UFO types as depicted by artist

[F2d5thCav]

Why do they mostly look like saucers?  Is that the most efficient shape.

Ya think about the leaps in scientific knowledge required to travel efficiently at their reported speeds and conduct the maneuvers they're credited with.  A saucer?

If the reports describing their behavior are accurate, I'm not sure I would call their motion 'flying'.  Thus the 'impossible' turns and what looks to the observers as acceleration.

BTW, the original ones reported in 1947 by Kenneth Arnold were more like shapes L2 and L4.

Cheers