Vertical Aerospace’s Andrew Macmillan on the VX4 eVTOL flight test campaign

By Alex Scerri | January 12, 2023

Estimated reading time 15 minutes, 6 seconds.

U.K.-based Vertical Aerospace is one of the front-runners in the eVTOL industry, recently stepping up its flight test activities with its VX4 eVTOL prototype last year. As the company plans to progress through its flight test campaign in 2023, we spoke to Andrew Macmillan, the company’s chief strategy officer, to learn more about its program.

Vertical Aerospace
Vertical Aerospace started crewed tethered flight tests with its VX4 eVTOL prototype in 2022. The company plans to begin untethered flights sometime this year. Vertical Aerospace

This interview has been edited for length and clarity.

Alex Scerri: Andrew, can you give us a brief overview of your path to Vertical Aerospace and your outlook for advanced air mobility (AAM)?

Andrew Macmilllan: I’ve been with Vertical Aerospace [since September 2021] and was previously chief strategy officer at London Heathrow Airport where I also covered various operational, sustainability, commercial and regulatory roles for over a decade.

When I had the first conversation with people from the eVTOL community some years ago, I found the idea very interesting but thought it was something a long way in the future. My view changed when I was approached to join Vertical Aerospace. I could see that the technology was coming together much faster than I had anticipated. Progress will be very rapid from the middle of this decade. 

Alex Scerri: Can you share some of Vertical Aerospace’s flight test activities and milestones?

Andrew Macmilllan: Vertical Aerospace has previously flown two other prototypes, and [in 2022], we’ve flown our first full-scale prototype of the VX4. We built this full-scale prototype with the aim to do crewed test flights. Ultimately, we are going to fly with a pilot and passengers, so it was worth engaging the challenges and complexity that comes with that. This included building a safety case needed to put a person in the aircraft. You also learn a lot from having an experienced test pilot onboard.

We obtained a permit to fly from the U.K. Civil Aviation Authority [CAA] in the summer. Our chief test pilot Justin Paines previously flew with Joby Aviation and was a test pilot for the Lockheed Martin F-35 and Harrier for many years in the military, so he has done a lot of VTOL test flying. Justin was onboard our first flight, and we have now done 14 crewed test flights with him and our other test pilot, Simon Davies, who is also ex-military.

We think we are the only eVTOL company to have done crewed test flights of a tiltrotor at full-scale so far. We’re seeing a lot of eVTOL test flying around the world, but most of it is done remotely and/or not at full scale. Subscale prototypes are an important step, but there is a ramp-up in learning once you go full scale. A lot of ground tests were done, including running the propellers continuously for up to six hours.

Alex Scerri: What was the driver behind starting with the crewed tethered flights?

Andrew Macmilllan: Safety is a company value for us at Vertical Aerospace. We built the VX4 to the same standard as commercial aircraft. That’s what the public expects and that’s what we believe is required for the kind of missions that we’ll fly over urban areas. In the U.K., the minute you put a person in an aircraft, the safety case becomes that much more stringent.

Even if you have an aircraft that’s perfectly capable of flight, by having it tethered, we can do a broader range of operations, including testing indoors. We are not after a great video but proving the safety of our aircraft on the path to certification.

Vertical Aerospace
Vertical Aerospace said it has now conducted 14 crewed test flights with chief test pilot Justin Paines, as well as test pilot Simon Davies. Vertical Aerospace Image

Alex Scerri: When do you expect to have the first untethered flight and what will be the trigger for that?

Andrew Macmilllan: We’re anticipating that in 2023. Again, it’s very much driven by the safety case, so instead of committing to specific dates, we prefer to say where we are and what the next step will be.

Alex Scerri: Do you plan to do your entire flight test program at Cotswold Airport, or do you plan to test in other locations?

Andrew Macmilllan: For the moment, we’ll continue flying at Cotswold Airport. It was a big transport base in World War II and has the size of hangars we need for our activities. There is a lot of space to explore the flight envelope. Eventually, we may look at other sites when weather and flight envelope expansion become a factor.

Alex Scerri: Is the aircraft you are flying now a representative aircraft for certification?

Andrew Macmilllan: It is certainly representative in terms of overall design and size. One of the things we are focused on is using the capabilities of the existing aerospace industry to deliver an aircraft that is safe, reliable and can scale up.

We are fortunate to have key partners, such as Rolls-Royce delivering the electric power units (EPUs), GKN Aerospace manufacturing the wings, Solvay working on composite structures, Honeywell providing the fly-by-wire software and avionics, Leonardo delivering the fuselage, etc. Some of those are embedded in this prototype. Others will come in as we continue testing.

By working with partners, we iteratively refine and upgrade the product. If you take Honeywell’s software, there are continuous upgrades as flight test data are fed back to them. The current prototype gives a very good sense of what the production VX4 will be like.

Alex Scerri: Besides the U.K. CAA and the European Union Aviation Safety Agency (EASA), are you looking into a concurrent certification with the U.S. Federal Aviation Administration (FAA) or other authorities?

Andrew Macmilllan: You’re right that we will first certify the VX4 with the U.K. CAA. Technically, Rolls-Royce will certify the EPUs with EASA. The U.K. CAA has adopted EASA’s SC-VTOL standard and will apply their own approach to that. This is important because it has several years of transparent public development and a real focus on 10-9 design safety. We are seeking validation with the FAA, and have over 1,400 pre-orders with customers around the world.

Vertical Aerospace
Andrew Macmillan is Vertical Aerospace’s chief strategy officer. Vertical Aerospace Image

Alex Scerri: Can you describe the strengths of your design?

Andrew Macmilllan: There has been a lot of creativity in designs across the industry, with hundreds of different concepts. For those focused on commercial service, we see a convergence of some common elements. The VX4 fits within that group with the required level of technology and financial backing, and will likely be among the first to market.

There is significant redundancy with no single point of failure. Wing-borne flight, together with short and conventional take-off and landing [STOL/CTOL] performance, gives us efficiency, as well as glide capability in contingencies. We are fully electric, so there are zero emissions, and our proprietary propellers are far quieter than a helicopter. From my experience at Heathrow, minimizing noise is critical when operating in urban areas.

From a business perspective, our industrial partnerships are key. We get the best technology from the specialists and receive great feedback from them, too — crucial for continuous product improvement.

Alex Scerri: You mentioned STOL/CTOL. Is this something you plan to exploit for normal operations or only for contingencies?

Andrew Macmilllan: It is certainly useful in contingencies. In terms of regular operations, it partly depends on how customers want to operate the aircraft and the locations they choose. One of our primary characteristics is VTOL. If you had the possibility to always use STOL/CTOL at both ends of a mission, you might choose an electrically powered conventional design. The advantage of the VX4 is that you gain the ability to operate in constrained urban environments.

Alex Scerri: What are your planned timelines for certification?

Andrew Macmilllan: We’re aiming for the middle of this decade for the U.K. and Europe.

Alex Scerri: Are you waiting for any technology to mature for the production standard aircraft, for example, the batteries?

Andrew Macmilllan: I’m convinced that all the core technologies are there, and we can already get good performance out of the batteries. The work we’ve been doing with Molicel has reinforced that, but you are right that there’s still work to be done since it is probably one of the most state-of-the-art components.

Alex Scerri: What do you think are the biggest challenges for the eVTOL industry?

Andrew Macmilllan: It’s a new class of aircraft and a new industry so it’s not going to be completely straightforward. You don’t have a commercial model until you’re certified. The regulators are demanding solid data, stringent tests, and a demonstration of the required safety levels. EASA’s SC-VTOL gives us clarity, and we find the open exchanges we have with regulators reassuring.

Vertical Aerospace is very much involved in the rulemaking process through participation in EUROCAE. We have leading roles in the battery and powertrain working groups. There’s clearly work to be done in areas like this since this will be the first time we use electric propulsion in certified commercial aircraft. We need to ensure that lithium-ion batteries are safe and certifiable. There is work we need to do to define standards and crucially, a lot of testing to be done.

An interesting challenge is public acceptance. You need to make the case that this is worth doing. This is a fantastic, interesting technology that will change the way we get around. There are some early indications that public acceptance is improving. McKinsey [& Company] did a study for EASA in 2021, which found that overall, 83% of respondents have a positive attitude toward AAM, and 71% said they would use an AAM service.

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