In-flight Airflow Measurements of a Cessna AgHusky Agricultural Aircraft

Abstract

A measurement system based on pressure probe techniques was developed and used to survey airflow speed and direction near the trailing edge of the wings and under the fuselage of a Cessna AgHusky agricultural aircraft. The main feature of the system was an airflow measuring rake comprised of eight, 5-tube probes designed to measure total pressure and airflow direction and two stream pressure probes to measure static pressure. The probes were encased in a 0.74-m long airfoil that was positioned vertically at numerous lateral positions 0.23 m behind the trailing edge of the aircraft wing and horizontally at several locations beneath the aircraft fuselage. The test flight protocol included three aircraft loadings (0-, 227-, and 454-kg hopper loads) and two airspeeds (145 and 185 km/h) at an aircraft wheel height of 1.5 m. The measurements indicated that air velocity, airflow yaw angle, and airflow pitch angle were all significantly affected by variations in aircraft loading, aircraft speed, and measurement locations. The air velocity ranged up to 195 and 235 km/h in the propeller slipstream at indicated airspeeds of 145 and 185 km/h, respectively. Velocities of 64 to 97 km/h were recorded near the underside of the fuselage where the airflow was blocked by spray system hardware. Outboard from the propeller slipstream, the air velocities were lowest in the area directly behind the trailing edge of the wings and highest either 0.203 m above or 0.305 to 0.475 m below the trailing edges of the wings. Airflow yaw and pitch angles were largest for the 145 km/h indicated airspeed with the 454-kg load and in the area below the fuselage and aft of the spray system hardware. Outboard of the propeller slipstream, the yaw angles did not exceed 6. The airflow pitch angles ranged up to 7 at the wing measurement locations with the largest downward angles occurring 0.102 to 0.203 m above the wings and the largest upward angles occurring directly behind the trailing edges of the wings. These results provide a basis for selecting and locating spray delivery equipment on agricultural aircraft in order to minimize the effects of airflow on the production of small droplets that are most subject to spray drift.