Principally the SU-27 with its Phasotron N001 pulse Doppler radar provided the Soviet Air Force with a look-down/shoot-down capability designed as a counter to the American B-1 bomber. But it also had to be designed to counter the newer generation of American fighters designed around the Energy Maneuver philosophy of aerial combat. The Kremlin came to the conclusion that it, too, wanted a high-low mix of aircraft with the Sukhoi design being selected as its premier interceptor, which could provide a BVR capability plus close in maneuverability on par with high end America fighters like the F-14 and F-15. The Mikoyan Gureyvich bureau was responsible for the development of a small lightweight fighter, principally designed to counter the threat of low end, cheap and maneuverable NATO aircraft like the F-16. That airplane became the MiG-29/-35 series of fighters.
I dunno if you would call a SU-27 an “F-15 killer”, though it was designed - at least in theory - to match it. Given what I’ve seen of the Russians in action in Ukraine as of late, I’m not personally impressed with at least their conventional capabilities. The Su-27 is inferior to the F-15 in terms of engine tech (Russian and Chinese engines are about 20 years or so behind modern western jet engines), mission systems and radar. Russian and Chinese guided missile tech is inferior to western weapons as well, taking the teeth out of the Flanker compared to the Eagle or the Tomcat.
The airframe, however, is surprisingly good, and follows a very pragmatic and functional design philosophy typical of Russian military hardware. For a ‘Teen Series’ fighter, the SU-27 airframe does offer a lot of advantages:
- It holds a lot of gas, giving it long legs to fly BARCAPS or fly deep into enemy territory on OCA missions, etc.
- High thrust to weight ratio offers good acceleration, climbing and sustained turning capabilities.
- Blended wing-body fuselage plus Leading Edge Root Extensions (LERX) vortex generators offer a low overall wing loading combined with excellent sustained high alpha maneuvering capabilities.
- The fly by wire systems along with an advanced air frame design offers good post-stall maneuvering capabilities, seen in modern variants like the Su-30, -35 and -37.
- The passive IRST capability combined with BVR IR guided missiles, helmet mounted cueing systems and all aspect off bore sight AA-11 missiles give it a big stick as well.
There are a lot of very enticing capabilities associated with the SU-27. But the limited engine tech plus inferior electronics tech handicap it compared with western equipment. It is a generation out of date compared to modern western fighters like the F-22A.
UPDATE: While I say that an SU 27 is not in the same league as American fighters, it would be an intriguing sight to see an SU-27 given a radome-to-tail overhaul and upgrade using western technology e.g. western jet engines, new cockpit, new mission systems and modern western weapons. In that fight, and against an F-15 piloted by an equally capable or lesser driver, the Flanker would be formidable adversary.