You guys need to be a little more serious about this
. The reason for the shape is not for flight dynamics but because the craft is really a time machine. The saucer shape is due to the massively powerful circular magnets (Fantasic radically ingeneous downright great enormous magnets or F.R.I.D.G.E magnets for short ) that allow the craft to enter the forth (sic) dimension and travel back in time. They are not aliens but rather humans from the future who have come back to try and prevent the development of the atomic bomb. Problem is they missed by a few km and a couple of years (bad maps and the print had faded from the old newspaper clippings). Why come back? Simple, in the future (about 3010) there was a massive nuclear war which turned the human race into 4 foot midgets with a big head and googley eyes (also their hair fell out and they turned green and lost all their teeth). They did not crash either you see the secret lab that developed the time travel technology was actually situated on top of a mountain created by the large nuclear bombs from the war. As the craft went back in time, the mountain dissapeared and they simply fell down killing all on board. The US govt is covering up the evidence as they do not want to get sued or lose their WMD by which they control the world so they are holding it for ransom. You can read all about this in the book of markology
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Mark