It's crunch time in the airliner business. Positive economic trends in
Asia foreshadow an imminent boom in transpacific and trans-Eurasian travel. With
their long lead times, aircraft manufacturers will have to decide very soon on
airplane designs to meet the demands of the next decade.
As with any other mass-flow problem, engineers face two choices: increase the flow speed or build a bigger pipeline. In aircraft design, the solutions come down to second-generation supersonic transports or 1000-passenger super-jumbo airliners.
Of the two, the subsonic Very Large Civil Transport (VLCT) seems the surer bet, since its technological hurdles appear lower. Still, with development costs for either aircraft projected to be ten billion dollars or more, it's a gamble no manufacturer takes lightly. Industry engineers are currently at work on both possibilities.
The VLCT challenge. Manufacturers' planned VLCT configurations seem to be zeroing in on a double-decker aircraft about the length of a 747. Artists renderings belie the size of the aircraft until one notices the number of emergency exits made necessary by the FAA rule requiring no more than 90 seconds to evacuate passengers in an emergency.
A VLCT's size and the need to integrate the plane into existing airport operations present significant design problems. "To compete effectively, our proposed A3XX airliner will have to offer a saving of around 15% in direct operating costs relative to the (Boeing) 747-400," explained Airbus Industrie's Adam Brown, vice president of strategic planning, in a recent speech concerning his company's plans for a super-jumbo. "Significant advances in aerodynamics, materials, systems, and manufacturing techniques will be required to meet that goal."
The aerodynamics challenge of a VLCT stems from the need to keep the wings relatively short and to minimize drag for economy's sake. "We've put emphasis on supercritical, advanced airfoils since they're more efficient at high coefficients of lift and high wing loading," says David Murphy, manager of advanced wide-body programs at Douglas Aircraft. "The result is that, in proportion to gross weight, we can fly efficiently with a smaller wing area than previous designs, and thus fit better into current airport infrastructures."
Techniques for controlling airflow over the wing may also play a part in improving the economics of a million-pound-plus airliner. Under study: laminar flow control by using engine vacuum to generate suction through thousands of laser-drilled holes on a wing's upper surface. Such a system would greatly reduce drag by forestalling the onset of turbulent airflow over the wing. Alternatively, a circulation-control system also under consideration would bleed high-pressure engine air over the leading and trailing edges of a large aircraft's wing to boost lift as needed. The concept would allow for smaller wings free of complex flap mechanisms. Nevertheless, sources say that designing these systems for low weight and simple maintenance remains a complex engineering task.
In contrast, engineers seem confident about the materials technology needed to keep down the weight of a VLCT. "We're estimating composites are to be roughly doubled in application as a percent of airframe relative to the MD-11," says Douglas' Murphy of his company's planned 600-to-800 seat