Low-altitude wind conditions on helios flight days at Kauai, HI

Aircraft using solar cell power for high-altitude long endurance missions are designed with very low wing loading and low operating airspeeds to minimize propulsion system weight requirements. Maximum cruise speeds nominally range from 20 knots at sea level to more than 50 knots at altitudes above 50,000 feet. Light wing loading and structural flexibility combine to produce noticeable responses to turbulence. Thus, minimal wind shear and runway wind speeds below 10 knots for take off and landing increase the assurance of flight safety for high-altitude solar-powered aircraft. This paper reviews the details of the low altitude wind profiles measured by rawinsonde on June 26th at Lihue on the southeast coast of Kauai as well as at the U.S. Navy Pacific Missile Range Facility (PMRF) airfield on the west coast of Kauai where the Helios solar powered airplane was operated. In-situ winds measured by the Helios along its flight track are presented for comparison. As a result of an in-flight mishap with the Helios on June 26, 2003, wind conditions for that day are also compared with winds at selected altitudes for previous flight days at Kauai, HI and Edwards, CA. Relative findings are discussed with respect to wind induced turbulence in the trade wind wake of Kauai.