Launch HN: H3X (YC W21) – High power density electric aircraft motors

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.

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 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.

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).

> As a rule, whenever one feels tempted to say "just do ", 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.