Nonlinear flight control using forebody tangential blowing

This dissertation is on the development and experimental demonstration of a new nonlinear approach to developing control laws for the lateral-directional dynamics of aircraft at high angles of attack using Forebody Tangential Blowing (FTB).; FTB is a pneumatic device that modifies the vortical flow over the forebody. The modified vortical flow in turn creates roll and yaw moments for control. FTB has been shown to be a very powerful means of generating forces and moments on aircraft operating in flight regimes where the effectiveness of conventional aerodynamic surfaces is reduced (e.g. post stall). Consequently, it provides a mechanism that could greatly expand the flight envelope of future aircraft systems.; One major factor that currently limits the use of FTB is that it is a highly nonlinear and uncertain effector. In particular, FTB can provide very powerful effects (e.g. forces and moments) at low levels of blowing but the characteristic relating input to output is highly nonlinear in this region. On the other hand, if higher levels of blowing are used, the characteristics become well behaved. Hence, the trade-off between robustness and control usage is particularly acute.; The goal of this thesis is to develop a technique that will yield for the first time robust control at small levels of blowing thus enabling a new level of efficiency in the use of FTB as a device for flight control at high angles of attack.; The approach developed is based on combining High-Gain Control (HGC) and Lyapunov techniques. By employing a robust inversion of uncertain static nonlinearities, the new control law can be applied to a class of systems represented by a cascade connection of a nonlinear system and an uncertain linear system. In particular, the nonlinear control approach is applied to the control of an aircraft utilizing FTB and can fully exploit the FTB efficiency. Simulation and experimental results are provided that demonstrate the effectiveness of the approach. Further, the design consists of a few simple steps and does not require a Lyapunov function for the entire system or upper bounds on the uncertainties.