Our HEPS only emits water vapour. It does not emit any carbon dioxide, NOx nor unburnt hydrocarbons, which are the greenhouse gasses emitted by a conventional turbine engine burning jet fuel that have the worst effect on global warming. Furthermore, burning jet fuel also releases sulphates, soot, and particulates, which contribute to poor air quality. Our HEPS does not emit any of the above.

Water vapour at altitude is considered a greenhouse gas but it is a condensable gas, that only spends on average 9 days in the atmosphere and does not accumulate. Carbon Dioxide is still, by far, the main culprit for global warming, not water. Conventional jet fuel and SAF still emit water when burnt and our HEPS will only produce approx. 1.5x more water per available seat – this is nothing when considering the other emission reductions.

Short answer: SAF is a good partial solution that can be implemented quickly, but HEPS is the more complete long-term solution.

Longer answer: SAF is only a partial solution because it only solves the carbon dioxide part of the problem and is still liable to release NOx, unburnt hydrocarbons, and soot.

SAF can only be said to be carbon neutral if carbon dioxide is removed from the air during its production, whether through biological means or direct air capture (DAC). Though this may be achievable, it comes with real challenges around obtaining a trustworthy feedstock supply. Direct air capture would guarantee that the SAF was carbon neutral (provided the energy used far DAC was renewable), whereas carbon capture through biological means always come with the uncertainty that the carbon stored in the biomatter is now being released instead of sequestered. At Stralis, it is our belief that if we have the means to capture carbon dioxide from the atmosphere, we should use that capacity to sequester carbon and push beyond Net Zero to carbon negative and start to undo some of the damage that we have already done to the planet. All this considered, SAF along with high-integrity carbon offsetting, serve as a good way to make immediate changes and can be a great improvement over fossil fuels but hydrogen electric propulsion will come out on top in the long run as it will have a greater impact on emission reduction, lower engine maintenance costs and offer lower fuel costs (for most scalable SAF production pathways you need more than 1 kWh of H2 to produce 1 kWh of SAF, then consider that you need to supply and process the carbon feedstock and that the HEPS is almost twice as efficient as a PT6 turbine engine).

Stralis anticipates there will always be a need for SAF in difficult to abate niches such as ultra-long-haul flight or supersonic flight.

At first glance it might seem that swapping out jet fuel for hydrogen in a turbine engine would be a simpler solution, but, turbines are already quite a complicated machine, which are expensive thanks to the high temperatures that they must operate at to be efficient. Nothing about hydrogen combustion would improve this situation, and in fact due to hydrogen embrittlement and differences in H2 combustion vs kerosene, many changes to the turbine engine design would be required.

Hydrogen electric on the other hand reacts hydrogen in a fuel cell at much lower temperatures which allows for simpler and more cost-effective components. This comes at a weight penalty versus combustion but is so much more efficient that the weight penalty is palatable.

Hydrogen combustion also has the unfortunate side effect of producing NOx as the combustion happens with air at high temperatures. So, whilst this is a zero carbon option, it still produces non-condensing greenhouse gas emissions and is therefore not sustainable.

Unfortunately, very little. It will enable smaller regional operators to achieve Net Zero, but they are not really the main contributors to global emissions. However, the 15 seat B1900D-HE is not where Stralis plans to stop. We will continue to develop larger clean sheet aircraft, optimised around hydrogen electric propulsion, that will compete with regional jets and narrow-body aircraft, in terms of range and capacity. Once our SA-1 product is in the market, we will begin to enable a future where anyone can fly sustainably without compromise and offer a solution that will have a sizeable impact on harmful emissions from air travel.

No. Hydrogen electric propulsion will be capable of supporting medium haul (up to 3000km) routes. Our initial retrofit product will only have a range of 800 km as it is challenging to fit enough hydrogen into an aircraft designed for conventional propulsion. Our clean sheet SA-1 will have a 3,000 km range. The range of a clean sheet hydrogen electric aircraft is sensitive to the efficiency of the fuel cell, motor and aircraft. Small improvements in the performance of these components lead to non-linear improvements in range. The architecture that Stralis is pursuing will only be suitable for propeller driven aircraft (for the time being) and that will limit the aircraft cruise speed and make longer ranges undesirable – once you start flying longer than 3000 km you want to fly in a jet for passenger comfort.

Yes. If they are not safe, they will not be certified and will not make it to market. If you are a paying passenger sitting on a Stralis aircraft, you can be confident that it will have been certified to the same high safety standards that any other commercial aircraft is certified to.

It is Stralis’s mission to build and support sustainable aircraft. Our HEPS is only sustainable if run with green hydrogen, that is hydrogen produced from the electrolysis of water, using renewable energy.

If there was a supply issue, and only hydrogen produced via other means were available, then you could run our HEPS an liquid hydrogen of any “colour” but the flights would not be Net Zero.

It depends on what you are comparing it against. If you compare it to a battery electric solution, then it looks pretty bad but if you compare to the other alternatives suitable for useful flight ranges, then it comes out on top.

Here, round-trip efficiency is how much energy from a renewable source, like a solar panel, makes it to the at the shaft of the propeller, accounting all the losses from processes along the way. The diagrams below show the round-trip losses for battery electric and then HEPS.

With battery electric, 75% of the renewable energy makes it to the propeller, whereas with HEPS, only 25% makes it. Unfortunately, batteries are too heavy and only allow for really short flights (~100km) so are unsuitable for the majority of flights in Australia.

The two main competing technologies for carbon neutral flights for commercially useful distances are SAF electrofuels and hydrogen combustion, their round-trip efficiencies are shown below at 12% and 14% respectively.

These efficiencies show that hydrogen electric propulsion gives the best round-trip efficiency by a large margin. This equates to cheaper fuel, and less demand on the growing renewable energy supply.

At Stralis we believe that climate change should be tackled from all angles, including finding a path to sustainable flight.

We recognise that there are cheaper ways to reduce humankind’s impact on the environment, such as rolling out electric cars, implementing high speed rail and getting renewable electricity into everyone’s homes, globally. We encourage private and public investment into these areas, as well as re-wilding parts of the planet to let nature work on the fixing the climate too.

That said, we believe that air travel will and should always be part of our lives. Especially in Australia with such distances between population centres and large swathes of sparsely populated land. Air travel transports essential goods and services to remote communities, connects families spread across the country and allows people to visit our most cherished places of natural beauty. At Stralis, we want this to continue but just without the negative impact on our environment – and we can do that. It is our goal to bring air travel to even more people then have access to it today, by working to make it more affordable, help local production of green hydrogen in remote areas and implementing technologies that make flying easier end safer.

Whilst the efficiency of a battery electric system is greater than a HEPS, batteries just do not allow for the range flown by most aircraft. Electric cars and trucks are less sensitive to battery weight and a battery electric system is the ideal solution for them, but this is just not the case for aviation.

An electric car in used normally in the city is unlikely to use its full charge on every trip, which is good for the battery and will allow for a high number of cycles on the battery, perhaps 1500 cycles, or more, and if the battery continues to degrade in a car, then you get a little less range and a little less maximum power – not the end of the world.

With aircraft, it is undesirable to carry around lots of extra battery that you don’t use, that is if you want to carry passengers. So, each flight, the battery uses almost all of its charge. This is tough on the batteries, which means they degrade quicker and might only be good for 400 cycles or so. Unlike a car, if an aircraft has reduced power or range, it becomes a safety issue, so you must replace the batteries once they degrade a certain amount.

All of this increases the operating cost of the battery electric system. Whilst it may still be cheaper to run than a fossil fuel turbine engine, combined with the range limitations, battery electric becomes a less attractive option for most commercial routes.

If batteries were better then Stralis would much prefer to pursue this option, given its superior efficiency, simpler system and zero-emissions, not even water. Unfortunately, it just isn’t the case, even with the most optimistic future projections of battery performance, we cannot see them being able to support any but the shortest of flights, which won’t have much impact on emission reduction.