131–140 of 272 posts
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What you are thinking of is not very different than an aerotow from an electric airplane.
I was just thinking about something autonomous. Basically a battery with wings. That way you don't need a plane with pilot.
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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?
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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.
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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.
So, to land at take-off weight, you’ll have to significantly strengthen the landing gear.
That already is 2.5 to 5% of the Maximum takeoff weight and 20% of the airframe direct maintenance cost (https://en.wikipedia.org/wiki/Landing_gear#Aircraft_landing_...)
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…
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From the article: > Even assuming huge advances in battery technology, with batteries that are 30 times more efficient and "energy-dense" than they are today, it would only be possible to fly an A320 airliner for a fifth of its range with just half of its payload, says Airbus's chief technology officer Grazia Vittadini. > "Unless there is some radical, yet-to-be invented paradigm shift in energy storage, we are going…
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…
Jet fuel is really about 12-15 MJ/kg when you take thermodynamic losses into account. So you;d need a battery 10 times as dense. Which likely isn't happening any time soon, but still.
I think with full electric aircraft it's not a case of 'won't work' but how big of a niche they can carve out. Probably the sector they'd compete in are general aviation and puddle jumpers.
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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…
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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…
Edit: I think I met the guy behind these. But I'm not sure, for lack of having asked for the name of the company. I certainly have seen a prototype that could have been the 348.
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The 80% figure are flights longer than 1500 km. 1500 and less are the 20%. So even if all those flights were switched to magic zero emission electricity, the aggregate improvement over the whole industry would barely beat the relative improvement between a 737 NG and a MAX. (yes, this is an apples to orchards comparison)
To be fair, the MAX has been zero emission for a couple months now.