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Maybe this is a big-city perspective, but I've understood that the main constraint driving aircraft size is runway capacity during peak hours. Airports already require a lot of land for handling a relatively small number of passengers. As building additional runways is often not feasible, the only way to increase passenger capacity is using bigger aircraft.

I fly between Helsinki and London often enough. On that route, the aircraft is typically either an A320 or an A350.

Yeah there will be some slot constrained routes that will certainly need to stick to the larger aircraft sizes, but many that can benefit from the flexibility of a smaller aircraft size if the operating cost was low enough. There are second city airport and regional routes that would benefit from the smaller plane size, as well as the market that is currently served by these types of planes - Asia pacific is one example of a growing turboprop market.

That's true for big airplanes. Small ones need a lot less runway. Which means they can land at smaller airports. Some of the electrical VTOL planes under development currently don't need airports at all and can take off from pretty much any flat surface.

The size of jet planes is dictated by fuel cost. Fuel is expensive. Large planes expend it more efficiently. But they are also loud and pollute. So people don't like them too close to where they live. When you use fuel by the thousands of liters per flight, it starts to add up in terms of cost. It's also why private jets are only for rich people. They burn hundreds of liters of expensive fuel per flight. Add to that the maintenance and staffing and you are looking at eye watering amounts per flight.

Hydrogen is of course not cheap currently but it might drop in price substantially as renewable energy gets cheaper. At that point a few smaller planes might be cost competitive with a larger jet fueled plane. But still, there are lots of logistical challenges related to getting large quantities of hydrogen to fuel planes. I doubt it will be very economical or practical any time soon.

My pet theory is actually that most short haul flight will shift to small, autonomous, electrical planes. They'll wipe out three of the largest cost factors in aviation: fuel, staffing, and maintenance cost (much less complex mechanical systems). They'll fly point to point rather than hub to hub; or at least tiny airport close to your origin to tiny airport close to your destination. If you want to fly further, you can just chain a few hops. It will work like an uber pretty much.

Inter continental flight is a different challenge. At least short term it's not feasible to do that with battery electric. Synthetic fuels and hydrogen look promising for that. But I wouldn't discount electric for that either long term. If battery breakthroughs keep on happening and we get some fancy solid state batteries delivering 2000 watt per kg or so, that whole game changes as well.

I think there are three markets:

* Short-haul flights, which often compete with cars and trains. Those could be plausibly served by electric VTOLs. If the claims about noise levels are true, the terminal does not need to be much larger than a city block.

* Medium-haul flights, like discussed here. The aircraft need to be much faster than the VTOLs proposed so far. Conventional runways seem to be necessary for efficiency, but they could be shorter than today.

* Long-haul flights that need big planes and long runways.

Airports that need runways are problematic, because the economic value they provide is low. There are often other more valuable uses for the land. In big and even not-so-big cities, airports tend to move away from the city over time.

For example, Helsinki recently closed the Malmi general aviation airport, which was conveniently located ~10 km from the city center. The area surrounding the former airport is now being developed as a medium-density residential area for 25k people. The runways were not long enough for current regional aircraft, and the facilities and the transit connections could not handle a meaningful number of passengers. As the alternate use as a residential area was worth billions, the airport could no longer be justified.

Short runways still need to be sited in cities. In a lot of areas airports are already so close together that the airspace is congested with all the conflicting paths and holding patterns; I think the worst example is NYC where Teterboro, JFK, LaGuardia and Newark make the airspace very suboptimal.

General aviation airports, as would the small cities they service, would get a second life. Instead of JFK, think of training airports like KISP, KFRG, KWV, KFOX, KHTO, KNPN, KMMU, KCDW, KLDJ N07, N51, KSMQ, N14 and a host of others in the NY/NJ area.

If you use GA airports near more prominent cities, using rail transit to get to nearby larger cities is worth the disruption. For example, with these aircraft, BED would have enough traffic to Boston to justify an extension of the Red Line through Lexington and Arlington.

There still isn’t a direct rail connection to Boston Logan, or LGA, or a whole host of other American airports, so expecting better results for GA airfields is a bit silly.

This aircraft isn’t very big. These types of regional puddle jumpers are only useful when connecting to major long haul aircraft, which is only really possible at large airports.

Yes, you are right. There is no direct rail for many of these GA airports. What I said was:

> justify an extension of the Red Line

It's obvious that even with small electric aircraft, there would not be enough traffic to justify the expense of rail expansion. However, point-to-point air flights would increase the economic viability of many small cities without the need for hub airports. For example, I was driving for business for a while to Burlington, Vermont. I would have welcomed a small puddle jumper from the GA airport 5 miles away to Burlington instead of having to drive to fly out of Logan. It would've been more expensive than driving, but it would have been more enjoyable since I'm the kind of passenger who leaves nose prints on the window. Flying from a local airport to Ithaca, New York (partner's family) would be a viable replacement for driving 6+ hours.

Many more possibilities become practical once you free yourself of the hub and spoke model and combine it with economical electric aircraft.

And the problem with paddle jumpers is that, regardless of the fact that hacker news craps on all mentions of self- driving artificial intelligence, well absolutely losing it over GPT style word tricks...

Highway self-driving is going to come. And highway self-driving will probably replace the regional flight. If I could sleep in my car to get where I was going while I drove me on highways overnight, it would probably replace all airline flights less than 800 mi and probably more.

You get to leave whenever you want. You got to take a far larger amount of baggage. It gets seriously cheap for a family. You can stop away along the way to rest. The seats are more comfortable. And when you get there you have local street transportation. No need to rent a car.

A self-driving RV van and the sprinter class or something like that makes it even easier.

Long term the way we currently do air traffic control does not scale to a much higher volume of planes. The current way of doing this is super stressful for pilots and controllers and relies on decades old technology. With autonomous planes, there will be a need for managing those that doesn't rely on such technology. ATC having conversations with some AI in a plane over a radio does not make sense.

The solution here is adding more automation and moving away from the way things have been done in the past century. Ultimately, the congestion has more to do with pilot and controller situational awareness and stress levels than with the air actually being congested.

As for physical places to land, that's a much easier problem to solve. Vtols basically need a glorified parking or some kind of field. Small planes need short runways. 3000 feet would be plenty for a lot of those. Less possibly.

3000 feet with the necessary height restrictions in either direction of the runway. And then there’s if NIMBYs let you increase flights at an existing airport, let alone open a new one.

PAE in Seattle has so many restrictions because airports are terrible neighbors, despite the clear demand for more than just SEA.

All the air traffic controllers reading these kinds of articles must be breaking out in cold sweat.

Most airports aren't big or constrained.

Instead, a huge problem with aviation is making flights between smaller cities viable. If the OP's planes get any lower operational costs or can profitably scale into fewer passengers, his company will have plenty of success.

Airplanes presented here looks like those in private jet category. So these are probably aiming to replace those first?

We are not really targeting the private or business jet market (though if someone wanted one for this purpose we wouldn't turn them away!). There is another impressive YC company that is that you should check out, Beyond Aero https://bookface.ycombinator.com/company/26134 We are really targeting a low cost commercial market - moving people and cargo. The smaller size is driven in part by the technology - with 50 seats being a good size to capture a large proportion of flying traffic - and partly that it will be faster and cheaper to certify and get a smaller aircraft into the market.

Depends on the city and airport.

Atlanta for example is a huge busy airport but also serves a lot of regional connections. I have flow in on a 757 and transferred to a much smaller regional jet to hop to a smaller city or town.

As long as we have the number from the OP (60% aircraft sold) it seems like it wouldn't matter where those aircraft go.

I always question if fuel cell / electric is really better than just burning the hydrogen in an engine.

We worked on an electric compressor motor for a fuel cell vehicle project once and it took more than one kilowatt (maybe 2 or 3 I don't recall) to run the compressor. An EV can do highway driving at a few KW so that seemed really inefficient. Aircraft run at higher continuous power so maybe it makes more sense, but I still wonder.

Yeah the compressor load goes up with power - we have a 27 kW compressor for our 120kW PEM fuel cell here in the lab (this isn't what is going on the aircraft). This is one of the issues we are tackling with our unique system architecture for the aircraft.

How is the noise difference between electric and combustion engine?

One thing we have learned on this journey is how much low noise is to our customers and the wider community - we have yet to really put this under test and try and get a cost number against it i.e. how much more would you pay for a quieter engine? What we do have is an opportunity to be much quieter, but there is always a penalty to pay in terms of size. For example, unlike a battery aircraft, we still have to provide the fuel cells with air and we can do that with large quiet ducts or small noisy ones - but larger ones take up valuable real estate and ultimately add weight to the system. What I can say is we will design it to be quieter than current jet engines, but where we draw the line is tbd.

Fwiw, I love flying the B787 for many reasons, one of them being the low noise level. But… I wouldn’t go so far as to pay more money for it. The noise factor is not a decision driver, where seat size/leg room and service definitely are when it comes to choosing an airline/route.

I've never flown on a 787 sadly but I have to say that the Embraer E195-E2 was also surprisingly comfy. Much more comfy than a 737, and thus far small jets had been terrible in my experience. Noisy, especially the back of the 717 beside the engines, cramped. But the Embraer was spacious and modern <3

The noise level is definitively a very important factor for the airplane operator.

A small low-noise plane can do some much more profitable routes than a high-noise one.

IIRC for powered paragliders, it turned out propeller noise drowns out ICE noise.

News articles frequently say that lack of aircrew availability is a major cost and constraint for air travel currently. Wouldn't moving to smaller aircraft exacerbate that issue? Or do you think it won't be a problem?

Did someone say autonomous flight?? only kidding, we are not pursuing autonomous flight in the near future. It is something we hear a lot about too, especially after COVID. I am not sure what the answer is here but we do see it as a temporary thing and expect that the market will sort itself out. Whilst fully autonomous flight may not be our focus, we hope to do some things that can reduce the workload of the pilot and perhaps help reduce the training burden of crew making the pathway to that career more attractive. We are actually co-located with Australia's biggest Aviation training provider so we receive a lot of feedback in this regard.

What are the runway requirements?

Can you comment on why not go down e.g., to a 10-passenger like the Pilatus (that lands on a 3000' runway)? It seems like the smaller planes straddle the private/commercial line, while a 50-passenger plane commits you to airline buyers. (i.e., even if not optimal for hydrogen electric, would a smaller-capacity target market be more commercially viable and diversify the risk of long-term development?)

We will be basing our requirements broadly on the current Dash8-300, so we are targeting around 4000ft for the SA-1, but we still have a lot of work before that is validated. It is desirable for us to go with smaller planes as it is faster to market, much lower program costs but we just don't feel that it will have the same impact - both as a business and on carbon emissions. As you go smaller, some costs increase per passenger, like crew and engine maintenance start to dominate at that <12 seat size, and whilst the Pilatus PC-12 is a hugely popular plane, its just not something that could compete with the major single-aisle market. Accessing this market is what would give us the edge and really allow us to build an unusually high number of planes.

Thanks stuart8ol for all the detailed answers in this thread. I learned several new things today (use of compressors for fuel cells to increase power density, logic of airplane sizes). This is the stuff I come to HN for! Also cool to see you using H3X motors - I remember their launch here, I was excited for them.

Good luck decarbonizing aviation!

My pleasure! Yeah working with the H3X team has been great. We are going to have them out at the airport before the end of the year, letting them run some tests on our set up. Will be fun.

> [..] to design a low cost, 50-seat aircraft that can replace a significant portion of the ubiquitous single-aisle (e.g. Boeing 737)

If your marketing strategy is to frontally target one of the big 2, be prepared to suffer and be in a world of pain. From the stories I've heard, Boeing tends to take that very personally and will do anything in their power to see you fail. And although I have not directly heard similar stories from Airbus, it's possibly safe to assume that they are also not choirboys..

Nevertheless, cool approach. Good luck to you.

50 seats doesn't compete with 737s, it barely competes with ERJs. That's not a big airplane.

Also outside the union scope clauses. It's a good place to start.

Honestly I'd rather they target the regional "puddle jumper" aircraft. Shorter runs would be an easier goal to achieve, and IMHO if there was a jet that allowed for more legroom/cargo space with less operating cost everyone would jump on it.

I'm close to two regional airports so 99% of my flying is a small jet to a hub and back again, and it's definitely the worst part of the trip.

Will you use electric motor from your previous company magnix? how do those motors compare to this other YC company h3x that is making electric motors for planes? https://news.ycombinator.com/item?id=26224709

Not this time around! We have selected H3X as our supplier for the motor for our tech demo and have signed an LOI for them to supply motors for our B1900D-HE retrofit aircraft. I would say that magniX has a more mature product and is further along the path to certification and its flown many of the recent and impressive electric aircraft first flights, including our competitor Universal Hydrogen. I'll always have a soft spot for the magni650, but at the end of the day, weight is critical on an aircraft and H3X are showing us a lighter product. We have a good relationship with H3X and have confidence that they will be able to meet the cert criteria in our timelines.

This sounds like a great proposal, and those 50-seat aircraft are the backbone of the mountain communities I grew up around in the PNW. Is there any loss in effectiveness in using standard atmospheric air (thanks to N2 and other non-oxygen components of air)? What do you do with the resultant H2O when the reaction is complete?

Yeah using standard air gives you a performance hit - but it is preferred to carrying around pure oxygen from a weight standpoint. We just exhaust the H20 from the aircraft. There are other things you can do, such as condense and capture, but everything comes with a performance hit that we don't think is worth it.

> Is there any loss in effectiveness in using standard atmospheric air

> What do you do with the resultant H2O

I can't imagine why an aircraft would ever want to carry its own oxygen supply, and capture the byproduct. Oxygen is heavy. Are you thinking of a spacecraft?

>Oxygen is heavy.

More specifically, hydrogen has an atomic weight of 1, whereas oxygen has an atomic weight of 16. For producing H20, that means you would have to carry 8x your hydrogen's weight in oxygen, if you don't use atmospheric oxygen.

Why is a 50 seater trying ti compete with 737s when 737s have 120-150 pax capacity. It seems like you should compete with ER175s and other regional jets instead. If you’re aiming to compete for thin MH routes then wouldn’t slots at airports be an issue for such thin routes?

The lowest hanging fruit is the current 50-80 seat turboprop market. Next would be the regional jet market and lastly we want to capture a sizeable portion of the single -aisle market. The reason we want to compete with/capture traffic served by 737s and the like is that the market is enormous - we are estimating $1.7T over the next 20 years if we were to replace single-aisle with our 50-seat, SA-1. The reason that we believe we could compete is because we believe that we could bring the CASM of the 50-seater down to be on par with a 737, and combined with the emission reduction we think that this is compelling offer for airlines. Our aim is not to have to compete with 737s at airports that are slot constrained but to make use of the 100s of underutilised airports across America. By bringing down the CASM of a 50 seater, we believe that this would increase the passenger traffic too and from those airport and make the currently thin routes more profitable.

I see, that makes sense. There's plenty of airlines like Ryan Air and Allegient who operate thin routes to secondary airports. A 50 seater seems perfect for operators who specialize in thin routes. How ironic if budget airlines beat traditional airlines in becoming carbon neeutral.

Also, how much air do you need go run the chemical reaction? Will your plane have an APU?

The air needed for the chemical reaction is pretty small, but we will also be drawing in some air for cooling and that will be around the same order of air that is used by a turbine engine. We will not have an APU per se, but we will have a small amount of battery to start the propulsion system and this can provide power to the aircraft systems for some time. We can also start up the fuel cells if need be to supply extra power, without turning the electric motor and propellers.

Thank you so much for these detailed answers! It’s really nice to hear from a professional in the field

I can't help but notice the resemblance to https://h2fly.de/ -- do you have any major differentiators in mind, or are you planning to try to beat them head-on?

We watch H2fly in very carefully! They are a really impressive company and their recent flight with liquid hydrogen is inspirational, and really motivates us. I believe we have some different fuel cell technology but the main difference is that we plan to develop the SA-1 as a clean sheet air frame that will be optimised for this new fuel type and propulsion system. H2fly are aiming to sell propulsion systems, perhaps we could be partners one day if their system performs better than ours.

[Maybe disregard this, as I'm not your requested audience, and I realize this is a tech/biz post to HN and you are deep in the details of confronting the unknown, but...] I think for pitch-deck/public communication, as soon as you say "hydrogen aircraft", immediately address or at least acknowledge "what could possibly go wrong-Hindenburg" and "why not batteries" (not para 3).

EDIT you could defer the issue with "Fuel cell electric aircraft"

BTW The first solar+battery electric aircraft world-circumnavigation got hardly any publicity, which puzzled me https://en.wikipedia.org https://news.ycombinator.com/item?id=9824570/wiki/Solar_Impu...

EDIT Since I'm already downvoted, I'll add: I wonder about fuel cells for powered paraponts/paragliders, where battery-electric are available, but aren't quite there yet vs petrol, esp for range.

Thanks - I hear you, safety around hydrogen is always a big concern. We do address it head on often but it will always come up in any conversation about it. The "why not batteries? question is audience dependent - some people have given up on batteries and others, they see that it works for EVs so expect it to work for aircraft too. Will keep your feedback in mind, especially for sales!

Another thing that is probably out of scope for OP is safety in handling LH at the ports. Presumably there would be many of these high-pressure tanks laying around ready to be swapped in (instead of pumped) and would sooner or later cause an accident. But it would be nice to have that problem to solve to begin with :-)

That is out of our scope as a business but it is something we have found we have to address head on with our customers and airport partners. They want to understand the whole logistics and associated safety from green H2 production to aircraft tank. We don't have it all figured out yet but we are working with some great partners on the problem. We have created a Hydrogen Flight Alliance here in Brisbane https://newsroom.bne.com.au/hydrogen-flight-alliance-launche... that includes, BOC (a Linde Company) and H2EC who are tackling the logistics and re-fueling of liquid hydrogen. Note that we are using liquid H2, which is more expensive than gas, but comes with a variety of benefits, one of which is that it is stored at low pressure. We could opt to store it just over ambient pressure but we will most likely go with storing it < 10 bar - much less than the 350 - 900 bar, that gaseous H2 is typically stored at.

Good, infrastructure matters: Birdseye, famous for fish, got freezers into supermarkets; Edison, famous for lights, constructed generators; Tesla (co), famous for cars, constructed charging stations.

Take a look at skyflytech.com They have a hybrid drone/canard design which is VTOL/STOL and achieves the efficiency of wings for distance flying. The propellers are angled at 45 degrees so no complicated tilting mechanism needed. Could be interesting for a clean sheet design.

Thanks - will definitely take a look.

What kinds of costs (time/$) is FAA certification projected to add? I assume there's going to be a lot of scrutiny around a new (for flight) engine tech.

Yeah certification is one of our biggest risks. Luckily for us there are already a few other companies that are breaking the ground here and the certification path is becoming less opaque. There is a lot of scrutiny for new propulsion types but the certification process is largely the same - its more that we don't have the luxury of experience and being able to point to "similarity" to show compliance. We are budgeting ~$50M for our 15-seat retrofit product development and cert and a bit more than 10X that for the 50 seat product.

Are you able to use an "experimental" aircraft/designation to do flight tests in parallel waiting for approvals?

Exactly! We will be flying "Bonnie" our Beechcraft Bonanza on an experimental ticket next year. We will then do the same for each of other programs. This helps us get the hours and data to support our certification process.

Awesome, thanks for the info! Very exciting project, good luck!

I wonder what the sweet spot for # of passenger for a given route is. You need to balance costs (crew, fuel, airport fees, ...) with revenue from passengers. On one end you can have a massive plane that flies once a week. But that's inconvenient for passengers who'd prefer more frequent flights. On the other end you frequently fly tiny aircraft... but that would have a high crew + airport fees overhead.

We think for a high proportion of routes 50 seats for hydrogen electric propulsion. We heard from a major airline that their network planners always want a smaller plane, for flexibility and a high load factor and the fleet planners always want a large plane for lower CASM and fewer aircraft, that tension has basically landed on the single-aisle size (180-200 seats) for most routes with conventional propulsion. But this changes with the technology as different cost drivers have different rates of change with seat count. A good indicative document is https://ntrs.nasa.gov/api/citations/20160007749/downloads/20..., this is asking "if you were to serve the market with only one plane, how many seats should it have?"

It seems like if the fuel costs were to go down, you'd want a larger plane, since crew and maintenance costs would make up a larger fraction of the costs?

[edit]

Looks like the site answers this; reduced maintenance costs when not having a high-temperature turbine are predicted to lead to similar CASM as a 737 despite being about 1/3 the seats.

I think that is a fair statement. You also have to factor in the capital costs, the aircraft purchase price per seat typically increases with aircraft size so it comes down to the balance there, between that cost increasing and other costs decreasing. The scales can tip either way depending on the circumstances. For a 737, we have that capital costs contribute about 40% of the CASM, whereas Crew is 4% and Maintenance is 16%. In conventional aircraft, the efficiency of larger engines really vs smaller ones really push towards larger aircraft.

We would love to do the analysis you are describing in detail. I'm thinking getting people movement data from google maps or something, using that to figure out where people are traveling to. Then use that to determine what traffic needs to go through the major airports and who would be better off going to local airports and really map the traffic in detail. Then overlay our cost data to see what is the real optimum. If anyone can help with that we would love to chat!

Using road traffic data to figure out final destinations of passengers is an interesting idea (I'm not sure you'd get much more granularity than "x% of [increased] road traffic associated with London Luton airport actually heads north of Luton away from London" though). I'm wondering if any airports have used traffic data to derive stats for their pitches to airlines; they certainly collate other facts and figures and do other analysis to try to convince airlines to serve them as well as neighbouring airports

Systematic data on "last mile" passenger origin and destination for a large number of airports sounds like a holy grail product for network development that would be a viable business in its own right, the problem being that none of the systematic sources of that information I can think of are likely to share it. Survey data like this may be as good as it gets https://www.caa.co.uk/data-and-analysis/uk-aviation-market/c...

At a macro level passenger demand is closely correlated with GDP and population growth (and the fleet forecast and aircraft valuation models most of the industry uses are based on pretty simple macro assumptions). So with city-level population/GDP figures combined with easily-obtained existing airline network/capacity data you can start identifying areas that are badly connected, perhaps ending up with some sort of gravity model.

Would love to chat about this sort of thing in more detail (I used to work at Flightglobal/Cirium and worked more recently on airline app startup projects, and my email is dtellett@gmail.com)

Good luck!

I’m curious as to how much of the development of the follow-on ground-up airframe can actually be done in Australia, though. To my knowledge the largest aircraft ever designed in Australia was the GAF Nomad, and that was more than 50 years ago!

Given the sheer scale of specialised engineering skills required, aren’t you going to end up having to have the majority of your engineering staff in the USA and/or Europe?

We were so close to buying an old Nomad for our tech demo! But we thought if we took it to an airshow, it would only get a small sub-set of attendees excited, compared to a Bonanza, which people seem to love. We would really love to do it all in Australia and think Australia is a great place to do the initial development work, flight testing our tech demo and retrofitting the first set of our B1900D-HE product. But we would, reluctantly, agree with you that the SA-1 design, testing and manufacturing would be at best global but most likely heavily centered in the USA. Its our plan to grow the team in the states, starting soon, and slowly shift the center of gravity as the projects move through maturity.

> All of our competitors are working towards a family of aircraft going upwards of 200 seats

Isn't ZeroAvia tackling smaller aircraft?

They are aiming to be the propulsion system supplier for future aircraft but crucially the are also targeting developing systems for a family of aircraft starting small and are working towards aircraft upwards of 200 seats. Our premise is to not look past 50 seats. If we were to design a 200 seat aircraft its CASM would not be much cheaper than the 50 seat if we aim to do a single aircraft type from the start, then we can aim for much higher volumes than aircraft programs traditionally achieve and ultimately bring our unit costs right down and undercut anyone else working on a family of aircraft.

Does someone have analysis of breakdown of flight costs?

fuel cost %

plane lease/mortgage %

aiport facility costs %

Pilot + crew + food/drinks costs %

Profit %

My understanding is that for hydrogen to take off, it needs to become significantly cheaper than jet fuel and just as much energy dense.

It varies significantly by airline, route and aircraft type. There is some open data on this from Form 41 filings sent to the FAA (here's a piece of analysis based on it https://www.faa.gov/sites/faa.gov/files/regulations_policies...)

Fuel and maintenance tends to cost more than the aircraft lease or financing/depreciation costs, so yes they'd have to justify it economically based on the fuel being affordable (and possibly lower maintenance)? In the near term, I think proponents of hydrogen aviation are expecting increases in taxes on jet fuel to do some of the work on operating economics, whilst they build out their own infrastructure.

Vimeo complains with the message: "Video is not rated. Log in to watch."

Would it be possible to rate your videos so that we can enjoy them without having to create a Vimeo account? Thanks!

Sorry - fixed now. Thanks for pointing that out.

This is amazing. I hope you succeed. Using hydrogen fuel cells seems like a clever way to get around the thrust/weight issues present in electric aircraft with heavy batteries.

Thank you! If batteries were 10X lighter than they are today, then we would definitely prefer them.

Makes sense. Another potentially interesting factor is that the max takeoff weight of a plane can be much higher than the max landing weight. If the plane is powered by conventional jet fuel, it can take on this extra fuel, fly father, and land much lighter than it took off.

Will the relatively constant weight of a hydrogen cell become a significant range limitation? Battery-powered aircraft have this problem as well. Very curious to hear your thoughts.

It is definitely a design constraint that we have to consider but at the same time the relatively small change in weight during the flight is also good for our balance, given we won't be putting the fuel in the wings. All in all, the sources of weight are pretty different between the conventional jet-kerosene versus our hydrogen electric propulsion, which is what is driving us to a clean sheet design to take maximum advantage of HEP. We are doing a 15-seat retrofit of a Beech 1900D as our first product, and while it is a great MVP, the landing weight constraint, amongst others, make it a little less capable, with 800km range, than the conventional version.

I have read that battery based aircraft would start to make sense if batteries were 2-3 times less heavy - do you think that this wouldn't be feasible for some type of aircraft?

Yeah even with today's batteries there is a business case for battery electric flight. Trainers, short hops across water and intracity + eVTOLs of course all make sense to tackle with battery. This is because the efficiency is good, the cost can be potentially very low and the infrastructure is manageable. But as a solution to decarbonising a large proportion of aviation - it doesn't work. We want to find a solution to serve the enormous number of passengers that fly up to 3000 km. If we can tackle that, we can cut more than 50% of aviation emissions.

If we ever get to that point, could your 50 seater be easily equipped with that, or would you redesign it from the ground up?

Best of luck! I can think of no cooler space to work in than next generation clean aircraft. Now, if only I wasn't completely hopeless at physics and chemistry...

Thank you, I can confirm it is the coolest job I have had so far, and I have done quite a few cool things. I can also tell you, as someone who studied physics, I have only really spent about 10% of my time in the last year doing any physics! So much other stuff to get through...

Why hydrogen electric and not hydrogen combustion directly?

There is definitely advantages of both. Direct combustion gets you a much greater specific power of propulsion, and the technology for turbine engines is so optimised that it sounds like a really attractive option. We expect we can get higher efficiency with fuel cells and the engine maintenance costs will be lower as fuel cells and electric motors operate at low temperature. Both of these cost drivers lead to a lower CASM.

I have seen claimed that the system with battery powered electric engine would become practically maintenance free. Can you comment on this based on your experience? How would fuel cell based system compare to this?

I think I would be hard pressed to say maintenance free but definitely significantly lower maintenance costs. Turbine blades are intrinsically expensive, made of titanium and operate at high temperatures under high loads. Electric motors have much simpler operation and when made at scale, can really benefit from a replace after 20,000 hours model, instead of a overhaul every 1800 hours, with 200hrs inspection intervals, which we see in some turboprop engines. Fuel cells and batteries are much the same, replace after a certain life, and with built in tolerance to failures. Unfortunately, with fuel cells, as opposed to batteries, we still have some balance of plant that will need maintained, compressors for example, however unlike a turbine engine, they don't operate at high temperatures and are a smaller part of the system, so we can design for much longer lifetimes that you can get away with in a turboprop. All this leads us to estimating 65% saving on engine maintenance. Battery electric companies are going after more like a 90% saving.

Are you the guys from Australia who were asking about Aerospace opportunities as an Australian company here on HN some time back?

No that wouldn't have been us. Hope the feedback they received was "Australian aerospace company - great idea!" though.

Congrats on the launch! Awesome to see a Brissy based YC startup!

What kind of FCs will you be using?

We can't share too much detail but it has higher operating temperatures (180C) than the standard PEM fuel cells that are typically used in automotive. This is key to a good aircraft solution.

Really cool!

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