Improved tunnel display for curved trajectory following: Control considerations

Improvements of a previously developed tunnel display for curved trajectory following are presented and theoretically analyzed. The success of earlier versions of this display can be attributed to the combination of the perspective tunnel image with a superimposed predictor symbol. The tunnel image provides the spatial awareness and preview of the trajectory forcing function, and the predictor provides vital guidance and control information. Two main shortcomings of these earlier versions, occurring for large and sluggish aircraft requiring longer prediction times, are addressed: 1) poor performance in transitions between straight and curved trajectory sections and 2) poor positional accuracy in the presence of biases or low-frequency disturbances. The two basic improvements addressing these shortcomings, and incorporated into an improved display layout, are 1) an algorithm for generating trajectory shapes that are well matched with the average vehicle response and 2) an actively driven predictor reference window, yielding improved predictor guidance information. The improvements combine the advantage of a vehicle path predictor that performs as a well-designed natural flight director, with improved curve transition behavior and improved positional accuracy in the presence of slowly varying cross winds.