Jet airplanes usually pack hundreds of passengers for long flights. But they also require long waits at major airports to get on board and complete those flights. Shorter flights, known as regional flights, of around 500 to 1,000 miles in distance are becoming something of a memory, as former air passengers turn to alternative means of transportation, such as buses, trains, and automobiles.
A number of innovators at startup company Zunum Aero, including researchers Matt Knapp and Waleed Said, hope to change these travel trends. They are developing hybrid gasoline/electric power trains and smaller battery-powered airplanes that can carry 12 passengers at a time, making it easier to fly from one small airport to another, without waits and without problems.
Zunum Aero, which is based in Kirkland, Wash., is backed by some key players in the air transportation space, including JetBlue Technology and Boeing. The firm’s novel hybrid-to-electric power train draws on technology advances made in recent years in hybrid-electric vehicles and battery technologies. The first flight tests of the small aircraft are scheduled for 2019, with plans to sell the hybrid-electric airplanes to airlines by 2022.
The planes have two energy sources—gasoline and batteries. The gas engine and fuel tank is mounted in the rear of the plane. The lithium-ion (Li-ion) battery packs are located in each wing to provide supplemental power as needed, such as on takeoff. Cruising power is supplied by a gas turbine linked to a generator, mounted in the back of the plane.
The hybrid-electric airplanes are powered by a pair of low-pressure ducted fans, each driven by an integrated 500-kW permanent-magnet motor. The fans, which provide high static thrust sufficient for takeoff, deliver high operating efficiency for low-cost cruising, with low-noise operation. The battery cells have a minimum power density of 350 W-h/kg. The battery packs are designed and mounted in the plane’s wings in such a way that they can be quickly removed and exchanged at an airport when there’s not enough time for a full recharge cycle.
In addition to the hardware, Zunum Aero’s researchers have proprietary algorithms to analyze an aircraft’s route and develop a minimum energy plan for that route. The plan is monitored and updated during a flight by means of on-board sensors taking continuous readings from the onboard motors, batteries, and fuel tanks, as well as from real-time data and weather reports.
The company is developing what they call a “copper bird” model of all electrical systems on the hybrid-electric airplanes. By evaluating some of the new flight systems on existing airframes, they hope to develop computer-aided-engineering simulations of key components so that they can be optimized for size and power to achieve the best flight performance in the lightest systems possible.
See “Electric Blue Skies,” IEEE Spectrum, May 2018, p. 27.