The use of acoustic wind profilers for Uninhabited Aerial Vehicle flight test activities

SOnic Detection And Ranging (SODAR) wind profilers have become valuable tools for monitoring flight day low-altitude wind and atmospheric turbulence for Unmanned Aerial Vehicle (UAV) activities. SODAR data allow for real time monitoring of wind speed, direction and wind shear up to an altitude of 1000 meters above ground level. These data are used for advance planning of flight schedules and well as for flight safety monitoring. Short term forecast for time of day when surface winds exceed UAV mission limits are enhanced by SODAR data.

Many of the UAV's developed for NASA's Environmental Research Aircraft and Sensor Technology Program are light weight, have long wingspans and low wing loading. As a result, these UAVs are relatively sensitive to ground winds and in-flight turbulence. The Pathfinder-plus and Helios Prototype have increased risk of damage on the ground if surface winds exceed 7 knots. In flight, control of these vehicles is also threatened in the presence of low altitude turbulence caused by wind shear or thermal activity.

This paper describes how data from the SODAR have impacted UAV flight day activities, including how the data are used to advise UAV flight crews and NASA Mission Directors on current and projected conditions. On one mission the flight time of the X-38 was moved up almost two hours due to the detection of high winds (greater than 20 knots) by the SODAR at altitudes at and above 300 feet AGL. The change in time was necessary to give ground personnel time to safely stow the parafoil before the winds increased above guidelines. Aircraft that will be discussed include Pathfinder-plus, Helios Prototype, Darkstar and the X-38 prototype of the International Space Station's "crew recovery vehicle."