The age of electric flight is finally upon us • Hacker News Board

Re: The age of electric flight is finally upon us

#121

Post by newsoul2019 » Fri, Jun 21, 2019, 5:58 PM UTC

stcredzero wrote: post #109

namirez wrote: post #106

As others have noted, electric flights require a major breakthrough in the battery technology. Here are energy density numbers for gasoline, jet fuel, and lithium-ion batteries: Gas and jet fuel specific energy density ~= 45 MJ/kg; Lithium-ion specific energy density Even worse, a jet engine is much better at generating power. A modern high-bypass turbofan engine can generate 10 kW/kg whereas an electric motor is aro…

Electric motors can enable something which jet fuel and gasoline cannot: beamed power. There could be a new class of vehicles which only have a small onboard power store for emergency purposes. The weight savings would be about 20%.

That is a fascinating idea, a plane being "handed off" from one beaming tower to the next, like a cell phone

Re: The age of electric flight is finally upon us

#122

Post by murkt » Fri, Jun 21, 2019, 6:01 PM UTC

gambiting wrote: post #42

isostatic wrote: post #35

Earlier quoted context omitted.

A320 family range varies from 5500km to 8700km, so "a fifth of it's range" is around 1500km, which is 80% of the industry emissions. I'm not sure of that quote either -- a lithium ion battery is currently about 1MJ/kg and 1MJ/litre. Jet fuel is 43MJ/kg and 35MJ per litre (values from from wikipedia) So a battery that's 30 times more energy dense will be in the region of jet fuel, and thus would presumably be able to…

Don't forget that the fact that the fuel is burnt up as you travel is a big factor in the range of an aircraft. The weight of batteries does not go down during the flight.

How much does this affect an aircraft range? I assume the mechanism is that lighter aircraft needs less lift, and less lift means less drag, less drag - less power on the engines - less fuel consumption - more range.

I somehow always thought that more weight of an aircraft lessened its range almost only because it needs much more power to take off and gain a cruising altitude.

Re: The age of electric flight is finally upon us

#123

Post by dmytroi » Fri, Jun 21, 2019, 6:08 PM UTC

marvin wrote: post #20

I fly gliders. Absolutely can't wait until my local club finally decides to get an electric single-seat self-launching glider, preferably with enough endurance to do some additional tens of kilometers after the launch, in order to avoid landing out if the weather dies out. It's a gamechanger with regards to both costs and convenience. No towplane, towplane pilot, no outlandings.

I also started to fly gliders, and it would be lovely indeed to have electric self-launching glider, though unfortunately atm there are just too few of them, most popular are Arcus E and ASG 32 El, both are too new (cost a lot of money) and too rare. I wouldn't mind if our club get one, but it might be more economical to get a few other high performance gliders instead (like get two ASW 27 instead of one ASG 32 El) as it much easier to deal with them in a club context (doing 5+ launches per day, maintenance, etc).

Most likely a first viable step would be to get electrical tow plane first.

Re: The age of electric flight is finally upon us

#124

Post by tristanb » Fri, Jun 21, 2019, 6:08 PM UTC

https://twitter.com/BenBrelje_says/status/106484220091004108...

https://twitter.com/BenBrelje_says/status/106485722028904038...

https://twitter.com/BenBrelje_says/status/106491195862390374...

To recap, based on financial statements the company:

used to be a "waste management" company that failed and was sold as a "public shell" to enable the formerly private company to go public and sell shares (the waste management business it was engaged in was an effort to commercialize a process to treat low-level nuclear waste developed by Russian scientists)

has $64 mil in debt apparently unrelated to aviation

has spent $3.8 mil on R&D for this project

has 8 R&D employees

only 2 of those 8 have any evident experience related to designing aircraft (pretty apparent from the "design").

Re: The age of electric flight is finally upon us

#125

Post by namirez » Fri, Jun 21, 2019, 6:10 PM UTC

murkt wrote: post #117

namirez wrote: post #106

As others have noted, electric flights require a major breakthrough in the battery technology. Here are energy density numbers for gasoline, jet fuel, and lithium-ion batteries: Gas and jet fuel specific energy density ~= 45 MJ/kg; Lithium-ion specific energy density Even worse, a jet engine is much better at generating power. A modern high-bypass turbofan engine can generate 10 kW/kg whereas an electric motor is aro…

1 kW/kg for electric motors looks a bit on the low side for me. Tesla Model S with the highest power rating has 581 kW, and I don't think that its motors weigh in for more than half a ton combined. I've found a statement that some version of their motors with 270 kW weigh 31 kg (70 pounds). Which amounts to 8.7 kW/kg and isn't far off from your 10 kW/kg estimate for modern turbofan engines. Also it's probably not the…

I stand corrected. I also found Emrax 268 which has a power to weight ratio of 10 kW/kg. But these are good only for small aircraft. It's much harder to maintain this power-to-weight ratio for larger motors. Emrax 268 is only 20kg, but a single engine of 777 weighs 8200kg. The ballpark for large motors at powerplants is currenly around 1 kW/kg [1]. But who knows; there might be a breakthrough in motors too.

[1] https://newatlas.com/siemens-world-record-electric-motor-air...

Re: The age of electric flight is finally upon us

#126

Post by roghummal » Fri, Jun 21, 2019, 6:15 PM UTC

base698 wrote: post #72

whamlastxmas wrote: post #57

Earlier quoted context omitted.

Stalling is a term also used with engines, and it's pretty clear he's talking about engines not working at altitude so "stall" is probably the correct term

Only with layman and in the media when incorrectly describing an aerodynamic stall and conflating two.

https://en.wikipedia.org/wiki/Stall_(engine)

Re: The age of electric flight is finally upon us

#127

Post by alex_young » Fri, Jun 21, 2019, 6:16 PM UTC

semi-extrinsic wrote: post #44

alex_young wrote: post #6

Earlier quoted context omitted.

The main source (95%) of hydrogen fuel in the US is a by-product of Natural Gas extraction ( https://www.energy.gov/eere/fuelcells/hydrogen-production-na... ). What problem are we solving by moving to hydrogen?

When you do steam methane reforming to produce hydrogen, separating out the CO2 is a necessary step in the process. Then it's just a matter of storing it underground, rather than just emitting it.

Are there any commercial examples of carbon sequestration? We've heard that line for decades now, if it's real there should be plenty of production sites by this point.

Re: The age of electric flight is finally upon us

#128

Post by [deleted] » Fri, Jun 21, 2019, 6:17 PM UTC

vosper wrote: post #116

rbanffy wrote: post #110

Earlier quoted context omitted.

You could mount batteries on pods that could be released if needed. Additional benefit would be that the pods could be replaced on the ground by fully charged ones for faster turnaround.

You can't really rain burning battery pods down on the landscape, though. What if the plane is over a populated area?

[deleted]

Re: The age of electric flight is finally upon us

#129

Post by base698 » Fri, Jun 21, 2019, 6:18 PM UTC

roghummal wrote: post #126

base698 wrote: post #72

Earlier quoted context omitted.

Only with layman and in the media when incorrectly describing an aerodynamic stall and conflating two.

https://en.wikipedia.org/wiki/Stall_(engine)

That's about manual transmission automobiles. I've never heard it referenced in aviation other than non-pilots or people who know airplanes.

Re: The age of electric flight is finally upon us

#130

Post by semi-extrinsic » Fri, Jun 21, 2019, 6:19 PM UTC

Robotbeat wrote: post #102

semi-extrinsic wrote: post #41

Earlier quoted context omitted.

You can't really go above the Armstrong limit (~60k feet) in a passenger airplane without adding huge complexity in handling the event of cabin pressure loss. https://en.wikipedia.org/wiki/Armstrong_limit

Pressurized cabins are going to be essential for electric flight to have any kind of reasonable speed (and range). It shows that the most impressive electric aircraft specs are for the pressurized Eviation Alice (1000km, minus margin for contingency, and 250 knots cruise). If you stay low enough to not require pressurization, then you have to compromise the lift to drag in order to have a decent cruise speed or you h…

All passenger jets have pressurized cabins, but they are working at lower pressure differentials than what you need above 60k feet, and they sometimes fail, with oxygen masks being the fail-safe.

If you go above 60k, and the plane experiences a rapid loss of cabin pressure, you have 60 seconds to restore cabin pressure before the passengers start dying. So the failsafe system will have to be massive. That increase in weight and complexity isn't worth the efficiency gains.

You mention Concorde, and indeed it had a very substantial failsafe system even though it only touched the lower end of the limit. Concorde had really small windows, so even with two windows gone it took some time to equalize pressure. The pilots had positive pressure oxygen masks, and the plane had the ability to drop altitude immensely fast in an emergency.