Putting Hybrid Engines in Planes

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Putting Hybrid Engines in Planes Putting Hybrid Engines in Planes
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Putting Hybrid Engines in Planes

by George Bye

April 7, 2010

Now that hybrid cars are standard, an aviation expert argues that it's time to put hybrid engines in the air.


This is the eighth and final part in an eight-part series on the future of transportation. See all the articles here.

Alternative energy advances have been remarkable. However, new technology, processes and products must be evaluated against the expense of bringing them to market. With a difficult economy, limited budgets and engineering resources, airplane manufacturers find it much more difficult to invest in developing new technology during tough economic times. Unfortunately, this means innovation can be delayed, perhaps when we need it most.

Innovation is sometimes inspired by incremental operational or cost benefits. It may also come as a result of a significant outside threat. Recently, several political, economic and industrial factors have combined in a manner that threatens aviation gasoline's long term viability. If innovation in aviation can progress, alternative energy may offer an answer to the potential halt of aviation gas production. Will these offerings be ready and broadly available in time? Are petroleum-based solutions going to share the stage with new biofuels? And, what about the high profile electric and hybrid technology that has swept through the automobile industry? Can aviation benefit from that learning curve and make a faster transition?

Electric motors are highly efficient, robust and do not lose power at higher density altitudes. They are also quiet and emission free. Perhaps most important for aviation, electric motors are relatively light weight. A 200-horsepower electric motor weighs only one-third that of an equivalent horsepower internal combustion engine. These features are certainly compelling. The critical question is how to efficiently get energy to the electric motor. For that, you need a battery.

The widely held perception is that batteries are heavy-very heavy-toxic, rupture easily, short circuit, catch fire, and are expensive. Research advances have eliminated many of these critical issues, at least in part. It is true that some battery configurations (and equivalent "fuel cell" technologies) are highly toxic. However, this is not universally the case. The baseline lithium ion battery chemistry is a recyclable salt, with low environmental impact. Recent advances in the internal configuration of the battery, particularly the layers, or separator, provides for a lighter, more efficient and sturdier battery. Together with new embedded battery management systems, concerns regarding energy spikes, thermal runaways and potential failure and fire have been greatly diminished. Still, are batteries ready for broad, mainstream airplane applications? Aren't weight and cost still a concern?

While new configurations and systems are often discussed, and eventually flown in the experimental category, many do not emerge to the larger certified marketplace. For many pilots, battery-powered flight remains merely a curiosity without practical application. A careful analysis of mission profiles and typical general aviation aircraft aerodynamics indicates the current battery energy density is about half of what it needs to be. Projections range from three to five years, perhaps more, before sufficient energy density is reached for a true battery-only propulsion system. Like energy density, battery cost is also a significant impediment to broad acceptance. Unit cost and operational cost effectiveness remain critical goals for mainstream market acceptance. But perhaps the largest barrier is the rigorous FAA certification process. Innovators with a goal of mainstream market acceptance view this process as the ultimate feasibility test.

Given the remarkable benefits and acknowledged limitations of electric propulsion, is there a way forward? The "first generation" answer may be provided with the energy balance of hybrid propulsion. As battery technology matures with energy density and cost improvements, the "second generation" propulsion technology may be all-electric.

To provide for the longer endurance mission requirements of the largest aviation market segments, a hybrid solution could include a small jet-fuel powered auxiliary power unit. Much like a hybrid automobile, this solution provides enhanced efficiency and reduced cost, while avoiding the expense and weight of an all-electric battery powered aircraft. The benefits of electric propulsion are not lost, but supplemented, with the high energy density of jet fuel.

Charlie Johnson, the former president of Cessna, "The time to accelerate incorporation of this new hybrid technology has arrived. Aviation is a vital market that will benefit from the environmentally friendly, lower cost, more efficient and higher performing aircraft."

Time is of the essence. A slow, pondering review has its risks. If actual flight tests prove out the theoretical projections, it appears that hybrid cost and performance features will be very attractive to the pilot-owner consumer. Much like the success of the Toyota Prius, the manufacturer that is first to offer a mainstream hybrid aircraft model may have an important market identity advantage.

Manufacturers are understandably cautious when it comes to adopting new technologies. Thorough, rigorous evaluation of each new innovation is an absolute necessity. New technology providers should work closely with major manufacturers and the FAA to ensure that the mandate of safety is never compromised. However, we must not hesitate to face the challenge before us. Too much is at stake. The development of electric hybrid technology will be expensive and time consuming. Hybrid technology has reached an inflection point where execution is now possible. All will benefit. Stakeholders from every corner will need to participate, collaborate, and invest-this innovation needs to make it through the gauntlet.

George E. Bye is a general aviation entrepreneur and an airline transport pilot with over 4,000 flying hours.  Mr. Bye is also an engineer and a former Air Force pilot who served in Desert Storm.  He is CEO of Bye Energy, Inc., based in Denver, Colorado.  Bye Energy is a technology innovator currently collaborating with other alternative energy providers to bring new energy technologies to general aviation.

Illustration by Dylan Lathrop.

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