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By Peter Lert

Project firefly has a 142 kW (190 hp) permanent magnet motor, and has the same output shaft speed as the standard IO-360. Photo by Phil Burmeister

Drop into the Aviation Learning Center and you'll see what at first glance looks like an aerial application version of the Schweizer 300 helicopter, minus the spray booms but retaining the big pesticide tanks. A second glance, however, reveals that these are actually battery enclosures; look between them and you realize that the 200-hp Lycoming is gone, replaced by an electric motor. Gone, also, are the original fuel tanks, as well as the maze of wiring and plumbing that decorated the original reciprocating engine installation.

This is Project Firefly, a research platform under development by Sikorsky Innovations in Stratford, Connecticut. Project engineer Jonathan Hartman explained that they began with a proven existing airframe to minimize re-engineering, then developed the electric power package to replicate the operating characteristics of the original gasoline engine. Thus, the 142 kW (190 hp) permanent magnet motor, developed by US Hybrid in Torrance, California, is mounted in the same location and has the same output shaft speed as the standard IO-360.

Everything "downstream" of the engine output pulley is the same as in the original helicopter, including the multi-V-belt primary drive, sprag clutch, transmission, and rotor system. The motor itself was originally developed for surface vehicle programs including electric trucks for the Port of Los Angeles and an electric-powered Humvee for the U.S. Marine Corps; converting it for the helicopter involved modifying its rpm and torque characteristics and changing from water to air cooling. US Hybrid also developed the motor controller, while the lithium-ion battery cells come from Gaia in Germany.

Total capacity of the 1,100-pound battery is 48.1 kWh, which should allow a flight time of approximately 15 minutes with reserves. First flight is expected later this year; at present, the Firefly helicopter is continuing with ground runs to validate the power system and gather data. Hartman noted that with an expected order of magnitude improvement in battery capability, they could begin thinking about real-world applications.
This fits with the generally established idea that a 20-fold improvement in battery capacity for a given weight would be directly comparable to internal-combustion power systems.

For more information, visit www.Sikorsky.com.

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