Measured Aerodynamic Interaction of Two Tiltrotors

The aerodynamic interaction of two model tilrotors in helicopter-mode formation flight is investigated. Three cenarios representing tandem level flight, tandem operations near the ground, and a single tiltrotor operating above thc ground for varying winds are examined. The effect of aircraft separation distance on the thrust and rolling moment of the trailing aircraft with and without the presence of a ground plane are quantified. Without a ground plane, the downwind aircraft experiences a peak rolling moment when the right (left) roto- of the upwind aircraft is laterally aligned with the left (right) rotor of the downwind aircraft. The presence of the ground plane causes the peak rolling moment on the downwind aircraft to occur when the upwind aircraft is further outboard of the downwind aircraft. Ground plane surface flow visualization images obtained using rufts and oil are used to understand mutual interaction between the two aircraft. These data provide guidance in determining tiltrotor flight formations which minimize disturbance to the trailing aircraft.