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Apparently, use of electric motors allows you to design aircraft with contra-rotating propellers- as is demonstrated in these electric racing aircraft designs: I had no idea this was possible, and this massively changes the game in terms of electric vs. internal combustion aircraft. For one, with contra-rotating electric propellers it's easily possible to pack twice as much Thrust into a given airframe as with an ICE design, allowing for higher speeds (in racing designs) ot larger wings and more space/weight for batteries (in actual utilitarian planes). It's also possible to achieve a much higher ratio of propeller-area to Thrust with the same Thrust- allowing for better performance at higher altitudes (electric engines also operate better than ICE ones at higher altitudes, due to not requiring Oxygen..) I could easily imagine an Electric passenger aircraft being designed someday with 5 sets of contra-rating propellers (1 on the nose and 2 on each wing), each with 3-4 blades rotating in each direction with a rather large propeller diameter, being used to support very high-altitude flight with electric aircraft for the inherent advantages this provides (lower drag for a given speed, less turbulence, more glide time/distance in case of engine-failure). At high altitudes electric propellers eventually reach their maximum torque and rotation-speed, and start to consume less and less electrical power as the Thrust produced and air resistance to rotation starts to fall off with even greater gains in altitude. So, if you climbed high enough you could eventually reach the point where 10 contra-rotating propellers (5 sets of 2) with large diameter blades spans and 3-4 blades on each propeller only draws as much electrical power, and produces as much Thrust, as a single propeller at sea level. However at this altitude, Drag would be greatly reduced- meaning you could (and would need to in order to generate adequate Lift to maintain altitude) fly substantially faster than that amount of Thrust would allow you to fly at sea-level. Even accounting for decreasing Lift/Drag at higher speeds, you could still cover far more miles of distance per kilowatt-hour of electrical power consumed with a design optimized for high-altitude flight and cruising at high altitude... This would lead to substantially extended max range compared to electric planes with lower cruising-altitudes, and might (just barely) allow for practical electric Transatlantic flights on a large plane (larger planes encounter less parasitic drag relative to their volume, and have less mass dedicated to cockpit computers, landing gear, and pilots compared to their payload) with a substantial portion of volume (maybe 50% of the plane's internal space) dedicated to batteries, for instance... Other videos worth watching on the topics of electric aircraft and high-altitude flight: (Above: a general overview of efforts at small electric aircraft...) (Above: a video on the development of "Alice", a proposed 800 km range passenger aircraft by Eviation...) (Above: Airbus and Rolls Royce' efforts at developing Distributed Electric Propulsion for large passenger jetliners- with company estimates putting a rollout date of about 2030-2050, target of 2042)

http://stgist.com/2015/11/asteroid-mining-and-space-refueling-stations-may-become-a-reality-by-2025-5886