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Penn State team investigates battery requirements for eVTOL applications vs EVs

The unique operating profiles and requirements of electric vertical takeoff and landing (eVTOL) aircraft—also known as flying cars—present formidable challenges to batteries. In a paper in the journal Joule, a team from Penn State University has analyzed the primary performance metrics required for eVTOL batteries compared with electric vehicle (EV) batteries.


EVTOL requirements on battery specific power and energy.

  1. Schematic illustration of a typical eVTOL trip.
  2. Representative battery power profile during an eVTOL trip.
  3. Required battery specific power in hover versus in cruise for the aircraft configurations being pursued by the industry.
  4. Trip distance versus consumed specific energy for three representative aircraft configurations.
  5. Battery energy breakdown for eVTOL trips with design-C and a 200Wh/kg battery pack.

From Yang et al.

Further, eVTOL batteries should continue functioning even after a safety incident occurs until a safe landing.

Notably, we highlight the importance of fast charging, which is essential for downsizing aircraft and batteries to reduce cost while achieving high vehicle use rates to maximize revenues. We stress that any fast-charging technology should fulfill three metrics simultaneously—charge time less than passenger swapping (5–10 min), charged energy sufficient for the next trip, and a long cycle life.

We experimentally demonstrate two energy-dense Li-ion battery designs that can recharge adequate energy for 80 km eVTOL trips in 5–10 min and sustain over 2,000 fast-charge cycles. We hope that these initial designs will spur exciting development of eVTOL batteries.

—Yang et al.


Battery requirements for eVTOLs versus for EVs. Note: EV batteries could have even lower C-rate (C/10) in city driving. Yang et al.


  • Yang et al. (2021) “Challenges and key requirements of batteries for electric vertical takeoff and landing aircraft”, Joule doi: 10.1016/j.joule.2021.05.001



also known as flying cars


The "Specific Power in Cruise" chart shows how all the startups reinventing the wheel will be very limited in capability compared to traditional aircraft design.

Excellent analysis. Next, they should do the same for electric vs conventional winged aircraft of all sizes.


Batteries, fuel cells and LH2 for air craft

Ed Hart

My talk: that chart confirms that there would need to be a major leap in battery technology before battery-electric flight is practical.

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What this research is about:
At the experimental level, the team tested a couple of energy-dense lithium-ion batteries that can recharge with sufficient energy for a 50-mile eVTOL trip in 5 to 10 minutes. Such batteries could sustain more than 2,000 fast charges over their lifetime.
Wang and his research group applied the technology that they have been working on for electric vehicle batteries. The key is to heat the battery to enable quick charging while making sure that lithium spikes are not formed which otherwise may impair the battery and can be dangerous. But it turns out that that heating the battery also allows rapid discharge of the energy confined in the battery to enable both take-offs and landings.
The researchers heated the batteries by integrating a nickel foil that brings the battery quickly to 140 °F.
You can read about Dr. Chao Yang-Wang earlier research "Thermally modulated lithium iron phosphate batteries for mass-market electric vehicles",here:

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Looking at the "Specific Power in Cruise" chart, the best candidates would be Slowed Rotor Compound VTOL. Two interesting eVTOl in this category are:
the Piasecki PA-890 (which is similar to the Karem AR-40 proposed for the US Army FARA program) and the Beta Technologies Alia-250c (the 250 relates to range so maybe a Alia-150).


I like the chart summarising EV vs eVTOL battery requirements - way higher. As I say in my post on the Vertical Aerospace article, neither the FAA or EASA are going to certify batteries until they have real world reliability test data to demonstrate achievement of required MTBF. They can't use automotive data to do that. Simulation will not be allowed. 2030 at best is optimistic.

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