Many different kinds of planes have been designed and scrapped as we learn more and more about flying. These are some of the weirdest designs to ever actually make it to the prototype stage and take flight.
Alexander Lippisch’s Aerodyne

An experimental craft from 1968. It looks like he just said to himself, "You know what? Let's just take the engines… and get rid of the plane! BAM!"
Blohm & Voss BV 141

A WWII German tactical recon aircraft, this plane was extremely unconventional for separating the engine and propellor from the cockpit. It looks all wrong!
Dornier Do 31

West Germany created this needle-nosed craft in 1967 as an experimental VTOL (Vertical TakeOff & Landing) plane.
X-29

Apparently wings don't HAVE to point backwards. This was a NASA technology demonstration craft used mostly in the late 1980's.
Avro Canada VZ-9 Avrocar

UFO! A secret craft back in 1959, this VTOL craft is the shape that most people think of when they think of a UFO, or a 'flying saucer'.
Hyper III

A NASA experiment from 1969, this craft is a lifting body craft. This means that the whole plane is designed to generate lift to fly rather than just a set of wings.
Northrop XB-35

An early flying wing bomber from after WWII, it looks like the designers of this craft just said: "We need more propellors!"
De Lackner HZ-1 Aerocycle Flying Platform

Designed in 1954 for taking one soldier on recon missions, this craft looks odd now when compared to modern drones.
Caproni Ca.60 Noviplano

"WE NEED MORE WINGS!" was the battle cry of engineers in the early 1900's as they tried to get things like boats to fly. Can you imagine, this prototype was intented to be for trans-atlantic flights? This design actually only flew once before crashing, getting towed to shore, and then burning to the ground the same day. Perhaps that was for the best.
Douglas XB-42 Mixmaster

A bomber from 1944, this is probably one of the most normal looking craft of the bunch. It was designed to go FAST (for the time) and had the propellor at the very back, much like where modern jet craft have their exhaust.
Libellula

A British experimental aircraft from 1945 that was designed to give the pilot the best view possible for landing on aircraft carriers. It uses a tandem wing design that puts the larger wings in the back unlike most modern craft.
Vought V-173

Basically a giant flying pancake, and endearingly referred to as such, this thing was built by the US Navy in 1942 as an experimental fighter.
The Airbus A300-600ST

The ST stands for "Super Transporter". It is now referred to as "Beluga" since it is so gigantic and rotund like a whale. It really can carry just about anything.
HL-10

Another 'lifting body' aircraft designed by NASA in the late '60s. It has a needle fora nose and a weird body shape that almost looks like wings, but isn't quite.
North American XF-82

They took two Mustang planes and stuck them together by one wing. The result was this new fighter with increased range.
Beriev Be-200 Seaplane

A Russian plane made in 1988. Why not land on water?
Stipa Caproni

An experimental Italian craft from 1932. It's like a jet for a fuselage, except if you were to take out the jet and just put in one propellor. Still flies!
The Caspian Sea Monster

Developed at the design bureau of Rostislav Alexeyev in 1966, this crazy plane looks frightening with the numerous engines strapped to the front, the Y shaped tail wings, and the fact that it lands on water.
Bartini Beriev VVA-14

This plane just looks plain beefy, like you would want it on your side in a bar fight. It is a Soviet vertical take-off amphibious aircraft – yikes.
McDonnell XF-85 Goblin

A tiny, prototype jet fighter designed in 1948. This little guy was actually supposed to be launched from the bomb bay of much larger bombing aircraft.
Ames-Dryden (AD)-1 Oblique Wing

A research craft from around 1980 intended to figure out if you could have a pivoting wing. I guess you can!
B377PG

NASA's "super guppy", another huge aircraft that can carry pretty much anything – especially spaceship parts.
Snecma Flying Coleoptere (C-450)

This french experimental craft from 1958 takes off and lands vertically like a helicopter, but can also supposedly rotate to fly sideways like a regular plane.
Lockheed XFV

Designed in 1953, this fighter craft could actually sit on it's tail and take of vertically.
X-36 Tailless Fighter

A prototype built for NASA in 1996, this jet plane was just a flat thing that could go fast.
Douglas X-3 Stiletto

Aptly named for it's shape, this craft was built in 1953 to try to study what an aircraft needed to be able to maintain supersonic speeds.
Martin XB-51

This "tri-jet" aircraft was made in 1949 as an experimental fighter. Two jets were up in front by the pilot, with the third at the center rear where most jets usually sit now.
Proteus

This piecemeal, tandem wing aircraft was built by Scaled Composites in 1998.