America's stealth bombers owe their shape to a Soviet physicist's equations
In 1962 the Soviet physicist Pyotr Ufimtsev published equations showing how an object's shape governs the radar echo it returns. The US Air Force translated the work in 1971, Lockheed built it into its bid for a stealth fighter, and it proved critical to both the F-117 Nighthawk and the B-2 Spirit.
Stealth, or low observable technology, means making soldiers, aircraft, ships, missiles and vehicles harder to spot by radar, infrared, sonar and other sensors, in effect camouflage for invisible parts of the spectrum. Visual concealment is ancient; Sun Tzu wrote about it in the fifth century BC and Frontinus in the first century AD. In seventeenth-century England, gamekeeper units were among the first to wear drab colours on purpose.
Early experiments were hit and miss. In World War I, German designers covered a few aircraft with transparent cellulose acetate, and in 1916 Britain flew a small airship with a black gas bag and silenced engine over German lines at night, gathering little useful intelligence. During World War II, Britain and Germany each invented chaff, clouds of material that blinded radar much as smoke hides things from sight. A German U-boat, U-480, wore rubber tiles with air pockets designed to defeat sonar, and may have been the first stealth submarine.
In 1956 the CIA tried wires, circuit-embedded coverings and absorbent paint to shrink the U-2 spy plane's radar cross-section, without success. Lockheed's Skunk Works, under Kelly Johnson, then built the A-12, cruising at 70,000 to 80,000 feet at Mach 3.2. A US Army request in 1968 for a plane inaudible at 1,500 feet at night produced the Lockheed YO-3A Quiet Star. Modern stealth design combines shapes that deflect radar waves with coatings that absorb them.
The technology spread in the twenty-first century. Russia and China both tested stealth aircraft in 2010; Russia built ten flyable Su-57 prototypes, while China produced the J-20 and FC-31. In 2017 China became only the second country to field an operational stealth aircraft.
Source: Stealth technology
