59375 - Revolutionary Vertical Lift Technology (Rvlt) Side-by-Side Hybrid Concept Vehicle Powertrain Dynamic Model 

NASA is currently investigating several Revolutionary Vertical Lift Technology (RVLT) concept vehicles representative of those expected to be used for Urban Air Mobility. This paper describes the development of a dynamic model of the powertrain of one of these, the Side-by-Side Hybrid concept vehicle, using the NASA developed Open Source Software packages, the Electrical Modeling and Thermal Analysis Toolbox (EMTAT), and the Toolbox for the Modeling and Analysis of Thermodynamic Systems (T-MATS). The Side-by-Side Hybrid powertrain consists of two turboshaft engines, two rotors, a motor/generator, and an energy storage device, along with shafts and gearboxes. The two engines are the main drivers of the system. They connect to the drivetrain through overrunning clutches, which allows them to individually disengage, if necessary. Since the rotors overlap, everything past the overrunning clutches must be geared together so the rotors turn at the same speed. This is achieved through the use of a cross shaft geared to both clutches, which is also connected to the gearboxes that turn the rotors. The third driver is a motor/generator geared to the shaft. This electric machine acts as a motor during hover and low speed flight to augment the engine power, while in cruise, it is turned by the shaft to generate power that charges the energy storage device. The nonlinear model captures the dynamic behavior of the system while simulating on turbomachinery time scales (15-20 ms integration step size), enabling much faster than real-time execution. The use of EMTAT, which is designed to simulate electrical components at the appropriate fidelity for interaction with the turbomachinery, makes this possible. EMTAT utilizes a steady state modeling approach for electrical devices, allowing the electrical performance calculations to be simplified, with high speed transient losses captured as a general efficiency loss. The powertrain model contains realistic control-related implementation features such as integrator windup protection and torque sharing between the two turboshaft engines. The Side-by-Side Hybrid powertrain model is a suitable testbed for concept of operations and optimization studies involving coordinated control of the engines and motor.