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Li ion batteries still have a LONG way to go in energy density compared to Jet A kerosene. Jet A, about 43 MJ/kg. Lithium ion, <1 MJ/kg.
I would be curious whether electric planes significantly reduce the carbon footprint of flying. My intuition is that you wouldn't be dumping CO2 and H2O (both fairly potent greenhouse gases) directly into the upper atmosphere, so it would be a huge win, but I am neither a climate scientist nor an aerospace engineer, so maybe I'm missing something.
https://en.wikipedia.org/wiki/Contrail#Contrails_and_climate
Li ion batteries still have a LONG way to go in energy density compared to Jet A kerosene. Jet A, about 43 MJ/kg. Lithium ion, <1 MJ/kg.
Aluminum-air batteries [1] are well studied in the past decade and there is lots more research going on there. Currently the state of the art for such a battery is about 4.7 MJ/kg and the theoretical maximum is as high as 28.8 MJ/kg, at which point the mass of the turbopumps and other fuel handling parts might make up the difference.
Of course there are issues, primarily the fact that they're not rechargeable and have to be chemically recycled. It's currently too expensive to do that now, but once we can do it economically, each airport will just have to have a stock of batteries and a robot to swap them on the jet and we'll have electric flight.
Li ion batteries still have a LONG way to go in energy density compared to Jet A kerosene. Jet A, about 43 MJ/kg. Lithium ion, <1 MJ/kg.
How about solar-powered planes? I would assume not having to carry an energy source (except for emergency use) is a huge efficiency win. And it's always sunny in the stratosphere (well, not at night).
The bigger you make the jet, the more of its surface you have to cover with solar panels. However, while the mass grows geometrically with the size because of volume, the surface area of the panels only grows exponentially (x^3 vs x^2). Just like with single celled organisms: at some point the surface area can no longer absorb enough energy to support the massive machinery.
There are tricks to increase surface area but the panels still have to face the sun so you're forced to make planes short vertically but very long horizontaly. I don't think existing airports would be able to support such a different design.
NASA has built a big model tiltrotor craft with 10 props to test this.[1] There's also the Latitude VTOL drone.[2] This simply has electric quadrotors for VTOL, plus a gas engine, wings, and prop for sustained flight. So it has the range of a winged drone, without the need for a runway.
[1] http://www.extremetech.com/extreme/188338-nasas-electric-ver... [2] https://latitudeengineering.com/products/hq/
Earlier quoted context omitted.
And where some of your footprint is fossil-based, industrial-scale scrubbers are a lot easier to install on the ground than loft into the air.
Or generate your fuel at each airport (algae), convert to biodiesel, and then dump into your tanks as usual. Batteries may rule on the ground now, but we're a long way off from liquid fuel getting tossed aside in the sky.
So basically, once we get technology that doesn't exist yet, we may get vehicles that take advantage of that technology.
Electric aircraft are a technology that does exist, already. Two different aircraft have been built and flown over the channel already. Electric airliners will require significant additional tech development, but the fact that planes have already crossed the channel multiple times is a pretty good start.
A related possibility is multi-rotor helicopters where the main power source is a jet engine, but the power distribution is electrical. One of the huge headaches of the Osprey is the mechanical linkage by which one engine can power both props. There are flexible shafts, U-joints gears, and a big clutch. This might provide a way to get to VTOL without insane mechanical complexity. NASA has built a big model tiltrotor…
Li ion batteries still have a LONG way to go in energy density compared to Jet A kerosene. Jet A, about 43 MJ/kg. Lithium ion, <1 MJ/kg.
See the hybrid car: the efficiency of a regular engine (VW Diesel not taken into account ;-) is relatively low. If an electrical engine can be twice as efficient, you only need half the energy...
A related possibility is multi-rotor helicopters where the main power source is a jet engine, but the power distribution is electrical. One of the huge headaches of the Osprey is the mechanical linkage by which one engine can power both props. There are flexible shafts, U-joints gears, and a big clutch. This might provide a way to get to VTOL without insane mechanical complexity. NASA has built a big model tiltrotor…