Do you love aircraft and flying, but feel that planar wings are revolting affronts to decency? Also, do you detest helicopters and other rotorcraft? If so, boy are you in luck, pal. Meet the Coléoptère.
The Coléoptère (which means "beetle" in French — man that word comes up a lot in my life) was an experimental VTOL aircraft developed by the French company SNECMA, which sounds absolutely disgusting if you say it out loud. The plane is like the front clip of a conventional fighter jet mated to the center of a giant turbojet engine. It looks sort of like someone stuck a fighter jet cockpit onto a colossal beer keg.
What's going on here is that the huge cylinder that surrounds the engine is an annular wing, or a ring wing, if you want to get all aero-slangy and look cool at pilot's bars. The plane was a tail-sitter, being able launch and land from a vertical position, and even capable of hovering vertically at a fixed point.
Annular/ring wings have been experimented with for years, and are known to eliminate the issue of wingtip vortices, which cause drag, because there are no wingtips at all.
Sadly, it was a failure. Not in the "looking bonkers" categories, where it was off the charts, but in the much more fussy "flying reliably" metrics. As Air and Space magazine said of the airplane,
Without the benefit of a large delta wing to dampen any rolling tendency during hover, the Coléoptère had the tendency to slowly spin about its vertical axis. Instrumentation also was spotty. On one flight, Morel called the vertical speed indicator "a fantasy" and complained of "an unacceptable imprecision in steering" during landing. Still, free flights often reached altitudes of several hundred feet.
It took many attempts to achieve horizontal flight, and even better, the pilot was pretty blind when it came to landing the craft vertically on its tail. The hard part was knowing where the ground actually was. Air and Space talked to the test pilot about this issue:
... the only way he could accurately gauge height was by listening for a change in pitch in the engine's hum. The test team whipped up a fix in which a contact light was tripped when a string on a pebble, dangling from the side of the engine, went slack as the aircraft approached the ground.
So, the fix to indicate ground proximity for this highly advanced, experimental plane was literally a rock tied to a string.
Based on that alone, I wouldn't consider this plane a failure.