NRC researchers are taking electrification to new heights to provide the aerospace industry with innovative solutions for decarbonizing the world.
In Saskatchewan, you might spot 6-seater Cessna Skymaster aircraft monitoring forest fires. In Africa, you could climb into one on a safari tour. Over far-flung tropical islands, you'd see them dispersing chemicals for mosquito control, or flying search-and-rescue missions. Today, you'll find one of these Cessna 337s at the NRC's Aerospace Research Centre in Ottawa, Ont., where researchers have turned it into a hybrid electric aircraft.
First built in the 1960s, these twin-engine planes became popular for their unique engine placement that simplifies a pilot's workload if a motor fails. Dubbed the "Mixmaster," this plane is different from typical propeller aircraft that have an engine on each wing. Rather, it has one engine on the nose pulling it forward and one on the back of the body pushing it. This push-pull configuration makes it ideal for the NRC's first major electric aviation project to set a course toward replacing fossil fuels with renewable energy, whether it's electricity or hydrogen.
In 2019, the Aerospace Research Centre partnered with the Energy, Mining, and Environment Research Centre, Design and Fabrication Services and Construction Research Centre to convert a Cessna 337 to hybrid electric power. Since then, a multi-disciplinary team of more than 40 researchers across Canada have pooled their talents and expertise to replace the aircraft's rear engine with a fully electric propulsion system that includes an electric motor, battery and supporting systems. It also has one of the highest-voltage electric systems to be commissioned on an aircraft to date.
According to Patrick Zdunich, the NRC's Technical Lead of the Hybrid Electric Aircraft Testbed (HEAT) project, aviation will follow the same path as electric cars, beginning with hybrids because the initial range is limited. "As in the automotive industry, we will eventually develop electric aircraft with very usable ranges." And hybrids are just a first step toward revolutionizing the entire aviation ecosystem.
Gathering speed with hybrid power
The HEAT project's Cessna 337 and the electric propulsion system have undergone a battery of tests and experiments in preparation for the plane's first flight at the Ottawa airport. "We evaluated its performance on a dynamometer, measured the noise level inside and out, and shook up the battery to test for vibration tolerance," says Zdunich. "Unlike in a paper study or simulation-only study, we rolled up our sleeves and got our hands dirty getting real experience in the design, test and build stages."
The unique centre-line thrust design of the Cessna 337 makes it ideal for electric conversion. A traditional twin aircraft with an engine on each wing would be difficult to balance, since the electric motor—about the size of a stack of dinner plates—is much lighter than the piston engine. "In this aircraft, we balance front to back by placing the batteries in the rear of the fuselage behind the pilot," adds Zdunich. "The centre-line thrust allows us to idle the front engine while we evaluate the performance of the electric system on the back." They can also shut down the test electric propulsion system without throwing the plane off balance and off course—and land it using the front engine only.
Reagh Sherwood, one of the NRC's research test pilots and project pilot for HEAT, reports that the team is writing on-aircraft operating checklists, ground and flight test plans, and risk assessments. It is also evaluating aircraft and subsystem safety, performance and human factors that are vital to the validation process. And this is the first time the NRC has tested a full aircraft electric power train from batteries to motor.
"The importance of this research goes far beyond the NRC's purposes," he says. "For example, the infrastructure and expertise that we have developed for HEAT can be used by aerospace industry clients wanting to design, test and validate their proprietary electric propulsion systems."
The team's findings and recommendations are also being shared with Transport Canada, the Canadian regulator. "One of the goals is to assist Transport Canada in developing criteria to certify electric systems and configurations for emerging aircraft," adds Sherwood. "New manufacturers will likely be seeking certification of a myriad different propulsion configurations, hybrid configurations, electric propulsion control strategies and flight profiles."
Prepared for takeoff
Zdunich points out that while electric aviation is still in the "Wild West" pioneering stage, it opens up vast opportunities. "We can develop totally new aircraft configurations while fighting the real crisis of climate change, since using hybrid or fully electric propulsion systems will eliminate direct carbon emissions."
Electrification will go a long way toward meeting targets for global action on climate change set by The International Air Transport Association (IATA). Goals include improving the fuel efficiency of the world fleet by 1.5% a year, stabilizing the aviation industry's total CO2 emissions through carbon-neutral growth, and cutting aviation's net CO2 emissions by 50% by 2050.
"But because this is a new frontier, we are finding innovative ways to mitigate new risks," he says. "Our work on the HEAT project illustrates what can be accomplished when a multidisciplinary team of researchers, technicians and engineers combine their expertise and resources."
And while electric motors will make planes cleaner and quieter, they will dramatically transform the way we fly. And that's another reason to keep an eye on the sky.