Photos: The blended-wing design of Boeing's X-48B

Now this was a flying wing. The Northrop YB-49 first flew in October 1947, propelled by eight Allison TG-180 turbojet engines. "Results of flight testing showed generally good performance," according to the National Museum of the USAF. "However, stability during simulated bomb runs and political problems doomed the flying wing." The 213,000-bound plane had a wingspan of 172 feet.

A second YB-49 suffered a fatal crash in June 1948. Among the five crew members killed was the co-pilot, Capt. Glen W. Edwards, for whom Edwards Air Force Base would later be named. Ground tests continued on the first aircraft until 1950 when that plane was destroyed during high-speed taxiing.