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fightglobal.com26 |Flight International| 1-7 May 2012

JOHN CROFT WASHINGTON

Winglet manufacturer Aviation Partners isbringing in a raft of new drag-reduction

technologies that could benefit both operatorsbottom lines and the environment

FUELSAVING

TIPS

Seattle-based Aviation Partners (API)is ready to flight test a slate of newtechnologies with the goal of allow-ing aircraft operators to boost fuel

economy and correspondingly produce lesscarbon without the need to buy new aircraft.

Fuel will be the most expensive commod-ity next to gold, so drag-reduction improve-

ments are going to be important, says JoeClark, president and founder of API. With

many of these aircraft, theres room for a5-15% improvement in drag during cruise.

Along with variations on the winglettheme, including spiroids, split winglets andscimitar tips, API is also investigating ways toreduce drag with modified wing shapes andplacement of vortex generators to prevent air-flow separation just forward of the aileronsand spoilers, and in aft-body areas.

Less drag means less thrust required by the

engines to maintain cruise speed, which cor-responds to lower fuel burn at that speed. The

new work comes on the back of APIs successin the airline industry with its first wave ofdrag-reduction add-ons: blended wingletswhich API produces for business jets or forBoeing commercial airliners via Aviation Part-ners Boeing (APB) its 55/45 joint venturewith the airframer.

To date, APB has provided winglet kits for4,400 Boeing 737s, 757s and 767s, saving op-erators an estimated 3.1 billion gallons (14.1

billion litres) of jet fuel as of mid-April, whichcorresponds to a carbon emissions saving of

ENVIRONMENTCOVER STORY

One of Aviation Partners

innovations is split wingletswith scimitar tips

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1-7 May 2012 |Flight International| 27fightglobal.com

spiroids regarding fuel economy and environ-mental friendliness for its next generation 737Max, targeted for entry into service in 2017with Southwest Airlines, but tail section clean-ups are on tap. Boeing says the aircrafts tailcone will be extended and the section abovethe elevator thickened to improve steadiness ofair flow. This eliminates the need for vortexgenerators on the tail, the airframer says.These improvements will result in less drag,giving the airplane better performance.

WINGTIPS MYSTERY

The wingtips remain a mystery. While allcommercial 737 customers are selecting APBwinglets for installation at the factory, Boeingcontinues to evaluate trade-offs betweenblended-type winglets and Boeing 777-stylehorizontally raked wing extensions used onthe US Air Forces P-8A Poseidon, a variant ofthe 737-800. Max concepts have shownblended winglets. For other aircraft in produc-tion, optimal design work was carried out atthe engineering stage, says Clark. Certain air-craft are so superb theres not much you cando. Clark says the Boeing 777 has the finestwing. There are a lot of others that need a lot

of help though.Help may also come in the form of upkeep.

Clark says API is considering continuous im-provement programmes in which an operatorwould have an aircraft inspected every sixmonths to a year to make sure drag reductionseals are properly gapped and leading edgeseals are not out of whack. Theres a lot of im-provement that can be had, he says. Seals getold and could be worn. We think there are waysto buy airlines or private jets another 4-5% indrag reduction due to the way the aircraft wearfrom a new-type state over the years.O

year were proven to reduce long-range cruisedrag by 11%. While significant, the idea of acash-strapped airline replacing blended win-

glets with an all-new winglet likely to requirecostly modifications to the wing, is a non-starter. Were looking at most of our technol-ogies to be retrofittable, says Clark.

However, spiroids continue to be the topicof research for the next-generation air transpor-tation system. The US government paid API $2million for the spiroid-equipped Falcon 50 testdata to evaluate wake turbulence informationas part of an effort to determine if such tech-nologies could reduce wake turbulence separa-tion criteria to decrease in-trail aircraft separa-tion distances. Clark says spiroids couldeliminate wake vortices in the near-field region

behind an aircraft.API is also looking inward from the wingtip

to gain fuel efficiency. Were looking at waysto reduce drag by different shapes, changingwing shapes or vortex generators, says Clark.At this stage, a lot of the work is in flow dy-namics. He adds that the drag clean-ups arenot uniquely targeted to jet transports but willalso apply to business jets and turboprops.,helping smooth non-optimal flow in the aft-body areas and preventing the separation offlow just forward of the ailerons and spoilerson most aircraft. Clark says he plans to flighttest some designs in the fairly near future

probably this summer.It is doubtful whether Boeing is looking at

ENVIRONMENTWINGLETS

API has tested its radical spiroid

winglets on a Dassault Falcon 50

To watch a video on the unveiling of Aviation

Partners blended split winglet concept, visit

flightglobal.com/scimitartip

I heard many airlines talking

about [winglets], saying its

the best bang for your buck

that you can getBILL ASHWORTH

President, Aviation Partners Boeing

more than 33 million tonnes. The companyestimates it will reach the 5 billion gallonssaved mark by the end of 2014.

Available for the 737-300/500/700/800/900,757-200/300 and 767-300ER, the compositewinglets decrease fuel burn anywhere be-

tween 1.9% and 5.6% for segments greaterthan 500nm (900km) in length, depending onthe aircraft model, while increasing range andpayload, take-off performance and aircraft re-sidual value, says APB.

It adds that operators typically see an in-vestment return on the $1 million winglets forthe 737, not including installation, in lessthan two years.

Airlines are primarily interested in fuelsavings, but a number of them are interestedin city pairs they can serve with the winglets,says APB president Bill Ashworth. The extra2.1-5.2% fuel burn decrease for the 757-200

translates to an extra 180nm in range, a keyelement in 757s being used for transatlanticroutes, for example.

I spent my entire career in the [mainte-nance, repair and overhaul] business and in-stalled a lot of winglets, says Ashworth, for-merly the president of Goodrich AviationTechnical Services and former head of the USFederal Aviation Administration aircraft certi-fication office in Seattle. I heard many air-lines talking about [winglets], saying its thebest bang for your buck that you can get. Itsmuch less complicated than engine improve-ment programmes. Nothing moves and main-

tenance is inexpensive.An augmented version of the blended win-

glet with a ventral fin and scimitar tips onboth fins, called the blended split winglet,was to begin flight testing on an API Boeing737 on 25 April, Clark says. The appeal of thesplit winglet over more radical but higher per-forming options such as the spiroid, is that thesplit winglet can be retrofitted to an existingblended winglet.

FLUID DYNAMICS

Modifications would include peeling back thecomposite skin of the blended winglet and

strengthening the structure to handle the ven-tral fin loads. It is not clear on the impact, ifany, the ventral fin will make on low-wingaircraft in terms of roll allowances for take-offand landing.

Based on computational fluid dynamics(CFD), API thinks the split winglet with scimi-tars will reduce blended winglet drag an extra2.5%. Blended winglets with scimitar tipsalone provide a drag decrease of 0.5%. Onour last two projects, CFD predictions havebeen within one-tenth of 1% of flight test re-sults, Clark says.

The more radical spiroid winglets API test-

ed on a Gulfstream II in 1993 and most recent-ly on a Dassault Falcon 50 business jet last

Aviation

Partners