Can You Fly By Firing Guns At The Ground?

It might be the preserve of fantastical action movies, but we've probably all wondered at some point or other if it's actually possible to fly through the air by firing bullets down at the ground.

Fortunately, you must wonder no longer, as Randall Munroe of XKCD has done the science for you. As he explains:

The principle here is pretty simple. If you fire a bullet forward, the recoil pushes you back. So if you fire downward, the recoil should push you up.

But can it be done? The short answer is yes. The longer answer is of course a little more involved, but amazingly interesting, combining guns with rocket science. For instance:

[O]ur optimal craft comprises a large number of AK-47s (a minimum of 25 but ideally at least 300) carrying 250 rounds of ammunition each. The largest versions of this craft could accelerate upward to vertical speeds approaching 100 meters per second, climbing over half a kilometer into the air.

And there is plenty, plenty more like that. Go read it. Now. [What If?]

WATCH MORE: Science & Health News


    Just don't get caught in the exhaust plume of such a craft...

    This system is already in use. Israel use it to fly over Gaza.

    Lead reaction mass, no way the throttle the engine except by varying the rate of fire, very expensive to run, lots of poisoned wild life. With ideas like this it is no wonder that the human race is in so much trouble!

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