winglets- whats the point in not having them!!

[pm07a2m]

hello all, i hope someone may be able to enlighten me on a question i have been asking myself!

Taking into account that winglets singnificantly reduce the amount of drag that is created on the wing tip hence increasing fuel efficency hence more money why aren't all a/c equipped with them!?!

I assume it will have something to do with stability or maybe for structural reasons... I know it is potentially a silly question but i cant come up with solid answer!

Thanks

[Check Airman]

On a new design, the wings may be sufficiently advanced that winglets don't make an appreciable difference.

On an older design (eg 727), it may be a matter of not being able to recover the cost of designing, certifying and installing winglets.

Notice that the 777 and 787 have simpler designs (raked wingtips) and older airplanes have the horrific looking blended winglets that seem to be in vogue nowadays.

[Lyman]

They add weight. They are an addition to an a/c, hence costly to acquire and install. Today's iterations are generally not tunable, they cannot be optimized through a wide speed range, limited to generally, cruise.

They stress the wing, adding more weight to accomodate added root and spar strength. They can hit obstacles on the ground. Probably more reasons...

[sonsama91]

It all comes down to the aspect of the wing
If the wings are able to create more lift to drag ratio the wings don't require winglets, rather becomes a added weight to the wings than being a performance feature.

[sevenstrokeroll]

I understand that winglets can REDUCE the demonstrated crosswind landing/takeoff component.

[compressor stall]

And on some a/c their economic benefit only becomes apparent on flights of greater than a couple of hours.

[john_tullamarine]

Some suggestions -

(a) wingtip treatment is an alternative, but generally not as good, way of getting what you get with a longer wingspan.

(b) we have a massive investment, worldwide, in airport infrastructure

(c) for the recent larger aircraft, wingtip treatment is a far cheaper alternative to not be able to get into existing aerobridges

(d) for smaller aircraft .. marketing .. they look good/modern/pretty/technologically with it/etc ... pick your choice

(e) as an add on there are structural penalties especially in fatigue but that may be a far better option than a very expensive wing redesign ?

(f) and, as Stallie suggests, not really a proposition for short range ops

[FlightPathOBN]

Well, there is certainly a can o wahtever.

The wing design must be balanced. There is an optimum wingspan for the ac config...
but that is optimum...

while the optimum wingspan for fuel efficiency at flight is X (that also depends on optimum) The wingspan must be able to work with all of the settings, and access, for it all to work.

With the 737, the wingspan optimum wingspan for each wing, ends up to be about 6 feet longer that the ac has. This is a function of better design software than 20 years ago, but also as a balance.
If the wingspan on the 737 were extended to the new optimum, the ac would no longer be a CAT C aircraft. Hence, it was found, that if you turn the wingtip up, you had an 'equivalent' wingspan, the software showed reduced drag, and therefore...better fuel efficiency.
But this was all based on the average model, of the wing section in flight.

So, what you really needed was more of a variable section, that would better perform though more phases of flight.

While the Airbus T and the end of the wing was really good, the software models didnt really understand how to properly calculate the results, hence a square peg in a round hole.
The recent 737 MAX winglet, appears to optimize more flight conditions, but in reality, still appear to use the same CFD models, which get you so far, but are still 40 year old technology.

In reality, we are seeing a transition.
From trying, at all cost, to keep within certain CAT wingspan requirements, to optimum wingspan design.

[Check Airman]

Given that the winglets are best suited for longer flights, why are they being fitted to 737's? I never could figure that one out.

[john_tullamarine]

if you turn the wingtip up, you had an 'equivalent' wingspan,

ballpark, sails are worth around 3/4 their length in span extension

why are they being fitted to 737's

same as for any design, it comes down to doing the sums and figuring the compromise .. unless, of course, the Chairman's wife just happens to like the look of them

[Mr @ Spotty M]

One other reason is that it also increases your maintenance costs, so if you don't need them, don't install them.

[Old Fella]

Check Airman. The B737-BBJ has a claimed range of 5980 nautical miles with up to 25 PAX or up to 5510 with 50 PAX. The RAAF use it as their primary VIP aircraft. Maybe that may help you figure it out.

[Old Fella]

For anyone who does not know, the JAL B747-400D is used on domestic services with high density seating and standard passenger capacity of 568, although up to 660 can be carried in one class configuration. Extra windows on the upper deck and lack of winglets are give-aways.

[chuzwuza]

The airline that i work for operates a fleet of several leased 757's without winglets. The owners of the aircraft have blocked the proposal to install winglets for the sole reason of the modification will roughly half the resale value of a high hour 757 due to the fact that the alteration in wing loading transfered to the fuselage will not allow the large freight door to be installed in the event of a cargo conversion. Its very common for high hour 757's to be snapped up by cargo operators. The airline or operator would see some financial benefit but the owner will be out of pocket long term.

[FlightPathOBN]

The wing configuration is an average design for optimization. Each configuration or use, would have a different optimized wing design.
The 737 first went into service in 1968 (?!?!?) damn!
Computer modelling and design have changed a bit, and due to access and CAT, the wingspan is stuck. turn em up, turn em down, or both..the longer and thinner at the end, the less 'theoretical' drag, and better economy, theoretically.
Of course, it has nothing to do with the ever reducing size or lack of outboard flaps...negating the size of that big round dork hanging off the bottom of the wing structure!

[Uplinker]

Winglets save around 2-5% fuel, but cost $100,000's to install.

It's simple maths really - draw a graph of installation cost and operating costs against the operating life of the airframe. The point where the lines cross defines your break-even point, and give you an idea of whether winglets are worth having for your particular route structure.

U

[Pontius]

For anyone who does not know, the JAL B747-400D was used on domestic services with high density seating and standard passenger capacity of 568, although up to 660 could be carried in one class configuration. Extra windows on the upper deck and lack of winglets were give-aways.

There you go Old Fella, just bringing your post up-to-date. All part of my pedantic git service ;)

[Sillypeoples]

Few pilots are capable enough to fly the aircraft to design limits, then seek that extra 5-10% performance.

It's beyond frustrating sitting in a plane all day long at lower altitudes, limited ranges, lower speeds, because the FAA is trying to buffer the performance envelope for a battalion of golf buddies, pals, idiots nephews, airline SOP robots, marshmellow first officers, unqualified owners, 200 hour ab initio wannabee pilots and so on.

[ramble on]

I would like to see if there is any benefit to variable or folding/extendable winglets - either in the lateral or longitudinal planes.

Modern technology and materials must have made this possible.

Folded for ground operations & high speed cruise & climb.

Extended for increased aspect ration benefits in takeoff, cruise and landing.

Any thoughts?

[john_tullamarine]

I was involved with such investigations as an undergrad in the early 70s. The idea goes back a long way.

[32SQDN]

Is the leading edge of the upturned winglet the same as the rest of the wing? If so, how does it reduce drag?

[FlightPathOBN]

I think that when you look at the bottom line, you have to consider exactly when the advertised benefits occur. The 5%-9% isnt for all phases of flight.

From Boeings chart, you can see that on take-off, there is little benefit.

From what it looks like to me, the benefit of winglets comes from a reduction in the angle of attack.

So for en-route, at the beginning when heavy, a decreased angle here would appear to be the most benefit. As the fuel load lightens, the angle would normally decrease, but there is a limit, or minimum angle for both with/without winglets, so, the benefits equal out at some point.

I suppose someone could actually calculate this out, and provide a real cost benefit analysis. So if the airline is really serious about the expenditure, perhaps this is the way to approach the issue.

In regards to the winglets providing a dampening effect in turbulence, I have not heard anyone say very much about this.

Swept wingtips and x wing configurations cloud the issue as well....

[Sillypeoples]

Winglets: Bolt on fibreglass. Big deal.

The fact that they cost serious money has more to do with capitalism, the business of aviation, then certification and such.

[john_tullamarine]

then certification and such.

There's a fair bit of resubstantiation necessary for wing structure, in particular. Certainly not just a case of bolting on some widgets with style and dash and away we go.

[Uplinker]

Perhaps an aerodynamicist can correct me, but isn't the purpose of winglets to reduce the tip vortices caused by the high pressure air underneath the wing rushing round at the wingtip to the low pressure region above the wing? In doing so, a spinning vortex is generated which causes drag?

Also, why are the Boeing winglets huge, but the Airbus A300/320/321 ones tiny? - presumably they have different performance?

U

[FlightPathOBN]

uplinker,

No: there are no tip vortices.
Certification: the bending moment of the wing is increased substantially with a winglet, Boeing had to 'prove' the forces under circumstances, especially with speed brakes, so that the forces were in bounds of the wing design, and additional reinforcement was not required (ie re-cert of the ac)
Winglets are a balance that must be considered, when deciding to purchased them, or in fact offer them.
In offering them, its a doubled edge sword, as an add on, you are basically stating shortcomings in the wing design of the aircraft. Much like the advertised increased benefits of the air system of the 787, vs your current platforms.
To compound the issue, offer a completely different winglet design on the 737MAX....

As stated before, the airflow over the top of the wing, as the section decreases, becomes turbulent, creating drag.
The winglet design moves that turbulence outward, creating less drag, and allows for a decreased angle of attack on the wing.
This has the most benefit on the beginning of the enroute phase of flight.
As the fuel load decreases, and the required angle decreases, the benefit of the winglet decreases vs the minimum required for level flight.

[cwatters]

Uplinker - There is a simple way to understand the main advantages of winglets...

High aspect ratio wings (eg long span narrow chord) are more efficient than low aspect ratio wings (short span, wide chord). Thats because the disturbed air at the wing tip represents less of a fraction of the span if the span is bigger. So anything you can do to increase the aspect ratio is generally a good thing.

Unfortunately you can't just increase the wing span indefinitely for practical real world reasons. Winglets work by increase the effective aspect ratio without increasing the span.

They aren't a totally free lunch. Increasing the efficiency at the tip effectively moves the center of lift (of each wing) outboard increasing the bending moment.

The AOA of the wing is easy to control. It's not so easy to adjust the AOA of the winglet. So the winglet might have to be optimised for one particular speed (eg cruise).

[henra]

It's not so easy to adjust the AOA of the winglet. So the winglet might have to be optimised for one particular speed (eg cruise).

Boeing has done some tweaking of the toe-out of the winglets on the 737 NG. Background was to reduce wing bending moment in order not to overload the structure.

They ended with a 2 degree toe- out.
Comparison of parasitic drag showed no appreciable difference to the 0 degree starting point.
However the AoA reducing effect off the winglets decreased slightly, thereby reducing the efficiency improvement by a small amount with flaps extended.
However, this is more then compensated by the reduction in wave drag, profile drag and trim drag (see figure 9 in linked document).
As a conclusion it appears the Winglet AoA is rather tolerant.

http://www.boeing.com/commercial/aeromagazine/aero_17/winglets.pdf

[Uplinker]

OK.

And what's the difference between the Boeing and the small Airbus winglets? Do they work in the same way?

U

[Linktrained]

Uplinker #31

You may find some of the discussion with Takata on 17 July 2011 on pprune.org af447 Thread no5 pages 392-397
may be of help...
I would guess at 40,000 hours/ aircraft's life when the wing-tips should provide a benefit. For the rest... just be grateful !

I think that they are both aeroplanes.

( Sorry, cannot redirect you, my computer/I ... too old !)

LT

[Sillypeoples]

I ponder the drag penalty of adding anything in the slip stream, and ponder if they are hyped to a certain extent.

Reminds of vortex generators....told that they wouldn't add drag in cruise...that was a lie, cost about 5 kts...but the slow flight advantages are worth it.

[Uplinker]

Thanks.

U

[Old Aero Guy]

Folded for ground operations & high speed cruise & climb.

Extended for increased aspect ration benefits in takeoff, cruise and landing.

Any thoughts?

I believe that Boeing is doing this exact thing on the proposed 777X.

[FlightPathOBN]

Its a bit of hype for sure...how to introduce advances in wing design, without telling everyone the previous design wasnt all that good!
Notice the 787, no winglets there....they use a raked wingtip design, which I believe is what the 777x and A350 will all have..

With the wing, the airflow at the leading edge is at the same velocity across the wing. The trailing edge, as the wing section gets smaller, the laminar flow begins to separate from the wing skin surface, causing turbulence, or cavitation, drag...much the same as in all of the oversimplified stall sections we have seen.
http://www.aviation-history.com/theory/lam-flow.jpg

The addition of the winglet reduces this turbulence in several ways. The one most likely to have the greatest benefit is the decreased angle of attack of the wing tip section.
This is fairly easy to correlate with data out there. From the charts, it shows that winglets have little difference in takeoff, and only slight increase when you get to heavy loading at higher altitude airports.

In cruise, when heavy, the winglets provide the most benefit. As the required angle of attack decreases with reduction in fuel load, the benefit of the winglet decreases.

If you are always running light, or short flights, you will likely see little benefit of the winglets...

[Linktrained]

Who can predict what " my" new fleet of aircraft will be doing in thirty years from now, all short haul and lightly loaded, or what ?

I flew some of the Silver Wing scheduled services between Manston and Le Touquet (20 minutes each way) AND on passenger charter flights to Idlewild and back in a Hermes 4a. Perhaps we ought to have changed our wings for each kind of flight ! (But only at our base !)

The Martin Mars flying boat military transports are still around as fire fighters, probably not considered when they were first thought about .

TL

[henra]

Notice the 787, no winglets there....they use a raked wingtip design, which I believe is what the 777x and A350 will all have..


It seems to be an general trend to increase the span of new airliners.
It seems the older designs have usually rather (too) short span. This is where the winglets shine.

When designed from the get go with the optimum span winglets probably won't bring enough benefit to compensate for the additional wave drag/form drag + the added structural weight + costs.
Maybe due to rising fuel prices the additional costs / restrictions resulting from airport fees / limitations with increased span seem to take a bit of a back seat compared to raw efficiency nowadays. Last but not least improvements in structural design/computation allow for longer, higher aspect ratio wings without excessive structural weight penalty.

Looking at further rising fuel prices in future I would not be surprised to see even longer span airliners potentially with slightly reduced cruise speeds.

[FlightPathOBN]

or this concept for the A340...

http://www.flightglobal.com/assets/getasset.aspx?itemid=40977

[Pugilistic Animus]

Folded for ground operations & high speed cruise & climb.

Extended for increased aspect ration benefits in takeoff, cruise and landing.

Any thoughts?
Quite possibly the structural ramifications militate against the success of that concept...:)

[FlightPathOBN]

Concur, adding that to the end of a wing would likely negate any benefit...

The 787 and 350 wing flex should be designed to prevent the wingtip angle of attack creating separation of the laminar flow over the top, thus reducing the drag....I can see the sweep helping with the twist, but this is a tall order...

Anyone remember this?

http://www.flightglobal.com/blogs/unusual-attitude/767-400ER%20wingtips.jpg

I am looking forward to looking at the wake vortex from the 787, and the 747-8.

[FlightPathOBN]

Luke Skywalker influence at Boeing...

http://www.aviationweek.com/media/images/fullsize/CommercialAviation/Airlines/AeroMexico/AeroMexico737MAX2AeroMexico.jpg