We take a deep dive with Limhi Somerville, Head of Powertrain at Vertical Aerospace, into the VX4 prototype – the only eVTOL designed, built, and assembled in the UK.
Q: Can you share with MEM an overview of the investment and opening of the new battery facility in March 2023?
A: “In 2022, we made a strategic move to bring battery design and manufacturing in-house, after recognizing our capabilities outpaced the market.
“Over the past four years, we’ve heavily invested in battery tech, building a world-class team at our state-of-the-art Vertical Energy Centre (VEC) in Bristol. The VEC is capable of producing a battery pack every two days and handles all but the most niche tests in-house—making it the UK’s most advanced aerospace battery facility.
“Since that decision we have progressed through an aggressive development program. For example, in 2020 we performed our first battery drop test in front of the UK Civil Aviation Authority (CAA), from a height of 50 feet. We have developed seven additional prototypes since then in order to progress through our ability to optimise a safe design for mass. Today we achieve a >80% cell to pack ratio.
“Our team, with experience from Jaguar Land Rover, Airbus, Rolls-Royce, Dyson and many others, blends automotive EV innovation with cutting-edge aerospace design, unlocking new power-to-weight ratios for eVTOL flight.”
Q: What are the advantages of working with Molicel and how have you developed your powertrain alongside this?
A: “We evaluated over 60 battery cell suppliers before choosing Molicel, a leader in high-performance lithium-ion cells. Molicel has a long history of innovation, powering everything from space equipment to record-breaking supercars.
“We believe we have one of, if not the highest performing powertrains in the world for this application. Multiple redundant paths for power delivery, super lightweight and torque dense on the motor whilst incredibly power efficient for every kg of mass across the rest of the powertrain.
“Our battery is eight times more powerful than the average EV battery, with rapid charging, pushing the VX4 to speeds of 150mph with 1.4MW of power. The UK government recognizes this innovation, backing us with Aerospace Technology Institute grant funding.
“Our high-voltage power distribution system maintains independence throughout its lifecycle whilst maintaining power delivery and energy accessibility. We continue to refine it, taking lessons from our prototypes as we move towards certification.”
Q: Can you explain what levels of iteration are required in battery development to arrive at a new aircraft?
A: “Each iteration goes through a minimum of four full-production design, manufacture and test stages. Alpha, beta, gamma and then delta after which it is manufactured for vehicle use – whether on a prototype or for the final iteration through the certification programme. eVTOLs have unique demands for battery cells, not just in terms of aerospace safety, but also the high-power needs during hover.
“While automotive advances in Lithium-Ion battery tech have pushed energy density forward, electric car cells still fall short of meeting eVTOL power demands. To bridge this gap, we’ve engineered our own battery cell chemistry, delivering high power with low resistance while maintaining energy density.
“We’ve completed all battery safety tests for the UK Civil Aviation Authority (CAA) on our latest prototype, including crash, thermal runaway, and vibration tests—along with over 1.2 million hours of cell testing. In total, we’ve conducted over 3 million hours of cell characterisation to ensure performance, safety, and cost-effectiveness.
“Our proprietary batteries were unveiled with the latest full-scale VX4 prototype in July, marking the first use in a piloted aircraft.”
Q: What makes your plane safer, cleaner and quieter?
A: “The VX4 eVTOL is 100 times safer than helicopters, with no single point of failure and a catastrophic failure rate of 1 in 1 billion—on par with commercial airliners. This is due to full redundancy across its power and propulsion systems, including eight battery systems, eight motors, redundant inverters and actuators. Any fault is automatically isolated, and power is redistributed by the triple-redundant flight control system.
“Running on an electric battery, the VX4 produces zero emissions. It’s also extremely quiet—at 50dBA in cruise, it’s quieter than urban background noise and 100 times quieter than a helicopter. This is thanks to our next-gen propellers, which spin at half the speed of helicopter rotors, dramatically reducing turbulence and noise.”
Q: What are the full applications of your technology as we move forward into the 21st century?
A: “Our technology is reshaping how we think about travel. We’ve relied on polluting ground transport for too long; eVTOLs open up the skies, offering a cleaner, congestion-free option for journeys up to 100 miles. It’s the biggest aerospace innovation in over 60 years, since Concorde. And we are making this happen from Bristol, an epicentre for aerospace in the UK.
“While electric batteries can’t yet power large aircraft, they’re perfect for smaller ones like eVTOLs. With battery performance improving by around 10% every 2-3 years, the future looks even brighter. I believe our innovation is inspiring the sector and driving new approaches to aviation.”
Q: How are you able to build such a lightweight airframe?
A: “We’re collaborating with top suppliers to design an aircraft that maximizes safety while minimising weight using the latest materials where we can.
“The latest VX4 is more powerful and lighter due to an impressive 20-30% increase in the power to weight ratio enabling the aircraft to reach high speeds.
“Our new proprietary propellers, for example, are made of carbon fibre composite using a single-shot cure process to maximise integrity while making them lighter.
“For aerostructures, we’re partnering with Leonardo and GKN. GKN, known for its composite wings and empennages on the Airbus A350 and Gulfstream G650, has provided Electrical Wiring Interconnection Systems (wiring harness) on all the VX4 prototypes. While Leonardo – pioneers in composite fuselage manufacturing and who crafted the complex fuselage for the Boeing 787 – has manufactured the composite fuselage and pylons for our latest aircraft.”
Q: How does your supply chain support your ambitions and service standards?
A: “At Vertical, we embraced a partnership approach from the outset, blending the expertise of our in-house team—comprising talent from industry giants like Airbus, Rolls-Royce, Leonardo, Jaguar Land Rover, and Dyson—with that of our global aerospace partners, including GKN Aerospace, Honeywell, Hanwha, Molicel, Leonardo, and Syensqo.
“By integrating their world-class technologies with our proprietary battery and propeller innovations, we create a mutually beneficial environment where we learn from each other. Our fast-paced start-up culture complements their extensive sector expertise, allowing us to meet aerospace safety standards and certification efficiently while manufacturing at scale and at lower costs than our competitors. This results in the safest and most advanced eVTOL on the market.
“Currently, 60% of the components and technology in the latest VX4 prototype come from these leading partners, a significant increase from 10% in the previous model. The latest VX4 is our most advanced and powerful version yet.”
Q: What goals/objectives has Vertical Aerospace set itself for the short and long term globally?
A: “We’re creating a new type of aircraft that’s never been attempted before and will be capable of transporting people across urban areas quickly, quietly and with zero emissions.
“We are unique in that we are the only player in the UK innovating in this space and we truly believe we have one of the best eVTOLs on the market with the most advanced technology built by the most experienced team.
“In the short term, our team is laser-focused on advancing the piloted test flight program for the latest VX4 prototype, which was unveiled in July. We’ve successfully completed phase one, which included multiple piloted tethered flights and ground runs across 20 test sorties, achieving 70 individual test points and measuring 35,000 flight and system parameters.
“Now, we’re moving into phase two: thrustborne testing. This will involve vertical take-offs and landings, as well as low-speed manoeuvres powered by the propellers. Following this, we’ll enter wingborne testing, where the VX4 will take off, fly, and land like a conventional aircraft. The final stage will be transition, the most challenging part, as we shift between thrustborne and wingborne flight. Once we complete the full testing envelope, we can showcase the VX4 through public demonstrations.
“Simultaneously, we’re working with the UK Civil Aviation Authority (CAA) to certify the VX4, which is collaborating closely with the European Union Aviation Safety Agency (EASA). This opens up significant export opportunities while we engage regulators in the US, Brazil, and Japan to expand our global reach. We’re also partnering to ensure that key markets have the necessary infrastructure for eVTOL operations.
“These efforts are crucial for our customers—such as Virgin Atlantic, American Airlines, Japan Airlines, GOL, and Bristow—who will integrate the VX4 into their fleets, turning a new way of travel into reality.
This represents a massive opportunity for the UK to leverage its manufacturing and engineering expertise to drive growth and enhance our existing skills base.”
Visit: www.vertical-aerospace.com
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