Vought XF5U "Flying Flapjack"

The XF5U "Flying Flapjack" was designed during World War II as a carrier based fighter. The unorthodox shape was designed to allow for a low-speed take-off and landing, but still allowed for a high top speed. It also aided in maneuverability. Though early tests were promising the XF5U never actually flew! One of the two aircraft built made several short hops, but before an actual flight was made the Navy canceled the project, due to the fact that jet propelled aircraft were making their way onto the scene. 

Goodyear Inflatoplane

In 1956 Goodyear Aircraft Company designed and built the Goodyear Inflatoplane. Built of rubber and nylon, it was designed to be dropped to downed pilots behind enemy lines, providing an escape vehicle. The pilot would unpack and inflate it, then hand start the engine, climb in and fly for up to 275 miles at a top speed of 70 miles per hour. 

The U.S. Army canceled the project as they could not find a "valid military use for an aircraft that could be brought down by a well-aimed bow and arrow."