By Elan Head

An award-winning journalist, Elan is also a commercial helicopter pilot and an FAA Gold Seal flight instructor with helicopter and instrument ratings. Follow her on Twitter @elanhead


Vertical Aerospace’s Tim Williams on the VA-1X

Tim Williams is chief engineer at Vertical Aerospace, having joined the U.K.-based startup earlier this year from Rolls-Royce. In his current role, he’s responsible for leading development of Vertical Aerospace’s winged, passenger-carrying eVTOL, which was revealed this week as the VA-1X. We spoke with Williams for a deeper dive on the five-seat, fully electric air taxi and how the company plans to take it through certification.

Vertical Aerospace VA-1X
Vertical Aerospace unveiled its five-seat, fully electric VA-1X air taxi on Aug. 26. Vertical Aerospace Image The VA-1X is very different from Vertical Aerospace’s previous eVTOL prototypes. What goals were you trying to achieve with this aircraft and how did those drive you to specific design solutions?

Tim Williams: The two aircraft that we’ve flown previously — so what we call the POC or the proof of concept about two or three years ago, and then the Seraph aircraft about a year ago — those were literally technology demonstrators and they were some of the building blocks to get us to where we want to really be. I think we always anticipated that we would be building a winged aircraft, because it gives us huge benefits in terms of range and payload. But as a new startup, we felt there were a lot of things we had to understand before we could launch into that final design. So those two previous aircraft were all about understanding battery capacity, understanding the noise, understanding redundancy in the aircraft, what would happen if we had a failure — just generally exploring that design space and understanding control systems and how we might move forward. So it was always part of a well-thought-out plan that we would try and learn, put those building blocks in place before we got into our final design proposal, which is we announced yesterday [Aug. 26].

Vertical Aerospace chief engineer Tim Williams
Vertical Aerospace chief engineer Tim Williams

[For our] market space, we’re trying to offer an aircraft that has the capacity to carry four passengers and a pilot. We clearly wanted to go over a useful distance, and hence we set the range of about 100 miles. So sizing the aircraft as we have and going with a winged concept, I think we can start to get to a position where we can achieve those objectives. One of the benefits we see from an eVTOL aircraft is that we can get the noise down quite substantially compared to a traditional helicopter, so we’re targeting noise levels 30 times quieter than a conventional helicopter. If you look at the use case of flying out of the Battersea Heliport in London, the number of flights per day is capped because of the noise levels of the traditional helicopter. If we can make big inroads into that, then we start to open up that market. So noise has been a big, big focus of ours. What were some of the key lessons from your earlier prototypes that have influenced your approach to the VA-1X?

Tim Williams: There were a few things. One example is when we were flying Seraph last year, we had vibrations in the airframe; quite low-level frequency vibrations. And it was causing the control system to become unstable and the motors were trying to respond accordingly and we were draining battery power incredibly quickly. So that was one key piece of learning: We need to make sure that we control the overall dynamic behavior of the aircraft. It’s those sort of things that have made us really consider where we put things like batteries. The single heaviest items we’re putting onto the aircraft is batteries and where you put them has a big influence on the behavior of the aircraft. So it’s led us to explore that design space and what is optimum.

Vertical Aerospace Seraph eVTOL
Vertical Aerospace’s Seraph eVTOL technology demonstrator during flight testing in Wales last year. Vertical Aerospace Photo And since you mentioned batteries, what are your plans for where to locate them on the VA-1X?

Tim Williams: We’re planning to locate the batteries actually in the fuselage. There’s a huge benefit in keeping the weight of the batteries as close to the center line of the aircraft as possible, [so] they’ll be in the front of the fuselage and in the tail section. Also, we can start using that weight to try and balance the aircraft as well. Clearly there’s some quite stringent safety rules around these batteries, particularly in the crash environment. So we’re having to do a lot of work to make sure that we can vent them properly and protect them, make their casing crashworthy, but I think we’ve got good solutions to do that. I saw you’ll be using lithium-ion batteries. Is there anything you can say about the cell technology or who you’re working with on that?

Tim Williams: We’re working with a company called Danecca, a relatively young company based in the U.K. So [the batteries] are based on fairly standard, readily available cells, but we’re doing a lot of work with Danecca to understand how we package them together, and we’re doing a lot of work with Warwick Manufacturing Group at Warwick University to help with the design of our battery systems. We have done quite a lot of testing so far. So for example, we have a really good relationship with EASA [European Union Aviation Safety Agency]. We had a drop test on the battery last year, we had EASA present whilst we did that test, and they were very complimentary on what we achieved and our openness and willingness to share our information with them. We also did a fire test on the battery, so we just pointed a flame at the battery and let it go and it stayed together for quite some time. So we’ve got quite a high degree of confidence that we’ve got a good battery system.

Vertical Aerospace VA-1X eVTOL
The VA-1X has four tilting propellers mounted in front of its 15-meter (49-foot) wing, as well as four pairs of lifting fans in the rear. Vertical Aerospace Image Can you discuss the propeller configuration? It seems fairly complex, but I assume that there are benefits that outweigh that complexity.

Tim Williams: As I mentioned just now, noise is a big factor. We wanted to keep the size of the rotors as small as possible whilst also providing the lift we need for vertical take-off. We also on Seraph spent a lot of time understanding redundancy in the system and what would happen in the event of a single rotor failure, and our conclusion was that eight rotors was probably about optimum, because if one motor fails, then effectively the other seven have to pick up an additional one-eighth of the load. So it was trying to balance that load requirement in the event of a failure.

We did look at some proposals where we would have had separate cruise rotors and separate lift rotors. The trouble with that is that you end up carrying around parasitic weight when you’re in one mode or the other. So, it felt to us that a tilt rotor concept gave us the optimum solution in that those rotors in the front contribute to flight both in vertical and in conventional flight. We designed the rear rotors so they will stow to minimize drag in [forward] flight, and also we’ve done quite a lot of work to try and minimize the interaction between the front and the rear rotors to reduce noise. Can you talk about what the transition will be like [from vertical to forward flight]?

Tim Williams: Once we’ve had a vertical lift-off and then start our transition, the rear rotors will stop. We’re planning on a stowing mechanism and a parking mechanism so they’ll be aligned to the airflow to reduce drag in conventional flight. The tilt rotors will transition from the upright down to the horizontal and provide thrust as per traditional propeller-driven aircraft. We’re partnering with Honeywell for our flight control systems, so we’re using one of their advanced fly-by-wire systems. So that will help us manage that transition. And obviously, transitions are difficult aerodynamically. Have you been modeling that transition or doing subscale or wind tunnel testing to understand it?

Tim Williams: We’ve done an awful lot of modeling and we still are doing a lot of modeling. We have a couple of rigs we’re in the process of building, they will be going into the wind tunnel shortly — there’s a fairly big wind tunnel in the Bristol area that we’re booked into. So yeah, we will be doing a lot of work in the wind tunnel, and I expect we’ll be going back there on quite a few occasions between now and 2024 [the target date for certification]. The renderings released this week show the pilot’s station and some basic flight controls. How do you envision the pilot controlling the VA-1X, and how much autonomy will be built into early production models?

Tim Williams: It depends on what you mean by autonomy. We are not suggesting we will have pilotless aircraft; that’s not one of our immediate plans. We anticipate a lot of automation to try and minimize pilot workload, though we do anticipate that the operators of these aircraft will be fully trained pilots. So we’re looking to reduce their workload, but not looking to go with “de-skilled” pilots, if you like. Our anticipation is that we have a throttle on the left-hand side of the seat, with just a fairly simple joystick on the right-hand side, and a couple of rudder and steering pedals as well.

As an aside, we’ve been developing our own flight simulator for this aircraft in Bristol. It is quite simple but we’ve got a test pilot who’s been working with us. He’s been helping us to set up a cockpit arrangement and controls. Michael [Cervenka], our CEO, was in the office last week and took advantage of his time there to actually have a go on the flight simulator — he beat me to it. His comment with the arrangement we have was that it’s a very simple aircraft to fly.

The VA-1X pilot station
The VA-1X pilot station. Vertical Aerospace Image What will be the process of launching the flight test campaign?

Tim Williams: Obviously, we plan to do as much work as we can in the simulator. And as we get more flight control laws and data from Honeywell, we’re building that into the system. We’re currently planning for our first flights to be with a pilot on board. And obviously we’ll go through the whole flight test campaign slowly and progressively and with the utmost attention to safety start to expand the envelope.

We’re planning to build a first prototype which we’ll take flying next year; that might not be the fully finished aircraft. We’re then anticipating that once we have some learning out of that initial prototype, we’ll be looking for probably another five aircraft to complete the certification program, of which I should guess two might be used as flying vehicles. Some will be used for structural testing and all the other ground-based testing we’ll have to do. Are you planning on following EASA’s Special Condition-VTOL [SC-VTOL] in terms of certification?

Tim Williams: Yes, we are. Clearly there’s a bit of an anomaly with the U.K. government deciding not to continue with EASA as its certifying authority, so our prototypes that we fly in the U.K. will be demonstrating compliance against CAA permit to fly rules, but it is our ultimate ambition to certify the aircraft against the full EASA SC-VTOL requirements. And to that end, we’re having some really advanced and in-depth conversations with EASA. We’re chairing some of the working groups, we’re putting together our organizational structure so that we can get our DOA [design organization approval]. Vertical Aerospace has a strong connection to F1. Can you expand on what type of technology and inspirations are coming from F1?

Tim Williams: Sure. So about a year ago, Vertical Aerospace acquired a company called MGI Consulting. And that was a company set up by a chap called Mike Gascoyne, who has worked with most of the big F1 teams. We’re hoping to use not only the technologies they have in F1, but also their agile, lean, and somewhat rapid approach to development. Clearly the Formula One world does things at pace, so we wanted to pull on that pace and agility they offer. But when you think about it, the cars that race in the Formula One world are designed against a really stringent set of requirements — their crashworthiness requirements, their side impact requirements, all their safety requirements they have to meet are incredibly stringent. So they also work in a very regulated world. We hope to pick up on some of their knowledge in that aspect, just to really enhance the safety of our product whilst being able to offer something that meets our weights and performance aspirations.

VA-1X interior
Vertical Aerospace is aiming for its VA-1X to start commercial air taxi flights by 2024. Vertical Aerospace Image Are there any other safety features of the VA-1X you’d like to highlight?

Tim Williams: We’ve gone into this with our eyes open I think, so we really have focused on redundancy in systems. We’re designing an aircraft that is capable of flying in the event of a motor failure or a rotor blade failure. We’re doing a lot of work to understand how we prevent cascading failures or one rotor knocking into the other, so we’ve got a really strong case. We’re doing a lot of work around safety and reliability assessment. Ultimately, we plan to certify this against EASA regulations. SC-VTOL, when you read through the requirements, you end up with a product which is commensurate in safety to a large civil airliner. There’s no reason why one of these aircraft should be any less safe than a large commercial aircraft. F1 is not high-volume manufacturing, and neither has traditional aerospace been. How are you designing the aircraft for ease of manufacturing and eventual volume production?

Tim Williams: Our first prototype will be a one-off and we’ll use probably some of the manufacturing supply chain that’s aligned to F1 to do that, but we are also talking to some of the big companies in the U.K. about partnering with them as part of our supply chain. We don’t actually anticipate making much of this aircraft ourselves; rather, we’ll be a final assembly organization. So we’re talking to companies who can support us, and we’re talking openly about the volumes that we’re hoping to achieve, and we’re getting a good response. Is there anything else that you’d like to highlight about the aircraft or the next steps for the program?

Tim Williams: No, other than to say we’ve got an incredibly busy year ahead of us as we start to put this aircraft together and do all the work we need to get the permit to fly our first prototype. It’s really exciting times for the company; I think it’s great for U.K. industry. And it’s great to be at the forefront of this next revolution in air transport.

This interview has been edited and condensed.

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  1. Kudos on a fairly detailed discussion of critical engineering and product development on this program. As a fringe participant in the emerging industry and a long-time VTOL enthusiast, I’m always excited to hear more on the technical challenges and problem solving that’s happening. Nice system architecture with this approach and wishing good luck to you all from Austin, TX.

  2. Very good understanding the technical challenges increases chance to deliver certified product. This is a big rarely today at EVTOL development teams. Bravo Tim!

  3. Lovely read, well done. I really enjoy how transparent and open Tim is regarding the technical aspects and his teams approach to the aircrafts redundancy design. Keep ticking those those regulatory boxes and get that prototype flying! As a pilot and a ‘big fan’ of vtol’s I look forward to flying her one day.

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