Project Firefly: Sikorsky unveils electric helicopter technology demonstrator


August 10, 2010

Sikorsky Project Firefly technology demonstrator

Sikorsky Project Firefly technology demonstrator

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Officially announced at AirVenture 2010, Sikorsky's Project Firefly sets out to demonstrate the feasibility and showcase the benefits of electrically powered helicopters. The technology demonstrator is based on an S-300C light helicopter, with a 190-horsepower electric motor replacing the standard piston-engine and lithium ion battery packs added to either side of the cabin. The result is a significantly more efficient system that – although it's expected to fall short of typical helicopter performance when the first flight takes place later this year – is just the tip of the iceberg for the new era of manned electric rotorcraft.

Along with the electric motor and battery packs, the demonstrator includes a new digital motor controller and next generation cockpit display. The drive train, rotors and flight controls from the S-300C have been retained and very little has been changed on the airframe, as the electric motor has been designed to pick up the same hard points as the piston engine it replaces.

The 190 hp (142 kW) motor built by Californian firm U.S. Hybrid from California is derived from a unit developed for ground based vehicles but, as Sikorsky's Tim Lauder explained to Gizmag, it's been specifically tailored for use in rotorcraft. These changes include an additional 40 horsepower, constant operation at 3200 RPM and forced air cooling as opposed to water cooling.

The battery pack from German manufacturer GAIA consists of 300 cells – 150 in each bay – with an energy density of 0.13 kW per kilogram.

Inside, real-time aircraft information including temperature for left and right battery packs, flight time remaining and voltage is shown on an interactive LCD monitor.

Performance and efficiency

The comparative figures Sikorsky has released for the testbed helicopter show huge improvements in efficiency. The main rotor output, for example, is 76.3 percent efficient in the electric version versus 25.5 percent for a Sikorsky 76D running two PW210S turboshaft engines on JetA fuel. The other notable comparison is heat loss, where the electrical system loses just 15 percent compared to 73.4 percent on the 76D according.

“Through the electrical conversion, propulsion efficiency of the aircraft has been increased roughly 300 percent from baseline," said Mark Miller, Vice President, Sikorsky Research & Engineering. "Electric propulsion also inherently simplifies the complexity of the propulsion system by reducing the quantity of moving parts, increasing reliability while reducing direct operating costs.”

While both the cruising speed of 79 knots and the gross weight of 2150 lbs are comparable to the S-300C helicopter, the big issue, as with electric cars, is range. The demonstrator has an expected flight time of 15 minutes (compare this to the 3.7 hrs the S-300C gets from its 32 gallons of fuel) but as battery technologies get better, this will improve exponentially.

Lauder sees lithium air batteries as one of the most promising of these developing technologies. "Lithium air batteries would be lighter (because they have no anode) and provide nine times the energy density of the current batteries, enabling three hour flights and rivaling combustion engines."

The problem at this stage is that these batteries are non-rechargeable, but research and development of rechargeable versions is ongoing.

It's safe to say that the future for electric helicopters is bright. As battery technology matures the value of the systems showcased on Sikorsky's testbed can only increase. Although the company has chosen to use an existing airframe to showcase the technology at this early stage of development, it is already looking towards ground-up designs that will run two electric motors – one in the main rotor and another in the tail rotor. This approach, like electric car designs that place motors at or in each wheel, will further reduce weight and improve efficiency by bypassing the need for any conventional drivetrain.

    Sikorsky electric helicopter specifications

  • Max Gross weight - 2,150 lb
  • Power 190 hp (142 kW) Permanent Magnet electric motor
  • Lithium Ion Battery - 45 Ah, 3.6 V, 3 cells in Parallel = 135 Ah, 100 set in series = 360 V
  • Forced Air Cooling
  • Endurance - 15 min
  • Max Velocity - 79 kt
  • System Efficiency - 79 % (Cruise), 91 % (Max Power efficiency)
  • + Sikorsky.

About the Author
Noel McKeegan After a misspent youth at law school, Noel began to dabble in tech research, writing and things with wheels that go fast. This bus dropped him at the door of a freshly sprouted in 2002. He has been Gizmag's Editor-in-Chief since 2007. All articles by Noel McKeegan

Whilst not being a chopper pilot I can not understand why manufacturers dont adopt the \"Coaxial\" rotor concept like the Russians favor. Amongst the advantages are very low vaibration smoother ride & the tail rotor can be dispensed with. AH well change is very slow they say!!.

Cheers Kiwi

John M

O.K. when do these \"magic\" battery\'s come into being? I don\'t care how \"efferent\" they claim to be but if the range or practicality isn\'t there then what good is it? I\'m all for electric\'s but they\'re going to have to stop thinking in terms of battery\'s! Fuel cells or some other means of making electricity, but I fear battery\'s are never going to cut it.


Dropping in a hydrogen fuel cell should take care of the range anxiety.

Lawrence Weisdorn

OK, so they opted for L-ion rather than L-polymer power cells (and in the air, I would too) but the side pods have to go. They have to integrate the batteries into the landing gear and body of this aircraft. Lithium polymer would allow for a shape that would mirror the aerodynamic (if you can call it that) shape of the bubble.

What they will find out is that safe, long operating time, rechargeable battery power is along way off. So, they\'ll want to use a smaller, purpose built turbine (probably 75kW) and several battery pods spaced around the copter for weight distribution. When battery power drops to 40%, the turbine activates and recharges the batteries in about 20 minutes. Four charges per tank of fuel and you have much better overall air time. If the batteries fail (partially or fully), the turbine could be shunted directly to the electric motor for as along as remaining fuel lasts. Best of both worlds.


I like this smart earth-friendly design. However, we are prisoners of past if the vehicle power source shaft- accelerator struggles with transmission reduced speed function at the process of movement. As result the energy consumption up to 80% is the additional heat of engine or motor. We must change mind to ignore saving energy by levers as is the hard gears since the gas or magnetic field too slowly creates the higher torques and requires much increased powers. The revolutionary patented methods create above 1,000 manual and/or automatic gearbox apparatus-accelerator designs that profitably for both manufactures and customers. Each design comprising the least numbers of gears could eliminate the function of acceleration system so that power source has only idle speed that creates condition dramatically to save energy and emission of modernized vehicles based on land, water and air, heavy-duty equipment, etc. There is brand new business which will grow when economy goes down.

Vladimir Abramov

I drive my EV\'s every day but this won\'t fly as they say. The eff is from energy on the ground vs in the air where it counts.

There are batteries like Alum or Zinc/air that can do the job, probably 1 hrs worth but even that is not very useful. A Lithium air if ever done could be 5 x\'s as long range but that is probably a decade away.

In aircraft energy capacity rules and liquid fuels are the way to go.

Maybe of they drop the weight by using composites, use 2 larger counter rotating rotors which are about 20% more eff than their system with the hub motors, a good idea, this might work with the alum or zinc air batteries.


It\'s good to see this in the making. In the model world, electrics are surpassing nitro (gas) models in performance. I have an electric model helicopter and car and (I\'m told) the car is faster than any off the shelf nitro model, over 70 mph! A Traxxus Rustler VXL if anyone is interested. It\'s truly insane to drive! Consant wheelstands! And goes for 15 minutes on a charge, so does the heli. I think there\'s a future in this technology, there\'s a huge focus on battery technology as the world shifts to electric everything and away from fossil fuels. It\'s all in the Lithium based batteries and brushless motors these days. Lithium will be the new \"crude\".


I\'m sorry, but the only way that electric aircraft will work is cellularly. Energy beamed to the flying electric aircraft from the ground (or the sun) will make it happen. That way, energy\'s true weight will be utilized. Imagine if we had to carry batteries from power stations to cities? Well, battery-powered aircraft is an idea just as strange.


Lol, Lithium is ALREADY the new crude. That\'s another reason for the Afghan war! (check their deposits) But the heli kicks ass, I wonder (like Muraculous) about a turbine to boost the range. Suppose it wouldn\'t be much of a study then, lol. Top effort lads

Craig Jennings

In the conventional helicopters, power transmission system takes the engine output (torque at a certain angular velocity) and transfers it to the rotors at another angular velocity and torque (main and tail rotor gear boxes). The company is looking for design that will run two electric motors(main rotor and tail rotor). The significant improvement here is that the quantity of the moving parts is reduced which increases the system reliability; the propulsion efficiency increase of 300% from baseline is claimed.

S P S Sabharwal

20hp electric motors can be as small as a coke can. What they need is a free-spinning main rotor, propelled by rotor-tip-mounted electric turbofans; hyper-efficient, no need for tail rotors, and it would look so cool. Heck - use a 2 blade rotor, make one turbofan reversable, and if you don\'t mind a zero-G freefall for a short while, you could lock the rotor and covert to \"fixed wing\" flight to cover large distances fast.


OK,I get it,a baby technolgy demonstrator of the vehicle as an electrically driven entity.It\'s not the final battery technology that\'s being tested,nor all the envisioned componentry that is the logical application of electric power in a helicopter. What really concerns me is the posibility of this craft being shot down by some paranoid redneck mistaking the battery packs for weapons pods!

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