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Dash 8-100 hybrid-electric demonstrator

The hybrid electric evolution 

By Chitra Narayanan and Jonathan Pereira

Published on: July 4, 2024
Estimated reading time 11 minutes, 58 seconds.

Advances in engines technology and progress by test beds such as National Research Council of Canada are propelling forward hybrid electric aircraft.

With their potential to increase fuel efficiency and reduce carbon emissions, hybrid electric aircraft offer an economically viable solution towards achieving net-zero carbon emissions. Advances in battery technologies and the increased use of sustainable aviation fuel (SAF) will be key factors that drive the transition to hybrid electric technology for a more sustainable future in aviation. 

Hybrid electric aircraft, like hybrid cars, combine two energy sources for propulsion—the conventional fossil-fuel-powered internal combustion engine (ICE) and the electric motor powered by batteries. The ICE and the electric motor may be used in tandem or alternately. Propulsion in hybrid electric aircraft systems is achieved using the series, parallel, or series/parallel architectures. 

In the series architecture, the electric motor generates the mechanical power to drive the propeller. The electric motor is powered either by a generator coupled to the ICE or a battery. In the parallel architecture, the propeller is driven by two independent sources of power – the electric motor powered by batteries and the ICE, which are both coupled to a transmission that drives the propeller. The series/parallel architecture combines the two architectures where the ICE can drive the propeller and can serve as a generator to charge the batteries. 

There are unique advantages to each of these hybrid propulsion architectures. The use of a single power source, as in the series hybrid, makes for a simple design that eliminates the need for gearboxes. Since the ICE does not directly drive the propeller, it can be operated at constant engine speed, which reduces wear and results in lower fuel burn and maintenance costs. 

The presence of two independent power sources in the parallel and series/parallel hybrids allows for flexible operation, such as using the electric motor for takeoff and landing and ICE for cruise. Importantly, the independent power sources provide powertrain redundancy, enhancing flight safety. This combination of simplicity, improved efficiency, and safety makes hybrid electric technology a promising step towards decarbonizing the aviation industry. 

Ampaire’s Eco Caravan, the first hybrid-electric regional aircraft. Ampaire Photo

Testing and deployment 

With the largest fleet of hybrid electric aircraft, Ampaire, a California-based company, is a leader in the testing and development of hybrid electric aircraft systems. Their hybrid electric EEL demonstrator aircraft, with a parallel hybrid propulsion system, completed 27,000 miles of flight and recently set records for both the longest non-stop flight of 1,135 nautical miles and the longest endurance flight of 12 hours with two hours of fuel remaining. They demonstrated a 50 percent reduction in fuel burn with their hybrid electric propulsion system in their testbed Skymaster. 

In an interview, Kevin Noertker, chief executive officer of Ampaire, highlighted the company’s development of their proprietary AMPDrive propulsion systems, designed for application in both commercial and general aviation sectors. Noertker detailed the versatility of the core AMPDrive hybrid propulsion system, which can be applied to various vehicle architectures, including VTOLs, urban air mobility vehicles, and drones. He emphasized the company’s commitment to demonstrating the capabilities of hybrid electric aircraft and dispelling misconceptions about electrified aviation. 

Ampaire has developed the AMP-H200 to retrofit smaller general aviation aircraft such as the Skymaster with this hybrid electric powertrain. Their AMP-H570 hybrid powertrain, which generates 750 horsepower, comparable to the power range of PT6A engines, is designed for mid-size turboprop commercial applications. Ampaire aims to provide a direct replacement of the PT6-114 and PT6-140 turboprop engines with the AMP-H570 hybrid powertrain for the existing Cessna Grand Caravan and other mid-size turboprop aircraft such as the King Air and Twin Otter. 

Using the AMP-H570 hybrid powertrain in the Cessna Grand Caravan, Ampaire demonstrated a doubling of fuel efficiency while retaining 95 to 98 percent of the aircraft volume. They achieved near-zero carbon emissions with their AMP-H570 powertrain using 100 percent SAF in a successful ground test conducted earlier this year. 

In an industry first, Voltaero, a company based in France, flew their patented series/parallel hybrid propulsion system in their Cassio 1 testbed using 100 percent SAF. Using their hybrid electric testbed aircraft, companies such as Ampaire and VoltAero have demonstrated the economic viability of hybrid electric aircraft and their potential for transforming short-haul flight operations. Others, such as Wright Electric, are targeting the hybridization of larger aircraft such as the BAe 146 for regional air mobility.  

These advances underscore the economic and environmental incentives for the large-scale adoption of hybrid aircraft technologies and their viability for short-haul flight operations. 

Air Canada has announced a purchase agreement for 30 ES-30 electric-hybrid aircraft under development by Heart Aerospace of Sweden. Air Canada Image

Innovations and opportunities in Canada 

With the goal of leading Canada’s transition to net-zero carbon emissions, the National Research Council (NRC) of Canada’s hybrid electric aircraft testbed (HEAT) project developed and successfully completed the flight test of their hybrid electric aircraft testbed Cessna 337 Skymaster. They replaced the 400-pound rear pusher engine with an 88-pound parallel hybrid electric motor with equivalent power for these tests. 

According to Patrick Zdunich, the technical lead of HEAT, the project aims to increase technology readiness and investigate certification pathways for hybrid aircraft. The NRC is developing an aero-optimized battery, one specialized for better weight and volume as well as thermal management. They are also establishing safety systems and standards for technologies to contain battery fire and prevent the release of toxic gases and smoke inside the aircraft.  

The NRC is also partnering with companies to help them advance their technologies and develop pathways to certification. 

In the commercial aviation sector, Pratt & Whitney Canada is developing a hybrid electric version of the De Havilland Dash 8-100, a 37-seater turboprop aircraft commonly used to serve regional routes. An electric motor powered by the Swiss-made H55 battery, will complement the Pratt & Whitney conventional engine and is projected to reduce carbon emissions and increase fuel efficiency by 30 percent relative to conventional jet-fuel-powered turboprop aircraft. 

In partnership with the NRC, Pratt & Whitney has also developed an advanced mobile charging unit that is compatible with the megawatt charging systems for high voltage power operations that can deliver 280 kW and 1500 volts. Pratt & Whitney plans to link the propulsion system with the battery developed by the company H55, which will be powered by the mobile charging unit, later this year.  

These examples of collaboration between industry and government, and the milestones achieved in the testing and development of hybrid electric technologies underscore the Canadian ecosystem that promotes the technology development for achieving net-zero carbon emissions. 

hybrid-electric variant of the Panthera aircraft in flight
The Pipistrel Panthera hybrid-electric variant takes off from Cerklje airport, Slovenia. Pipistrel Photo

Looking ahead 

Hybrid electric aircraft have the potential to significantly reduce the environmental impact of the aviation industry and help accelerate its transition toward net-zero emissions with the use of sustainable aviation fuels and impactful carbon offsets. Hybrid electric propulsion systems can be applied across various aircraft types and can potentially improve fuel consumption between 5 and 40 percent for large commercial and regional aircraft, respectively.  

Air Canada’s investment in the hybrid electric startup Heart Aerospace and its commitment to purchasing the ES-30 hybrid electric aircraft for regional operations illustrates the growing interest in this technology. In the Canadian North, where many communities rely on turboprop aircraft like the King Airs, Beechcraft 1900s, and Cessna Grand Caravans, transitioning to hybrid electric models could be revolutionary. Retrofitting these aircraft with hybrid powertrains such as Ampaire’s AMP-H570 could transform these operations by improving range and safety. 

The economic impact of hybrid electric aircraft is most profound for short and medium-haul regional routes, which account for around 30 percent of the global commercial fleet. Hybrid aircraft can reduce the operating costs for airlines due to the reduced fuel burn and maintenance costs. The use of electric motors during takeoffs and landings will enable these aircraft to operate in noise-sensitive areas and minimize exposure of ground staff to harmful fuel combustion emissions.  

Faster adoption of electric and hybrid electric aircraft technology requires key developments in several areas. First, upgrades to airport infrastructure for rapid charging, and technological advances that improve battery energy density are required. Second, training personnel to operate and maintain the new powertrains and the creation of parts inventories for hybrid aircraft will be critical drivers for this technology. Finally, establishing robust regulations and certification standards to ensure safe operation of these aircraft will facilitate widespread adoption of this technology and pave the way for a sustainable future in aviation. 

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