Development of Flight Control Law for Improvement of Uncommanded Lateral Motion of the Fighter Aircraft

Abstract

The Abrupt Wing Stall (AWS) at moderate Angle-of-Attacks (AoA) and transonic flight conditions can result in uncommanded lateral motions such as heavy wing, wing drop and wing rock that degrade handling qualities, mission performance and safety of flight for the aircraft. This phenomenon caused by asymmetric wing flows makes it difficult to perform precision tracking or maneuvering in the transonic flight envelope. According to the previous research results, this substantial phenomenon has occurred in a large number of the fighter aircraft programs, typically at the early flight test development stage, and a lot of budgets and efforts are required through the development period of the aircraft. To compensate for this drawback, Free-To-Roll (FTR) wind tunnel test is adopted as a method to identify the uncommanded lateral motions of the aircraft and improve the flight characteristics at the configuration design stage. However, using only the existing control methods such as the feed-forward control methods as well as the configuration design can reduce limitedly the uncommanded lateral motion. Besides, the feedback control methods using optimal control, adaptive and neural network control which do not provide a deterministic solution are limited to obtain the airworthiness certification. This paper presents a new design approach in which uncommanded lateral motions of the aircraft can be reduced even more than the existing methods. That is the additional augmentation control method, using angular acceleration measurement, that improves the flight characteristics using a feedback control technique based on the Incremental Nonlinear Dynamic Inversion (INDI). To evaluate the performances of the proposed control method, we perform the frequency-domain linear analysis and time-domain numerical simulations based on the mathematical model of advanced trainer aircraft. The evaluation result reveals that the proposed control method reduces effectively uncommanded lateral motions and improves the handling qualities of the aircraft.