Use this instead of gearbox:
https://www.exro.com/technology/coil-driver
Launch HN: H3X (YC W21) – High power density electric aircraft motors
111–120 of 169 posts
Re: Launch HN: H3X (YC W21) – High power density electric aircraft motors
#112Electric 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 reducti…
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.
Re: Launch HN: H3X (YC W21) – High power density electric aircraft motors
#113Use 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.
Re: Launch HN: H3X (YC W21) – High power density electric aircraft motors
#114Earlier quoted context omitted.
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).
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 :)
Re: Launch HN: H3X (YC W21) – High power density electric aircraft motors
#115For 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?
Re: Launch HN: H3X (YC W21) – High power density electric aircraft motors
#116Electric 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.
> 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.
Re: Launch HN: H3X (YC W21) – High power density electric aircraft motors
#117Given 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…
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…
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.
Re: Launch HN: H3X (YC W21) – High power density electric aircraft motors
#118Small 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...
Re: Launch HN: H3X (YC W21) – High power density electric aircraft motors
#119Earlier quoted context omitted.
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 l…
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.*
Re: Launch HN: H3X (YC W21) – High power density electric aircraft motors
#120Curious 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.)