Engine Failure of an Aircraft
How would an aircraft behave in case of a failure like faulty engine, flap malfunction or faulty control logic? This example models and simulates the response of a Hawker Siddeley aircraft after an engine failure.
Model of the Aircraft
A built-in model of a Hawker Siddeley HS-121 Trident 3B is used. It is connected to an autopilot that follows a reference trajectory. The Trident 3B has an unusual design, with an additional, smaller, booster engine that starts producing thrust when a threshold value of the throttle demand is exceeded. At around 35 mins, the left engine of the aircraft fails.
A model of a Hawker Siddeley HS-121 Trident 3B aircraft is used. It has two turbofan engines mounted on the fuselage, and a turbofan engine and a booster turbojet engine are mounted on the vertical tail.
Control Response for Longitudinal Motion after Engine Failure
After the left engine failure at 35 mins, all the remaining engines go full throttle. However, the aircraft is not able to provide enough thrust to sustain the given velocity at the cruise altitude, resulting in deceleration.
The top plot shows velocity and altitude. Velocity drops after the left engine failure, despite all remaining engines having full throttle. The middle plot shows the throttle positions of the right and left engines. The last plot shows the throttle positions of the tail engine and the booster engine.
Control Response for Lateral Motion after Engine Failure
The top plot shows how the autopilot starts applying both ailerons and rudder to compensate for the generated yaw moment (due to differential thrust right after the left engine fails). Later during the simulation as the aircraft has descended and decelerated (such that it sustains a steady level flight with the remaining engines), it can also be seen that both the ailerons and rudder are still being deflected and the aircraft is flying with a small roll angle to be able to fly straight forward.
The top plot shows deflections of the ailerons and rudder. The yaw moment due to thrust differential is compensated for by deflecting the ailerons and rudder. The middle plot shows the reference track angle given to the autopilot and the actual track angle. The aircraft can both fly straight forward and make turns with differential thrust after the left engine failure. The last plot shows the roll angle around the body x axis.