HELIOS CRASH REPORT NASA BLAMES TURBULENCE FOR EXPERIMENTAL CRAFT'S FAILURE.

Byline: Jim Skeen Staff Writer

EDWARDS AIR FORCE BASE - Normal turbulence brought down the record-setting Helios prototype aircraft last summer, according to a NASA mishap report released Friday.

NASA simply lacked the analytic tools to predict how sensitive the solar-powered 247-foot-wingspan airplane was to atmospheric disturbances, the report said.

``The board determined that the mishap resulted from the inability to predict, using available analysis methods, the aircraft's increased sensitivity to atmospheric disturbances such as turbulence following vehicle configuration changes required for the long-duration flight demonstration,'' NASA said in a release accompanying the report.

The June 26, 2003, crash off the coast of the Hawaiian island of Kauai occurred as atmospheric turbulence caused the outer wingtips of the highly flexible aircraft to bow abnormally high upward, causing the aircraft to become unstable.

The aircraft began to experience pitch oscillations that became increasingly more severe, pushing the aircraft faster than it was designed to fly and eventually tearing it apart.

The Helios was in Hawaii to test a fuel cell to power it at night, part of an effort to create aircraft capable of staying aloft for weeks or even months. Such craft could operate essentially as low-flying satellites, relaying communications signals or studying the environment.

In 2001, Helios set a world altitude record for winged aircraft of 96,863 feet. The airplane cruised at speeds ranging from 19 to 25 mph.

The flight testing was conducted under NASA's recently concluded Environmental Research Aircraft and Sensor Technology program, which was overseen by NASA Dryden Flight Research Center at Edwards Air Force Base.

ERAST was aimed at developing technologies that allow companies to build unmanned aircraft that can carry out the dull, dirty or dangerous missions that would be impossible or impractical for manned aircraft.

``We are going to use what we learned from Helios and the Helios mishap to develop better high-altitude, long-endurance vehicles,'' said NASA Dryden spokesman Alan Brown.

The Helios prototype broke apart and crashed into the ocean during a checkout flight over a U.S. Navy test range off Kauai.

Changes made to the aircraft to accommodate the 520-pound fuel cell, mounted at the centerline of the aircraft, and two 165-pound fuel tanks, mounted near each wingtip, reduce the aircraft's robustness and weakened its safety margins, the mishap report said.

``Lack of adequate analysis methods led to an inaccurate risk assessment of the effects of configuration changes leading to an inappropriate decision to fly an aircraft configuration highly sensitive to disturbances,'' the mishap report said.

The report did praise the NASA and AeroVironmental, the company that designed and built the Helios prototype, for creating '`most of the world's knowledge in the area of high-altitude, long-endurance aircraft design, development and (testing).''

NASA said it remains committed to the development of high-altitude, long-duration flight aircraft.

``The mishap underscores our need to assess carefully our assumptions as we push the boundaries of our knowledge,'' said Dr. Victor Lebacqz, associate administrator for NASA's Office of Aeronautics. ``It should not, however, diminish the significant progress AeroVironmental and NASA have made over the past 10 years in advancing the capabilities of this unique class of aircraft on many successful flights, including Helios' record-setting flight to just under 97,000 feet altitude in August 2001. It is important that we learn from this experience, and apply the board's findings and recommendations to help ensure the payoffs of such vehicles are fully realized.''

Jim Skeen, [phone]

james.skeen(at)dailynews.com

CAPTION(S):

2 photos

Photo:

(1 -- color) NASA's Helios prototype, a record-setting solar-powered, 247-foot-wingspan airplane, soars over the water.

(2) The aircraft floats at the surface of the ocean after the June 26, 2003, crash off the coast of the Hawaiian island of Kauai that was determined to have been caused by normal turbulence.