Business Jet Performance: Winglets

Dave Higdon | 1st March 2002

Dave Higdon

Dave Higdon writes about aviation from his base in Wichita Kansas. During three decades in...
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Aviation Partners’ pioneering mods made for speedier- more-efficient bizjet.

Maybe you’ve heard this joke: An aviation inspector shows up on the ramp of a business man whose company plane just had two new props installed with blade tips canted aft to reduce tip losses and sound levels. The inspector- not up on the latest advances in propeller aerodynamics- grounds the plane until the 'damaged' props are replaced- then wants to cite the owner for flying away. The inspector’s punch line: 'Somebody should have tipped me off.'

Well somebody has tipped off the operators of quite a number of Gulfstream II and BBJ business jets- judging by the growing number of blended winglets installed from Aviation Partners Inc. As the beneficiary of performance improvements from a drag-cheating modification on our company plane- it’s hard not to wonder why everybody doesn’t want them.

The problem is- only two business jets currently enjoy eligibility for installation of API’s sleek carbon-fiber works of aerodynamic artistry. While that limitation may someday change as the number of airplanes for which API builds winglets grows- for the moment the owners of GIIs and BBJs should refrain from gloating.

What a drag: Tip vortices sap speed and squander fuel

Jet engines may be doing their best to suck- squeeze- burn and blow to push airframes around the sky- but airframes don’t always do all they can to make that work easy for those engines. Friction drag- induced drag- all drag- inevitable though it be- any drag is too much drag.

Years of experience- of trial-and-error- of instinct and increasingly precise computer science have brought to the fore methods to make the airframe less resistant to engines’ influence.

API uses one of the simplest looking solutions for one of the most persistent of drag sources: Those horizontal vortices that spiral off each wing tip. These so-called 'horizontal tornadoes' act like elastic bands to hold back each tip of an airplane wing.

At low speeds- those vortices cover enough area to serve as a significant hazard for any aircraft too close in-trail; at high speed and high altitudes- the vortices stretch thin and spin at a higher rate- still generating a hazard albeit a smaller one. And this view may change- given research from Canada that shows how vortices in shear layers may actually grow strong enough to damage an airframe. So reducing the power and influence of tip vortices improves both aircraft performance and- theoretically- the safety of any following aircraft.

In 1991- API’s founders Joe Clark and Dennis Washington hit on a way to improve an existing attempt to clean up tip-vortices: The winglet. The use of sharp angles in the transition between wing and winglet often generated its own negative impact.

Realizing that the air moving span-wise and aft along a wing needs a smooth transition area to depart the wing cleanly- the new company worked on perfecting a large-radius transition into what came to be called 'Blended Winglets.'

What makes the wing-like appendage work goes beyond the large curve that transitions the wing surfaces from horizontal to vertical.

The cord- taper and sweep of the winglets also factor into the shape- direction and speed of air leaving a wing at its tip. After extensive testing and refining- the company landed its first approval for the Blended Winglet and other aerodynamic mods for the first Gulfstream business jet- the GII.

Performance Payoff: GIISP gives more of what we fly for

Indeed- those mods work at many levels from which the operator can choose results most desired and fly accordingly. Faster? Farther? With more? From less? The operator of a GII with Aviation Partners’ Blended Winglets can match the flying to the desired outcome. And these are outcomes worth going out for.

Aviation Partners designed its product- the GIISP winglet- with a higher aspect ratio to help lower high-speed drag but without sacrificing solid low-speed characteristics and high-speed buffet margins. The company uses a design that optimizes aerodynamic loading while avoiding vortex concentrations that produce drag.

Compared to old-style winglet designs- Aviation Partners’ product demonstrated an effectiveness level more than 60% greater than conventional winglets of the same area but with angular transitions.

And you really do get something for the money- weight (less than 200 pounds) and downtime (about two weeks). The effect of the blended winglets’ drag reduction includes an increase in fuel efficiency of about 7.3%- which can translate into a range gain of about 200 nautical miles and an increase in cruise speed to Mach 0.8 from Mach 0.74.

Depending upon the speed you fly- you could save as much as 1200 to 1500 pounds of fuel on a typical 51/2 to 6 hour flight; you could also cruise up to 2-000 feet higher- thanks to the higher climb efficiency that the winglets bring.

As part of the GIISP conversion- Aviation Partners removes the GII’s standard wing fences and replaces them with three small 'shark’s teeth' vortilons under the wing. This change further enhances low speed handling and increases operational safety margins.

The company uses carbon-fiber composite technology to enhance the structural integrity of the winglets and for the cleanest finish possible. In fact- there are other pleasant side effects from the blended winglets: Enhanced longitudinal and directional stability- which improves handling in rough air. But it is that combination of speed-increase and fuel savings that make the conversion worth the effort.

By the numbers- Aviation Partners reports these changes in fuel consumption and cruise speed:

Fuel consumption reduced over 7% at speeds between 0.75 Mach and 0.80 Mach.
0.80 Mach for same fuel as standard GII at 0.75 Mach.
210 NM increase in range.
30 knot increase in speed.

And regarding improved handling- the company cites these enhancements:

Faster climb to initial cruise altitude.
Improved second segment climb.
Two engine climb improves 5%.
Single engine climb improves 10%- 12%.
Better longitudinal dynamics improve handling at long range cruise speeds.
Enhanced speed and altitude stability.
Step climbs reduced or eliminated.
Climb directly to FL410 or higher.
Stalls more easily recognized and controlled.

Rounding out the conversion’s benefits are the near total lack of maintenance needed after what’s generally a brief time needed for the conversion. The company tells clients to expect downtime to install the GII Performance Enhancement System not to exceed 14 working days: 10 working days for the airframe mods- the balance to paint and finish the plane.

Depending on the use of the plane- the savings in fuel and time could well cover the costs of the conversion.

In fact- so effective is this design that Boeing Business Jets has entered into a joint venture with Aviation Partners to equip all new BBJs with Blended Winglets as standard equipment.

BBJ and Boeing 737 operators have found that higher speed and lower fuel consumption are only part of the benefits package. The ability to use shorter runways or carry more payload is an asset- as is the reduced emissions and smaller noise footprint brought to the Next Generation 737 through the use of the eight-foot-high Blended Winglets designed for the BBJ. And there’s more: Improved climb- more direct and less stepped; higher single-engine safety margins; lower operating costs and higher efficiency.

The technology is already expanding through the realm of Boeing 737 operators. And there are more than a few business-jet users with a ship that lacks such performance-enhancing hardware that would love to write a check that would save them money. Aviation Partners has more to come.

API’s latest drag reduction 'twist': Spiroid Winglets

With everything else going on- it might be understandable for an innovative company like Aviation Partners to cruise on its success for a while. But there’s nothing this company likes more than finding new ways to improve performance. The latest format for those efforts is something radical the company has been testing- a new concept dubbed 'Spiroid Winglets.'

Resembling a large loop of rigid ribbon material attached to each wingtip- this completely looped structure has actually come out of the wind tunnel for its initial flight-test series on a G-II. In those tests the Spiroid Winglets reportedly reduced cruise fuel consumption by more than 10 percent. According to Dr. Louis B. Gratzer- designer of the Spiroid Winglets and former Boeing Chief of Aerodynamics- the Spiroid eliminated concentrated wingtip vortices- which represent nearly half the induced drag generated during cruise. On a wing with Spiroid Winglets- Gratzer explains- 'vorticity is gradually shed from the trailing edge.'

According to API’s CEO Joe Clark- developing and certifying Spiroid Winglets likely will take several more years. But the already patented Spiroid-Tipped-Wing shows that there are new frontiers still available for improving our airplanes.

API has its hands full

At $520-000 for the GII- and slightly higher for the BBJ- Aviation Partners’ Blended Winglets may be one of those rare expenses that pays its way in the long run. That was the whole idea at the start – saving money by improving performance with reduced drag.

With the addition of the BBJ program- API is now full-tilt into meeting demand for both designs- even as it continues work on new projects. Fortunately- the events of the past six months hasn’t impinged on business aviation to the degree it did on the airlines – while making some operators even more interested in saving money with their existing birds. That combination of products for old and new business jets bodes well for a company that can markedly improve the efficiency of both. After all- saving money on flight operations is something that’s never a drag.

MI: www.aviationpartners.com

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