Mission Analysis and Aircraft Sizing of a Hybrid-Electric Regional Aircraft

Abstract

The purpose of this study was to explore advanced airframe and propulsion technologies for a small regional transport aircraft concept (~50 passengers), with the goal of creating a conceptual design that delivers significant cost and performance advantages over current aircraft in that class. In turn, this could encourage airlines to open up new markets, reestablish service at smaller airports, and increase mobility and connectivity for all passengers. To meet these study goals, hybrid-electric propulsion was analyzed as the primary enabling technology. The advanced regional aircraft is analyzed with four levels of electrification, 0% electric with 100% conventional, 25% electric with 75% conventional, 50% electric with 50% conventional, and 75% electric with 25% conventional for comparison purposes. Engine models were developed to represent projected future turboprop engine performance with advanced technology and estimates of the engine weights and flowpath dimensions were developed. A low-order multi-disciplinary optimization (MDO) environment was created that could capture the unique features of parallel hybrid-electric aircraft. It is determined that at the size and range of the advanced turboprop: The battery specific energy must be 750 Wh/kg or greater for the total energy to be less than for a conventional aircraft. A hybrid vehicle would likely not be economically feasible with a battery specific energy of 500 or 750 Wh/kg based on the higher gross weight, operating empty weight, and energy costs compared to a conventional turboprop. The battery specific energy would need to reach 1000 Wh/kg by 2030 to make the electrification of its propulsion an economically feasible option. A shorter range and/or an altered propulsion-airframe integration could provide more favorable results.

Conceptual Design of Operation Strategies for Hybrid Electric Aircraft

“…The chemical energy is converted into mechanical energy. This process has a relatively low efficiency of about 40% [14], which even decreases for lower power ratings of the turbine [26]. A ducted or unducted fan is mounted on the main shaft of the gas turbine to provide thrust.…”

“…Reports from NASA [33], the BHL [34] and Masson et al [35] predict gravimetric power densities between 7-25 kW/kg for HTS motors including cryogenic cooling with efficiencies from 95-99.5%. The efficiency of electric motors is not highly dependent on the rated power output in comparison to gas turbines [14]. As a design requirement for the PMAD components the rated voltage of the electric propulsion system is needed.…”

“…In the LEAPtech project, distributed propulsion, its aerodynamic effects [11] and larger aircraft with aft fuselage propulsors [12] are investigated. In their PEGASUS concept [13,14] a wingtip propeller architecture is applied for a regional aircraft, highlighting the propulsion system and different fixed battery energy settings. The PEGASUS concept shows that battery hybrid to conventional propulsion vehicles offer a limited economic competitiveness for low battery specific energy (<600 Wh/kg) and high electricity costs.…”

A Review of Concepts, Benefits, and Challenges for Future Electrical Propulsion-Based Aircraft

“…Such configurations inherently deprive the aero-propulsive synergistic benefits, if propulsors are not strategically placed close to the wing body surface of the aircraft. Nonetheless, such reformed concepts found application in Parallel Electric-Gas Architecture with Synergistic Utilization Scheme (PEGASUS) design, which adapts to a distributed architecture with two wing-tip propellers, two inboard propellers and one aft fuselage BLI fan to get additional aerodynamic benefits [42,43]. In addition to the fuel efficiency benefit, the design showed potential for operating cost improvements owing to the added redundancy in the system.…”

“…In regional segment, the Parallel Electric-Gas Architecture with Synergistic Utilization Scheme (PEGASUS) concept was studied; with a particular focus on the operational cost aspect [42,43,97]. Suitable for a regional transport segment, a 50 PAX aircraft with a parallel hybrid architecture was assessed with varying degrees of electrification and in battery energy density on a 600 nm mission range.…”