File:Bell X-1 - Smithsonian Air and Space Museum - 2012-05-15 (7271417452).jpg

The Bell X-1-1, Air Force Serial Number 46-062 (originally designated XS-1), the first manned aircraft to break the sound barrier, on display at the Smithsonian Air and Space Museum in Washington, D.C.

On March 16, 1945, the United States Army Air Corps and the National Advisory Committee for Aeronautics (a federal agency established in 1915 to conduct research into aircraft and rockets, and folded into NASA in 1958) contracted with Bell Aircraft to build three experimental, supersonic test aircraft to obtain data on how to break the sound barrier.

The sound barrier was proving a very difficult thing. As planes approached the speed of sound, air in front of them would become so compressed as to actually form a barrier that slowed the aircraft down. As planes attempted to pierce this cone of compressed air, they encountered severe turbulence which caused them to spin out of control and crash. Attempting to push past the barrier causes shockwaves that make control surfaces on wings and rudders inoperable.

The first way to overcome these problems is by adding a moveable stabilizer to the tail -- that horizontal fin at the back of every airplane. The second way is to overcome drag through the use of thinner wings, and swept-back wings. A third way was to radically streamline the aircraft itself.

Bell Aircraft built the X-1 to resembel a Browning .50-caliber machine gun bullet -- a projectile known to be able to break the sound barrier, and which was stable in supersonic flight. In 1947, with compression still a problem, Bell added the moveable stabilizer. (The British had developed the Miles M.52 unmanned aircraft, which invented this device and which had shown that stabiliy could be gained during "transonic" speeds -- e.g., as one passed through the compression wave.)

The X-1 used a four-chamber liquid propellant rocket engine built by Reaction Motors. It burned ethyl alcohol diluted with water and liquid oxygen. The engine was theoretically throttleable, by turning on or off one of the four engines.

The X-1 was designed to be taken into the air by a modified B-52, then dropped. Its first flight was an unpowered glide flight on January 25, 1946. On October 14, 1947, Air Force Captain Charles "Chuck" Yeager broke the sound barrier in the X-1. His recorded speed was Mach 1.06 (807.2 mph).