Effect of Trail Aircraft Trim on Optimum Location in Formation Flight

Abstract

Aircraft flight generates vortices that induce nonuniform wind distribution in their wake. A trailing/follower aircraft will experience induced wind components and gradients with various magnitudes and directions, depending on its location relative to the leader. This paper explores two methods of determining the relative location for optimum formation flight, termed the sweet spot. The relative location with the highest lift-to-drag ratio on the follower is denoted as the static sweet spot. In the second method, the trail aircraft is trimmed by adjusting the thrust and control surfaces to maintain its commanded position relative to the lead. The relative location requiring the least thrust is then assigned as the dynamic sweet spot. The results showed that, depending on the trail aircraft size, the static sweet spot might differ from the dynamic sweet spot. The effect of the leader weight and follower size on both static and dynamic sweet spot was also studied. It was discovered that the static and dynamic sweet-spot location changed when the size of the trail aircraft was modified. It was also observed that the static sweet spot remained the same but the dynamic sweet spot changed when the lead aircraft weight was modified.