This is the Northrop “Gee-Whizz” Decelerator Sled. As you can see, it's not an airplane--it is, as its name would suggest, a sled. It was built used in tests after WWII to better understand the injuries sustained during pilots in aircraft accidents. They would launch this thing down a 2,000 ft. long track at up to 200 mph and then abruptly stop it, creating a deceleration of up to 46 Gs, all with a human person inside. The project was run by Dr. Col. John Stapp, who himself made 26 runs on the sled, suffering "concussions, cracked ribs, broken wrists, and retinal hemorrhages," proving that test pilots (and test...sledders?) are truly a different breed. He felt that these injuries were worth the information these tests provided, saying, "I took my risks for information that will always be of benefit. Risks like those are worthwhile."
The upshot is that the results of these tests led the Air Force to call for redesigned cockpits and pilot harnesses. These tests also led to the Highway Safety Act of 1966, which required seat belts in all new cars sold in the US beginning in 1968.
