Small unmanned air vehicles (UAVs) have been used to collect samples of pollen, plant pathogens, and other biological particles within the earth's surface boundary layer (from about one to fifty meters altitude) and the planetary boundary layer (from about fifty to one thousand meters). These samples provide valuable information concerning the release, transport, and deposition of biological particles, with important implications for food safety and agricultural practices. In some sampling applications, it is essential that the UAV's speed and altitude be precisely regulated, which suggests the use of an autopilot. Because the biological sampling apparatus may dramatically alter the UAV's flying qualities, however, the autopilot must be robust to large, fast changes in the dynamic model parameters. This paper describes the application of a new adaptive control technique, referred to as L1 adaptive control, which quickly compensates for large changes in the aircraft dynamics, providing an effective platform for aerobiological sampling.