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In the 21st century, we were promised flying cars, robot maids, and jet packs. We got mechanized, autonomous vacuum cleaners instead. Penn State researchers are now studying the requirements for electric vertical landing and takeoff (eVTOL) vehicles. They also design and test potential battery power sources.
Chao-Yang Wang holds the William E. Diefender Chair in Mechanical Engineering and is the director of the Electrochemical Engine Center at Penn State. “I believe flying cars have the potential to eliminate a lot more time and increase productivity and open the sky corridors for transportation,” said Wang. But electric vertical takeoffs and landing vehicles are extremely challenging technology for the battery.
Researchers defined technical requirements for flying car batteries and reported on a prototype battery in Joule on June 7, 2021.
Wang stated that batteries for flying cars require very high energy density to keep you in the air. They also need very high power for takeoffs and landings. To go vertically up or down takes a lot of energy.
Wang also notes that batteries must be quickly recharged to generate high revenues during rush hour. Wang sees these vehicles flying frequently and often landing, needing to be restored promptly.
Wang stated that the vehicle would make 15 trips per day, twice daily during rush hour, to justify its cost. “The first use of the car will be to transport three to four passengers approximately 50 miles from a city to an international airport.
These batteries must also be weighed as the vehicle must lift and land the batteries. Wang estimates that the eVTOL will reach speeds of 100 mph on short trips and 200 mph on long trips.
Two energy-dense lithium-ion battery packs were tested experimentally by researchers. They can charge with enough energy to provide enough power for a 50-mile eVTOL journey in just five to ten seconds. These batteries can withstand more than 2000 fast charges during their lifetime.
Wang and his team used the technology they had developed for electric vehicle batteries. It is essential to heat the battery to enable rapid charging. Heating the battery allows for fast charging of the battery energy to enable takeoffs and landings.
Researchers heat the batteries using a nickel foil, quickly bringing it to 140 degrees Fahrenheit.
Wang stated that the three necessary attributes for eVTOL batteries work in opposition under normal circumstances. Fast charging is reduced by high energy density, and the number of recharge cycles can be reduced by fast charging. We can do all three with one battery.
The unique feature of flying cars is the requirement that batteries retain some charge. A flying car battery cannot be fully discharged in the air, unlike cellphone batteries, which only work if fully charged and recharged. It needs the power to keep the vehicle in the air and on land. A flying car battery must always have a safety margin.
The internal resistance of a battery that is not fully charged is low. However, the greater the remaining charge, the more difficult it becomes to put energy into the storm. Recharging is usually slower as the battery gets full. Recharging can be slowed down by heating the battery.
Wang stated, “I hope the work we did in this paper will give people a solid understanding that we don’t need to wait another 20 years before we finally get these vehicles.” “We have shown that the eVTOL can be commercially viable.”
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