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alberth

Is this EV or Hybrid?

The founder seems to sneak in the word "hybrid", around 1m30 mark in the video below.

https://youtu.be/nM86DBOqgPM?si=5unXLmPxk6M_kmuN&t=86

Note: not being negative, I just want to ensure I understand correctly since the title might imply something else.

Update: confirmed, it does use aviation fuel.

> "The airplane will also include a reserve-hybrid configuration, consisting of two turbo generators powered by sustainable aviation fuel. The reserve-hybrid system is installed to secure reserve energy requirements without cannibalizing battery range, and it can also be used during cruise on longer flights to complement the electrical power provided by the batteries."

https://www.heartaerospace.com/newsroom/heart-aerospace-unve...

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Hybrid after the first 125 miles, total range 500 miles. Their problem is diversions - an incident at the destination airport may mean an passenger aircraft may need to land at an airport which could be a couple hundred miles away. The hybrid powerplant throws the fuel efficiency numbers off so goal is not to run it unless needed, but they could not get certification without it.

For anyone looking for the reference, it's stated at 10:16 [0]

[0] https://youtu.be/nM86DBOqgPM?si=BdoZzp1Dxa4S3C_9&t=616

Yes it's super misleading. All the marketing and title is calling it "electric" where in reality it's a hybrid electric-gas airplane with a 125 mile electric range. Aviation uses nautical miles yet they advertise 125 statute miles so the number seems bigger (125 statute miles = 108.62 nautical miles).

It would be like Toyota marketing the Prius as an electric vehicle, then buried in their presentation sneaking in the gas propulsion. Same with Chrysler Pacifica (32 mile electric range).

So what do regular aircraft do when they run out of fuel? They require a forced landing. Aircraft fly with a buffer of fuel though to avoid such situations, so why can't an electric aircraft fly with a similar buffer on it's range? ie. Always fly less than the current charged range of the aircraft.

Simply put, batteries are heavy.

Something like 1/30 the energy density of liquid fuel. Plus unlike fuel, a discharged battery weighs virtually the same as a charged one.

Regular aircraft fly with enough fuel to change into at least one other airport in an emergency (ideally two).

That aircraft would need a very large battery to do that, and it's way more efficient to have some burnable fuel there that you'll never actually use.

Regular aircraft are required to have enough fuel to be able to divert to the alternate airfield in their flight plan plus all the margins for taxiing and waiting for a landing clearance. If a plane is low on fuel they can declare an emergency and get priority over other traffic, but that obviously is disruptive and should not happen on well planned flights unless something pretty significant happens after takeoff.

> and should not happen on well planned flights

You make it sound like it is acceptable for a badly planned flight to have a fuel emergency. It is not.

If there is a fuel emergency (or the plane lands with less than 30min of fuel) there will be an incident investigation that treats the situation as serious as if the plane had crashed. If the investigation discovers it was nothing more than bad planning, (at minimum) the planning procedures will be changed to ensure it never happens again.

Badly planned flights should not happen. Pilots who don't carefully plan their flights end up dead quickly. Lack of fuel is one of the easier to handle things that can go wrong from bad flight planning.

Can you give an example of a "badly planned flight"? And did local regulators agree with your opinion?

My dad dreamed of being a pilot and when I was a kid he subscribed to the flying magazine (or something like that I don't remember that name.) every single issue had the last story being "I learned about flying from that" and nearly every single one was a case of bad planning, usually a case of flying into bad weather because of the bad planning.

LaMia Flight 2933 - https://en.wikipedia.org/wiki/LaMia_Flight_2933

The pilots took exactly enough fuel to reach their destination. They didn't have enough fuel to divert to an alternative airport. They didn't even have the mandatory 30min of reserve fuel. They did not account for a minor holding pattern just before landing (ironically, because another plane had a fuel leak).

The crew failed to declare a fuel emergency, and crashed 18km from the airport. They had only been in the hold for 10 min when their engines ran out.. they were very short of fuel, the pilots knew they were short. They should have diverted (or declared a fuel emergency) almost an hour earlier, but they didn't want anyone to know how close they were cutting it.

> there will be an incident investigation that treats the situation as serious as if the plane had crashed

No the investigation isn’t as serious as if the plane had crashed. In July 2026 nine planes simultaneously had a fuel emergency in London. You bet it’s different from nine planes simultaneously crashing in London.

It helps to understand different kinds of fuel emergency. Declaring a fuel emergency to get to a diversion airport is very very different from having 30 minutes of fuel left.

Well, obviously it's going to be a much easier investigation, especially when you can interview all the crew.

But still very serious. 9 simultaneous fuel emergencies could have easily overwhelmed ATC and snowballed to worse issues.

Something lead 10 different aircraft to make the exact same mistake and find themselves without enough fuel for a safe diversion. There will be recommendations to try and prevent it from happening again.

Lots of down votes on this but it is a legitimate question. The goal is likely to have the majority of flight off of batteries. That being said, the total weight of the emergency fuel plus generators is likely far less than the weight of the extra batteries they would haul around for the safety margin they need. So they end up lighter and more capable AND don't need to burn fuel. That being said, I wouldn't be surprised if they didn't start the generators during critical phases so they may end up using some fuel for a flight, but not much. Total guess on that though.

> That being said, I wouldn't be surprised if they didn't start the generators during critical phases

I somewhat doubt that. Part of the advantage of the design is that the generators don't need to be sized as big enough to power take off, climb and a potential go-around on landing. They only need to be sized as big enough for cruising.

So powering them up during critical phases wouldn't help with safety. If anything, normal operating procedures might actually require shutting them down during critical phases.

What this does mean is that the batteries need to be reasonably full when it comes into land, possibly as high as 50%. And most go arounds will require immediately powering up the generators, so it probably needs to be fuelled for all but the shortest flights.

> That being said, I wouldn't be surprised if they didn't start the generators during critical phases so they may end up using some fuel for a flight, but not much.

I would guess the opposite. Many parts in a turbine engine are "lifetime limited" by number of engine starts. That is, you are required to tear down the engine and replace certain parts after a certain number of engine cycles.

That makes the economics of the turbine hybrid radically different if you need to start it every time you land vs. only the rare cases where you need to dip into fuel reserves.

For example, the PT6A (a common 500-1000hp turboprop) requires the turbine and compressor disks to be replaced every 16,000 cycles. That's about 5 years of commercial service at 4x round trips per day. But if you only start the engine once in every 10 flights, now those components (theoretically) last for 50 years of flying.

> vs. only the rare cases where you need to dip into fuel reserves.

There aren't that many existing flight routes that will fit into the 125 mile range (though the existence of this plane might change that), so I suspect we will see most of these planes go into service on slightly longer routes. So they will probably still need one cycle per flight.

Though... The video isn't quite clear if the 125 miles is what they can fly without starting the turbines or if it's what they can fly without needing the turbines ready to act as an emergency reserve. I actually suspect it's the later and this aircraft can make it to 200+ miles without starting the turbines.

Where I live, there aren't that many 125 mile flights, but there are a lot of 200 mile fights.

I also suspect the turbines are sized so that only need to start one of the two turbines on most flights, which would extend lifetime a lot. Ideally the turbines would be sized so that one is enough for cruising, and with two you can actually charge the batteries after a go-around (enough to enable a second and third go-around)

> Aircraft fly with a buffer of fuel though to avoid such situations, so why can't an electric aircraft fly with a similar buffer on it's range?

Because the required buffer is HUGE and we’re at a point where electric planes barely have enough energy for the actual route. So they’re doing the sensible thing here, flying the actual route electrically and falling back to combustion if the plane needs to divert.

To that point, the battery capacity they’ve got, rough envelope math, is maybe 10 minutes beyond reserve. They’d likely need at least double, probably triple battery capacity to fly useful routes all-electric with enough reserve stored in batteries. The turbines are a great move.

> They’d likely need at least double, probably triple battery capacity to fly useful routes all-electric with enough reserve stored in batteries.

Yup. And to bring this point home:

"Only" doubling the battery capacity likely eats well over half of the payload capacity, in terms of mass. So your 38 seat plane is now a 19 seat (or fewer) plane.

Unless they have a whole new airport and flying experience, I don’t think a lot of people are going to fly just 125 miles. That’s less than two hours of driving. It would be 2 hours of just airport shenanigans much less the flight itself.

There are a fair number of connecting flights that this is a good fit for. For example, I fly out of Madison, WI regularly and almost always connect through Chicago, which I believe is right around the 125 mile mark.

Used to regularly take the shortish flight from Boston to Chicago, and then a bus >3x as long to Madison to see family, because the puddlejumper was too expensive or not even running.

> 125 miles … That’s less than two hours of driving.

I don’t know where you live or what you drive, but I just punched in a destination 200 km away as the crow flies, the Alps are in the way and I’m looking at five hours of driving.

Also, water.

Rookie numbers. As the crow flies it's 250km between me and my old town. Used to drive back and forth a lot back in the days and it takes everything from 8 hours to 10 hours depending on the route you take and whether you hit the ferries on schedule or not. Plus 30 minutes for resting and eating. Flying takes 50 minutes in a propeller airplane + travel to and from airports and airport shenanigans (not too bad at these small airports). If you take the morning flight you'll be in town by the time people start showing up for work. If you drive you'll be in town by the time people start leaving work.

Depending on the cost, and availability, 125 miles gets you within easy public transit range of NYC from Boston.

Now, of course, most of the hassle of getting to NYC from Boston is transit to and from the airport. And of course, transit from JFK, Laguardia, etc into the city.

There are at least 5 capable airports/airstrips closer to me than Logan or T.F. Green. Only one of them, Worcester, offers NYC flights. Worcester is almost an hour from me on average, and a bit more expensive. It’s an hour from takeoff to landing (I’ve arrived 10 minutes before takeoff, at the PARKING LOT many times without it being an issue).

If they can get this in and out of even smaller airports, like in Stow, MA, which is beyond capable, it will be a gamechanger.

Too bad Amtrak can't run good service. This is a perfect area for high speed trains, but instead the service is too slow and not frequent enough.

Without noise, over time, travel will change.

There will still be some noise. But yes, it’ll be less noisy.

Could be useful for hub and spoke type systems, where you fly from a smaller city to the main hub, and catch a connection from there.

Even then there are lots of flights in Europe that are between cities less than 1 hour apart.

This idea generally makes more sense in Europe than the US, I think.

Their first customers were from the Nordics, if you watched the video

Electric propulsion would eliminate the local environmental impact of emissions justification for the short-haul flight bans that are floated and/or implemented [1] from time to time in Europe. It makes sense to spray less jet/avgas exhaust when possible. Of course, if the ban reasons include noise abatement or evil conspiratorial machinations, they're still on the table ;)

[1] https://en.wikipedia.org/wiki/Short-haul_flight_ban?#Overvie...

Perhaps, but almost all of those shorter trips are routes that should have fast train service anyway.

Mandalay to Bagan, Oaxaca to Puerto Escondido, Chiang Mai to Pai… shitty mountain and hill roads can make short plane distances take forever

SFO to sac and Monterey, lax to (SD, Santa Barbara, etc) could be good for those “I live in a 50k person town and need to get to a hub” flights.

Of course those -should- be easy on trains too…

You don't drive to islands.

Bridges are a thing

Yeah, and they require a place to build. Do you think bridges between the Hawaiian islands is feasible?

Report recently from my area.

https://www2.gov.bc.ca/gov/content/transportation/transporta...

There was no mention of Hawaiian Islands in the comment.

To your question… Feasible: no; Possible: yes.

I live in the Caribbean. For island-hopping airlines this would be a godsent.

But I doubt we have the capital to buy them new.

Just in saved maintenance they'd probably pay for themselves within a few years.

> 125 miles. That’s less than two hours of driving.

Assuming you have a straight road in that direction with a speed limit that allows an average speed of more than 100km/h.

Not much airport shenanigans in the small island hopping nations and the fjords this is aimed at. 125 miles in 2 hours is assuming flat, straight, high-speed, low-traffic roads. Sure, people might not use these to fly SFO → LAX or back, but they likely will use them to go ABZ → LSI, and the "check-in and security shenanigans" are, errr, quite relaxed, compared to what you might be used to at JFK...

There's a ton of small routes that just aren't getting much service now because of operating costs - the founder speaks to that in the video - that this could serve.

A slightly larger aircraft able to do ~300 miles on battery and then say 1,000 in hybrid mode, might resurrect the economically unviable but relatively fast LHR/LGW flights down to NQY. The six hour drive is pretty, but... yeah...

300 miles is very viable for a lot of routes. Not 125 though.

> Unless they have a whole new airport and flying experience, I don’t think a lot of people are going to fly just 125 miles.

There are a lot of "island hopper" and bushpilot mini airlines in the world. The current world record is a route in Scotland that, on good days, takes less than a minute of flight time [1].

It is much much easier to supply such islands with electricity (there almost always is a power grid tied to whatever the nearest mainland is) than to continuously haul fuel around.

And in Croatia... that is easy enough distance to cover Rijeka-Zadar for example, which is about three hours worth of car or bus drive.

[1] https://en.wikipedia.org/wiki/Westray_to_Papa_Westray_flight

If you're going through a small airport, or hopping on a plane at an FBO, there are not long lines and invasive screenings, you just identify and go

Honestly, I'd feel better knowing it has a reserve system in case there's any issues, even if the batteries have more than enough power, beats having it and never using it, than needing it and suffering as a result.

Do current aircraft have a backup in-case their fuel tanks run dry?

There's reserve tanks or more generally reserve fuel for emergencies. Other than that there's no propulsion backup for when the fuel runs out, instead redundancy comes from multiple independent fuel tanks.

> redundancy comes from multiple independent fuel tanks.

And in larger aircraft, multiple independent engines. See for instance ETOPS

https://en.wikipedia.org/wiki/ETOPS

From the pictures, I see that this new aircraft has 4 engines. So it should be adequately resilient to single engine failure.

Current aircraft have * MULTIPLE HOURS* of fuel tanks. Compared to dozens of minutes of battery that this thing has.

Typical reserve requirement is 30 min for a turbine aircraft (45 for piston). Given the 125 mile battery-only range and the probability that it flies at at least 200 kts (230 mph), it’s pretty unlikely to hit even a 30 min reserve on only batteries. I like the design, I think they get the problem and have a decent solution for it

The most common flight on my island is to the island about 50 miles away from us.

We pay about $120 for the privilege, which takes 20 minutes of flying.

So I think even in this case the reserve capacity is "needed" (for the reserve requierement), but I can see them realistically being able to fly between the islands purely on electric power.

> and have a decent solution for it

Unless we ignore the additional maintenance cost of having to completely different proportion systems to maintain (and it is worse than a twin engine plane, because the propulsion systems are different, so you have to stock up on more different kinds of parts and possibly have different kinds of mechanics on staff to understand them)

Something that wasn’t super clear to me was whether the turbines are actually used for propulsion or if they’re used solely as generators to recharge the batteries/power the electric motors. I could honestly see it going either way.

Having the turbine, electric motor, gearbox, and potentially clutches to isolate the turbine or electric motor from the transmission seems pretty viable though. This would waste a little bit of power keeping the turbine spinning (unless there are clutches) but would also ensure that the turbine’s been spun recently, the oil pumps are primed and the bearings are lubed and ready to go.

Not that I’m saying a turboprop turbine like a PT6A is a simple device, but compared to a high-bypass turbofan like you’d see on a 737 or A320, they are considerably simpler.

Edit: looking quick, the time-before-overhaul (TBO) on modern PT6As can be up to 6000 hours, with a ~2000hr Hot Section Inspection. I’m not sure how “spinning but not burning fuel” counts on TBO, but it should at least mean the HSI is simple.

Yea, that wasn't super clear to me, either.

But... given that turbine APUs already exist for ground power and are already engineered to be as light as practical, my naive guess would be that it's easier, simpler and faster to just use a COTS APU as a series hybrid rather than trying directly couple a turbine to the propeller.

On inspections and overhauls: I'd expect that not needing to start the turbine at all on a given flight massively helps the economics of the airplane. Turbines often have parts that must be replaced after a given number of (startup) cycles, and that's going to be especially important for a turbine that is only expected to run for a short time (if at all) at the end of a flight.

If you only start the turbine on, say, 5% of flights, that means you get 20x as many flights before overhaul/inspection. I could see that being incredibly attractive to airlines.

> Typical reserve requirement is 30 min for a turbine aircraft (45 for piston).

For private, yes. For airlines, the requirement boils down to basically enough fuel to "fly to the intended destination as scheduled, then loiter for XX minutes, then fly at normal speeds to a pre-designated alternate, land".

For short flights, that means the fuel loaded at departure can be more than twice what is actually needed to get from A to B...

Which is why the hybrid approach is fairly clever: You can use it for ~125 mile flights, and remain 100% electric on ~95% of flights. Whereas, without the reserve turbine the practical limit would be ~60 miles. On the ~5% of flights requiring more range, you're still mostly operating on electricity.

    > You can use it for ~125 mile flights, and remain 100% electric on ~95% of flights.

The video says that in the United States about 1 in 1000 flights are diverted from their intended destination airport.

Yes, they also have ramjet turbines which generate electricity from the movement of the plane on a backup circuit.

Yes the are strict regulations requiring them to carry extra fuel; despite its weight having a real cost. Carrying extra battery would be too heavy even compared to having a whole extra engine.

The real benefit really seems to be that the electric motors have a much smaller failure rates than mechanical ones running near their top rpm. The hybrid motor can run at a much optimized RPM, so the idea is that this will improve the overall safety margin of the overall design. I could be wrong, but that's what the video said.

One would assume that all combustion engines used in aviation run at an optimized RPM?

At cruise, yes. However during takeoff and go around they run at higher RPM to develop more thrust. Using batteries for takeoff and only using fuel for cruise or backup power is smart.

I think it's even more than that. The hybrid engine has to run one single RPM to drive a generator, it can be vibration insulated, probably needs to be only smaller because it doesn't have to provide the high max power the conventional motors have etc.

It's why I believe hybrid cars that use a gas motor only to charge the batteries are more reliable and more efficient.

RPM is one thing, but the other is that engines run more efficiently at altitude due to the temperatures being much lower there.

So basically like diesal-electric trains? My understanding that's almost certainly outdated was that the issue with electric planes was weight due to batteries, so added mass from a generator sounds bad.

Having the generator as backup means you need a lot less battery though, so it saves weight overall.

I remember reading about making ground effects electric planes for this reason. You need a reserve, but if your plane could double as a boat and was flying over water, that would satisfy the requirement.

As long as water conditions allow for a safe landing. In much of the world that severely limits when you can operate due to storms or ice. In practice routine use of ground effect vehicles will be mostly limited to lakes and inland seas with fairly benign weather. Like I don't think we're going to have regular passenger service from San Francisco to Los Angeles or Detroit to Cleveland.

Ground effect planes are already pretty limited to calm water situations. Like between Seattle and Victoria, or maybe Seattle and Vancouver. I would say the Alaskan marine highway would be a good fit, but that is mostly for freight and cars.

According to the founder, he can make the economics of short trips (1-2hr) work with all-battery.

He cannot make them work if he has to store enough battery to fly around for an additional hour or two searching for an airport to divert to in an emergency, which is an FAA requirement.

So he has the heavy battery bank for regular trips costing almost nothing per flight-hour, and the expensive fueled backup system for emergencies.

Seems like an extremely practical way to handle that requirement without hauling around a ton of extra battery capacity that will rarely get used.

The X1, which is what flew, is all electric. The ES-30, their proposed product, is hybrid.

Surprised they are not using linear opposed piston crankshaftless generators to make an extended range EV aircraft.

Smaller, lighter, simpler, cheaper, and more flexible about fuel.

https://www.youtube.com/watch?v=NeG4zLlFkak

Linear engine starts around 11:19

Turbines are extremely reliable and well-understood in aviation propulsion

This! Anything unproven makes the flight certification process longer. They already have to get their electric side certified, might as well make the backup generator as easily certified as possible.

Good point. Only have one new tech at a time.

Generation II then.

My father, a mechanical engineer, was a tireless advocate of the hypocycloid crankshaft mechanism. In the 90s, hybrid vehicles with a hypocycloid-based generator feeding the batteries that make the electric motors go was the application he was going for, especially since hypocycloids function best at constant RPM.

I say this with all sincerity, I love this sentence:

"My father, a mechanical engineer, was a tireless advocate of the hypocycloid crankshaft mechanism."

For some reason just reading that brought a smile to my face.

From mechanical engineers I’ve met it almost seems a requirement that they have something they tireless advocate for.

Yeah. I bet he was.

But on this flight it did not have a combustion engine, I assume it was fully electric and if so, the title is 100% correct.

With limited information form their web site, both. Being able to run pure electric while switching to fossil fuel. [0]

The way modern hybrids can charge from an outlet, I classify them as EV-Hybrid, and only use gas if need be vs older ones that only charge through the gas engine, Hybrid.

[0] https://www.heartaerospace.com/es-30

It uses aviation fuel only after the electric battery is empty. And uses the fuel to run generators, the motors are all electric.

Its hard to call that the largest electric aircraft IMO. It's electric until it can't, then its not.

Well, technically, it's always electric. Sometimes the source of that electricity is from the battery system, and sometimes it's from an onboard generator.

Nah, electric means battery

You can't dip into emergency fuel for non-emergencies, cause then you could have a real emergency. It's not like a hybrid car that people could run completely on gasoline. So sounds like this plane would be electric almost all the time.

Why do the generators specifically need aviation fuel? They aren't the actual motors.

I think the video states they are actually turboprop engines

Ok that makes sense

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