  This paper investigates the utilization of differential thrust to help a
commercial aircraft with a damaged vertical stabilizer regain its
lateral/directional stability. In the event of an aircraft losing its vertical
stabilizer, the consequential loss of the lateral/directional stability and
control is likely to cause a fatal crash. In this paper, an aircraft with a
completely damaged vertical stabilizer is investigated, and a unique
differential thrust based adaptive control approach is proposed to achieve a
stable flight envelope. The propulsion dynamics of the aircraft is modeled as a
system of differential equations with engine time constant and time delay terms
to study the engine response time with respect to a differential thrust input.
The proposed differential thrust control module is then presented to map the
rudder input to differential thrust input. Model reference adaptive control
based on the Lyapunov stability approach is implemented to test the ability of
the damaged aircraft to track the model aircraft's (reference) response in an
extreme scenario. Investigation results demonstrate successful application of
such differential thrust approach to regain lateral/directional stability of a
damaged aircraft with no vertical stabilizer. Finally, the conducted robustness
and uncertainty analysis results conclude that the stability and performance of
the damaged aircraft remain within desirable limits, and demonstrate a safe
flight mission through the proposed adaptive control methodology.
