World's first electric-plane aerotow with Siemens SPD260-powered Extra 330LE, © Jean-Marie Urlacher
With electrification spreading through many types of transport, one vehicle still remains largely absent in using electrons for propulsion: aircraft.
Automakers have been building commercially viable electrified cars—in whole (electrics) or in part (hybrids)—for more than two decades now. Meanwhile, the aerospace industry has languished.
There's a reason for that: When it comes to aircraft, range is more than just an anxiety problem.
According to a recent blog post by SAE, electric aircraft are on the horizon, but they have some mountains to cross before they can be commercially available.
Battery capacity, in the aviation world, is Mount Everest. Current batteries simply don't have a high enough energy density to be viable.
The engineering society compared the Siemens SPD260 electrical motor the company is testing in an Extra 330LE experimental aircraft to a fuel-powered counterpart, the 300-hp Continental that powers the Cirrus SR 22.
Siemens SPD260 electric motor in Extra 330LE
The Continental ICE is capable of 260 minutes of flight time on 250 kg of aviation gasoline in the Cirrus. The same plane powered by Siemens' electric motor and 250 kg of lithium-ion batteries would have a flight time of just 20 minutes.
Using that same model, SAE estimates batteries would need to be much more energy dense, about 1 kwh/kg, to rival that of avgas.
The lithium-ion batteries Samsung is rumored to supply Tesla have an energy density of 300 W·h/kg, meaning we have a while to go.
But there's hope we'll cross the gulf between today's battery energy density and that needed to go airborne sooner rather than later.
"Starting with 117 wh/kg in 2008 the battery energy density doubled by 2015 reaching 250 wh/kg, and will almost double again between 2015 and 2018 reaching 450 wh/kg," reports the SAE blog post.
"At that pace, by middle 2020’s we may expect new batteries, most likely beyond lithium, and new fuel cells, capacitors, or a combination of them all reaching 1000 wh/kg storage capacity."
Solar Impulse 2 solar-powered airplane
Once battery development reaches the critical 1 kwh/kg, near silent aircraft won't suddenly fill our skies.
Certification procedures, powerplant management, and numerous other controls and rules will need to be up to aviation-grade quality before electrified commercial flight is truly possible.
Until then, privateers and big industry alike have been pushing electric propulsion development.
Airbus, the manufacturer of the largest commercial commuter aircraft, conducted its first test of the Airbus E-Fan electric aircraft in April 2014.
The company planned to bring two- and four-seat versions of the E-Fan prototype aircraft to production with power coming from two 30-kw (40-hp) electric motors spinning two eight-blade ducted fans.
Airbus hoped it would be the first step toward creating an electrically powered 90-passenger regional commercial jet.
Airbus E-FAN electric aircraft
Instead, Airbus cancelled production of the E-Fan earlier this year, replaced with plans to bring a hybrid-electric regional jet to market by 2030.
Meanwhile, the Solar Impulse team made history in 2016 when its Solar Impulse 2 became the first aircraft to circumnavigate the globe on solar power alone.
Before you pin your hopes on solar power to solve the today's battery energy-density issues, Solar Impulse 2 took more than 16 months to complete the journey over 17 stages at an average speed of 41 knots (47 mph).