A380 demos ‘gee whiz’ weight performance

 - October 25, 2006, 6:50 AM

To professional aerospace observers, there should be no such thing as culture shock, but even after several years of Airbus A380 gestation some of its vital statistics retain their “gee whiz” characteristics. Not least are the new mega-jetliner’s design weights, taking off at up to almost 1,235,000 pounds and landing at more than 851,000 pounds.

But flight-testing of the behemoth has seen even these values exceeded: during noise-measurement trials in Spain last month, the first A380 (S/N 001) took off at more than 1,245,400 pounds. This was followed by a touchdown at 1.212 million pounds–more than 42 percent above the nominal max landing weight.

Handling of the aircraft, which when certified will be the world’s largest airliner, has exceeded some Airbus expectations. Performance is said generally to be close to overall predicted behavior.

Little more than seven months after the twin-deck, quad-aisle jetliner’s April 27 maiden flight, Airbus is approaching the 500-hour mark with about 20 percent of expected flight-test time already logged on the first three ships to fly (S/N 001, S/N 004 and S/N 002).

Before S/N 004 and S/N 002 entered flight-test in mid-October and early November, respectively, Airbus had been flying up to 85 hours a month, according to flight-test senior vice president Fernando Alonso. Initial flight-testing demonstrated higher-than-expected lift, lower-than-calculated approach speeds and favorable stall behavior.

Flight-envelope Exploration

Although ultimately not completely representative of production aircraft, S/N 001 has explored the flight envelope to establish A380 aerodynamics as the last two test aircraft are prepared for flight.

The A380 has flown at 375 knots, compared with an expected 340-knot maximum operating speed in lower airspace, and at Mach 0.96 in support of the planned upper-airspace Mach 0.89 maximum operating Mach number (Mmo).

By last month, the aircraft had demonstrated about 300 low- and high-altitude stalls–“all benign,” according to Airbus, which said it has also flown at “well below 100 knots.” During maximum-weight noise trials, Airbus has demonstrated approach speeds of “around 138 knots–some three to four knots lower than expected,” according to Alonso.

He said the A380 has “the best stalling we have seen [on any Airbus]” and at “significantly lower” speed than expected.

The aircraft has shown a “very good” coefficient of lift, attributed to the sheer size of the wing, which has been driven by considerations of airframe stretch, as well as the desire for a low approach speed.

Different settings of leading-edge slats and trailing-edge flaps have led to more efficient arrangements than predicted, said Alonso, “When we increased flap to 26 degrees, we found maximum lift and [hence] best takeoff distance; we’re getting higher lift with no significant increase in drag.”

By last month, handling work, including flutter, had been completed, while investigations of air conditioning, fuel management, electrics and other systems had all been “normal.”

The third A380’s third flight was scheduled to take it to Hamburg, Germany, where it would receive the first airline interior. Performance testing continues on S/N 004. S/N 002 is earmarked for initial upper- and main-deck cabin development, including internal noise and cold-weather trials.