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Northrop “Gee-Whizz” Decelerator Sled

Note: This artifact is on display in the National Aviation Hall of Fame.

This vehicle was developed to test the effect of deceleration forces on humans and related equipment as encountered in aircraft crashes, ditching, rocket-powered seat ejections and parachute-opening shocks.

Built by Northrop Aircraft, in April 1947 the sled was mounted on a 2,000-foot missile launching track at Muroc, Calif. (now Edwards Air Force Base). Up to four solid fuel rockets, producing 1,000 pounds of thrust each for five seconds, produced a maximum sled speed of about 200 mph. The braking unit brought the sled to an abrupt halt, producing the desired deceleration effect of up to 50 Gs, or 50 times the force of gravity.

The first human to ride the sled was then-Capt. John P. Stapp on Dec. 10, 1947. Between April 1947 and the final run in June 1951, more than 250 sled tests were made using dummies, animals or humans. Volunteers, including later-Col. Stapp, subjected themselves to a deceleration force of more than 35 Gs on some tests.

"Gee-Whizz" Braking System
Forty-five sets of hydraulic clasp-type friction brakes were used in the main braking system for the "Gee-Whizz" sled. The brakes were mounted along a 47-foot braking section of the track. When tripped mechanically by movement of the sled, the brake shoes engaged two braking rails on the underside of the sled carriage and brought the sled to almost a complete halt. By using different numbers of brake shoes and rockets, sled speed and the degree of deceleration force could be predetermined up to a maximum design limit of 50 Gs. In the event of a main brake failure, an emergency cable arresting gear was mounted near the end of the track to halt the sled.