Modelagem dinâmica de helicópteros com motores não ideais.

Abstract

The non-ideality of energy sources used in mechanical systems, in general, has been studied more thoroughly at mechanical engineering. Knowing how a non-ideal engine affects the system is realy important, because of undesirable effects resulting from the interaction between the structure of the equipment and the energy source, like Sommerfeld Effect. This one happens when there is some imbalance, from the engine, the rotor hub or in the system blades, promoting instabilities shown in the system acceleration and slowingdown process. The mechanical system modeling excited by engine is normaly based in the assumption that all of the power supplied to the engine is converted in useful work or considering that the energy loss happens in the coupling of the engine. However, this is a simplification done to reduce the system complexity, making the moviment equations solution easier, but there are also conditions in which energy is dissipated in the structure by vibrating moviments. In helicopters, dynamic effects, as discussed previously, are responsables for major accidents. Ground Resonance for example is a widely known phenomenon in the aeronautical evironment which occours when the excitation generated by the engine reaches the aircraft natural frequency, when this last one is in the ground. The contact between the helicopter and the ground progress a system change, when compared to the aircraft in flight, causing an unwated dynamic responce. The present work presents the modeling of a helicopter (divided in models HT1 and HT2), which was carried out with the development of system energy equations, followed by the non-ideal motor equation, using a simplified torque curve, besides linearization of equations, allowing to obtain a system of matrices, representing the aircraft. The dynamical responses of the models were also presented, showing that the aircraft presents dynamic instability when they are driven with frequency near to some natural of the fuselage. Also, the complexity related to the construction of a system of equations capable of coupling the ground resonance model to the non - ideal motor was verified, showing that the simplification of the torque curve limits the ability to represent the model with real operating parameters.