(Originally appeared in Mental_floss magazine, vol.5, issue 3, cover dated May-June 2006; also available online at http://www.mentalfloss.com/blogs/archives/10324)

1. The Monowheel

In 1869, French craftsman Rousseau of Marseilles built the first in history’s line of unsuccessful monocycles. Sitting inside the monowheel, a rider steered the contraption by shifting his or her weight in the desired direction. As if that wasn’t difficult enough, the massive outer wheel remained directly in the rider’s line of sight at all times. Braking was also potentially hazardous, as stopping too abruptly would cause the rider to be propelled forward along with the outer wheel. But perhaps the biggest strike against the monowheel was the immediate comparison of any rider to a gerbil—something even the French wouldn’t tolerate.

2. The Daihatsu Trek

It’s a car! It’s a bed! It looks suspiciously like a child’s toy! For the outdoorsman who has everything except a really expensive Big Wheel, there was the Daihatsu Trek. A single-passenger off-road vehicle, the Trek not only allowed drivers to travel to remote areas, it also gave them a place to bed down for the evening. With its collapsible seat, steering wheel, and roll bar, the boxy monstrosity from 1990 offered all the comforts of a really cheap motel room. And while we can’t be sure why the car never made it past the concept stage at Daihatsu, we can only guess members of the off-road focus groups felt silly driving a Transformer.

3. The Avrocar

Much more after the jump.

A quasi hot potato of international engineering, the Avrocar was initially funded by the Canadian government, designed by a British engineer, and eventually assumed by the U.S. Defense Department as part of the Cold War weapons race. The UFO-like contraption was 18 feet in diameter, but only 3 feet thick. It featured vertical takeoff and landing and was designed to reach speeds up to 300 mph while remaining elusive to radar. Unfortunately, the two-person craft was never able to stabilize at heights above 8 feet, nor travel faster than 35 mph. After eight years and more than $10 million, the project was abandoned in 1960.

4. The Dymaxion

Buckminster Fuller was many things—inventor, philosopher, Nobel Peace Prize nominee, and bearer of a name that makes Frank Zappa’s kids feel average. Among his many architectural and engineering creations, Bucky tried his hand at automobiles. In 1933, using a V-8 engine loaned to him by Henry Ford, Fuller built the Dymaxion car. Truly a wonder to behold, the Dymaxion was nearly 20 feet long, got 30-plus miles to the gallon, held up to 12 people, had a maximum speed of 120 mph, and could do a U-turn in 20 feet, thanks to a single rear wheel that controlled the steering. Unfortunately, the car’s steering appears to be at fault for a fatal accident at the 1933 World’s Fair, when the Dymaxion was rubbernecked by another car. Although later evidence placed fault on the driver of the other car, negative publicity surrounding the wreck caused investors to pull away from the project, and Fuller was freed up to build geodesic domes and work on his friendship with John Denver. The fortunate outcome of the Dymaxion’s failure? Denver’s hit tune, “What One Man Can Do,” which was written for Fuller.

5. Da Vinci’s Clockwork Car

Leonardo da Vinci is renowned for his forward-thinking sketches and intricate designs, which included blueprints for a bicycle, a submarine, and a helicopter. But you can’t win ’em all. Da Vinci also designed a three-wheeled wagon-like device—often referred to as the clockwork car—that never really lived up to the hype. Its spring-operated design makes it the first-known concept for a self-propelled vehicle. And because it was designed without a driver’s seat (though a secondary steering column was present) and was meant to be programmed along a specific course, the clockwork car is also thought to be one of the world’s first robots. Some speculate that faulty interpretations of da Vinci’s notes prevented the success of his ideas, but there’s plenty of evidence to the contrary. When engineers finally constructed a working model of the car in the late 1990s, it only traveled 40 feet.

6. The KAZ

Originally designed in 2001 to push the limits of electric automotive technology, the KAZ (Keio Advanced Zero-emission) vehicle is part science-fiction, part sports car, part limousine, and entirely unattractive. But the beauty of the KAZ lies in its eight wheels, each powered by its own battery, which allow the luxury concept car to reach speeds in excess of 190 mph without emitting any pollution. The car’s design also makes for a safe ride because what would normally be the engine compartment is a crushable zone, reducing risk to the driver. Sadly, the KAZ came off as less luxury automobile and more cartoon, sending the designers back to their drawing boards.

7. The Bell Rocket Belt

Everyone who grew up watching “The Jetsons” and playing with the Steve Austin action figure dreamed of a day when people travelled to and from work via jet pack. The tease: a rocket belt developed under military contract by Bell Aerosystems in 1959. The hydrogen peroxide-powered Small Rocket Lift Device (SRLD), also known as the Bell Rocket Belt, was flown successfully throughout the 1960s. Unfortunately, the contract was later dropped, due largely to its limited flight duration (it held only 21.5 seconds worth of fuel). Although the belts are still used occasionally for entertainment (the opening of the 1984 Olympics and, most memorably, in the film “Thunderball”), our adolescent dreams of rocket-powered backpack flight will be confined to the silver screen and the funny pages for a while longer.

8. The Amfibidiver

If you’ve been looking to practice your spy skills, this is your toy. The Amfibidiver is a car that’s also a boat that’s also a submarine. All you have to do is find a way to fit your tuxedo underneath your scuba suit. Of designing the 007-mobile, Belgian inventor René Baldewijns says it was easy. “Just take one dream, the fuel tank of an airplane, two bicycles, the motors from five electric wheelchairs, the hull of a sailing boat, seven drink containers (a real justification for that empty bottle collection), several kilos of resin, a few garden seats, and several miles of electrical cables.” Voilà! You’ve got an Amfibidiver! Baldewijns built a prototype for the machine, but his health problems caused the project to be shelved before it found commercial realization.

9. The Superbus

In 1988, Czech-born architect Jan Kaplicky attempted a feat that flew in the face of all odds: bringing change to Britain. The Superbus was a sleek, aluminum-bodied craft that charged itself at bus terminals and had the ability to lower its frame at stops to make it easier for passengers to enter and exit. The design was rejected in favor of the traditional red, double-decker Routemaster buses long associated with London’s public transportation system. Was the Superbus truly hideous, or was it just one step closer to the 20th century and a decent dental plan? We may never know.