In the field of sustainable aviation, Ascendance, a French startup founded in 2018, is making significant progress with its innovative STERNA technology. Today, we're speaking with Jean-Christophe Lambert, co-founder and CEO of Ascendance, about the company's groundbreaking hybrid-electric propulsion system and its vision for decarbonizing air travel.
Jean-Christophe brings valuable insights to our conversation, having led Airbus' E-Fan project and now leading Ascendance through successful funding rounds. As we explore the potential of STERNA and its applications in aviation, from the hybrid-electric eVTOL ATEA to larger aircraft, Jean-Christophe offers a unique perspective on the future of sustainable flight.
Q: Can you explain how Ascendance's hybrid-electric propulsion system, STERNA, works and what its advantages are over fully electric or conventional propulsion?
STERNA is a breakthrough hybrid electric propulsion system that intelligently combines electric batteries and internal combustion engines to optimize aircraft performance while significantly reducing carbon emissions (by up to 50%). The system works by leveraging the strengths of both electric and conventional propulsion, using electric power during takeoff and climb when energy demand is highest, and then seamlessly transitioning to the thermal engine during cruise when power demand is lower.
The advantages of STERNA over all-electric or conventional propulsion are significant. First, it reduces fuel consumption by up to 50% compared to traditional aircraft propulsion systems. This translates into a significant reduction in carbon emissions, with STERNA capable of reducing aircraft carbon emissions by up to 50%. In addition, STERNA's modular and scalable design allows it to be easily integrated into a wide range of aircraft, from small air mobility vehicles to larger regional passenger aircraft.
Another key advantage is STERNA's future-proof design. In the future, the system can run on Sustainable Aviation Fuel (SAF) or even hydrogen, enabling further reductions in carbon footprint as these cleaner fuel sources become more widely available.
Q: What technical challenges have you faced in developing the ATEA aircraft's vertical takeoff and landing capabilities while maintaining efficient forward flight?
This is the critical question: How do you balance the requirements for Vertical Take-Off while maintaining sufficient performance in forward flight to have an actual market fit? The question is not complete without considering safety requirements to make it as safe as a commercial airliner, as required by the certification.
Performing both take-off and cruise with only battery technology proved inefficient and too limited in terms of performance to replace part of the existing fleet. This is why we went with hybrid-electric technology and powered the aircraft with STERNA.
But then, the transition phase - which is the moment where you switch from a vertical flight to a horizontal one - is not only complex from an aerodynamic standpoint but also from an energetic standpoint: you need to switch the flight mode from vertical to horizontal like the other ones but also need to switch from an electrical boost to an optimized engine running on fuel. This was one of the triggers for why we developed the Hybrid Operating System - one of our core technologies - which continuously optimizes the balance between electric and fuel propulsion and is absolutely critical in managing the different power requirements for vertical and horizontal flight modes.
And let’s be honest: weight is always at the top of the list regarding technical challenges. Making the airframe as light as possible, keeping battery weights as low as possible (fortunately, we’re hybrid, so it’s easier for us), and maintaining a sufficient margin regarding the max weight authorized by the certification is not easy. Still, we’re delighted by the work our team has been performing and the great technical partners who have joined us on this journey and are vital to delivering this new aircraft.
Q: Looking beyond ATEA, how do you envision Ascendance's technology being applied to larger aircraft or different aviation sectors in the future?
A: Ascendance envisions a broad application of its STERNA technology across multiple aircraft sizes and aviation sectors. Ascendance's vision has always been to decarbonize commercial aviation, but - you need to start somewhere, so we've started with an eVTOL to decarbonize helicopters first and then support the transition of the entire commercial aviation industry to sustainability.
STERNA's modular and scalable design is critical to its potential for broader application. The system can be easily integrated into a wide range of aircraft, from small air mobility vehicles to larger regional passenger aircraft. This flexibility positions STERNA as a versatile solution for different aviation sectors, potentially including commercial passenger flights, cargo transport, and even military applications. STERNA will first address turboprop aircraft (e.g., Cessna Caravan, Pilatus PC-12, Daher’s TBM, Piper PA-46, etc.) and regional aviation such as ATR or Dash-8.
Over the next five years, Ascendance expects STERNA to be integrated into a growing number of aircraft. This expansion will reduce operating costs for airlines and operators and drive innovation and efficiency across the industry. The system's compatibility with sustainable aviation fuels (SAFs) and hydrogen further enhances its long-term potential and aligns with the industry's goal of achieving net-zero emissions by 2050.
Ascendance's work with the European Aviation Safety Agency (EASA) to develop standards for electric and hybrid propulsion systems also indicates that the company is preparing for broader adoption of its technology across the aviation industry. This forward-thinking approach suggests that Ascendance is positioning STERNA to play a significant role in shaping the future of sustainable aviation across sectors and aircraft sizes.
