Wake sensing for aircraft formation flight

It is well established that ring aircraft in formation can lead to improved aerodynamic efficiency. However, successfully doing so is predicated on having knowledge of the lead aircraft's wake position. Here, we develop a wake sensing strategy to estimate the wake position and strength in a two-aircraft formation. The wake estimator synthesizes wing-distributed pressure measurements, taken on the trailing aircraft, by making use of an augmented lifting line model in conjunction with both Kalman-type and particle filters. The various estimation algorithms are tested in a vortex-lattice simulation environment, thus enabling the effects of modeling error to be analyzed. It is found that biases in the position estimates no longer arise if a particle filter is used in place of the Kalman-type filters. Filter divergence is observed when the relative aircraft separations are held fixed. This divergent behavior can be alleviated with the introduction of relative aircraft motions, for example in the form of a cross-track dither signal.