Powerplant Design and Performance Analysis of a Manned All-Electric Helicopter

This paper describes the conceptual design of three all-electric powerplants-a battery-only, a fuel-cell-only, and a battery-fuel cell hybrid powerplant-for a manned ultralight utility helicopter (Robinson R 22 Beta II-like) and carries out a comparative evaluation of performance delivered by each. The new powerplants consist of a combination of high-pressure proton exchange membrane fuel cells, 700bar type-4 hydrogen storage, a compressor-expander, lithium-ion batteries, and an alternating current synchronous permanent magnet motor. The key conclusion is that a hybrid powerplant that combines high specific power of batteries in hover and high calorific value of hydrogen in cruise delivers a superior performance compared to either system alone. The efficiency is higher than current rotorcraft piston engines but the key limitation is its low specific power, which is half of the current engines. Only 60% of the original payload can be flown (90kg solo pilot) for a duration of 35min (including 11min hover) over a range of 47km under high/hot (4000 ft/95 degrees F) conditions. The paper lays the foundations of performance analysis for all-electric rotorcraft, benchmarks the best performance achievable with current state of the art, and quantifies future technology targets to enable performance comparable to existing internal combustion engines.