Raked Wingtips vs winglets

[teghjeet]

Could someone please enlighten me on the difference in the aerodynamics of Raked wingtips vs the winglets?

[747FOCAL]

They both do the same thing. Reduce wingtip vort drag. :)

[CR2]

Could it be said that winglets are an improvement to older wing design, whereas wings with raked tips are a new design?

[Mad (Flt) Scientist]

Since winglets tend to be more 'upright' than raked wingtips, one would expect the 'winglet' to generate more force in the (aircraft) horizontal plane and hence have a greater forward thrust component than a 'raked wingtip', but also expect the latter to generate a slightly greater vertical force component (assuming similar overall forces).

Of course, one must not forget marketing hype - god forbid a certain manufacturer be seen to be copying another :)

[747FOCAL]

Mad (Flt) Scientist ,

Not this arguement again. There may be some forward thrust associated with winglets, but not enough to even show as anything in the combined forward moment of the entire airplane caused by the engines.
:)

If Raked tips are "New" technology, why do I have concept pictures of a 707 with them installed dated from the early 50s?

:confused:

[Bre901]

Lots of threads about winglets/wingtips : search (http://www.pprune.org/forums/search.php?s=&action=showresults&searchid=1040601&sortby=lastpost&sortorder=descending)

Maybe there should be a sticky on that topic :E

[teghjeet]

747FOCAL,CR2,Mad Flt Scientist and Bre901 thanx for your inputs.
I am however seeking something like:-
1. the effect on Airflow on Top sfc of wing behaviour
2. Effect at Transonic range ....
3. etc,
spoonfeed if possible. I am currently out of touch with High Sped Aerodynamics.

[zerozero]

Aerodynamically, raked wingtips and winglets provide similiar benefits--except, as noted, winglets have the additional benefit of providing a small forward vector that contributes to overall efficiency.

Both effectively increase the wing span without the penalty (tight parking) of extra long wings.

Lots of winglets are after-market modifications (easy installation, slight weight increase).

The raked wingtip is pretty much designed into the wing before manufacture, a la the 777.

I hope that helps!:cool:

[Edit: I forgot to address your specific questions. 1) The wingtip vortex is an inefficiency. If you can move it off the wing then you leave more surface available for generating lift. Both the winglet and the raked wing tip move the vortex off the wing tip *as much as possible*. This increases the efficiency of the wing. 2) Flight can be subsonic (no shock waves), trans-sonic (first evidence of shock waves), super-sonic (greater than M1.0), and hyper-sonic (greater than M3.0). A commercial airliner's cruise speed is limited by the critical Mach Number (when shock waves first develop). Therefore, most normal cruise will never see shock waves develop with or without winglets. There's just no bearing of the winglets on shockwaves (for our purposes). The important phenomenon at work is the treatment of wingtip vortices.]

[teghjeet]

Thank yoiu Zero Zero for your information. It has indeed been very helpful

[Cejkovice]

Agree totally with ZeroZero.

Winglets/fences and raked wings are more popular now especially when you need the performance produced from a larger wing area but don't want to increase the wingspan outside a certain length e.g. may limit airport operations

[Frank Poncherello]

I think it has something to do with increasing the Aspect Ratio. Winglets create a smaller increase in the Aspect Ratio, and the associated decrease in induced drag is thus less.

Raked wingtips are a quick way to increase wing area, without making a massive modification to the wing structure (stringers and spars mainly). They can be designed to distribute the loads so that they have minimal impact on the outboard wing section.

Something like that anyways!!


:confused:

[teghjeet]

Thanx cejkovice , frank. Really informative inputs

[MaseratiGhibli]

Installed raked wing tips onto the newest 777, the 777-300ER (extended range) airplane. The 6.5-foot (1.98-meter) raked wing tips are highly tapered wing extensions used to improve an airplane's performance. The raked wing tips reduce takeoff field length and increase fuel efficiency and climb performance. Each wing tip weighs 105 pounds (48 kilograms) and are installed using 12 bolts.

[safetypee]

A notice on the wall of the Hatfield Aerodynamics Design Office (birthplace of the Airbus wing):- ” only bad wing designs require winglets “

Many, many years later ‘end’ plates were fitted on Airbus aircraft.

[teghjeet]

Thank you maserati and safetypee. It is ironic how we often become the thimgs/ people we criticise...

[SR71]

Couple of comments...

747FOCAL,

50's? Try this NACA report from the 20's:

NACA Report of Wingtip design (http://naca.central.cranfield.ac.uk/reports/1924/naca-report-161.pdf)

The argument has raged for almost a century!

teghjeet - You can see the exact effect on the pressure distributions of comparative aerofoils in the same report.

Prandtl found in the 20's that an elliptic planform was what was reuiqred on a finite wing for minimum induced drag. Hence the reason for the Spitfire's elliptic planform. The only aircraft I know of with that planform.

If you do the maths, you find induced drag is proportional to the inverse of the aspect ratio, AR, for an elliptic planform. For non-elliptic planforms, you can correct the previous expression with a correction factor

Hence, the higher the AR, the less the induced drag, or conversely, the better the L/D ratio of the wing.

Winglets effectively increase the AR because they reduce the downwash.

The problem with other solutions such as raked wingtips is that whilst AR is increased, its at a weight penalty that is linked to an increasing taper-ratio with the associated torsional rigidity problems.

Boeings Aero 17 Site (http://www.boeing.com/commercial/aeromagazine/aero_17/winglet_story.html) includes some interesting information.

And just for reference zerozero, hypersonic flight is M > 5.

:ok:

[teghjeet]

SR , thank you for the info. I have already gone through the reports.

[A-3TWENTY]

On the A-320,the wing tips increase the T/O and approach climb limit weight in 8% and the fuel consuption is increased in 2,8%.

In Aircrafts with the "blended winglets" like the 737`s NG, the fuel consuption may increase something around 7%.

:ok: :ok:

[teghjeet]

Thanks for the details A three twenty

[747FOCAL]

Winglets don't increase fuel burn they decrease it. English is obviously not his first language.

[swh]

747...

Technically, winglets do increase fuel burn as they add weight to the aircraft and increase profile drag...they do improve the Oswald’s efficiency factor for the platform which will reduce the induced drag...however this is a trade off on sector length.

Winglets are not normally installed on 737NG or 747-400s used on short sectors as there is no or little efficiency gain for the weight gain.

:bored:

[teghjeet]

thanks guys....
esp swh & 747 FOCAL

[enicalyth]

Sometimes we accept too uncritically what the manufacturers say and reporters report. Not that long ago in discussion with one maker he asserted that fuel consumption would improve by 14% at one remove thanks to new wing technology.
On closer analysis what emerged was this. Option 1 was increased wing area and wing span leading to a 2% improvement in L/D at one spot on the curves. From 16.0 to 16.32 by memory but improved engine economy permitted M0.78 instead of M0.74 for the same fuel flow so that although L/D had gone up by only 2% the product ML/D had improved by 7.5%. Next, Option 2 was to add fancy wing-tip treatment which improved L/D to 17.28, an increase of a straight 8%, again for that one spot on the curves. But by comparing ML/D for M0.78 with ML/D for M0.74 there was the hyped 14% increase in “efficiency”. All well and good but 6% of this was thanks to better engines, quite a lot to do with less induced drag associated with a better aspect ratio and only some to do with airflow at the wingtip. From a sales point of view the impression was meant to be that it was all down to the fancy wing-tip technology that the other guys did not have. Some of this was true but a few critical minutes writing an Excel spreadsheet took the lid off the tin. My guys went and bought that aircraft anyway but the choice had a lot more to do with all the other factors in operating and financing an airline. Decision made that was not how much of the press saw fit to report it. But when you sup with the devil always sup with a long spoon. I’m not saying for or against tip technology. Just beware the salesman’s statistics and partisan "My dad's bigger than your dad" views. I am more than happy to receive the paycheck and fly whatever.