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Boeing seeks NASA input as it unveils anti-vortex system

Guy Norris/SEATTLE

Boeing is pressing NASA to join it in a research effort to flight test the company's newly patented anti-wake vortex system, which it claims could increase runway capacity by up to 20%.

Revealing details of the invention for the first time, Boeing aerodynamics engineering chief Robert Kelley-Wickemeyer says he is " proposing a joint study with NASA, which makes the most sense. We are also knocking on the doors of airports to interest them."

Boeing is keen to set up flight tests involving NASA's Boeing 757 testbed and the agency's heavily modified Rockwell OV-10 Bronco research aircraft, which has been used in previous wake vortex work.

The system uses the control surfaces in what Kelley-Wickemeyer calls "sloshing the span load". The resulting changes in spanwise pressure distribution "imparts an instability in the vortex network behind the aircraft", he says.

This "fools mother nature" by causing the vortices to interact more closely and quickly behind the aircraft. The vortices cancel one another out, rather than staying isolated and curling energetically into tight rotors that trail the aircraft for several kilometres.

The result, tested in water in the US Navy's David Taylor Model Basin near Washington DC, is that the vortices combine into low energy, horizontally aligned "smoke rings". Aircraft on approach are separated by varying distances, depending on their weight, to avoid the instability dangers caused by flying through vortices. With the new system, flying into the these would be like "driving over a few small bumps", say Kelley-Wickemeyer.

The anti-vortex system would be activated during final approach and involves cyclically deflecting the inboard and outboard ailerons. Inboard ailerons would be slowly and symmetrically deflected upwards, while the outboard ailerons would act in reverse, and vice versa.

The cycle would be repeated continuously during approach, generating the span loading instability and defusing the vortex energy.

"We would slowly, smoothly and rythmically deflect the ailerons up and down," says Kelley-Wickemeyer, who adds that "it would not be flapping like a bird, but it would be moving smoothly like an old man waltzing".

To counteract the pitching moment generated by the changing centre of lift over the swept wing, the system would automatically engage the elevators, which will work in harmony with the ailerons to cancel out any movement in pitch moment.

Flight tests are required to define the practicality of the system for aircraft of 757 size and greater.

"We know the basic physics, but we don't know what the implications are for the structure, and what it might do to the ride quality," says Kelley-Wickemeyer. The programme is aimed at increasing runway capacity, rather than eliminating the wake vortex hazard. The company believes the vortex dissipation could help reduce separation for "heavy" aircraft, set at 7-9km (4-5nm), to 5 km.

If the system proves workable, Boeing says it will offer it under licence to Airbus. "Safety should not be a competitive issue, and neither should airport capacity," says Kelley-Wickemeyer.

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