This piston engine model extends the EngineBase model and models the thrust and mass (if weight estimation method is used) of a piston engine.

Parameters

The required parameters for the piston engine model are listed in the Propulsion tab, as shown in Figure 1.

Figure 1: Required input parameters for piston engine model.

Should the value of any of the estimated properties listed in the Estimated Properties parameter tab be known (such as engine mass), the equations can be bypassed by entering the known value directly to the respective parameter input field.

The remaining parameters listed in the Propagated parameters tab are propagated from the AircraftBase as the propulsion system is compiled in PistonPropulsion, and thus they can and should be left unchanged.

Thrust Available

The thrust available (T_avail) for piston engines is solved through dividing the power available (P_avail) by the total velocity (v_tot), and the factors for representing the propeller (η_prop) and power transmission efficiencies (η_mech) are also added, thus

.

For solving the power available, a relation presented by Gudmundsson [1] is used

,

where P₀ is the engine power at sea level, ρ_alt is air density at flight altitude and ρ₀ is air density at sea level.

Fuel Consumption

The parameter for brake-specific fuel consumption (BSFC) is propagated to the energySystem component, where fuel consumption calculations are performed.

Drag

The piston engine is considered to be installed completely inside the fuselage, and the drag due to propeller is omitted. Thus, the piston engine model currently has no drag.

Mass

If the weight estimation method is used and no engine mass is entered by the user, the engine mass is solved by using empirical relationship based on the given P₀ parameter value, as presented by Erä-Esko [2]

.

The mass of the propeller is then added on top of this estimated engine mass.

The engine moments of inertia are estimated to be insignificantly small, and thus a default value of 0.001 kg/m² is used, which, however, can be overwritten by entering another value in the Estimated Properties parameter tab.

References

[1]  Gudmundsson, S. (2016). General Aviation Aircraft Design. Elsevier.

[2]  Erä-Esko, N. (2022). "Development and Use of System Modeler 6DOF Flight Mechanics Model in Aircraft Conceptual Design."
      Available at: modelica://Aircraft/Resources/Documents/EraeEskoThesis.pdf.