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Science

The Electric Airplane Is Coming 187

Posted by Unknown Lamer
from the but-what-about-flying-electric-cars dept.
An anonymous reader writes "The electric car is so yesterday; electric airplanes are coming. A battery electric-powered ultralight aircraft has been flying for the last year. A series-hybrid motor glider and a concept for an all-electric, 50-seat passenger plane were introduced at the Paris Air Show."
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The Electric Airplane Is Coming

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  • by JustinOpinion (1246824) on Tuesday July 26, 2011 @03:32PM (#36888020)
    What you're describing will not work. You're trying to violate the laws of physics, similar to proposals of perpetual motion machines. It's a neat thought experiment, in order to identify the problems, but it won't work in the real world.

    From basic Newtonian mechanics, we know that for every force there will be an equal and opposite reactive force. A closed system will not be able to achieve motion without an external force: either a force applied to other objects (e.g. pushing against the ground, or pushing against (a.k.a. 'blowing') a fluid like air or water) or by ejecting matter (as in a rocket).

    Specifically regarding your design: As I understand it, you basically want an object where internally forces are applied to inclined planes, in order to push the planes 'upwards'. You imagine that this can be done in a way where there is no corresponding opposing force also pushing the object downwards. You try to get around this problem by imagining a decoupling where internal masses are momentarily not touching the main mass: so you have one piece that fires a 'bullet' horizontally, which hits the inclined plane (pushing it upwards). You imply that this means there is no corresponding opposing force. However you mention offhand that you will recover the 'bullets' and reuse them. But if the bullet hits the inclined plane, and pushes it upwards, then the bullet will be correspondingly deflected downwards. When the bullet hits the recovery mechanism, it will impart to it a downward force equal and opposite to the upward force that the inclined plane felt. The two forces will cancel out: the plane is pushed up, the recover mechanism is pushed down.

    You can imagine putting the recovery mechanism further away from the inclined plane. But, at best this just creates a time lag between when the inclined plane is pushed upwards, and the bullet-recovery mechanism is pushed downwards. So the vehicle will jolt up-down but on average will stay in the same place and thus will not hover against the constant force of gravity. This is inescapable since the planes and the recovery mechanism are mechanically coupled to one another. The only way to solve this is to remove the recovery mechanism, and let the bullets shoot out the bottom of the object, so that the planes are pushed upwards and the opposing force is carried away by the bullets, out of the object. Of course 'flying' by shooting a gun downwards is generally inefficient, which is why we've invented things like helicopters, which push air downwards instead. That way you don't have to carry around a bunch of bullets; you just use the mass and hydrodynamic properties of the fluid you're flying through.

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