Soon after the Wright Brothers flew 120 feet on Dec. 17, 1903, the race to the skies was on. Inventors from around the world worked frantically in their workshops to create aircraft that would fly faster, longer and higher. Many would succeed.

But littered across the course of aviation history were some major missteps in the attempt to make humans fly safely and securely. Here are five of the most spectacular aircraft that flopped for a variety of reasons.

1. Caproni Ca. 60

Caproni Ca.60 experimental flying boat on Lake Maggiore in 1921The Caproni Ca.60 was intended to be a 100-person flying aircraft. (Photo: Gianni Caproni/Wikimedia Commons)

One of the earliest and most visually striking of early aircraft was what became known as the Caproni Ca. 60. It was an Italian 9-wing monstrosity that carried eight separate engines along with the human payload. It was designed not only to fly but also to stay afloat on bodies of water. After construction, it was tested in early spring of 1921. The results were promising enough to warrant a second attempt. This follow-up flight ended with the plane crashing down into Lake Maggiore on the Italian/Swiss border and breaking into thousands of pieces. More pieces fell off into the water as the plane's remains were being dragged to shore. The remaining pieces are currently on display in two Italian museums.

2. H-4 Hercules

The H-4 Hercules (the "Spruce Goose") sits in the waterThe H-4 Hercules was intended as an bulk troop carrier for World War II, but the plane never flew in unfriendly skies. (Photo: Federal Aviation Administration/Wikimedia Commons)

Howard Hughes's famous H-4 Hercules (a.k.a. the "Spruce Goose") was another plane known for its short shelf life, in this instance due to unfortunate timing. Planned during World War II, the plane would be designed to carry more than 700 soldiers or two armored tanks. It was made of birch, not spruce, and had the longest wingspan known to history: 321 feet (a Boeing 747-100B, by comparison, has a 196-foot wingspan). It made one short test flight in November of 1947 but was almost immediately made redundant by the ending of the war.

The Spruce Goose changed hands several times over the years (at one point the Disney corporation bought it), and it is currently on display at a museum in McMinnville, Oregon.

3. Republic XF-84H

Republic XF-84HThe Republic XF-84H was dubbed 'Thunderscreech' for its noisy presence in the air. (Photo: U.S. Air Force/Wikimedia Commons)

The Republic XF-84H was a plane that looked great on paper: a fast airplane with a turbine engine and a supersonic propeller. But from its first flight in July 1955, there were problems. First, it could take up to 30 minutes to warm up before it could leave the runway, making it practically useless for military missions. Then there was the noise. Legend has it that once up to flight speed, the plane's noise could be heard up to 25 miles away under ideal conditions. Headaches and severe nausea were reported by the pilots and spectators nearby. The U.S. Air Force decided to cut its losses, and the program pursuing improvements to the XF-84H was closed down in 1956.

4. Convair NB-36H

The Convair NB-36H in flightThe Convair NB-36H was powered by two small nuclear reactors, and that meant it could stay in the air for a long time. (Photo: U.S. Air Force/Wikimedia Commons)

If the XF-84H can claim to be the loudest known airplane, the Convair NB-36H can safely hold the title of the most dangerous one. The bomber plane was powered by small nuclear reactors within the plane itself. The Convair took a functioning plane, gutted it, and installed such items as 12-ton lead panels and thick lead glass in the windows. Two nuclear engineers were required on the test flights. The main advantage of a plane such as the Convair is that it could stay airborne without needing to refuel for long spans of time. Almost 50 successful test flights between the autumn of 1955 and the spring of 1957 were performed (over largely unpopulated areas of Texas and New Mexico), but the plane was taken out of circulation anyway.

HZ-1 Aerocycle flown by soldier 5. HZ-1 Aerocycle

While not technically a plane, the HZ-1 Aerocycle belongs on this list primarily for its novelty. Intended to let soldiers maneuver easily over enemy lines, the HZ-1 was basically a one-man open-air platform helicopter. The steering was done by way of the soldier shifting his weight in the direction he wanted to go, much like the navigation of modern Segways. After the military expressed interest in the airborne vehicles, three manufacturers began to build prototypes. New bells and whistles were installed such as large fuel tanks and water landing equipment.

Despite the possible military uses, the HZ-1 project was abandoned in the 1950s due to problems with the vehicle itself and difficulties in training military personnel to fly the mini-copters.

Science and industry have refined air travel into a staple of modern life, but along the way there were bumps in the road from the humorous (the Goodyear Inflatoplane that was made out of rubber and nylon but was easily destroyed by enemy attack) to the bizarre (the Christmas Bullet fighter biplane that featured no support for the wings, causing them to flap around wildly before crashing).

But things aren't so different now. Engineers continue to push the envelope of construction to make aircraft fly faster, longer and higher — and sometimes that requires pushing the limits of plausibility.

5 aircraft designs that didn't quite fly
Here are five of the most spectacular aircraft that flopped for a variety of reasons, including the Spruce Goose and a nuclear-powered plane.