Analysis of the dynamic behaviour for AS350 helicopter rotor with modified blade - Development of the model and analysis of tip loss case

The aim of this master’s thesis is to evaluate the impact in the dynamics of the Aérospatiale AS350 helicopter blade because of the modification performed to the tip and its potential loss during flight. Specifically, the Silent Eco Wing (SEW) replaces the original tip and is designed to modify the end vortices generated by the helicopter blade, thereby reducing noise and drag. This master's thesis work is carried out with Benedetta Maria Vittoria Borlizzi - university colleague – in collaboration with TPS Aerospace Engineering Srl, a leading company in the aerospace with expertise in aeronautical product and parts design and certification. Multiple analyses are conducted to bring results that are always – going forward in the reading – more congruent with the actual case in terms of imbalance and change in the aerodynamic load developed. First, to evaluate the effects of the SEW on the AS350 helicopter blade, the study uses a simplified model of flapping dynamics, in which the rotor allows only the degree of freedom of flapping for the blades, and these behave like a rigid beam hinged in the hub center. While Momentum Theory is used to predict the rotor-induced velocity for a given rotor thrust, with BET (Blade Element Theory) the cross section of each rotor blade is simplified to a two-dimensional aerodynamic profile that produces aerodynamic loads such as lift, drag, and pitch moment. The results include the comparison of the flapping angles between a blade with the SEW and a blade without the SEW. The thesis also develops a model that simulates the rotor behaviour of the helicopter under study more accurately. To do this, a code that studies the dynamics of the AW109's articulated rotor is created and compared – for validation – to experimental data available for this helicopter. The model is then modified and adapted to the AS350 helicopter. In the upcoming section the effects of the loss of the SEW for a rotating blade of a three-bladed rotor – the AS350 rotor – are examined. It is shown how the response of a damaged blade changes, because of an imbalance in the rotor, and how this affects the motion of the rotor disk. The follow-up work will be to compare this data with experimental data given by flight tests through sensors placed on the rotor blades.