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Launch HN: H3X (YC W21) – High power density electric aircraft motors
229 points by jjsylvestre on Feb 22, 2021 | hide | past | favorite | 164 comments
Hey HN!

I’m Jason, one of the co-founders at H3X (https://www.h3x.tech). We are building the lightest electric propulsion systems in the world. Our first product is a 250kW (330HP) integrated motor drive in a 18kg (40lb) package. It combines the electric motor, inverter, and gearbox into a single unit, resulting in an ultra-high-power density solution for electric aircraft (and other mass sensitive applications).

In terms of electrification, we believe the aircraft industry is where automotive was ten years ago. There are many companies working on eVTOL and single-seaters, but very few are working on large commercial single-aisle electric aircraft such as a 737. This class of aircraft is absolutely critical to electrify as it accounts for the most passenger-miles [1] and is the biggest slice of the pie in terms of aviation emissions. Beyond the environmental impact, there are huge potential cost savings from both fuel (or lack thereof) and reduced maintenance for airlines.

Aircraft are very mass sensitive so there are two main technology challenges that need to be solved to enable this class of electric aviation –

(1) High energy density and efficient energy storage (batteries, hydrogen fuel cells, etc.)

(2) Light, efficient, and high-power density electric propulsion systems (electric motors, power electronics, gearbox)

There are many people working on (1) and great strides are being made [2][3]. We are focused on solving (2). A study done by the DOE determined that for a 737 to complete a five-hour flight, the propulsion system must be >12 kW/kg [4]. Today, best-in-class systems have a power density of 3-4 kW/kg. With our first product, we are targeting 13 kW/kg, making it an attractive solution for near-term Advanced Air Mobility (AAM) applications as well as an enabling technology for the aviation industry to enter the next stage of electrification.

There are some cool things we are doing with the electromagnetics, power electronics, and the integration between the systems to get to the 13 kW/kg. There is not a single magic bullet, but rather a combination of multiple technological advances - 3D printed copper stator coils, high frequency SiC power electronics, and a synergistic cooling system to name a few.

Our origins in electrification stem back to our college days where we built Formula-style electric racecars (s/o to Wisconsin Racing FSAE!). During year 1 of the program, we got so fed up with our COTS motors and inverters, we decided to go clean slate and build our own from the ground up the following year. Those were super happy fun times. Lots of dead IGBTs and all-nighters in the shop, but in the end, we got everything working and delivered! It was a true test of resilience and taught us how to GSD. Great preparation for starting a company. This led us to grad school and it became apparent during this time that the electric aircraft industry was a sleeping giant ready to be woken. We felt uniquely positioned to capitalize on this opportunity, so after about a year in industry, we left our full-time jobs and went all in.

We’ve got a long road ahead - aviation is tough, there’s no denying that. In addition to the engineering challenges, there are also major certification barriers. However, CO2 is a serious problem and right now the major aviation players don’t have a compelling plan to meet the goals laid out in the Paris Agreement. Innovation needs to come from the outside and that’s what we’re doing at H3X.

I’d love to hear your guys thoughts and would be happy to answer any questions you have.

Sources:

[1] https://www.transtats.bts.gov/tables.asp?DB_ID=130

[2] https://www.theverge.com/2020/9/22/21449238/tesla-electric-c...

[3] https://hypoint.com/, https://www.plugpower.com/

[4] ASCEND DE-FOA-0002238




Given that the batteries weigh a lot more than the motors, I would have thought that motor efficiency (which scales battery size) was much more important than motor weight.

My back-of-the-envelope is:

- Assuming 0.4 kWh/kg for batteries, and they have to run for 4 hours, then the total mass per kW is 10 kg (batteries) and 0.08 kg (motor).

- A 1% increase in motor efficiency could eliminate 0.1 kg of batteries, which would let you double the weight of the motor.

- (My analysis is invalid if you need much higher peak power than cruise power.)

I'm curious how you optimize the entire system for such trade-offs.


This is an excellent question. For narrow body aircraft we've studied, they require high propulsive power during the takeoff and climb phases, and a fraction of the peak propulsive power during the cruise phase. One aircraft we looked at required 30-35MW during takeoff and ~10MW during cruise.

So, thrust power and system level power density (kW/kg) are critical during takeoff/climb and cruise efficiency is important for minimizing energy consumption.

Like Audunw mentions, its very application dependent as well. It all boils down to the propulsion system mass fraction. For lower PSMF, efficiency matters more once you are above a certain power density. For higher PSMF, power density matters more. There is an optimal balance of efficiency vs. specific power for every aircraft. We can "tune" our technology relatively easily depending on what that balance is to maximize range.

I'll let my cofounder Max chime in since he does a lot of vehicle-level architecture and optimization. He's been doing some studies for rotorcraft and planes to look at how specific power and efficiency impact range/endurance so I'm sure he can expand on my answer a bit.


The other part is that there's a straightforward trade-off between specific power and efficiency. Two motors on the same shaft can each be run at half the current, and since power loss due to resistance is: P=I^2*R, your losses due to resistance would halve. (There are, of course, other loss mechanisms.)

So it's good to start out with a really high specific power because you can often trade that back for efficiency.


But that big max/cruise delta disappears as soon as you ditch the wings and go 'copter, which seem to dominate all use cases where electric is anywhere close to viable.

Where motors excelling in W/g could absolutely shine is the still empty area of hybrid planes that downsize their combustive propulsion to cruise requirements and carry batteries only for those short periods of peak power demand.


Would you use a generator or a directly connected ICE?


Certainly not a generator, at least not unless there was some miracle fuel cell fuel. The "electric boost" would need to be completely idle most of the flight (which creates some interesting challenges regarding conversion of electric torque to air movement).


This is a fascinating analysis of hybrid electric planes

https://link.springer.com/article/10.1007/s13272-017-0272-1

I think the idea is worth exploring. Esp with superconductors an electric powertrain could have lower losses than mechanical.


Oh, that's sobering. All the referenced modeling seems to start with hypothetical batteries many times lighter than we have, and even then they only give minor emissions reduction hardly beyond what we are used to from e.g. succeeding generations of 737. And only under the assumption that the electricity used is completely emission-free.

And why even bother modeling constant power split? You might just as well linearly interpolate between conventional and an all-electric design and call it a day. Everything interesting about hybrid propulsion happens when the ratio is varied with power demand.

What's interesting is how much mass they account on the electric side in addition to the battery. This kind of validates H3X.


> One aircraft we looked at required 30-35MW during takeoff and ~10MW during cruise.

Do you envision some airframes to include assisted take-off technology? (JATO and the like, even catapults)


A simpler alternative could be to just have an electrified runway. The plane draws power from power rails embedded in a runway, or something like that. So, it doesn't switch to batteries until it's in the air.

You could even have a long cable that hangs behind the plane and keeps an electrical connection until you're a few hundred feet up. (I'm picturing it connected to something like a slot-car that travels in an electrified track that could extend a mile or so past the end of the runway.) When you get to the end of the track, the cable (which could probably belong to the airport rather than be part of the plane) releases from the plane.

(This would help marginally with range, but doesn't really help with power density, unless you're limited by the voltage and current available from the batteries rather than the power of the motor.)

I keep wondering if there could be a way to re-charge in flight so that battery range/weight wasn't such an issue, but that's a hard problem.


As a rule, whenever one feels tempted to say "just do <x>", it's time to wait and think. Because, if it's "just" about doing something, why isn't it being done already?

In this case: let's say it's feasible to retrofit runways to use this system (it probably isn't) and look at a few issues.

For instance: "the cable releases from the plane". No system is fail safe. What happens if the cable does NOT release from the plane? What happens if it snags during the takeoff roll? What happens when there's wind gusts?

If there's no cable, and it's "just" a rail, presumably the plane is taking off aligned to the rail. What happens if the alignment is off? Or is the 'rail' supposed to keep the plane straight? If so, what about the force distribution on the plane's landing gears or (if a specialized system is installed), in the fuselage?

So say you have such a system and everything has been retrofit. What happens if there's an issue with the land-based generator during the take off roll? Would the aircraft still have enough power to perform the take-off from the onboard batteries? If so, this is just about range and the system would never be installed, as aircraft would be certified with the lower range instead. If not, it's a disaster in the making.

> I keep wondering if there could be a way to re-charge in flight so that battery range/weight wasn't such an issue, but that's a hard problem.

There isn't unless you can transfer power from elsewhere. In-flight "refueling" from another plane is out of the question. You are essentially left with beamed power from ground stations (or orbital if we are really forward thinking). That might theoretically be feasible (planes don't have a very large surface area so the power delivery system would probably look like a weapon and mostly behave like one). Engineering it is another matter, not to mention practicality.


We’ve been launching airplanes with steam catapults for many decades, albeit in an environment where we’re willing to take more risks than to go see Grandma, but many of the catapult concerns are areas where we have decades of experience and hundreds of thousands of successful cat shots.


But the catapult isn't for saving on energy that needs to be carried on the aircraft. It's simply that you can't build engines and propulsion systems on a plane with the desired takeoff weight when you have as short a runway as you do on an aircraft carrier


Regardless of the underlying driver to implement it, we've solved some of the concerns that GP mentions for ground-assist launches, so there is a body of experience/work we can easily build upon.


It is the same thing. The high power for takeoff shortens the runway from 7km to 400m.

We could do the same thing with cars and equip them with a super aerodynamic body and a 7kw engine, it could do 80kph.


> As a rule, whenever one feels tempted to say "just do <x>", it's time to wait and think. Because, if it's "just" about doing something, why isn't it being done already?

In this case, the simplest counter to that question is just that electric aircraft barely even exist at this stage, due to battery weight issues.

That isn't to say this is a great idea (a small boost in range probably isn't worth the additional complexity), but we just don't know at this point what electric aircraft will be like down the road when they're more common and people have figured out what works and what doesn't.

> For instance: "the cable releases from the plane". No system is fail safe. What happens if the cable does NOT release from the plane? What happens if it snags during the takeoff roll? What happens when there's wind gusts?

We already have this figured out for gliders and tow planes, and that's a cable designed to withstand the full thrust of the puller plane without breaking. A power cable can be designed to disconnect if it's yanked too hard. It can also be made to just plain break if it snags.

> So say you have such a system and everything has been retrofit. What happens if there's an issue with the land-based generator during the take off roll? Would the aircraft still have enough power to perform the take-off from the onboard batteries? If so, this is just about range and the system would never be installed, as aircraft would be certified with the lower range instead. If not, it's a disaster in the making.

I'm assuming the plane has batteries and intends to go somewhere. If it has enough batteries to actually go anywhere useful, it should have more than enough batteries to circle around and land immediately if there's a problem with the power cable. This is no problem. Gas planes generally should be prepared to emergency-land at any point during takeoff and ascent (in a field if necessary) in case of complete engine failure, and this would just be more of an "oh, I guess we have a couple minutes less range than I thought I was going to have, and I'll have to land sooner" sort of situation.

> There isn't unless you can transfer power from elsewhere. In-flight "refueling" from another plane is out of the question.

It's not out-of-the-question in the sense that we couldn't do it if we wanted to, it's just incredibly inconvenient and probably not a problem that's worth trying to solve with current technology because the result wouldn't be useful. In-air refueling currently exists with gas planes, and it could be done with electric aircraft with a power cord instead of a fuel tube. It wouldn't be energy efficient and the tanker would probably have to be gas-powered, so it doesn't make sense environmentally. It would also take a very long time to recharge, given current battery technology. You'd be better off just flying a gas plane that has ten times the range or so to begin with.

Alternatively, you could swap batteries mid-air, but how would that even work?

Like I said, transferring energy to in-flight aircraft would be best, but I'm not aware of a way to do it that would be practical (i.e. doesn't involve technology we don't have, or building megastructures across the landscape, or wasting energy in other ways). Maybe we'll get the energy density of batteries up high enough that it doesn't matter before we figure out high-power long-distance wireless energy transfer. Or maybe we'll be using liquid fuel in planes indefinitely. For right now I think figuring out a sustainable way to make liquid fuel from electricity is probably the easiest route, if we're just trying to get off of fossil fuels for aviation in the short term.


> You could even have a long cable that hangs behind the plane and keeps an electrical connection until you're a few hundred feet up.

I can assure you this will never ever happen. It’s wildly impractical, improbable, and sounds extremely unsafe. Sure, it’s theoretically possible, but that’s about it.

The NFPA is not going to add a code section in the NEC for hundreds of feet long live electrical conductors being pulled into the air by a plane and then disconnected in mid-air, and the FAA isn’t going to allow it either.


Tow planes and gliders routinely fly with a disconnecting cable between two aircraft, and that seems at least as impractical and unsafe (or it would if you were proposing it as a new idea). Though maybe that's the sort of thing that's "grandfathered in" from earlier, more permissive days of experimental aviation.

I think the strongest argument against using a power cable during takeoff is just that it's not worth the effort and complexity just for a slight increase in range, except in rare situations or planes that normally make very short flights and don't want to be weighed down with extra batteries (like the aforementioned glider tow planes).


> Tow planes and gliders routinely fly with a disconnecting cable between two aircraft

This is true. However, the cable is not carrying KW or megawatts of electricity, it's just there for tension, to transfer forces from something else to get the glider airborne.

Technically, you don't even need the tow plane, some places perform winch launches (or car launches!) exclusively. This is very common where general aviation is not as common.

Should the cable not detach (extremely rare), it can be cut at the other end. Cutting a live cable should be much more interesting. Other issues, the glider can release it. The glider will most likely be fine, even if the flight is now cut short.

Gliders are very light and still the cable weights a lot. That's probably the limit of what's practical. There are some gliders with electric motors, they don't need all that much power, by definition. Some can even self-launch.


> Tow planes and gliders routinely fly with a disconnecting cable between two aircraft, and that seems at least as impractical and unsafe (or it would if you were proposing it as a new idea). Though maybe that's the sort of thing that's "grandfathered in" from earlier, more permissive days of experimental aviation.

A tow cable does not have live electrical conductors in it.


They allowed 737 MAX 8, so maybe, who knows?


Or for an even simpler alternative, just get towed into the air as motorgliders are (the ones with sustaining motors but not auto-takeoff).

I wonder if this tech might be better suited to self-launching motorgliders than GA.


It certainly seems like something that will be towed.


None of the things you mention would have a significant effect on range, and all could be replaced with a nominal increase in runway length. If an aircraft cannot produce sufficient power to take off, it cannot produce sufficient power to climb.... And to be efficient, it must climb as high as possible, ideally to 30k feet or more. You are talking about the first 30 seconds... But it needs to keep it up for 30 minutes.

Take off assists are for ultradshort runways.


Or how about a large battery pack that drops back to the ground after take off, eliminating it’s weight from the airframe?


I think most forms of assisted takeoff technology would reduce electrical power requirements for takeoff, but not put much of a dent in the climb power (unless you can catapult/ JATO all the way up to cruising altitude, which would be challenging). Since climb power is still significantly higher than cruise power, and is effectively thermal steady state for these components (10-20min), it would still drive the propulsion system sizing.


You still need enough reserve power at the end of a flight to do a rejected landing/go around, or you won't get certified. If you are relying on some kind of catapult, rail gun, or rocket assist to take off, not sure how that happens.


An early rejected landing still requires less power than a static takeoff, so you could get by with a mix of craft and assistive power.


You could have another aircraft tow you, like gliders sometimes do. Doesn't seem terribly practical though.


That could be a great use case for lighter/smaller electric motors, since a tow plane could take off, assist with takeoff, turn around and land, charge, and repeat. The tow plane wouldn't need as large of a battery pack, but having good power to weight for towing other plants to whatever altitude is very important.


I feel like this is something that drones/100% automated ops can really help with.

Power satellites (basically giant solar arrays transmitting power) are also interesting (https://www.geekwire.com/2020/space-force-will-test-solar-po...).

We could have these complex automated systems to make electric aircraft much more viable, which is cool in theory.


Power satellites are interesting. But here's the thing:

For most aircraft (except some gliders), covering them fully with solar panels is not even close to the power they need in cruise, correct?

So a power satellite would have to generate _at least_ the same W/m2 as the sun (around 1.4kw/m2( just to break even with a solar panel, but most likely much, much more, by orders of magnitude.

For a 747, I've seen figures from 90 MW to almost 200MW. If the receivers were at the wings only, that would be almost 6MW per square meter if you take the lower figure.

For a target as small as a plane, this would look like an energy weapon from science fiction.

Even something like this would not cut it:

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

For general aircraft the numbers look better. Then again, they are much smaller.

I can't wait for power satellites to be deployed, but they will mostly be servicing ground stations.


Not exactly what Talyn Air is doing, but along the same lines- separating out the "lift/climb" vehicle from the "cruise" vehicle. It can actually be a very compelling design!


Keep in mind that an electric motor isn’t limited by the amount of oxygen in the air. As a result it can fly significantly higher where there is far less air resistance.

Since air density is proportional to the square of the elevation this can lead to significant efficiency gains. Believe it or not, partly as a result of this, the SR-71 had it’s best mpg at peak speeds.


A simple physics-based plane model (like the one we made to understand vehicle-level impact of our technology development) dictates that the range-optimal cruise speed is proportional to 1/sqrt(air density), so it makes sense that the blackbird was more efficient at high speed when at high altitudes (admittedly, this simple model is subsonic, and there are a lot of other factors for supersonic flight).

Since having lower air density also means you need a higher lift coefficient (angle of attack) to produce the required lift, and then you have more lift-induced drag (which goes with the square of the lift coefficient). I think air density more or less washes out when it comes to its impact on range. That being said, you cover the full vehicle range at a higher velocity at higher altitudes, so it certainly seems like there would be significant benefit from a travel-time perspective.

All that being said, there are significant high voltage insulation challenges at higher altitudes, which is something we are working on.


That's really not too accurate. The most efficient aircraft are sailplanes (the high end ones usually have a motor, BTW), and they operate at lower altitudes typically. Lift-to-drag of 70 has been achieved. The SR-71's L/D is probably classified still, but probably around 7 or so.

The issue is a certain aircraft has an optimum cruise altitude. If you try to fly fast at low altitude, it'll be horrendously inefficient. If you try to fly higher, you'll often be beyond the maximum lift coefficient so you'll be less efficient or you'll stall.

To first order, efficiency is independent of cruise velocity.

The range for an electric aircraft (this is basic physics) is: Range = (battery specific energy) * efficiency * (L/D) * (mass_battery/mass_total)/gravity.

Altitude and air density and velocity do not directly figure into the calculation as you pick your cruise altitude to maximize your (L/D). And maximum L/D depends somewhat loosely on Reynolds number (which, granted, does depend on speed) and especially Mach Number. If you can keep totally subsonic flow (i.e. usually up to about Mach 0.5), your maximum (L/D) doesn't directly depend on speed.

Sailplanes increase their speed (at optimal glide ratio) by putting on ballast. You can achieve the same effect by cruising at higher altitudes.*


We are definitely saying the same thing in very different ways.

Just using the drag polar approach and neglecting second-order effects (assume negligible dependence on Re, sufficiently subsonic so negligible impact of M, and linear lift coefficient region aka no stall), we get the following (I'm skipping a lot of intermediary steps):

Cd = Cd0 + k*Cl^2 -> Cd0 is the parasitic drag coefficient -> k is the lift-induced drag coefficient -> Cd is the overall drag coefficient

Range is maximized when Cd0 = k*Cl^2 (parasitic drag = lift-induced drag) -> Cl is a function of speed: since the required lift is constant, more speed = less Cl required = less lift-induced drag -> maximum L/D is achieved at this range-optimal speed

This speed can be calculated exactly from the total weight (W), air density (rho), lifting area (S), and drag coefficients:

range-optimal speed = sqrt((2*W/(rho*S))*sqrt(k/Cd0))

As long as you always operate at this range-optimal speed (aka speed for maximum L/D) which is a function of air density (and therefore altitude), the equation for range reduces significantly:

R = endurance*velocity, where endurance = battery energy / drag power, and we know the equation for drag power...

Simplifies to:

R = E*eta/(2*sqrt(Cd0*k)*W) -> R is range -> E is battery energy -> eta is total system efficiency

Dimensionally, this equation is of course the same as yours, with an energy being divided by a force to get a distance. The key point I am trying to make is that if you just look at that equation with no context, speed and air density are not present anywhere. But what is hidden in the assumptions is that you are assuming that you are operating at the maximum L/D speed given the air density at any particular altitude. Going back to my other comment, range at the range-optimal speed does not depend on air density or velocity directly, but lower air density at higher altitudes will result in a higher range-optimal speed, and hence less travel time for a given range.


Oh, yes, precisely. That’s one thing about air travel that people don’t really understand. They think fast = inefficient, but as long as you’re supersonic, speed is roughly independent of efficiency. You can have you cake and eat it, too!

This is not really true for any other transportation method. Cars and buses and boats and even trains have an efficient vs speed trade off especially at higher speeds.

And there is an efficiency advantage of speed in that you can get by with just a cramped seat because your trip time is short, a few hours. A similar trip in a conventional train, cruise ship, zeppelin, or sailboat may require bringing along basically a small apartment (or “sleeper car”) which is much heavier and can destroy the efficiency advantage you might have otherwise had. And the same vehicle can be used many more times for the same route if its speed is much greater, which (combined with the lower vehicle weight per person) reduces the effective embodied emissions of the vehicle per passenger mile significantly.


> there are significant high voltage insulation challenges at higher altitudes

What are these challenges? How does having a near vacuum cause trouble with ~1kV potentials?


The phenomenon is due to Paschen's law (there is a good wikipedia article on it). The breakdown potential of a gas is minimized at some pressure, and in the case of air, that pressure is < 1 atm, and corresponds to a specific altitude.

I can't go into much detail, but we are working on addressing this in a couple different ways in our insulation system design.


Unless I am missing something obvious, lift-induced drag is largely independent of altitude. However, parasitic drag is significantly reduced by lower air pressure. Thus the advantage from high altitude flight.


Less dense air -> higher angle of attack required to produce required lift -> true lift vector is more offset from vertical -> horizontal component of lift is actually producing drag

Like I said in the other comment, if the plane is operating at the range-optimal speed, I think the air density does not impact the range capability (it cancels out) but it does increase the range-optimal speed, allowing for faster travel.


Drag required to make lift is only a subset of total drag.

A car for example doesn’t need to produce lift, but it still displaces air which causes drag. The same is true of an aircrafts fuselage, which is generally not used to generate lift but still increases total drag. https://en.wikipedia.org/wiki/Parasitic_drag

Also, an aircraft is generally designed so that at cruse speed and altitude the wing incidence angle provides appropriate lift. https://en.wikipedia.org/wiki/Angle_of_incidence_(aerodynami.... Which means at optimal curse distance the cabin would almost perfectly level independent of optimal cruse speed or altitude.


Yes, the range-optimal speed is where the parasitic drag is equal to the lift-induced drag.

If you go through the analysis, the air density drops out of the range equation if you assume are operating at the range-optimal speed (which is higher at lower air densities).


> the range-optimal speed is where the parasitic drag is equal to the lift-induced drag

Not quite true -- range-optimal speed is where the sum of those terms is minimal. With some assumptions, this is where the derivative is 0, dDrag/dv = 0, and since derivative is linear, this means: the range-optimal speed is where the (infinitesimal) increase of parasitic drag (with speed) is equal to the decrease of lift-induced drag (in other words, opposite derivatives).


Using the simple drag polar approach,

D = A*v^2 + B/v^2 (D is total drag, first term is parasitic drag, second term is lift-induced drag)

dD/dv = 0 where v = (B/A)^(1/4)

Plug in v = (B/A)^(1/4)

D = sqrt(AB) + sqrt(AB), aka dD/dv = 0 exactly when parasitic drag is equal to the lift-induced drag


I stand happily corrected :)


That’s only relevant up until you approach the speed of sound. Passenger aircraft are designed to stay subsonic for a host of very good reasons.


Definitely, for sure. Like I said in the other thread, supersonic is a whole other thing, and I don't think anyone is trying to electrify anything supersonic any time soon :)


Propeller efficiency decreases at high altitude though.


> Given that the batteries weigh a lot more than the motors, I would have thought that motor efficiency (which scales battery size) was much more important than motor weight.

I guess that depends on what kind of airplane you are making. If you're just making the same kind of airplanes we've been making with ICE, but with electric motors and batteries instead, you're probably right.

But if you're making an electric airplane from scratch, there's a lot you can do if you have a really light motor, which can drastically reduce drag.

Look at Maxwell X-57 for instance: https://www.youtube.com/watch?v=-HvZ7c0F9ik

If you're going to have lots of motors on the wings, they better be as light as possible.

I'm guessing the increased efficiency from a design like that can easily be as important as the efficiency of the motor itself.


These are all great points- everything is very interconnected in these vehicles, and there is a lot of potential upside in high power density distributed propulsion (like on the Maxwell).

In characterizing the vehicle-level benefit of power density, it is definitely important to consider the X kg of structure required to support 1 kg of motor/inverter/gearbox/etc.


Excellent points about associated structures! However for the motors, isn't it the case that the support structure design is dominated by the thrust loads, which should vastly exceed the motor mass? For sure, there is some non-thrust-related structure to react the motor's mass, e.g., inertia from a harsh landing, but how much extra is it? This is much more the case with power/mass optimized motors like yours.

Consider an ideal case - you achieve the same power with negligible mass, say 1kg. How much structure in my aircraft using your motor could I really eliminate vs your current model?

And the real case, switching from a competitor's similar-power motor to yours, how much additional structure weight can I save by switching, beyond the obvious great advantage of your motor's weight savings?

(Obviously, these answers massively depend on other factors, but... )


Yeah, there are a lot of factors that play into this. A couple things come to mind:

1) Considering megawatt-class machines are necessary for many future applications, the mass of the motor+inverter+gearbox (especially using best current technology) definitely adds up.

2) With a very distributed propulsion system, motors that end up near the wing tips have a big moment arm compared to the ones typically tucked under the wing root


Excellent point about the moment arm and control issues! I'm definitely all about maximizing power-weight and strength-weight ratios...

I am wondering about the ratios you are achieving, and about the issues of scale.

Do things get better as you scale up? I notice you mentioning the state-of-the-art at 3-4 kW/kg, and you shooting for 12 kW/kg.

This is even substantially better than small scal T-motor UAV motors at around 7w/g [1]. The chart shows them peaking at 3181W and weighing 453g.

So, I'm wondering what scale factors may be working in your favor at your scale vs the single-digit kW scale.

Also, any plans to scale slightly smaller (I'm involved in such a project)?

[1] https://uav-en.tmotor.com/html/2021/Antigravity_0119/668.htm...


From an active mass (electromagnetic parts, power switches, etc) perspective, our specific power is relatively consistent from 100 kW up to 1 MW. TBD on lower or higher than that.

The biggest difference is the total mass specific power (including housing, bearings, etc) usually gets worse at much lower powers (1s-10s kW), because these components become a more significant fraction of the total mass.

The 12 kW/kg number is continuous output power / total system mass (active + inactive, including motor, inverter, gearbox, housing, bearings, etc). If you isolate just the motor to compare, it is much higher than 12 :)

We do have plans to develop a ~100 kW (maybe a bit smaller) unit in the future, but when is TBD.


> - A 1% increase in motor efficiency could eliminate 0.1 kg of batteries, which would let you double the weight of the motor.

Wouldn't it be much simpler to state that a 1% increase in motor efficiency could eliminate 1% of battery weight? (trying to get the theory clear)

---

Obs: This is only approx. valid if efficiency is already high. If efficiency was very low, e.g. 2%, then 1% more (going to 3%) would enable eliminating 1/2 - 1/3 = 1/6 = 16.7% of the batteries.

An equation to describe this situation, assuming constant energy need, is Eb = Em / n, where Eb is energy provided by batteries, Em the work of the motor, and n efficiency.

Also, the energy need should indeed decrease with decreasing battery weight, amplifying this effect even more, but at high efficiency the correction isn't too large. Equations omitted because there are too many assumptions (acceptable battery mass fractions, energy usage vs weight, ...).

(A starting model would be: Maircraft = Mbatteries + Mconst; Mb = aEb; Em ~ Ma^p ; Em = ( k(aEb+Mc) ) ^ 1/p; Is p~=1?; Eb = kMc/(n-a*k); )

So in principle an 1% increase in motor efficiency gives even more than 1% of less battery weight!

A complication however is that batteries have power constraints as well as energy constraints (how power constrained . If the peak power only has to be sustained over a very small period, this would allow complementing energy-dense sources (batteries) with power-dense sources (capacitors). However, some power-dense sources do not last long enough to cover the peak-power intervals, so they would not fit.

If the following diagram is to be trusted:

https://commons.wikimedia.org/wiki/File:Power_vs_energy_dens...

Then for my guess of 5 minute take-off constant peak power time lithium-ion still has the greatest power density, which means other sources should not be combined.

You can use variations in chemistry among Li-ion cells to achieve this tradeoff, but those limitations provide a slight negative correction (greater efficiency giving less mass gain).

Those effects would need to be combined.

Anyway, there is a lot of interesting performance and Operations Research (Linear programming) optimization here.


I have more questions, why are you not using silver, around 106% better conductance of electricity, but also a better conductor of heat?

And cooling, lots of big electrical plant uses H2 for a cooling medium as it has about 22 times better heat transfer than air - I can see the peroblems, but you can't light up 100% H2, it's when it gets some air with it is the problem.

I actually have a bucket load more, I am Elec Eng/Func Safety/Systems Integrator/Embedded guy and many years ago did my final engineering project on a software package to design high frequency inductors optimised for weight or efficiency, for space use. So all in all I am super interested to see how you go and what you can squeeze out. Will you run a blog or update of some kind?

May your end copper (silver) be short, if you have any.


Silver is crazy expensive compared to copper, and the tradeoff isn't worth 6%. Also, 3d-printing pure copper is relatively new, and I'm not sure there is as much of a business case for 3d-printing silver (from the perspective of the companies making these metal AM machines), since the demand is lower because of the cost. Lastly, there are actually some loss mechanisms in the motor where the lower resistivity of silver would actually hurt you (proximity effect from flux crossing through the stator conductors, producing eddy currents).

We want to start simple with cooling, hence the water/glycol. There certainly could be some opportunity to use something different (maybe with certain fuel cells and liquid hydrogen already onboard?). Regardless, the thermal resistance from hotspot to coolant is dominated by conduction resistances inside the motor, and is less a function of the convection resistance from the housing to the coolant.

We will be sending out a newsletter occasionally, there should be a link at the bottom of our website.

Thanks for the questions!


Silver is heavier than copper.

That's why people were so upset when carbon nanotube yarns happened to be poor conductors.

People were thinking of super light motor windings.


Aluminum has the best conductivity/mass out of all of the common conductors. Motors are actually more volume constrained than mass constrained for the windings, which is why copper is typically used there instead.


Copper is also 60% better in the thermal conductivity properties as well, which is another critical property.

Power density in an electric motor is really based on how fast you can remove heat from the motor. I'm involved in sizing industrial servomotors, but even there you have 1s/10s/60s power ratings.

I wonder if H3X can post higher power levels for takeoff, assuming it starts cold and the flight plan calls for throttling back after a certain altitude is reached. And even in the event of an immediate 150% power return to runway after a 150% takeoff, the motor might only have slightly degraded the winding insulation; it can almost certainly exceed its ratings once for long enough to get back to the ground.


Yes, thermal conductivity is of the utmost importance at the continuous current densities we are designing for.

That being said, typically the effective thermal conductivity of the winding (perpendicular to the axis of current flow) is limited by the insulation (strand and/or turn) and the encapsulation/varnish. As a result, changing the thermal conductivity of the conductors themselves will have much less impact on the total thermal resistance (from winding hotspot to coolant) than changing the insulation and encapsulant thermal conductivities.

At these very high power densities, the thermal RC time constants inside the motor are very short (small motor = small thermal capacity, low thermal resistance by design). Therefore, even for a "short" 10 minute takeoff, most of the motor will have already hit thermal steady state. As such, the motor needs to be able to run at takeoff power continuously. There has been a lot of fun discussion elsewhere in this thread about how to tackle that aspect of the problem (given that takeoff power is typically 3x cruise power).

I will say that we are working on developing a high thermal conductivity (> 1 W/m-K) and high temperature (> 300 C) insulation system.


In medium to large generators the winding pitch makes a big difference, but this is also optimised for fault current (as in the winding pitch selected) depnding on the installation being compact or spread out.


It’s just a weird idea, but cant you use hollow copper winding, and run the coolant liquid trough that?


Yes, this is one variation of what is referred to as "in-slot cooling". Keep in mind that putting coolant inside the slot removes precious conductor cross-sectional area. There is a tradeoff to be analyzed, and in some situations it can make sense. However, in-slot cooling does lock you in to having a liquid cooling system, whereas the design we currently use (coolant channels integrated into shared housing) could be modified to be air-cooled if it makes sense to do so.


Thank you for taking the time to reply, and the confirmation that this might be a valid idea in a situation where the tradeoff makes sense.

But more importantly thank you for Your contribution to reducing air pollution by electrifying airplanes!


LOL, just had exactly the same thought.


Perhaps by the time this is viable (battery limited for now) carbon nanotubes will be inexpensive enough to use for conducting both heat and current.


Thanks for writing this up!

Ad the pilot of the plane with two 285HP piston engines with an MTOW around 5,700 pounds, I am curious: what kind of endurance could I get if I replaced my fuel tanks with about 1000 pounds of batteries and used your motors? Assume operating at 225 HP during climb, cruise and descent and full power during takeoff and initial climb out (5 minutes or less). Thanks! (Reference Cessna 310R for more details.)


You guys should contact (some of) the F1 teams. They would certainly love to have more efficient motors in their hybrid PUs. A 5kg saving is literally worth millions in that business. Also Formula-E might be interested, but I don't know how free they are in their choice of material, so you might want to talk to the organizers.


Yeah this is definitely a market we're looking into - both KERs and Formula E drive units. Great product-market fit.


As long as people are considering radically different markets, go all the way to the extreme. E-bikes, one-wheels, e-motorcycles. Something's got to carry you over the desert of waiting for aviation certification.


First hires should be people with strong SAE-ARP4754A and SAE-ARP4761 experience. Get your safety assessment correct first. Understand how to build a FADEC function with appropriate development assurance and hardware reliability. Then build your extended team (or outsource). Good luck!


Absolutely. Appreciate the advice Nate!


The 480nm number is really impressive at this size. Especially at 5000rpm with the 4-1. Compared to a ICE motor that weighs ~200kg, you effectively free-up 40kwh~80kwh (80 if you believe the 400w/hr claim that Tesla makes) of battery capacity right there. I think there's still a long way to go, but seeing things like this and planes like Pipestrel's electric planes, GA electric planes are more and more feasible.


Absolutely. It's easy to focus on comparing what we are working on with the other (few) electric solutions being built out there, but compared to combustion engines the specific power is a big step change. When you combine that with improved specific energy (either from cutting-edge batteries like what QuantumScape is working on, or cutting-edge fuel cell systems like what HyPoint is working on), you can see the path to GA electric planes and even small business jets is not far off.


Oh I've got many questions :)

1- Isn't a HW startup really hard compared to software? Like the ideas are like yet-another-social-media-site or a SASS but in hw one needs to do the embedded programming, the mechanical design, the software, marketing and *then* the novel idea that sells. How do you do it?

2- How do you manage to find the expertise to build a viable product? How did you find investors?

3- Any tips/books you'd recommend for hardware/engineering related startups?


1. There are parts that are certainly harder and there is one part I can think of that may be easier.

- Harder: Longer and more expensive iteration cycles, MVP can be expensive, manufacturing and production required to scale, expensive certification

- Easier: Raising money (sometimes) especially if you are a moonshot with a big vision. Good example is Boom Supersonic.

Good news is there has never been a better time to start a hardware company than today. Iteration cycles are becoming shorter due to advances in rapid prototyping and there is a lot of capital available, especially in electric vehicles and sustainable tech.

Peter Thiel talks a lot about this in Zero to One, but much of the innovation that’s been done in the past decades has been in the digital space. We have so many problems that require innovative hardware solutions and I think now we are just beginning to scratch the surface.

2. We all met through Formula SAE in college. This is a great place to meet super talented engineers and is why Tesla, SpaceX, and the other top companies in the world recruit heavily from these programs. It teaches you both the hard skills and the soft skills. If you are still in college, I would recommend getting involved in teams like this.

3. I haven't really read anything hardware-startup specific, but I love Zero to One and find myself rereading it all the time.

Would love to hear other peoples thoughts on this as well. Good questions


I'm not in the field, but from my perspective, aviation is super, super conservative. That is one of the reasons why we have GA still using leaded gasoline in engines that are largely unchanged from the 1950s. F1 is basically the exact opposite, they are pushing the bleeding edge of technology all the time.


My perspective might be biased, since for the 30-odd years I've been in industry, I have done mostly embedded systems.

Those things you mention are skillsets: software, mechanical engineering, electrical engineering, etc. Sometimes you find them all in the same person, sometimes you have separate bodies doing each one, but at the end of the day it's a staffing issue.

I'd say it's less that it's "hard" and more that iterations are slower and costly and the less capability you have in-house, the slower it is. If you have a full machine shop and a Stratasys 3D printer onsite, a lot of things can happen faster. If you're doing garden-variety industrial automation, there's far less risk than designing state of the art humanoid robots.

There is a spectrum of difficulty, like everything. In my case, I was doing this stuff freelance, in my spare bedroom at age 25, so it's not that hard.


I worked in a start-up doing High Altitude Solar powered UAV's (ultra-light carbon fiber airframes, etc.)... your motors would have been awesome for that. Flying above 50k feet has a host of challenges.

Wish you guys a bunch of success...exciting times.


Thanks! Yes, high-altitude UAVs is a great application for our motors. We're developing a new insulation system for our coils so we have spent a lot of time looking into the challenges high altitude poses - corona, cooling, all sorts of fun stuff. Lots of altitude chamber testing in our future!


Amazing. My view on this is that the combination of electrification and autonomous flight removes most of the cost advantage large airplanes have over small ones.

People seem to obsess over replacing large jets with large electrical planes but forget that the reason those exist at all is fuel economies that you simply don't have with electrical planes. A big jet has a better fuel economy than a small plane per kg of load. Bigger engines run more efficient. That's why private jets are so expensive to fly. A transatlantic flight burns quite a few tens of thousands of dollars worth of fuel. But it's not a problem because the plane is full of hundreds of people that each pay quite a bit of money for the privilege.

The same is not true for electric because the battery mass means large planes are pretty much impossible currently. Smaller planes on the other hand are feasible now and could get to interesting ranges pretty soon with even only modest improvements in technology. The low cost of electricity means that even if there was an advantage, it would matter a lot less. That makes the pilot the most important part of the cost of flying the plane from A to B (i.e. variable cost).

Many small electrical planes without a pilot would be able to transport people for vastly less than a single big jet (autonomous or not). Initially over small distances but with the help of better batteries or fuel cells, long haul flights should be doable as well eventually. The fuel/electricity cost for that would be a lot more modest than e.g. flying a 777 across the Atlantic. There is not much of a benefit over using a large airplane vs using many smaller ones. Even the cost of buying them could be better. E.g. the list price of the Eviation Alice would give you budget for about 30 of those for the price of a 777. That's an unreleased first generation electrical plane using pretty outdated tech (because certification takes that long).

So, I would say focus on small to medium sized planes and mass producing those because that is where the action is going to be short term. Think point to point connections of airports that you currently can't fly to because of noise restrictions. Anything under a 500 miles basically. That's a new market that is currently not economical with conventional planes because of noise and fuel cost.


This is really exciting, congrats on the launch! Exciting to see engineers coming from college engineering teams like FSAE -- I was a member of a solar boat racing team, which is a very similar problem space and also relies on "stacking efficiencies" in your drivetrain system.

If you don't mind, I have a few questions about how you collect data and evaluate the performance of your motor quantitatively. Do you have any particular software stack for data collection? I see the motor communicates over CAN -- Is that just to send control signals, or do you also expose sensor readings like temperature, power input/output, etc? Lastly, did you need to write any custom software to collect/visualize motor performance and what does that look like?

The reason I ask is because I'm in the early stages of building a data collection & analysis platform for experimental hardware (https://www.telemetryjet.com/), targeted at small engineering teams or individuals. I don't want to focus too much on what I'm building (this is your thread!) so I'll just say in general I'm really interested in learning more about how small engineering teams like yours collect & utilize data in the engineering process.

Congrats again on the launch.


CAN is pretty typical interface for inverters & drives. We communicate the commands via CAN and receive currents, temps, speed, torque, and errors back via CAN. We are using PCAN systems at the moment. In the past, GUIs that I have used are Kvaser, Vector Canape, ATI Vision, and LabView. A lot of our post processing is done in MATLAB, Excel, or python. Feel free to reach out directly if you would like more insight.


The main technical surprise to me from your pitch is the integration of power electronics and motor in one package. Your windings, at 96.7% efficiency and 200 kW, need to dissipate 6.6 kW of heat. Your SiC FETs are more efficient and therefore produce less heat, and while they can take high temps, are more efficient at lower temperatures. Why not connect the inverter to the motor with a short cable, and package those separately?


Tight integration removes an entire housing and cold plate from the inverter design (++ specific power). Allowable SiC die temperatures are ~175 C these days, which is pretty awesome.

The inverter and motor are on opposite sides of the coolant, and so heat from each flows into the coolant. The mechanism by which the motor would heat the power electronics is via increasing the coolant temperature, which to some extent is mitigated by maintaining an appropriate flow rate given the loading conditions.


An interesting anecdote I listen to during a conference on eVTOL. A long flight with an electrified 747 will require more power from the grid than Heathrow's electricity consumption for half a day.


Certainly. Infrastructure is actually one of the biggest technological challenges for flight electrification. This is one area where hydrogen / fuel cell might have a leg up since it can physically/geographically decouple the power distribution from the airport itself (whereas for battery electric, unless you want to swap tens of tons of batteries between flights, you need charging infrastructure at the airport itself- and charging many 747-sized planes simultaneously at C-rates of at least 1 would require an obscene amount of power).


I’ve recently taken up flying - it’s by far the best thing I’ve done :)

I’ve seen electric motors changing gliding drastically these last few years and a proper electric engine for GA would be a game changer.


Have you considered to jettison some of the batteries during and/or after take-off?

Probably not just drop them, maybe a controlled glider or similar, plus what are the posibilities for an in the air charge by tether to another plane?

Final super radical idea, have some iflatable high chord wings for take off at low speed high drag and lift, then ditch them somehow once at altitude and can do a anouever with stored height to get speed. (Or a lift blimp).

As you say, the take off is where the problem is.


Love the brainstorming. As you mentioned, "decoupling" the cruise mode from the takeoff mode could make a lot of sense. One of the most innovative and feasible solutions I've seen is from a former YC company called Talyn Air https://www.talyn.com/

They have a nice animation showing the lifter and the cruiser vehicles.


An electric trolley plane? Basically add a rail in the runway that powers the plane through take off, with the batteries engaging once in the air.


Or, more like an upside down tram, get the first big bunch of acceleration from ground electricty that doesn't count for weight.


If the mass fraction of batteries on the plane is bounded by some not too large number (I'd guess at most ~30%?), then your range increase will be less than that. Given the increase in complexity, risk and additional hardware neutralizing those changes, I don't think battery ejection (via gliders or anything else) is viable.

Mid-air refueling (e.g. via drones swapping batteries) would be more plausible, but it still seems like a risky and complex operation -- think of turbulence, weather events, remote flight routes, etc. (but maybe it's possible to get it reliable enough).


Can I get one to put in a jet ski and or electric boat?


Uh, some motor controls questions...

What per-unit impedance are you targeting for the stator winding?

Does the motor controller need an LC output filter to keep the motor's high-frequency current reasonable (thus forming an LCL with the stator winding), or is the stator winding inductance sufficient on its own?

What techniques did you employ to get a wide speed range? Is it an interior permanent magnet machine, surface-mount permanent magnet machine, etc...

Does the controller have a common-mode filter of any sort to cut down on the common-mode bearing current?

Are you building off of 1200V SiC 'FETs or 1700V?


I'll let @mliben comment on the motor questions.

The motor inductance is relatively low so we're running a high switching frequency (40-60kHz) to maintain reasonable phase current ripple. No output filter is used. Also, our phase busbars are very short so we don't run into the transmission line effects you typically see with fast switching SiC/GaN and phase cables.

We are looking into some advanced modulation schemes and switching topologies to reduce CM bearing current. Also looking into hybrid bearings with ceramic balls. This is definitely an area of active research, but we are trying to get away from a CM input filter as they can be bulky and heavy.

Right now, we are using 1200V SiC MOSFETs.


I dunno man, there is no silver bullet for high dV/dt, and SiC are harsher than most. Low-permeability core material and high switching frequency can help keep an LC filter compact.


To add to what Jason said-

The characteristic current of the machine is roughly the same as the maximum inverter current, so at maximum power the power factor is between 0.7-0.8. This also means the flux weakening capability (CPSR) of the machine is very good, although that isn't particularly useful in these propeller-load applications. In many applications the machine would spend most of the time at ~0.6pu speed and ~0.5pu torque (cruise), where the power factor is > 0.9.

I can't discuss the specific rotor design, but I will say it is a very high flux machine.


Why assume that the future aircraft fundamental design has to remain same and electrify the trusters? Current aircrafts have evolved into their current shape from restrictions and capabilities


The big advantage of using existing airframes is that you dramatically reduce certification costs and commercialization time. If you can "retrofit" an existing airframe with electric propulsion, then you can get to market a lot faster.

You're absolutely right though - changing the airframe design and moving to distributed propulsion can lead to improvements in aerodynamic efficiency, L/D, and fault tolerance.


You may know this, but your motor will likely (should) be certified separately from the aircraft.


I appreciate the advice here. We are actively investigating the FAA Part 33 cert, but a standalone cert for a commercial electric drive hasn't been fully defined yet.


Why aviation?

Why design first (solution looking for problem)?


This is a good question. Aviation has the largest market space for this motor application. The aviation certification time frames are quite laborious, but we are mitigating this by diving into some other markets in the short term.


When can we buy a motorcycle with this in it? I'm joking, but you know someone wants to kill themselves that way.

On a more serious note, what other applications do you intend for these?


haha yeah, 100% I'm sure someone is already considering it... (looking at my co-founder eric, he loves motorcycles)

We have received significant interest for high performance ground and marine applications, which we plan to leverage in the short-term as a way of getting lots of in-situ run-time for our technology without the hurdles of certification. We will be pursuing the long road to certification in parallel.


Also, cargo UAV is a big one right now. Many UAM companies are using this as a stepping stone to start generating revenue while they certify their aircraft.

Marine is a big one though.. especially in Scandinavia. Lots of interest in electrifying boats and ships there.


Is the scale of the engine for marine applications very different to aviation? Ferries usually have huge hulking diesels so I'm curious what the equivalent electric powertrain is like.

I'm also assuming that a scaled down version would be ideal for personal watercraft?


We are planning to add a MW-class machine to our portfolio in the next five years which could serve as a nice replacement for the dirty diesel engines on these larger ships.

Looking at Taiga Motor's electric jet ski, 250kW would be a bit on the high-side. It would also be a very expensive jet ski :) https://taigamotors.ca/watercraft/


I would look at utility and patrol boats, like RHIBs, for your motor application. I bet it would fit very well together.


In marine use, as a former ship driver (naval, not commercial, so needs could vary), I would prefer a larger number of small engines I can vector rather than one or two larger engines. It removes the need for tugs from both the maneuverability standpoint since you have vectoring and the safety standpoint since you could have redundant systems.


Don’t many modern ships already have this? I recall watching “Big Ships” or some such on Discovery Channel about 15-20 years ago where they explained ships already having multiple stern and aft, starboard and port, “pods” either with jet streams or rotors.


Sure, but having driven ships with those, they're not as maneuverable as they could be. It takes time to deploy the pods and often they aren't available at high speed.


Now that makes a lot of sense. Unlike side thrusters, you'd be able to use all engines to provide forward movement for max speed while also using the same engines for low speed maneuvering.


Hey, my neighbor had a small home built plane that was powered by an old 2 cylinder generator engine. Maybe you should sell yours as generator engines too?

(Yes I'm kidding. I know. I'll stop trying to trick thermodynamics.)


The funny thing is that’s a pretty common way to get three phase power from single phase supply.


Really? That's amazing.


Also, leaf blowers and trimmers. I'd pay to have my neighbors' gas powered ones replaced.


Great to see some fellow Badgers aiming to make a dent in the universe. 3x higher power density is a huge leap, looking forward to watching you make it happen!


On Wisconsin!


So... in layman terms, can I buy this, strap on the Boeing 737 instead of turbine and fly? Will I need 2 units, for each wing? Or how does it work?


Well, you would need significant energy storage either in the form of batteries or hydrogen + fuel cells as well :)

Our technology demonstrator is a 250 kW machine, but we have plans to scale up to the megawatt class in the next few years. Like Jason mentioned elsewhere in the thread, tens of megawatts are required for a narrow-body jet like the 737. There is significant aerodynamic benefit from having multiple distributed propellers/fans as opposed to two-four big ones, and likely this is the path forward for electrification of these larger planes, i.e. a lot more than 2-4 units, with single-digit megawatt capability per unit.


Are ya'll doing any crazy multiphysics topology optimization to optimize magnetic fields, heat transfer, and fluid flow?


We take the 80/20 approach here. We start with analytical design (can be done pen on paper, but typically happens in excel/etc) to get a high-level view on the "continent" of design possibilities. This can be done readily with magnetic circuit models and thermal resistance networks.

From there, we identify the best high-level design traits and begin some optimization work to get most of the way to a fully-optimized solution (this is more FEA-based, both mechanical, magnetic, and thermal). This gets us climbing up the right "mountain" on the continent.

At this point, we put the pens down and start building something, because we will learn more building a prototype and iterating than we will spending too much time in simulation-land.

In parallel, we have been putting together a workflow to co-optimize the design across mechanical, magnetic and thermal simultaneously. Thus far the jump across each discipline has been a bit more on the manual side, but automatic co-optimization is a long term project, and would get us to the "peak" of the mountain.


Why assume that the future aircraft fundamental design has to remain same and replace the turbofan engine with an equivalent electric motor?

Current aircrafts have evolved into their current shape from restrictions and capabilities of combustion & jet engines.


Curious about whether you're looking at silicon carbide as a replacement for IGBTs for your inverters. Is the technology practical yet? (I'm a big fan of IGBTs but there's always room for improvement.)


Whoops. Just noticed you mentioned SiC on your website. Guess the answer is yes. Great minds.


Yep! SiC was part of the design DNA from the beginning.


How do you compare with Magnax?

Also: We're developing high energy density battery packs (cells of 400wh/kg+, packs at 300-350wh/kg), might be interesting to team up. Hit me up on LinkedIn: Bernd Rietberg.


In general, Magnax seems to be focusing on automotive, which changes the driving factors in the design significantly (partial load efficiency becomes very important, cost is #1, etc).

In the aircraft world, Magnix has been doing some really awesome work. Their motors + inverters are about 4 kW/kg continuous. Our multiple areas of technology development should put us >12 kW/kg, which would be a 3x improvement. We are excited to build and iterate on a rapid pace to get there as soon as possible (hardware is, of course, hard :)


https://heartaerospace.com/, YC W19, is building a full electric plane if anyone else became interested.


Is anyone working on a hybrid system? I'd imagine having extra electric motors would help with taxi manoeuvrability, give extra boost from takeoff and could save fuel while cruising.


Yes there is a lot of development being done in the hybrid space as energy storage solutions aren't quite good enough for the longer range flights currently. One example is a VerdeGo Aero. Hybridization is also a good transition technology to all electric solutions as the electric infrastructure continues to grow.


Use this instead of gearbox: https://www.exro.com/technology/coil-driver


It's a common misconception that different ways of connecting and/or driving coils can emulate a CVT, multi-speed gearbox or single speed gear reduction. The maximum continuous torque of a motor is purely a function of the maximum continuous airgap shear stress, which itself is a function of flux density and current density. Doesn't matter how you connect or drive the stator coils, you are always limited by the current density in the windings.


this is super interesting! are you planning on working with an experimental manufacturer? would love to see this running on an Sling TSi or RV-10 similar GA airplane.


Which DMLS platform are you using to print these components?


For a typical aircraft, say like a Cessna, does the weight of an engine and auxiliaries be equal in weight to batteries, fuel, generator and motors?


@jjsylvestre - what are your thoughts on ZeroAvia?


Love what they are doing. I would consider them one of the leaders in the pack right now. Val has a practical vision to get to market on a timeline that is very compelling. Hydrogen FC is very promising for long-range flight applications due to its high energy density so I think they are focusing on the right things.


Small electric aircraft are already available. They're mostly used as trainers.[1] Range is poor, but they're great for practicing takeoffs and landings. The motor isn't the problem. As usual, the battery is.

[1] https://electrek.co/2018/04/27/all-electric-trainer-plane-ai...


If you don't mind sharing - what is the airgap diameter (presuming it's a radial flux motor)?


For our technology demonstrator, we have a pretty small rotor. Future direct drive designs (typically higher power as well) will have much larger diameters.

I can't be too specific, but you can probably get an idea of the rotor size from the preliminary datasheet (and/or CAD model) that you can download from our website. We have dimensions of the outside of the unit. Remember that the inverter is in there as well!


exciting work! i'm curious has to how you think about hte tradeoff between power and efficiency? I guess you need to design for very high specific power for peak power requirements (takeoff / landing manoeuvres) but can still achieve good efficiency in a cruise


Do you think a supersonic, VTOL electric aircraft is theoretically feasible?


a LOT of energy is required to fly supersonic- IMO the energy storage side (battery and/or hydrogen fuel cell) has a long way to go to make supersonic flight remotely feasible.


Paging Elon..


Theoretically, yes I think so. There are some key enabling technologies (energy storage and electric propulsion) that need to be developed further before something like that could be built.


Electric passenger aircraft are not and will never be viable, but I would sure like to see super lightweight electric sustainer motors for gliders. Paired with regenerative braking and/or solar cells on the wings you could probably keep a glider in the air indefinitely.


Ampaire (among others) is already making great strides in general aviation. With significant improvements in specific energy (see QuantumScape, HyPoint) and specific power improvements (what we are working on) coming in the next few years, shorter flight routes that were previously not profitable will become profitable (300-500 mile range, > 10s of passengers)- and that’s only the first step. Maintenance cost reduction and of course fuel cost reduction create a very good business case.


To clarify my stance, building an electric version of a dash 8 (for example) is totally possible, but range would be limited and I doubt it would be cost competitive with high speed rail. There may be a niche for planes like that servicing rural airports and chartered flights for the wealthy, but you're never going to fly transatlantic routes.


> Electric passenger aircraft are not and will never be viable

Why not? "Never" is a very significant word, but if you have sound reasons for using the word here, I'm genuinely interested in your thoughts on the matter.


Maybe not never ever, but not within our lifetimes. Not without some massive unforeseen breakthrough in battery technology or life extension. Electrifying a large long-haul commercial passenger aircraft like a 737 would require batteries with a specific energy at least two orders of magnitude better than current state of the art. For reference, actual batteries have improved less than one order of magnitude in the past century.

Really the closest thing that seems plausible would be a hybrid design using small batteries to provide peak power for takeoff and fuel cells to provide the bulk of the energy. But I'm not confident that would actually be significantly better than manufacturing synthetic fuels with renewable energy and burning them in traditional jet engines.


Is there an analog for regenerative braking in the flying EV world?


Interesting question! On helicopters, you can use autorotation to land safely even when your engine broke.

On planes, I'm not so sure. I suspect most of the braking forces while flying come from the drag of the normal plane body, so you can't really capture them.


Not OP but... maybe in a situation where one would normally deploy spoilers?

Larger aircraft require a way to bleed off energy from landing (assuming additional drag from flaps won't be sufficient), depending on their approach. Smaller aircraft usually does not have speedbrakes and can make do with power changes and flaps.

Propellers are giant speedbrakes if not feathered. Maybe in a "speedbrake" situation they could be allowed to "windmill" and do some regen? Not sure how important this is as one would be normally landing very soon. Other situations that do not involve descent, just reduce power.


I have a dumb question.

How much noise will these make?


A trick question. How heavy is your gearbox, and not a motor?

Getting ridiculous power to weight ratios on electric power is not that hard if you opt for super high RPMs.

By my standards, what matters in electric motors are their torque per weight.


It’s integrated in the motor as specified in the post


What are gearbox servicing requirements?


Initial gearbox design life is ~40k hours. Bearing life is expected to be upwards of 10k hours. Additionally bearings are designed to be easily replaced. Oil change interval is to be determined during endurance testing.




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