Andrew Doyle/BRUSSELS
Boeing aerodynamicists believe they have discovered a revolutionary technique for tackling aircraft wake vortices and hope to begin flight testing the system "as soon as possible".
Details of the design remain secret because Boeing does not expect to be formally granted a patent until next month, although the company says its patent application has been approved.
The system works by causing an aircraft's wing-tip vortices to collide with each other a short distance behind the aircraft. This results in them dissipating quicker, creating "smoke rings" that feel like a series of small speed bumps if encountered by following aircraft . "It's mutually assured destruction," says Bob Kelley-Wickemeyer, Boeing Commercial Airplane Group chief engineer aerodynamics.
"The approach we used to achieve this was to put a disturbance in the vortex network near the aircraft so that the network collapses upon itself within 3nm[5.6km] of the aircraft," he says.
The aim is to enable air traffic controllers to safely reduce the lateral separation between aircraft during approach, increasing the capacity of congested airports.
The system has been tested in a windtunnel and at the David Taylor Model Basin water tank near Washington DC. The success of the tests using aircraft models persuaded Boeing to patent the idea and carry out flight tests.
"The model is a generic aircraft that allows us to replicate the span load of many aircraft," says Kelley-Wickemeyer. "The next stage is to test it on a flying aircraft."
The company is in talks with NASA with the aim of using the agency's Boeing 757 testbed for the flight trials. This is the favoured option because NASA has specially instrumented aircraft available to measure the air disturbance behind an aircraft in flight.
Kelley-Wickemeyer believes that if the flight tests are successful, the system could be fitted to in-service aircraft after 2005. "I believe it will be retrofittable to the majority of existing aircraft," he adds.
Boeing stepped up its studies after the 757 was found to produce unexpectedly powerful trailing vortices, following an investigation into the crash of a business jet at Orange County Airport in California six years ago. The 757 was subsequently reclassified as a "heavy" aircraft, putting it in the the same category as the 747 and other widebodies.
Separations of up to 5nm (9.25km) are required between heavy aircraft and smaller aircraft following them on the approach, compared with the usual 3nm (5.6km) minimum.
The 757 is particularly prone to the vortex problem because it does not have an inboard aileron separating the inboard and outboard trailing edge flaps.
Finding a way to safely reduce aircraft separations on approach could help airports cope with an expected sharp increase in aircraft movements, which the US company believes will occur as markets continue to fragment, particularly in the Asia Pacific region.
Boeing says that if the technology proves to be feasible, it hopes Airbus will adopt it under licence.
Source: Flight International