This is a sidebar to the Vertiflite article, "Tier 1 Engineering Pioneers Electric e-R44".
Electric vertical flight is not new, but it has taken decades for the enabling technology to mature.
Forty years ago, Fred and Bradley Clark at Orlando Helicopter Airways (OHA) teamed with electric vehicle entrepreneur Roy Kaylor of California to convert a Korean War-era Sikorsky S-52 to battery-electric power at Stanford International Airport in Florida, with $50,000 in financial support from NASA (see “Orlando Helicopter’s Electric Sikorsky S-52,” Vertiflite, Jan/Feb 2022).
Four 60-hp (45-kW) alternating current (AC) starter/ generators from turbine engines were mounted around a central transmission input shaft, and linked by tooth belts, replacing a 245-hp (182-kW) piston engine. The 410-lb (185-kg) powerplant could produce 240–300 hp (180–225 kW) for 10 minutes, using as many as 14 heavy 72-Volt lead-acid batteries, weighing a total of 600 lb (272 kg), installed in the rear passenger compartment.
Following eight months of ground runs, the helicopter briefly hovered in November 1983 to become the first passenger-carrying electric helicopter to get off the ground with batteries onboard, but the project was abandoned in June 1984.
In 2008, Sikorsky Innovations embarked on the development of a battery-electric research helicopter called Project Firefly, based on the Schweizer (then- Sikorsky) S-300C.
The 190-hp Lycoming HIO-360-D1A 4-cylinder engine was replaced with a US Hybrid air-cooled permanent magnet electric motor of equivalent power, coupled with a lithium-ion energy storage system from Gaia Power Technologies of Germany; the batteries weighed 1,150 lb (520 kg) and offered 15 minutes of endurance. Following lots of media and tradeshow promotion, Sikorsky shut down the Firefly project before the helicopter ever flew. Reportedly, the demonstrator was heavy and underpowered, with challenging thermal management issues.
The first free flight of the Solution F electric helicopter demonstrator (shown) in Venelles, France, on Aug. 12, 2011. Designed and piloted by Pascal Chretien, the helicopter showed that piloted electric vertical flight was possible. Work ended after the aircraft demonstrated its objectives, with a maximum endurance of six minutes (see “From Concept to Prototype in 180 Days,” Vertiflite, March/April 2012).