Stability and Control Analysis of a Rudderless Aircraft with Rotary Horizontal Tail

Abstract

Removing the vertical tail on an aircraft has the potential to significantly increase efficiency and range. However, in conventional configurations the vertical tail provides essential lateral and directional stability. A solution to this loss of stability is a rotary horizontal tail, whereby the horizontal tail rotates to provide yaw moments to stabilize the aircraft. This technique is similar to how some birds rotate their tails to induce rolling and yawing moments. This study sought to determine the feasibility of controlling a standard aircraft modified with a rotary horizontal tail by modeling an aircraft similar to a Cessna 172. First, an aerodynamic analysis using a vortex lattice method solver was completed to determine the drag reduction benefits of the modification. Then, a static and dynamic stability analysis was conducted to assess the impact of the modification. Last, three feedback controllers were designed and applied to stabilize and control both the conventional and modified aircraft, and the performance and robustness qualities of each were compared. The first controller was an optimal state-feedback linear quadratic regulator. It was found that this controller design resulted in similar time-domain performance between configurations, but the robustness of the modified model, characterized by the closed-loop transfer matrix, sensitivity functions, and direct perturbation, was significantly degraded compared to the conventional model. The second and third controllers were a state-feedback guaranteed-cost design, which resulted in nearly equivalent robustness between the two configurations. However, the time-domain performance of the modified system was found to be degraded compared to the conventional system. Therefore, from this study we are able to conclude that it is feasible to stabilize and control an aircraft with a rotary horizontal tail configuration, but there will likely be a greater trade-off between performance and robustness compared to a conventional aircraft.