All-Electric Sikorsky Firefly: Setting the Curve

By Dale Smith - Rotor And Wing

Progress continues on Sikorsky’s Project Firefly. While the manufacturer has not released a timetable for the test program, the modified Schweizer S-300C is nearing its first flight, according to reports. Project Firefly was unveiled at this year’s Oshkosh AirVenture. But this is no ordinary S-300—it could be a look into the future of helicopters.

“This is a technology demonstrator and research platform that will let us explore the technology, partnerships and technical collaboration required to push vertical electric flight technology forward,” explained Chris Van Buiten, director of Sikorsky Innovations. “It’s fun for us. This is familiar territory for Sikorsky. Back in the day, we made the first practical helicopter, so we’re used to starting these new curves.”

Project Firefly may be the beginning of a new technology curve, but Van Buiten said the Innovations design team was careful to choose a trusted helicopter platform for the demonstrator. “The guiding rule the team came up with was ‘spend every neuron on the electrons,’ don’t change the primary vehicle. Focus on the right motor, batteries, control and display. Do all the learning there and when we get good at that, design a new vehicle around it,” he added.

The S-300C’s open design made swapping the Lycoming piston engine with the 190-hp (142 kW), high-efficiency electric motor much simpler. Firefly’s designers were even able to use many of the original drivetrain components. According to the company, the entire electric/controller system weighs in at only 180 lbs and through the electrical conversion the propulsion efficiency of the helicopter has been increased ∼300 percent from baseline.

Power comes from twin battery compartments, which are mounted on both sides of the cockpit area. Each battery pack houses 150 individual, 45 Amp-hour lithium-ion cells. At first glace it looks like an agricultural hopper set-up without the spray boom. If you think the design was purely to simplify installation, you’d be half right.

“The batteries were compartmentalized on the side of the helicopter to be rapidly changeable so that as technology matures, we can quickly switch to the new batteries,” Van Buiten said. “We can give the form factor to different suppliers and they can deliver a new system that grows our endurance.”

Installing the new electric motor and battery system weren’t the only changes the Project Firefly team made to the S-300C. They also made significant alterations to the cockpit pedestal by removing the analog engine instruments, replacing them with a new LCD multifunction display.

“We’ve been doing a lot of work as to how to get the pilot real-time health monitoring information on his electric propulsion system,” explained Jonathan Hartman, program manager for Project Firefly. “Without the familiar vibrations and engine noises it becomes difficult for the pilot to start telling how the system is doing.”

Sikorsky has “installed sophisticated health monitoring sensors throughout the motor, controller and battery packs,” he added. “This information is fed real-time to the cockpit LCD. The pilot can see how the system is performing. One of the primary gauges on the screen will be a distance-to-empty display like you have in your car. The pilot will see just how much power he has available depending on the maneuver he is doing at the time.” Van Buiten added that the X2 Technology demonstrator and Project Firefly “really bookend an exciting spectrum of change for helicopter performance and capabilities.”