Bartini Beriev VVA-14 • The VVA-14 started off as a ground effect sea-skimming craft (like an ekranoplan), but with the addition of some detachable wings, it could lift off completely and spent over 100 hours in flight during testing. The Soviets developed it in the early 1970s as a way to tackle Polaris missile submarines. It was actually supposed to be able to lift itself vertically, too, but the required 12 extra engines were never installed, and the VVA-14 is currently rusting away in pieces outside a Russian museum. (Pics) (Video)

Northrop Tacit Blue • Northrop started messing with stealth technology in the late '70s and early '80s, and so the company created Tacit Blue (also affectionately known as "Whale") to demonstrate that it was possible to be stealthy and curvy at the same time. The design of the aircraft caused it to be inherently unstable in both pitch and yaw, so quadruply redundant fly-by-wire systems were used to keep it under control. Tacit Blue was finally unveiled to the public in 1996, after spending eleven years hidden in a secret bunker somewhere. (Video)

Avro VZ9 Avrocar • Avro Canada's Avrocar was intended to be an actual VTOL flying saucer. The eventual concept was to develop a saucer-shaped fighter jet capable of zipping around at Mach 3.5, but the Avrocar prototype had issues getting much beyond a ground effect hover, continuing stability problems made liftoff a bad idea anyway, and it generated so much heat that it would melt its own instruments after just a few flights. The Avrocar program ended in 1961, but if nothing else, the Avrocar ended up being one of the world's first hovercraft. (Video)

Goodyear Inflatoplane • The Inflatoplane was developed in only 12 weeks in 1956. Uninflated, the entire aircraft (engine and all) fit into a box just over three feet on a side, making it ideal for airdrops to troops stranded behind enemy lines. The plane inflated to 25 psi in about five minutes with a bicycle pump, and it could fly nearly 500 miles at a stretch. Problem was, as the military pointed out, the uses for an airplane that could be brought down by a well-aimed bow and arrow were somewhat limited. (Video)

Sikorsky X-Wing • Yes, NASA actually did build an X-Wing. It wasn't a helicopter, or an airplane, but it attempted to incorporate the best aspects of both. The X-shaped rotors could be used to take off vertically, and then they could be stopped mid-flight and turned into an additional set of wings to generate more lift. The program ended in 1988.

Mil V-12 • Only two prototypes were made of these giant Russian helicopters. They were intended to ferry ballistic missile components, and were capable of lifting nearly 90,000 pounds up to 7,000 feet, a record that still stands. By 1974, though, the missiles that the V-12 was designed to carry were being phased out, and the project was canceled. (Video)

NASA AD-1 • Variable geometry wings allow aircraft to maintain efficiency at both low and high speeds, but traditionally, this involves sweeping a pair of wings back and forth. NASA's AD-1 has just one wing that it could pivot during flight, from completely straight up to a forward and backward sweep of 60 degrees. While tests showed promising increases in efficiency, the little plane got nasty when its wings were swept to their maximum, so the design wasn't taken any further. It may come back in 2020 as a UAV. (Video)

Antonov A-40 • Ferrying heavy armor around a battlefield is always problematic, so it sure seems like a good idea to just kludge on some wings and a tail and turn tanks into gliders. The Soviets tried this in 1942, and the prototype demonstrated that the concept was unworkable, but only because they didn't have a powerful enough aircraft to tow the A-40 in the first place. The tank plane actually flew quite well during its one test flight, and the crewmen were able to drive it back to base at the end.

FanWing • It's still just a prototype, but the FanWing will become a small two-seater craft just as soon as the company can convince people that it's a good idea. The FanWing combines propulsion and lift surfaces into one unit, forcing air over its own wings using long fans, which also helps it take off in extremely short distances. It's very quiet, practically impossible to stall, and if the engine quits on you you can auto-rotate to a safe landing like a helicopter. (Video)

NASA LLRV • The Lunar Landing Research Vehicle was little more than a downward-facing jet engine with a seat bolted to it. It was used to simulate the handling characteristics of the lunar landers, and after takeoff, the engine was throttled back to support 5/6th of the weight of the craft to simulate lunar gravity. The balance of the thrust was provided by hydrogen peroxide rockets, allowing the astronauts to practice landing under simulated (but still pretty real) lunar conditions. (Video)

Aero Spacelines Pregnant Guppy • Actually called the Pregnant Guppy, this transport was the first in a series of ludicrously oversized aircraft that have resulted in the Airbus Beluga as well as Boeing's Dreamlifter. The Guppy was specifically designed to transport stages of the Saturn I rocket, and despite its appearance, it flew very well. Aero Spacelines was asked to build four bigger versions, which were called Super Guppies, and one of them is still used today by NASA to ferry space station components. (Video)

SNECMA C450 Coléoptère • The Coléoptère was basically just a gigantic turbojet engine with a cockpit stuck onto the front. It was designed to be a VTOL aircraft, with the turbojet cowling forming what's called an annular wing to generate lift in level flight. It hovered successfully in 1959, but crashed while trying to get the vertical to horizontal transition figured out.

921-V Flettner Plane • The Magnus Effect is a phenomenon where a spinning object in a fluid generates thrust; it's what causes a baseball spinning in air to curve. You can apply the same principle to a spinning cylinder attached to an airplane, and the 921-V used a bunch of these cylinders instead of wings to reportedly get airborne (and then crash) in 1926. This propulsion method is currently being applied to boats since it also works kinda like a wind sail, and can result in fuel savings of up to 40%.

Lockheed Martin P-791 • This chubby fellow is a hybrid airship, meaning that it relies on lift from its blimp parts as well as lift that's generated from air moving over its curved hull like an airplane wing. It's very efficient, and can stay aloft at 20,000 feet for up to three weeks providing surveillance or transporting equipment. The P-791 first flew in 2006, and development is continuing. (Video)

White Knight Two • It was a tough call putting White Knight Two on this list instead of the original White Knight, but when it comes down to it, two fuselages plus four engines plus a detachable spacecraft (!) pretty much takes the cake. White Knight Two was designed as a carrier aircraft, hauling Virgin Galactic's Space Ship Two up to 60,000 feet for an air launch. One of the hulls is a practice hull for tourists headed to space, while the other is for passengers who get a high altitude view of the Earth. (Video)

McDonnel XF-85 Goblin • The XF-85 was designed to fit snugly into the bomb bay of a B-36. It was called a "parasite fighter," and as many as three of them would hitch a ride with a bomber, deploying in mid-air to defend their mother ship and then docking again when it was finished by latching onto a hook. This turned out to be much easier said than done, though, and the program was canceled in 1949. (Video)

Vought V-173 • The "flying pancake," as it was called, utilized a lifting body design, where the body of the aircraft itself served as a wing. The V-173 was very robust and straightforward to fly, and its testing program in 1942 and 1943 generated all kinds of panicked reports about flying saucers. It proved promising enough that the Navy asked for a prototype version of a fighter aircraft that could fly 550 mph or hover if necessary, but before that program could get much beyond taxi tests, it was canceled in favor of more modern jet fighters. (Video)

Scaled Composites Boomerang • The first stab at a plane like this was by the Germans in 1937, in the form of the BV-141 reconnaissance plane, which used an asymmetrical configuration to maximize the view of the pilot and the observer. Scaled Composites used the same idea to design a twin-engined airplane that would be easy to control in the event of a single engine failure. The prototype flew in 1996, and was able to fly faster and further than equivalent conventional twin-engined aircraft without sacrificing payload.

Caproni Ca.60 • The Caproni Ca.60 embodied the philosophy that if you add enough wings and engines, you can get pretty much anything to fly. Funny thing is, it worked. Sort of. During its first test flight in 1921, the Ca.60 achieved an altitude of 60 feet, which is frankly pretty impressive. It crashed shortly after achieving this feat, and then it burned up. Oh well. (Video)

UTIAS Ornithopter • This airplane flies like a bird. Literally, it flaps. A small jet adds some horizontal thrust, but the motorized flapping wings are actually doing most of the work. The University of Toronto's ornithopter aircraft made a successful 14 second flight in 2006 which ended in a minor crash, but it seems to be more of a proof of concept design and the aircraft isn't exactly practical. (Video)

Convair F2Y Sea Dart • The Sea Dart was a supersonic aircraft that could float. Its jet engines were mounted topside to keep them from ingesting spray, and as they throttled up, a pair of skis extended into the water to allow the craft to hydroplane up to takeoff speed. By the time the Sea Dart first flew in 1953, carriers were starting to become more appealing, and while the Sea Dart was briefly considered as a submarine deployable aircraft, all production was eventually canceled. (Video)

Convair XFY Pogo • The Convair Pogo was a VTOL aircraft intended to protect convoys at sea without requiring an aircraft carrier. The Pogos would live in little houses on the decks of convoy ships themselves, taking off vertically like helicopters when needed, transitioning to level flight to do their business, and then landing again vertically. The planes themselves were generally pretty good, but they were extremely difficult to land, and since jet fighter development was leaving the Pogo in the dust anyway, the program ended in 1955. (Video)

HZ-1 Aerocycle • As horribly dangerous looking aircraft go, the Aerocycle is definitely close to the top of this list. It was intended to be a cheap and easy to fly reconnaissance helicopter for the army, with most soldiers able to figure out how to fly it in about 20 minutes. You controlled it by shifting your weight around on the platform you stood on, sort of like a Wii Fit. After a pair of crashes in which the two sets of contra-rotating rotor blades collided with each other and exploded, the project was discontinued.

Caproni Stipa • This fat little airplane was essentially the first ducted fan aircraft in the world when it flew in 1932. The design offered plenty of benefits, including efficiency and stability, but the gigantic fuselage created so much additional drag that every performance gain was canceled out. Arguably, the modern turbofan engine that you see on jet airliners today is a descendant of this first design. (Video)

Rockwell XFV-12 • The XFV-12 was supposed to be a VTOL aircraft that could replace the Harrier jump jet. The rear engine exhaust nozzle closed up, and the exhaust was instead diverted downward through slats in the wings and front canards, creating lift. The XFV-12 was able to get off the ground and hover, but just barely, and the project was eventually canceled in 1981 when the power issues couldn't be resolved.

Custer CCW-5 • Aircraft get lift not from the speed of a wing through air, but the speed of air over a wing, the crucial difference being that if you can cause air to move over a wing surface fast enough, the aircraft doesn't need to be moving to take off. By using its engines to pull air over its special "channel" wings, the CCW-5 was actually able to lift off vertically, although the lack of control surfaces that were functional without airflow kept this from being a realistic way to get airborne. (Video)