Modeling of Mechanical Transmission for Hybrid-Electric Propulsion Aircraft

The thesis focuses on the purely dynamic rotation model of a dual-stage planetary transmission for a hybrid turboprop aircraft for regional transport. The model generates the mass of the entire transmission and the dynamic response of the same as a function of the relative phases of flight, through precise inputs (power and rotational speeds of turbine and electric motor, propeller speed and overall gear ratio). The first chapter focuses on how aircraft transport affects CO2, NOx and other pollutant emissions. It continued by analysing what were the possible design proposals of the various companies in order to promote greater electrification of aircraft and reduce the carbon footprint following what is already happening in the automotive industry. Finally, in what legislative context such manoeuvres were dealt with in European (European Union’s Clean Sky 2) and international (International Civil Aviation Organization) fields. It continued by analysing the existing conventional architectures for turboprop and turboshaft aircraft of some manufacturers (Pratt Whitney, Rolls Royce and General Electric Aviation) in order to derive, in first approximation, both the power densities of the transmission alone and that of the entire engine through an empirical estimate. Subsequently, in the second chapter, three possible architectures were chosen (Off-Set, In-Line and Mixed) and the same were dimensioned both in conventional propulsion and in hybrid propulsion. All aimed at maximizing the specific power and compactness of the transmission, thus arriving at the choice of the hybrid planetary dual-stage (In-Line) architecture with electric motor axial flow at low speeds, coaxial to the turbine, connected to the first stage carrier with a power density of about 18 kW/kg. The third chapter focuses on the dynamic analysis of the transmission, which has been simulated through a model with concentrated parameters: the gears are modelled as a full disk with concentrated inertia; transmission shafts as torsional springs with stiffness and damping dependent on mass and inertia; meshing by non-linear springs, with stiffness in one case and in another case dependent on the frequency of meshing, positioned parallel to dampers. All this was accompanied by models that simulated the behaviour of the gas turbine, the electric motor, the propeller, the angle of the propeller and the atmosphere. The fourth chapter analyses the results of the dynamic model in the various phases of flight of an aircraft, such as take-off, ascent, cruise, descent and landing, in conventional propulsion, hybrid and totally electric. Finally, the fifth chapter sets out possible future developments in work.