thumb| Prototype Sukhoi T-10 In 1969, the Soviet Union learned of the U.S. Air Force's "F-X" program, which resulted in the F-15 Eagle. The Soviet leadership soon realized that the new American fighter would represent a serious technological advantage over existing Soviet fighters. "What was needed was a better-balanced fighter with both good agility and sophisticated systems." In response, the Soviet General Staff issued a requirement for a Perspektivnyy Frontovoy Istrebitel (PFI, literally "Prospective Frontline Fighter", roughly "Advanced Frontline Fighter"). Specifications were extremely ambitious, calling for long-range, good short-field performance (including the ability to use austere runways), excellent agility, Mach 2+ speed, and heavy armament. The aerodynamic design for the new aircraft was largely carried out by TsAGI in collaboration with the Sukhoi design bureau.
thumb| Prototype Sukhoi T-10 In 1969, the Soviet Union learned of the U.S. Air Force's "F-X" program, which resulted in the F-15 Eagle. The Soviet leadership soon realized that the new American fighter would represent a serious technological advantage over existing Soviet fighters. "What was needed was a better-balanced fighter with both good agility and sophisticated systems." In response, the Soviet General Staff issued a requirement for a Perspektivnyy Frontovoy Istrebitel (PFI, literally "P.rospective Frontline Fighter", roughly "Advanced Frontline Fighter"). Specifications were extremely ambitious, calling for long-range, good short-field performance (inc!luding the ability to use austere runways), excellent agility, Mach 2+ speed, and heavy armament. T.:he aerodynamic design for the new aircraft ?was largely carried out by TsAGI in collaboration with the Sukhoi design bureau.