Northrop
Northrop X-21
The Northrop X‑21 was a United States research aircraft built by Northrop in the early 1960s to explore advanced wing‑control concepts and high‑speed aerodynamics. Developed under a joint USAF‑NASA program, the X‑21 first flew on 5 May 1964 from Edwards Air Force Base and completed a test program that lasted until late 1966. Its most distinctive feature was the thin, highly swept laminar‑flow wing equipped with a boundary‑layer‑control system that used suction ports and blowing slots to delay flow separation at transonic speeds. The airframe employed an aluminum‑skinned semi‑monocoque construction with a cockpit pressurised for up to 30 000 feet, and it was powered by a Pratt & Whitney J57‑P‑13 turbojet delivering 10,000 lb thrust. Flight control was augmented by an early digital flight‑control computer that allowed precise adjustment of the suction system in real time.
The X‑21’s data proved that active boundary‑layer control could significantly improve lift‑to‑drag ratios, a finding that influenced the design of later high‑performance fighters and the development of laminar‑flow technology on commercial jets. Although only one prototype was built, the program’s results helped shape modern aerodynamic research and remain a landmark in experimental aviation history.
The X‑21’s data proved that active boundary‑layer control could significantly improve lift‑to‑drag ratios, a finding that influenced the design of later high‑performance fighters and the development of laminar‑flow technology on commercial jets. Although only one prototype was built, the program’s results helped shape modern aerodynamic research and remain a landmark in experimental aviation history.
