Back in 2009, as part of NASA’s Aeronautics Research Mission Directorate’s Integrated Systems Research Program; the Environmentally Responsible Aviation (ERA) Project was initiated which explores and documents the feasibility, benefits and technical risk of vehicle concepts and enabling technologies to reduce aviation’s impact on the environment.
Inspired by this project Engineering students at the University of Virginia have simulated a hybrid electric plane, or in simpler words, a plane that operates with an internal combustion engine coupled with an electric motor, that is capable of carrying 50 people. In order to test the feasibility of hybrid propulsion systems for propulsion aircrafts, the team of undergraduates led by aerospace engineering students Sohail Ahmad and Kelly Thomas using Flight Optimization System (FLOPS) software, evaluated several potential designs based on existing propulsion systems and airplanes. The goal was to test the feasibility of hybrid (internal combustion engine + electric motor) propulsion systems for passenger aircraft.
The goal of this project is to reduce aircraft consumption and noise while making it environment friendly with minimized emissions. The team decided to have the plane powered by batteries during takeoff and landing, letting the internal combustion engine (ICE) take over during the main flight, powering the propellers as well as recharging the batteries for landing.
They started with a base model, the ATR 42-600, a twin-turbo propeller commercial airliner aiming to determine if converting this plane to a hybrid propulsion system would result in better fuel efficiency and lower emissions. Both series and parallel architecture were studied. In series, the propeller is powered solely by an electric motor. The internal combustion engine charges the batteries and runs an electric generator that in turn drives the motor. In the parallel architecture however, the propeller can be powered by the electric motor and/or the Internal Combustion Engine. According to the results that the team obtained, the parallel design was more efficient for this purpose.
A number of factors including the crucial power-to-weight ratio and energy density were considered while selecting the battery. Another important factor, to be considered, was the battery lifespan. According to the FLOPS modeling that the batteries needed to provide enough energy for a thrust of 6208 lbs (2816 kg) at a velocity of 335 ft/sec (368 km/hr) which equals to 1567 kW per engine (it’s a twin-engine plane). Using Lithium-polymer batteries, they ended up with a total battery weight of just less than 13,000 lbs (5900 kg).
Their research brought them to the conclusion that retrofitting with current technology would not achieve the desired results. However, when technology advancements to the year 2025 were extrapolated, the team concluded that an overhaul would be more fuel-efficient than a standard ICE-powered plane for relatively short distances. “The retrofit imposed significant constraints on the design”, explained the students, “which is sort of like converting your old Ford Taurus to a hybrid model.” They believe that phenomenal results would be achieved if a new aircraft, specifically designed to work with a hybrid propulsion system is designed. Either way, the results lead us to expect from the hybrid aircraft in the future.