Stralis (YC W23) – Hydrogen electric aircraft for medium-haul travel

Hi HN, we are Bob and Stuart from Stralis Aircraft (https://stralis.aero). We’re taking advantage of hydrogen electric propulsion technology to design a low cost, 50-seat aircraft that can replace a significant portion of the ubiquitous single-aisle (e.g. Boeing 737) market that makes up ~60% of commercial aircraft sold. We are starting out by developing the propulsion system for a 6-seat Beechcraft Bonanza. So far, we have installed and tested the electric motor and performed some benchtop fuel cell testing. Here’s a quick video showing what it looks like these days: https://vimeo.com/879966330. Next step is to perform some system testing with a COTS fuel cell, whilst we progress our own fuel cell development. We are currently working through setting up our hydrogen electric propulsion test lab at Brisbane International Airport, which will allow us to rapidly prototype subsystems and generate the data we need for the 50 seat, SA-1, design. Quick fly through video of our facility here: https://vimeo.com/884325165

Airlines are anticipating the need to de-carbonise, driven by legislation or by customer pressure, but there is not yet any emission-free aircraft solution that is practical and cost-effective to adopt. Other solutions are either too heavy, like batteries and automotive industry fuel cells, or too expensive and inefficient, like sustainable aviation fuel. It is important to get a low enough CASM (Cost per Available Seat Mile) to allow operators to switch to a sustainable solution without having to dramatically increase ticket prices.

Bob and I met at a company called magniX, who develop high specific power electric motors. magniX quickly identified aerospace as a major market for their technology but at the time, most of the customers were working on battery electric solutions for de-carbonizing air travel. We were personally involved in 3 aircraft platforms (that have flown) that used our motors. Whilst we are super proud of what we achieved and overcoming the technical hurdles to fly those planes, it became clear that batteries were never going to be the solution to de-carbonising a significant portion of air travel. We went on to work at a few different sustainable aviation companies, and slowly became convinced that hydrogen would be the only technology that would have a chance of achieving the goal of sustainable aviation. There is a lot of public discourse on what is the best technology to solve this high-stakes problem, but instead of arguing about what can and can't work, we decided it would be best to dive into the technology and give our best go at what we think has the best chance.

Our propulsion system is quite straightforward—we carry liquid hydrogen in a composite, vacuum insulated storage tank. We boil off the hydrogen and feed it into the fuel cell. We take air from outside the plane to supply the fuel cell with oxygen. Hydrogen and oxygen react in the fuel cell and produce electricity, with water vapor being the only by-product. The electricity then powers a lightweight electric motor that spins a propeller.

Unlike most other fuel cell systems, we use the oxygen supply air to cool the fuel cell as well — removing the need for large, heavy and draggy external heat exchangers. This is achieved through our choice of fuel cell membrane with a much higher operating temperature (180 C). We remove the weight of the heat exchangers but also reduce the weight of the propulsion system as we don’t need to overcome the extra drag created by the radiators. All of this combines to reduce the fuel cell system weight by about 40%, which equates to a doubling of our payload capacity and, therefore, half the CASM, when compared to a conventional PEM fuel cell system.

In addition to our tech, we are also approaching the market differently. We think that a 50-seat aircraft is the optimum size for an aircraft with our hydrogen electric propulsion. This is different from conventional turbofan technology where the optimum size appears to be about 200 seats. All of our competitors are working towards a family of aircraft going upwards of 200 seats (Airbus are only focusing on larger aircraft) but we think there are diminishing returns from building larger hydrogen electric aircraft. Instead, we are honing in on a 50-seat design, optimized for hydrogen electric and designed with automotive manufacture methods in mind. There could be a market demand for up to 50,000 aircraft within the next 25 years, driven by more efficient, point-to-point routes. Most other aircraft programs deliver around 1,000 units, which generally doesn't warrant a large amount of automation, and keeps unit costs high.

Hydrogen fuel cells are not new, but we think the need to de-carbonise, the reduction in renewable energy costs, and the improvement in component technologies such as motors, power electronics, batteries etc. make today the best time to pursue this solution to sustainable air travel. We would love to hear from any of you who have worked in aerospace, sustainable aviation fuel (the biggest alternative to hydrogen) and the hydrogen industry. We would also like to hear from people who fly often, and airlines, to learn how important a switch to a sustainable solution is to you. Looking forward to reading all the comments!