Simulink Modeling of Fighter Aircraft Longitudinal Motion: Pitch Rate Control

The purpose is to use Simulink to simulate a (much simplified) model of the longitudinal motion of a fighter aircraft. The 'angle of attack' is the angle between the direction a plane is pointing, and the direction in which it actually moves through the air. For a plane flying at approximately constant altitude, this is equivalent to the 'pitch angle', as illustrated in Fig. 3. This angle is important because it produces a lift force perpendicular to the axis of the plane, and hence a 'normal acceleration', (also shown in the figure).

The pilot wants to be able to control the pitch angle, and does so ultimately by rotating the front fins, and tail elevators of the aircraft, shown in Fig. 4. The first task is therefore to model the effect of these movements on the 'pitch rate', where

b. Pitch Rate, q The rate at which the pitch angle changes, (the 'pitch rate', q), is determined mainly by the angle of the front fins of the aircraft shown in Fig. 4. Indeed aerodynamic modelling shows that this relationship can be described by the differential equation: Q(s)/d(s)=(7.25s+11.27)/(s^2+3.1s-8.82)

Sketch of pitch rate response to a step change in the control input here Comment on the response

The sketch of the pitch rate response shows that the system exhibits overshoot and oscillations before settling to the new steady-state value. The overshoot indicates that the pitch rate initially exceeds the desired value before settling down, while the oscillations indicate that the system is continuously adjusting to reach the desired value. Overall, the response suggests that the system is stable and capable of tracking changes in the control input. However, the oscillations may need to be reduced for more precise control of the pitch angle.