Boeing 737-800 Winglet

[Olowookere Devost]

Boeing has now developed, built* and are installing their own winglets for the 737 MAX family. The "Advanced Technology" winglet combines rake tip technology with a dual feather winglet concept into one advanced treatment for the wings of the 737 MAX.". They are split-tipped, straight-edged winglets for the 737 MAX. (see photo below)

Winglets are also available for Classics. The first winglet equipped 737-300 flew in Nov 2002 and gained its FAA supplemental type certificate (STC) on 30 May 2003. Winglet equipped Classics are known as Special Performance (SP).

If winglets are so good, you may wonder why all 737s dont have them. In fact 85% of all new 737s are now built with winglets, particularly the 800 and 900 series and of course all BBJs. It comes down to cost versus benefits. Winglets cost about $725,000USD and take about 1 week to install which costs an extra $25-80,000USD. Once fitted, they add 170-235kg (375-518lbs) to the weight of the aircraft, depending upon whether they were installed at production or a retrofit. The fuel cost of carrying this extra weight will take some flying time each sector to recover, although this is offset by the need to carry less fuel because of the increased range. In simple terms, if your average sector length is short (less than one hour) you wont get much the benefit from winglets - unless you need any of the other benefits such as reduced noise or you regularly operate from obstacle limited runways.

There is a small difference in rotation rate for aircraft with winglets installed and, as a result, the crew needs to be cautious of pitch rate. There is approximately a unit take-off trim change between non-winglet and winglet aircraft so the green band is slightly different for winglet aircraft. Finally, the dry maximum demonstrated crosswind limit is slightly reduced with winglets to 34kts. According to APB this is because the FAA will only let us document the max winds experienced during flight test... so if we had been able to find more crosswind, then the 33kts might have been more. There appears to be no weather cocking effect due to winglets.

Description
Winglets are wing tip extensions which provide several benefits to airplane operators. The winglet option increases the Next-Generation 737's lead as the newest and most technologically advanced airplane in its class. These new technology winglets are now available on 737-800s as well as on the Boeing Business Jet (737-700 and 737-800).

By allowing a steeper climb, winglets pay off in better takeoff performance, especially from obstacle-limited, high, hot, weight-limited, and/or noise-restricted airports. Performance Improved climb gradients increase 737-800 allowable takeoff weight (TOW).

Winglets lower drag and improve aerodynamic efficiency, thus reducing fuel burn. Depending on the missions you fly, blended winglets can improve cruise fuel mileage up to 6 percent, especially important during a time of rising fuel prices.

The addition of Aviation Partners Blended Winglets to the 737 Next Generation has demonstrated drag reduction in the 5 to 7% range that measurably increases range and fuel efficiency . In addition, the Blended Winglets allow the 737-NG to take off from higher, hotter airports with increased payload.

With winglets, you can be a good neighbour in the community you serve. They enhance performance at noise-restricted airports and cut the affected area by 6.5 percent, saving you money on airport noise quotas or fines. By reducing fuel consumption, winglets help lower NOx emissions by 5%.

By increasing Payload Range and Overall Performance, Blended Winglets add flexibility to fleet operations and route selection. Air Berlin notes, "Previously, we'd step-climb from 35,000 to 41,000 feet. With Blended Winglets, we can now climb direct to 41,000 feet where traffic congestion is much less and we can take advantage of direct routings and shortcuts which we could not otherwise consider."

Airplane provisions
Structural modifications to accommodate the winglet include strengthening the wing's centre section and other internal strengthening on the wing. These enhancements are done in the normal production process. Various systems changes have also been made to accommodate winglet installation.

Operational Considerations
There is a small difference in rotation rate for airplanes with winglets installed and, as a result, the crew needs to be cautious of pitch rate. There is also approximately a unit take-off trim change between non-winglet and winglet aircraft so the green band is slightly different for winglet aircraft.

This is a 737-200Adv, L/N 628, fitted with mini-winglets. This is part of the Quiet Wing Corp flap modification kit which gained its FAA certification in 2005. The package includes drooping the TE flaps by 4 degrees and the ailerons by 1 degree to increase to camber of the wing. Benefits include:

Boeing has now developed, built* and are installing their own winglets for the 737 MAX family. The "Advanced Technology" winglet combines rake tip technology with a dual feather winglet concept into one advanced treatment for the wings of the 737 MAX.". Using what they call"NaturalLaminar Flow Technology"

The AT Winglets measure 8 feet from root to top of winglet and a total of 9 feet 7 inches from bottom of lower tip to top of higher tip. The top portion is 8 feet 3 inches and the bottom portion is 4 feet 5.8 inches. The ground clearance of the bottom tip is 10 feet 2 inches.

Boeing claim they will give 1.5% fuel burn improvement over current technology winglets. They explain this as follows:"The AT winglet further redistributes the spanwise loading, increasing the effective span of the wing. The AT winglet balances the effective span increase uniquely between the upper and lower parts and therefore generates more lift and reduces drag. This makes the system more efficient without adding more weight."

*Two suppliers are manufacturing winglets for the 737 MAX programme, GKN and Korean Air Aerospace Division in South Korea. Production of the GKN winglets is at the GKN site at Cowes on the Isle of Wight in the United Kingdom with final assembly at GKN's facility in Orangeburg, South Carolina.

The new split scimitar winglets with which United Airlines is retrofitting its Boeing 737-800 and 737-900ER fleets look similar to the winglets which feature on the new Boeing 737 MAX family. United estinates each set of split scimitar winglets will reduce by 2 per cent the fuel burn of any Boeing 737NG on which they are installed Once the split scimitar winglets are installed, United expects the winglet technologies installed on its 737NG, 757, and 767-300ER fleets to save it more than $200 million per year in jet fuel costs. United will begin retrofitting its 737-800 and 737-900ER fleets with the new winglets beginning early next year, once testing and FAA certification of the winglets are complete.

Take a look at the photo at right showing the wingtips of a United Airlines 737. These two-part Split Scimitar Winglets are now undergoing Federal Aviation Administration certification testing at Grant County International Airport at Moses Lake, Wash.

These subtle increases in fuel efficiency are significant in the heated battle between Boeing and competitor Airbus over orders for their competing re-engined models of their narrow body aircraft, the 737 Max and A320neo, respectively.

The retrofitted winglets also are important for carriers in their own cost-cutting efforts. Aviation Partners estimates the Scimitar winglets will save United Airlines, its first customer, 57,000 gallons of fuel a year for each 737-900 ER.

That joint venture has been enormously successful, and has sold and installed its original blended winglets on more than 4,000 737 NGs (Next Generation). These days, nearly every new 737 NG rolls off the Renton line with the blended winglets already installed.

So while Boeing will be using its own advanced technology winglet on future 737 Max aircraft, Aviation Partners Boeing already has landed 455 firm orders and options for its Split Scimitar Winglets, and expects to get a lot more. These winglets are being purchased by airlines such as United, to be retrofitted onto the wings of existing aircraft.

The testing at Moses Lake is being handled by Aerospace Testing Engineering and Certification LLC, which has leased 23,000 square feet there, according to Pat Jones, executive director of the Port of Moses Lake.

Aviation Partners has started showing airlines a split-tip winglet with blended, "scimitar"-edged feathers as a retrofit option that the joint venture estimates can reduce fuel consumption by 2.5 to 3% on next-generation 737s. The move precedes a launch decision by the board of directors of the Aviation Partners Boeing (APB) joint venture, but that approval should come "shortly", says Joe Clark, founder of Aviation Partners, the Seattle-based firm that designed the standard blended winglet ordered on more than 4,600 737NGs. Aviation Partners unveiled the scimitar-edged winglet last October and launched flight tests on a 737 Boeing Business Jet in April, which confirmed the estimates of computational fluid dynamics models to within one-tenth of a percentage point, Clark says. "We are very pleased with what we've achieved," he adds. While APB prepares to offer a scimitar-edged split-tip winglet on the 737NG, Boeing is readying a straight-edged split-tip winglet on the 737 Max.

Both companies claim to have arrived on the split-tip configuration for the 737 at nearly the same time by coincidence. Aviation Partners had no prior knowledge of Boeing's "dual-feather" split-tip winglet for the 737 Max, and has received no information on the design from its joint venture partner, Clark says. For its part, Boeing also was unaware of the Aviation Partners design when it began working on the Advanced Technology (AT) winglet around June 2011, says Robb Gregg, a chief aerodynamicist for the 737 Max. "As I was looking at the configuration, we needed to get more performance out of it and really the only place we hadn't spent a lot of time was looking at the [wing]-tip," Gregg says. Boeing completed trade studies between August and September last year, he says, then fabricated a set of optimal shapes for testing in a wind tunnel. Although the split-tip design appears to be a new innovation, it traces back to Robb's previous work as a chief aerodynamicist at McDonnell Douglas. The airframer that merged with Boeing in 1997 had pioneered the installation of winglets on airliners in the mid-1980s. The MD-11 entered service with an up/down winglet, with a shortened lower surface forward of the upper surface. The lower surface was shaped to improve stall characteristics at low-speed, Gregg says. McDonnell Douglas also proposed a split-tip winglet for the short-lived MD-12, a late-1980s concept for a four-engined double-decker. As the chief aerodynamicist of the MD-12 concept, Gregg says, he proposed the split-tip to optimize lift of a wingspan artificially constrained to a length of 64.9m (213ft) to fit into existing airport gates. Likewise, the 737 Max also demanded more performance than a blended winglet could produce. "Because we needed more performance to satisfy the customers we felt we needed to push the technology a bit further," Gregg says. A split-tip wingtip has never been tested in flight test, and Boeing currently has no plans to test the 737 Max AT Winglet on a surrogate platform. Boeing is confident that computational fluid dynamics models have predicted drag characteristics accurately, Gregg says. At the same time, Boeing is not convinced a split-tip winglet will produce performance improvements as a retrofit option on the 737NG, although it has not conducted an analysis yet. Holding Boeing back is the knowledge that the AT Winglet increases the aerodynamic loads on the outboard wing section. "The better the winglet the more load it's going to drive outboard. Otherwise it didn't do anything for you," Michael Teal, chief project engineer on the 737 Max, said in a July interview. "The question is how difficult it would be to retrofit," he added. "You're getting out there on the end of a wing; it's not that thick. It's not something that's easy to take apart and add gauge to." Despite being joint-venture partners, Boeing and Aviation Partners also have different views on the margin of benefit provided by a split-tip winglet. Boeing predicts the straight-edged split-tip on the 737 Max will contribute 1.5% to fuel burn reduction. Aviation Partners, on the other hand, is proposing a 2.5% to 3% benefit from installing the scimitar-edged winglet on the 737NG, which shares the same airfoil as the 737 Max. Even so, Aviation Partners is optimistic that scimitar-edged split wing-tips will be retrofitted on as much as 60% of the 737NG fleet, Clark says.

c80f0f1006