Rotorcraft Propulsion System Hybridization for Enhanced Safety and Performance

Herein, the case for hybridization will be made, primarily as a means for enhancing safety. Utilizing a case study of a popular light turbine helicopter, it will be shown that augmentation with a parallel hybrid electric system, under two critical operational failures, safety can be significantly enhanced. Conceptual design of two powertrain architectures for parallel turbine-electric hybrid propulsion systems will be examined in sufficient detail to quantify their relative impact in comparison with the existing conventional turbine-only powertrain. Initial trade studies were performed to minimize system weight, utilizing current state-of-the-art components and technology. Commercially available motors, inverters and battery systems were selected for the study. Two architectures were chosen and exercised for three operational scenarios: requirements for 21/2 minutes of emergency power, 5 minutes of emergency power and 10 minutes of emergency power at takeoff/climb power level. Relative cost and benefit are quantified by performance impacts including payload capacity impact, range, rate of climb, and high-altitude performance for the different sized battery packs required for each of the 3 emergency power durations. The key benefits are safe recovery from two serious failure modes: inoperative engine and main gearbox failure. The rough "performance cost" for this safety enhancing modification is a loss of about 1/3 of the nominal useful (passenger + baggage) payload, assuming full fuel capacity operating at maximum gross takeoff weight.