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

Variable speed rotors represent an innovative research field for the development of new rotorcraft designs. Issues related to employing a main rotor variable speed are numerous and require an interdisciplinary approach. For this reason, a preliminary effort has been made 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 both the helicopter and engine model is necessary to adequately determine the correct rotational speed corresponding to minimum fuel consumption. More than 10% fuel saving is shown to be feasible. The results obtained employing a variable speed main rotor are broadly discussed, and future possible applications of the methodology are suggested.