Harnessing Energy Efficiency for Electric Helicopters

Electric propulsion has the potential to revolutionize the way people and goods move. The U.S. Department of Energy says that fully-electric and hybrid-electric vehicles powered by batteries, super capacitors, and fuel cells have the potential to “increase energy security, improve fuel economy, lower fuel costs, and reduce emissions.” Yet, until a few years ago, no one was equating such vehicles with the standard vision of “high performance.” There were no electric supercars cruising down the highway, and there was only one drag racer that burned rubber using electric motors.
But recent advances in technology have allowed companies like Tesla and organizations like Formula E to bring the terms ‘high performance’ and ‘electric vehicles’ into mainstream vocabulary. And while such advances in energy efficiency continue at a rapid pace, they seem to be limited to the automobile industry. As of now, electric helicopters and airplanes are not dotting the sky on a daily basis. So what’s stopping the electric revolution from coming to a heliport near you?
The answer has everything to do with Newtonian mechanics and defying gravity.

Overcoming Gravity

The first challenge facing an airplane or a helicopter versus a car is cruise efficiency. At highway speeds, a car is significantly more efficient. An internal combustion engine is designed to be most efficient at these speeds, and on the highway, acceleration and deceleration (which takes energy) is minimized. This is important when thinking about electric vehicles, because batteries and other energy storage technologies today simply aren’t as efficient at storing their energy as gasoline and other liquid fuels. This means more weight for the same amount of stored energy. Thus, any energy a vehicle can save through efficient operations equates to a reduction in that weight penalty, reducing cost and increasing performance.
Airplanes and helicopters do not earn such an efficiency boost. Even at their most aerodynamically efficient, helicopters generate one half to one third the efficiency benefit that cars enjoy. As a result, more energy has to be stored on board, which requires more batteries, which leads to a heavier vehicle that requires more energy to fly. It’s a design loop that can quickly spiral out of control.
Rotorcraft face the additional energy burden of needing to hover when landing, requiring a surge of energy at the least convenient point for electric energy storage devices. Hovering is the maneuver where rotorcraft expend the most power per unit time (i.e. energy) as the aircraft works against both momentum and gravity. The issue that hovering creates is not the energy required, but when it is required. As a battery, as an example, is discharged, its voltage drops, and its ability to make power degrades. At the end of its charge, right when a battery wants to stop working, is exactly when a helicopter needs those same batteries to work at full strength.

Shake, Rattle and Roll

The second challenge facing this technology is that all air vehicles, helicopters in particular, are vibration machines. Vibration wears out people, parts, electrical connections, all of the critical pieces of the system that are required to stay in the air. As a result, any component on an aircraft, even though it may perform very similar tasks as a component on a bus or a car, needs to be overdesigned to meet these new requirements. Often, the unique characteristics of airplanes and helicopters mean that existing parts have to be designed again, as they were never originally intended to withstand punishment close to the environment in an aircraft.
The unique safety aspects of helicopters also make a challenging set of requirements for any storage technology. Unlike cars, there is no ‘shoulder of the road’ to pull over to in case of emergency. Helicopters must be designed to be able to deal with significant failures and keep flying. The need to increasingly rely on volatile chemistries to obtain the required power and energy densities in aviation must be weighed against the ability of a system to mitigate the failures that are statistically increasingly likely to occur.

So will there ever be electric helicopters?

If you were to shake one of those Magic 8 Ball toys and ask this question, you’d most likely get the ‘All Signs Point to Yes’ answer. Electric storage technology is advancing at a rapid rate, and it’s hard to imagine a future which wouldn’t include alternately-powered aircraft. However, there’s a catch. To get there, the industry needs step-change advances in the energy and power density of storage technologies, and needs technologies that can survive in some of the world’s harshest environments.
From the perspective of a business case, those challenges could seem daunting. After all, what is needed is a completely superior battery than what the automotive industry ($$ billions in R&D in this area, millions of units sold annually) needs for an aerospace industry that produces thousands of products a year and spends $$ millions in R&D in this area. If the aerospace industry was only willing to pay what the automotive industry pays, or wait as long as they do to adopt technology, then the math would never work.
So here’s the secret: aerospace companies will pay a premium for superior technology, and are generally more comfortable with working with completely new technology, risk reducing it, and getting it out to the market than other transportation industries. Airplanes cross oceans and helicopters hover because engineers took daring risks on just emerging technology to push the boundary of what’s possible. And as aerospace customers continue to want more performance, the need to continue to put money and manpower into disruptive technologies will only increase.

But I have the answer to your problem. What do I do now?

Apply for the Sikorsky Innovations Entrepreneurial Challenge. Win some non-dilutive funding ($25K) and gain access to one of the world’s leading aerospace companies.