A methodology for determining the optimal rotational speed of a variable RPM main rotor/turboshaft engine system

Variable speed rotors represent an innovative field of research for the development of new rotorcraft designs. The problems Issues related to employing a main rotor variable speed are numerous and require an interdisciplinary approach. For this reason, a first effort has been made in the present paper to understand the performance implications of coupling helicopter trim and turboshaft engine simulations. Following this, two different models of a UH-60 Black Hawk helicopter and a GE T700 turboshaft engine are implemented and validated against experimental data. Then, an optimization algorithm is employed to find the optimal main rotor speed with the aim of minimizing fuel consumption. Different simulation cases are analyzed to quantify the benefits related to the optimal main rotor speed depending on flight condition, altitude and helicopter gross weight. It is found that coupling the helicopter and engine model is necessary to adequately achieve the correct rotational speed corresponding to minimum fuel consumption. More than 10% fuel saving is shown to be feasible. The results obtained by means of numerical simulations are widely discussed and future possible applications of the methodology are suggested.