The Postal Service issued two X-Plane stamps in two denominations on March 17, 2006, in New York, New York. The $4.05 (Priority Mail) stamp and $14.40 X-Plane (Express Mail) stamp was issued in a pressure-sensitive adhesive pane of twenty. The stamps were designed by Phil Jordan of Falls Church, Virginia.
The X-plane is a series of US aircrafts developed for technological experiments. Featured in the stamp is a computer-generated image of the X-15 plane from NASA studies. The North American X-15, a rocket-powered research aircraft, bridged the gap between manned flight in the atmosphere and space flight. After its initial test flights in 1959, the X-15 became the first winged aircraft to attain hypersonic velocities of Mach 4, 5, and 6 (four to six times the speed of sound) and to operate at altitudes well above 30,500 meters (100,000 feet). Its wings that sweep backward, along with the skinny shape and pointy nose, help this airplane fly so fast by minimizing shock waves at supersonic speeds. The stamp shows the X-15 rotated upward to reveal the most surface area.
The design includes a ghosted "X" on the left side of the stamp and text under the image reading, "Computer-generated aerodynamic study of an X-Plane." 100 million stamps were printed by the Banknote Corporation of America, Inc. and Sennett Security Products in the offset process with microprinting "X-PLANE" and "USPS"
Postal Bulletin (February 16, 2006)