boeing evolve from the 777 - 787 and 748 wings. Having said that they are generally a great mod to older designed wings but some argue that it takes a longer leg to really see the profit from them.

To answer the OP's question, the 777 has a raked wing tip (as does the 787 and the 747-8) which does the same job, ostensibly, as a winglet. What it does is change the way the vortices roll off the end of the wing, so the winglet is not necessary.

For the 744: Only one winglet allowed to be removed and IIRC the MEL only refers to a reduction in performance limited weight, something in the region of 9.5T and an enroute climb performance penalty of about 4.5T.:8

777-300 and -200LR have raked wingtips. 777-200 has the standard wingtip.

5-6% fuel savings is the number I've seen (737-800 and 757-200 w/RR's)

Is the 737-800 wing a newer design then the 777's? I'd guess so. So it's not necessarily just a older wing that would benefit from a winglet.

787 wing flexes about 12' from static at 1G. That, along with modern design and materials, has to help with reducing wingtip drag.

It's a 757 wing that somebody put on a copying machine and punched in 70%.

And why, when a winglet is removed, does the airplane not roll uncontrollably if they are so effective?

The 747 wing droops when full of fuel and is substantially higher when low on fuel. Because of the sweepback, the winglets must be out of the airflow direction when either drooped or raised, and only streamlined when at mid fuel. There must be a drag penalty at the beginning of the flight and at the end, so are they really any use?

Or just look good.

I've never understood the high price put on them. Certainly they reduce drag, increase range, but trying to get half a million for them, always seemed a hard sell to me. For the most part they are a bolt on item.

In the really old days they just put a fence about halfway down the wing. Ala Hawker 700 and G-1159. eventually the winglet will go the way of the fence.

The largest gain for the 737 was in 2nd segment climb I believe.

They are certainly not bolt on items. The 767 APB winglets also require the retrofit of massive reinforcement straps inside most of the length of the wing to support the extra weight and forces generated by their addition.

Fuel saving in order of 5-6%. Saving comes from less fuel needed for trip due to drag reduction, and less fuel needed for carrying the additional fuel not now needing to be burnt - and all despite carrying an additional 1-1.5T of winglet around.