Engineering students at the University of Virginia have simulated a hybrid electric plane that’s capable of carrying 50 people. Using Flight Optimization System (FLOPS) software, the team of undergraduates led by aerospace engineering students Sohail Ahmad and Kelly Thomas evaluated several potential designs based on existing airplanes and propulsion systems. The goal was to test the feasibility of hybrid (internal combustion engine + electric motor) propulsion systems for passenger aircraft.

Image: University of Virginia

The project was inspired by NASA’s Environmentally Responsible Aviation (ERA) project, whose goals are to reduce aircraft fuel consumption, emissions, and noise. The team decided to have the plane powered by batteries during takeoff and landing, since these take place in congested areas. the internal combustion engine (ICE) would take over during the main flight, powering the propellers as well as recharging the batteries for landing.

Starting with a base model, the ATR 42-600, a twin-turbo propeller commercial airliner that seats 48 passengers, the team set out determine whether converting this plane to a hybrid propulsion system would result in better fuel efficiency and lower emissions.

The students tested both series and parallel architecture. In series, the propeller is powered only by an electric motor. The ICE’s jobs are to charge the batteries and run an electric generator that drives the motor. In the parallel architecture, the propeller can be powered by the electric motor and/or the ICE. They determined that the parallel design was more efficient for this purpose.

What about batteries? Obviously, power-to-weight ratio is crucial in aircraft, so they sought the battery with the best energy density. There are other factors, of course, such as battery lifespan. FLOPS modeling told them 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). This equated 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 under 13,000 lbs (5900 kg).

In the end, they found that retrofitting with current technology would not achieve the desired results. However, when they extrapolated technology advancements to the year 2025, a retrofit would be more fuel-efficient than a standard ICE-powered plane for relatively short distances (300 miles or so). The students concluded that the retrofit imposed significant constraints on the design, sort of like converting your old Ford Taurus to a hybrid model. They believe that a new aircraft, specifically designed to work with a hybrid propulsion system, could be feasible using current technology. Either way, the results show promise for the future of hybrid aircraft.

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