One of the great success stories of the last decade in aviation has been the development of winglets, an Aviation Partners success. Now factory installed on virtually all Boeing 737s, these devices are becoming ubiquitous with “modern” commercial aircraft and are often thought of by the public as differentiating a newer model from an older aircraft.The “conventional wisdom” in the industry is that winglets significantly increase fuel economy, and provide about a 5% benefit in fuel economy for aircraft that utilize them. The reality is that those benefits occur only in specific high altitude flight regimes, and that a more realistic average fuel savings benefit, for typical domestic operations, is about 0.5%.
The reality certainly doesn’t match the hype, and even Airbus will soon be offering “sharkets” on its A320 because competitively its airplanes, despite being more efficient with their small wingtip fences for most flight regimes, don’t look like the new Boeing’s.
So why is everyone installing winglets on their aircraft? Hype, and not fully analyzing the advantages and disadvantages associated with them.
Winglets change the operational characteristics of an aircraft, and while they operate well at high altitude, above FL390, they require a slower climb to be as efficient as a non-winglet equipped aircraft in that regime. As soon as you speed up during climb, the fuel efficiency advantages of a winglet equipped aircraft turn negative, and rather than climbing at 330 knots after 10,001 feet, a winglet equipped aircraft needs to climb at 250 knots at FL100, 260-270 knots at FL150, 270-280 knots at FL180 to match climb fuel economy of a non-winglet equipped aircraft.
While more efficient at high altitude, for many flights on the US east coast and west coast, where heavy traffic areas exist, a flight may not get above FL270, and never reach the altitude at which the efficiency of winglets kicks in. And at those lower altitudes, cruising at more than M0.71 will result in an increase in fuel consumption because of the weight of the winglets and parasitic drag.
Airlines operating aircraft in a mixed fleet of winglet equipped and non-winglet equipped aircraft need to modify their operational speeds to maximize efficiency as well as procedures, as aircraft that are winglet equipped handle differently than those without winglets. This can be particularly important on landing, particularly on wet or snowy runways.
Winglets add lift to the wings, which results in faster speeds for the aircraft in ground effect. While jets typically increase speed by 7-8 knots in ground effect, winglets exacerbate that process, with speed increases of 10-12 knots once power is off. Without different operating procedures, it is easier to overrun a runway in a winglet equipped aircraft than one without winglets, as the speed change in ground effect can increase landing distances. And because winglets generate additional lift, the effectiveness of braking can be minimized unless pilots pull back on the yoke to firmly transfer weight from the nose wheel to the main gear and wings, which is not a part of normal operating procedures at many airlines. The potential for a runway overrun is more significant with a winglet equipped aircraft unless operational procedures are modified, as evidence by a couple of recent events.
In addition, winglets add weight to the wingtips of an aircraft, more than 1,000 pounds for a typical Boeing. This has an impact on the strength of the wing, effectively weakening wing torsional rigidity and introducing aeroelastic issues that must be compensated for, currently accomplished by the installation of about 100 pounds of depleted uranium in the leading edge to reduce the twist on the wing generated by the winglet installation. A basic 737 has a high gust tolerance, well in excess of regulatory standards, but one modified with winglets will lose much of that margin above regulatory requirements.
A rule of thumb for most aircraft is that its cost is about 3% of any additional weight carried in fuel each hour. For a winglet equipped aircraft, operating on short-haul routes with virtually no fuel efficiency benefit, a winglet equipped aircraft could, depending on operating procedures, have a negative, rather than positive, impact on fuel economy.
If you don’t believe the numbers, run a flight plan for a short-haul flight that doesn’t go above FL330 for a winglet and non-winglet equipped aircraft. The fuel differential will be about 0.5% better, not the 5% commonly repeated by pundits in the industry.
The position we take is not unique. Russian aerospace, for whom winglets are not a new technology or idea, have decided not to use them on the Sukhoi SuperJet or on the forthcoming MC-21.
The reality is that the payback for winglets will take about 10 times longer than marketing brochures would imply, unless all your flights are long-haul operations operating above FL390. For Air New Zealand’s 767s, winglets make perfect sense for their long-haul operations. For short-haul domestic operations, one must question the payback of winglets, which certainly isn’t going to be quick with a 0.5% fuel benefit. We wonder whether taking on 1,000 pounds of revenue belly cargo, rather than saving 0.5% of fuel with winglets, might generate a better economic result for an airline.
Are lease residuals are a factor that should be discussed?
Marketing trumps good sense. .. again?
Quite an interesting and intriguing post.
“The reality certainly doesn’t match the hype, and even Airbus will soon be offering “sharkets” on its A320 because competitively its airplanes, despite being more efficient with their small wingtip fences for most flight regimes, don’t look like the new Boeing’s.
So why is everyone installing winglets on their aircraft? Hype, and not fully analyzing the advantages and disadvantages associated with them.”
This doesn’t sound like typical behavior of customers (aircraft operators) that ponder every percentage point of performance and insist on provisions in the contracts (with airframers and engine makers) regulating promised vs delivered performance (i.e. price adjustments or refunds/penalties if the agreed performance levels are not met).
So, in this case, customers that are ordinarily fastidious about such contractual concessions from their equipment suppliers simply bought the hype wholesale?
Or am I misunderstanding that paragraph?
Do airlines like US’s Southwest or Alaska operate wingleted aircraft for “hype?” Have they, “not fully [analyzed] the advantages and disadvantages associated with them?”
If these aircraft, “operate well at high altitude, above FL390,” and have all the mentioned disadvantages below why hasn’t the airlines demanded a change, like folding winglets? Have regional airlines flying, for example, Embraer’s E-jets, Bombardier’s CRJ’s been duped? Do business jets like Gulfstream or Daussalt Falcons have winglets just for good looks?
We’ve seen retrofits on some long range/higher flying aircraft, like 757’s & 767’s, but why not on the long range high flying A380? And, was Aviation Partner’s business plan based on just pure marketing and, “conventional wisdom?” Is Airbus wasting time, money and resource on A320 & A330 winglets just for “hype?”
I’d love to see some documentation supporting your position. I find it very hard to believe that companies for which profit margins can be so thin as to often be non-existent, just buy into ‘hype’ without running the numbers.
Really having a hard time believing this article at face value.
@ ISTAT, appraisers suggested that winglets, on average, add $1-$1.2 million in value to the aircraft. If anyone has hard numbers, surely it is the appraisers?
And if they are right, wouldn’t that suggest the average yearly savings are in the $350,000-450,000- range (2.5-3 year payback)?
Mr. Arvai,
Please checkout the work of three high school students (two seniors, one junior) who proposed an alternative approach for the winglets….these bright young students won CT Science & Engineering Fair award and will be representing state of CT at the ISWEEEP Olympiad.
http://www.youtube.com/watch?v=nukPT8l9M0o&feature=relmfu
and also do searches on CT Science Fair winners.
Only BS reported from the Boeing PR !
Airinsight has been more serious in other times !
So …
6% when needed for the B737 (And B757)!
And when Airbus appears with 3 1/2 %
No more interest for the winglets !
Conspicuous indeed !
AP will be happy to know they equipped thousand planes for years, just for nothing !
And winglets customers, of course , did’nt notice any fuel economy, and still order winglets !
Please be more serious next time !
Just read John Croft on FlightGlobal !
http://www.flightglobal.com/news/articles/aviation-partners-winglets-on-all-factory-built-737s-this-year-370560/
While I am not questioning the numbers as such, I’d like to point out that I’d expect the numbers to be different for each airplane and mission. So just by running a flight plan for a specific model on a specific route I’d actually be very surprised to see the 5% quoted by marketing. Only overall analyses might warrant reliable numbers, and along with some others here I doubt that airlines squeezing the penny out of their operations would by into something which makes the airplane more inefficient, just because it looks cool.
Also, I’d like to question the speed increase in ground effect (does the speed really increase? I would assume it bleeds off, and less quickly with winglets) and especially the proposed handling technique “pilots pull back on the yoke to firmly transfer weight from the nose wheel to the main gear and wings”. In my understanding firmly pulling the yoke would – unless stalled – lead to an increase in angle of attack and thus in a lift increase. The described weight transfer to the mains should be taken care of when the ground spoilers are up. Please elaborate, if anyone has thoughts on that.
Ernest,
very interesting. Is your assessment based on your understanding of flight physics, based on data from actual flight operations, or based on third party analysis?
In my younger days, when I made paper airplanes, I found that when I folded the ends of the wings UP, as in winglets, the plane performed better. This was back in the 50’s. Did I miss something?
Kind of makes sense. I work for Air New Zealand and i hear the B767 is doing better than first predicted and achieving 5% savings but they just about always are flying 6-10hr sectors. But now we are getting the A320 sharklets and so far i’ve heard there are no fuel saving benefits!! Most of our A320’s go across the Tasman so only a 3hr flight. Domestically its a 1hr flight average!!.
…In addition, winglets add weight to the wingtips of an aircraft, more than 1,000 pounds for a typical Boeing. This has an impact on the strength of the wing, effectively weakening wing torsional rigidity and introducing aeroelastic issues that must be compensated for, currently accomplished by the installation of about 100 pounds of depleted uranium in the leading edge to reduce the twist on the wing generated by the winglet installation. A basic 737 has a high gust tolerance, well in excess of regulatory standards, but one modified with winglets will lose much of that margin above regulatory requirements.
++++
Obviously APB is clueless about the weight issue . .
http://www.flightglobal.com/news/articles/aviation-partners-winglets-on-all-factory-built-737s-this-year-370560/
. .Although the winglets increase the operational empty weight of the 737 between 100-236kg (220-520lb), depending on the model, the associated benefits include an increased range of 130nm (241km) or payload increase from 1,996-2,303kg.
Of course they have installed only a few thousand of them- I’m sure your study will be a wake up call !!!
There’s a lot of “might” and “if” in this article. As in 737s “might” not get above 270, or “if” they go faster than certain speeds. As someone who flies airlines at minimum twice a week, on both short and long flights, throughout the united states, i have yet to hear over the PA system of us flying below 270, except in turboprops.
As someone who flies planes for a living as well, the issues of runway overruns due to winglets and the higher ground effect speeds…i would assume the FAA would place in the aircraft operating handbook and type rating programs information on balanced field length that would be updated for the new configurations. Also, the 121 operating rules state something along the lines of having X amount of runway, plus a clearway of X amount, with a climb gradient of x amount.
Finally, on the overall fuel burn benefits of winglets, 5% or .05%, savings are savings. With the amount of fuel an airline goes through a year, even the smallest bit can probably pay for the modification itself very quickly
There. Variable folding winglets proposed by a few kids. Next they have to industrialize the concept…
Design a hinge that won’t freeze up and won’t need much maintenance.
Integrate controls into flight computers.
Re-enforce the wings even more.
Moreover, these three kids have to convince everyone, especially Ernest S. Arvai, moving winglets are not just for passenger amusement.
AFAIK Airbus has ( applied for?) a patent on flexible wingtip devices for span extension.
Turned down winglets that extend via wingflex from flight loads.
The A380 wings already go slightly in that direction with their
unloaded drooped shape. Contrast the straighter wings on the
787 that loose span from upward flex .
Argg.
That should have been a reply to :
RH Hastings on April 11, 2012 at 3:19
I have been saying of many years….winglets are fads! Just as “T” tailed aircraft are fads…no real advantage with either configuration. The Boeing 787 design effort probably the most significant effort to minimize fuel burns in recent years does not include winglets. Why? No significant advantage!
Sounds like a potential case for the design of an alternative.
Is a cheap, light, and reliable foldable or retractable version out of the question? Still have a weight penalty but you can take away the speed and drag limits.
Can it be cost effective across a fleet when the winglet only deploys when the conditions are beneficial?
There are many cars on the road with rear spoilers. We know they have little effect at the speed most people are driving at. But they look sexy and are still very popular.
There could be a similar passenger appeal towards winglets. It must therefore be a factor that airlines have to take into consideration. So if a particular airline has a flying profile that does not justify the addition of winglets they might still buy the winglets in order to attract or retain more passengers. And just like a used car with a rear spoiler will command a higher price so it goes with the residual value of an aircraft with winglets.
Winglets can be compared to aircraft range. Most airlines don’t use the range most of the time. But it’s there in case they need it. Whenever an aircraft has to fly a high altitude profile it will greatly benefit from winglets. Like for the range, the potential is always available. But for an airline like Southwest, where the vast majority of flights are too low to benefit from winglets, it becomes a less obvious decision. Unless passenger appeal and aircraft residual value compensate for potential shortcomings like additional weight, gust tolerance and runway overruns. I certainly would like to hear what the airlines have to say on this issue.
What would be interesting is a study of the benefits of winglets on a modern aircraft like the CSeries. Does it have winglets because it also has a long range? Is the weight penalty minimized because it has a composite wing? Is the material itself better suited to respond to the torsional forces induced by the winglets? Is a black wing easier to optimize aerodynamically to better benefit from winglets?
Lots of questions remain to be answered. But we must thank Ernest Arvai for this eye opening article. The author must have expected that it would generate a lot of controversy. It stands as tribute to his courage and integrity to have run against a prevailing paradigm.
If the winglets did NOT pay for themselves in a reasonable amount of time, OR if they did NOT save fuel on an airlines route structure, they would NOT either upgrade older models or pay an additional cost for installation on NEW planes.
IF there were overall performance problems on takeoff or landing, you can be sure it would be well documented.
Properly designed winglets are more than end plates, and are different than the NACA/NASA early versions of same.
The author is speculating based on some sort of unreferenced data/analysis
In opposition to the analysis are several hundreds of small- medium- large aircraft flying with versions of same
The 787 features raked wingtips, another wingtip device that operates along similar lines. There was a plan for winglets on the shortened 787 variant that was suspended due to lack of interest.
Exactly, if coolness counted as much as it does for automobiles, every airline would fly Concordes.
Of course Boeing PR has a bias- but at the same time- they do a good job of presenting what they claim are facts and data. Would that the author provided similar ?
http://www.boeing.com/commercial/aeromagazine/articles/qtr_03_09/article_03_1.html
. . . Airlines have been gathering operational data on blended winglets since they first began flying airplanes equipped with the modification in 2001. These benefits include:
One operator flying 737-700s had three years of data showing a fuel savings of 3 percent.
Another operator flying 737s also reports that blended winglets are helping reduce fuel consumption by 3 percent, or about 100,000 U.S. gallons of fuel a year, per airplane.
Other airlines are projecting results based on historical flight data about airplane models recently equipped with blended winglets:
An operator with a fleet of 767-300ER airplanes estimates that installing blended winglets will save 300,000 U.S. gallons of fuel per airplane per year, reducing CO2 emissions by more than 3,000 tonnes annually.
An airline that recently began flying 767-300ERs with blended winglets anticipates that each airplane equipped with the winglets will save up to 500,000 U.S. gallons of fuel annually, depending on miles flown. The airline plans to install winglets on its entire 58-airplane fleet of 767-300ERs, which could result in a total savings of up to 29 million U.S. gallons of fuel per year and a reduction of up to 277,000 tonnes of CO2 emissions annually. ..
And quite a few diagrams and history are also available on that site with references.
BTW- check the details found at
http://www.boeing.com/commercial/aeromagazine/aero_17/winglets.pdf
Hopefully, this will put the authors version in perspective
Can or will the author provide credible support for the following . . .” Winglets change the operational characteristics of an aircraft, and while they operate well at high altitude, above FL390, they require a slower climb to be as efficient as a non-winglet equipped aircraft in that regime. As soon as you speed up during climb, the fuel efficiency advantages of a winglet equipped aircraft turn negative, and rather than climbing at 330 knots after 10,001 feet, a winglet equipped aircraft needs to climb at 250 knots at FL100, 260-270 knots at FL150, 270-280 knots at FL180 to match climb fuel economy of a non-winglet equipped aircraft.. . “
It seems the A380’s gull wing (“unloaded drooped shape”) is not that easy to manufacture and requires special somewhat secret processes & equipment to install the skins (notably the lower skins). Now, the rib feet cracks on the lower of ribs 24-26 are reportedly caused by faults in this manufacturing technique and materials selection, but could the “wingflex” at this location be problematic?
Dear Mr. Arvai,
I have been lucky enough to have operated the B767 for the last 9 years. 5 of those on aircraft without APB winglets, and the last 4 years, with them installed. I believe that you are using unsubstantiated rumors to formulate your piece.
The numbers on Takeoff Analysis and Performance in our manuals are unequivocal in showing that the Winglets perform in a very positive manner, not only in the cruise portion of the flight but also and perhaps greatly, in Takeoff Performance. To cite some examples:
1. On the runways that we are very limited, with the winglets, we have performance numbers (and have utilized them for our benefit) that allow in many cases takeoffs with 4 to 5 thousand more KG´s of weight. That is per flight. As one of those runways is at an airport where our route is not far away, this translates directly into 4 to 5 thousand KGs more payload…PER FLIGHT! This alone provides a substantial additional income source for the company.
2. Due to the lower drag factors associated with the wing having winglets installed, the Optimum Cruise Altitude is increased in the 767 by 700 ft for all weights. This does´t sound like much, but in reality, it allows us to economically climb 2000 ft higher for the initial portion of the cruise on long sectors. Where before we maintained an initial cruise altitude of 29,000 ft, now we can climb to 31,000 ft at those heavy weights. When very heavy, it is best to consume that initial fuel in the most efficient way possible, and the winglets allow us to fly 2000 ft higher giving us better fuel flows at cruise right from the start of the trip.
Furthermore, the comment regarding overruns is highly skeptical. Overruns are usually attributed to unstabilized approaches o with contaminated/slippery runway conditions. These factors will occur on an aircraft with or without winglets. I assure you, from personal experience, that 144 kts is 144 kts whether I have winglets or not. The aircraft having winglets do float more, but having problems on touchdown comes out to not using proper technique or not following procedures. I have yet to see a runway overrun analysis where the Investigating Authority attributes the accident to the aircraft having winglets.
I would also like to comment on the fact that you state that Airbus know that their “old” technology endplates (as installed on the A320 family and the A380) but are going along with the Sharklets just for marketing purposes. I firmly believe that should they know that the old technology is better, they would go “all out” in making everyone believe that this is true, instead of investing valuable time and money in certifying the Sharklets.
When my company began the installation of the winglets on our aircraft, I had the opportunity to fly a sector on a straight winged airplane, followed a few hours later by a good friend of mine in a winglet equipped airplane. We had the opportunity to compare the results of the flight at the destination over a few drinks, and we were initially let down. We found that they had flown 8 more minutes consuming 500 kgs less fuel (with the winglets). But to our amazement, they had flown with 6000 kgs more payload! So immediately, on one flight we were hooked and knew that this was a great thing.
Thanks for your attention.
Sincerely,
SEQU
I suggest you read NASA report NASA-TM-81892, Flight Evaluation of the Effect of Winglets on Performance and Handling Qualities of a Single Engine General Aviation Airplane. Their views based on actual flight testing are at great variance to this article.
Geeze- after two years and a few hundred/thousand airplanes built nor retrofitted with winglets/endplates/sharklets/scimitars/ etc with bucu documented facts re fuel savings- there is still some naysayers or people who want to plow the same ground re old NASA reports?
Yes there are some flight regimes for which winglets may not be as good as ” raked” tips, etc dependant on airplane size, speed, and load factors.
Why not give it a rest and look up actual published- credible data over the last DECADE??
If you read the report you will find it totally supports the advantages of winglets even on lower speed general aviation aircraft. I am not a naysayer as I have actually designed and tested winglets on lower speed aircraft and the advantages in high angle of attack flying such as takeoff are not small.
Dear Mr. Arvai:
Most airlines operate on the thinnest of margins. It is true that some airlines are poorly managed but most of them do pay considerable attention to fuel burn. Without refuting your claims one by one, your assertions are not borne out by the physics or the accumulated data. Regardless of the fact that clean-sheet designs may in some cases favor alternative wingtip designs (such as raked tips) there are now thousands of aircraft with winglets saving their operators money every day. As they say, never let facts get in the way of a good story. Mercifully you are not consulting for the airline that I work for.
What Mr arval **may** be confused about is perhaps referring to old ( over a decade ) history as to how winglets came about on BA 737 airplanes ( not to be confused with prior use on small jets ). This was the result of a Boeing internal battle taking place in the late 90’s-early 2000’s when BA was “bought out” by MDC. The MDC aero types were infused into the BA commercial side about the same time as BA was working on the NG versions of 737. Those aero types had been pushing the ‘ mdc” inboard trailng edge ‘ wedge” used on the DC-10/11 to try to correct the aero design shortfalls resulting in a shortfall of range/payload on DC-11, such that MDC had to subsidize a few emply seats on long flights. BA had by that time spent a few 10’s of millions on the ‘new’ 737 wing for a realatively small impprovement. The founders of Aeropartners were ex BA types- and were trying to get BA to include winglets on the 737. The MDC types gave all sorts of reasons why not, and were pushing the ‘ wedge ‘ bit. At the same time, BA was selling the BBJ version of 737. But those buyers were not suitably impressed by getting a BBJ that was not externally different from a few hundred commercial 737,s. Sort of like why buy the chrome wheel spinners ? So on the premise that if it could be shown there were NO negative effects of the neat looking winglets on performance, BA agreed to run a few tests. The tests compared wedge, new wing, winglets, etc. The data was such that the BBJ could offer them .
There was still internal strife on the issue- but based on credible improvements in short range flights, A german ” local ” carrier ( forget which one) agreed to accept a few 737 with winglets. The rest of course is history.
The above is the long version of why winglets got a chance-which WAS the equivalent of Chrome spinner hub caps for your corporate/private jet.- they DID- do look neat.