This class is the engine base model, which all engine types extend, and contains the structure to model thrust and drag forces acting on the engines as well as the forces and torques due to the mass and inertia tensor of the engine (if the weight estimation method is used). Additionally, the fuel or energy consumption is calculated in the energySystem component, and the engShape component visualizes the engine if no complete CAD model of the aircraft is used.

The equations defining the thrust available, drag force, dimensions and mass properties of the engine are found in the respective engine type models, namely the TurbofanEngine, TurbojetEngine, TurbopropEngine, PistonEngine and ElectricEngine models.

Solving Net Thrust

The net thrust is essentially the product of the thrust available and the throttle position command (deltaThrotCmd), which usually ranges from 0 to 1. When the aircraft is on the ground, the possible thrust reverser is enabled, thus increasing the throttle position range below 0 as far as the value of the engine parameter negThrust is. Figure 1 shows how the switch between the throttle position ranges is made at the altitude of 5 m. However, takeoff, taxiing or landing currently cannot be modeled in the Aircraft library.

To simply model the engine dynamics, the product of the thrust available and throttle position is put through a CriticalDamping component to get the actual net thrust generated by the engine.

Figure 1: Model to calculate the net thrust.

Application of the Forces and Animation

Figure 2 shows how the net thrust is sent to the energySystem for fuel/energy consumption calculations and how the net thrust and drag forces are applied at the engine reference point frame (engineRP), which refers to the rear end of the engine. Similarly, the bodyEng and engShape components representing the mass properties of the engine and the engine visualization, respectively, are connected to the engine reference point frame.

Should the weight estimation method not be used, the bodyEng component will be disabled and both forces and engShape will be routed through the fixed zero translation (translEng) directly to the engine reference point frame. 

Figure 2: Application of the forces at the engine reference point when weight estimation is used.