Oscillations may have doomed flying wing

By Jan TenBruggencate
Advertiser Kaua'i Bureau

LIHU'E, Kaua'i — The oscillations of the Helios flying wing, which crashed into the ocean between Kaua'i and Ni'ihau June 26, may have played a role in its breakup, the team investigating the crash says.

The unmanned experimental aircraft fluctuated up and down before breaking up and crashing, an interim report said. The report said the crash may have resulted from the interactions between the different systems aboard the aircraft.

"There's not one single factor here," said Alan Brown, a spokesman for NASA's Dryden Flight Research Center in Edwards, Calif. "There are some very, very complex interactions here."

Helios was powered by solar power cells during the day. When it crashed, it was carrying the heaviest load it ever handled. The plane weighed just 1,600 pounds in 2001 when it set a world altitude record of 96,863 feet, but the additional weight of two 180-pound hydrogen tanks, the fuel cell, compressor and associated plumbing brought its total weight to more than 2,300 pounds. The extra gear was needed for the test of keeping it aloft overnight.

A NASA investigation board on Monday finished collecting witness statements and other data available on Kaua'i. In its interim report, the team said the aircraft broke up after suffering "undamped pitch oscillations that led to a partial breakup." The crash occurred about a half hour after its takeoff from the Navy's Pacific Missile Range Facility at Barking Sands.

"The board believes the undamped pitch oscillations may be related to the complex interactions between the aerodynamic, structural, stability and control and propulsion systems on a flexible aircraft. However ... much work needs to be done to discover the primary causes of the mishap," said a press release from Dryden Flight Research Center.

Helios builder AeroVironment is conducting an independent investigation. The NASA team is to deliver its report on the cause of the crash by Sept. 30.

The plane's wreckage will be shipped to California for further study.

Both NASA and AeroVironment said they are continuing the development of both solar and fuel cell propulsion systems for unmanned aircraft designed for long duration flight. The agencies are trying to develop a vehicle that can remain aloft for weeks or months at a time, relaying sensor data about the Earth below it, or serving as a communications relay platform.

This report contains information from the Associated Press.