Launch HN: H3X (YC W21) – High power density electric aircraft motors
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:
168 comments
[ 3.2 ms ] story [ 232 ms ] threadMy 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.
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.
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.
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... )
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
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...
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.
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.
Do you envision some airframes to include assisted take-off technology? (JATO and the like, even catapults)
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.
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.
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.
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.
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).
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.
A tow cable does not have live electrical conductors in it.
I wonder if this tech might be better suited to self-launching motorgliders than GA.
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.
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.
We could do the same thing with cars and equip them with a super aerodynamic body and a 7kw engine, it could do 80kph.
Take off assists are for ultradshort runways.
So it's good to start out with a really high specific power because you can often trade that back for efficiency.
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.
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.
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.
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.
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.
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.
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.
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).
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).
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
What are these challenges? How does having a near vacuum cause trouble with ~1kV potentials?
I can't go into much detail, but we are working on addressing this in a couple different ways in our insulation system design.
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.*
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.
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.
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)
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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.
Wish you guys a bunch of success...exciting times.
On a more serious note, what other applications do you intend for these?
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.
Marine is a big one though.. especially in Scandinavia. Lots of interest in electrifying boats and ships there.
I'm also assuming that a scaled down version would be ideal for personal watercraft?
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/
(Yes I'm kidding. I know. I'll stop trying to trick thermodynamics.)
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?
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.
- 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
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.
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.
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.
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.
Why design first (solution looking for problem)?
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.
They have a nice animation showing the lifter and the cruiser vehicles.
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).
Current aircrafts have evolved into their current shape from restrictions and capabilities of combustion & jet engines.
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.
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!
That's why people were so upset when carbon nanotube yarns happened to be poor conductors.
People were thinking of super light motor windings.
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.
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.
But more importantly thank you for Your contribution to reducing air pollution by electrifying airplanes!
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.)
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!
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.
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.
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.
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.
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.