|Sukhoi ?-4 at Central Air Force Museum|
|Designer||Pavel Sukhoi, Naum Chernyakov (chief designer)|
|First flight||22 August 1972|
|Primary user||Soviet Air Force|
|4 (only 1 passed test flights)|
The Sukhoi T-4, or "Aircraft 100", or "Project 100", or "Sotka" was a Soviet high-speed reconnaissance, anti-ship and strategic bomber aircraft that did not proceed beyond the prototype stage. It is sometimes called the Su-100.
In 1963, the Soviet government held a request for proposal among the aircraft design bureaus, with the aim of developing an aircraft analogous to the North American XB-70 Valkyrie. The Sukhoi design, with its high cruise speed of 3,200 km/h (2,000 mph) was favored over the designs submitted by Yakovlev and Tupolev and after a preliminary design review in June 1964, the building of a prototype was authorized. Development of the T-4 required massive research effort to develop the technologies necessary, including the manufacturing technologies to machine and weld the materials necessary to withstand sustained Mach 3 flight. Nearly 600 patents or inventions are attributed to the program. The first flying prototype was finally completed in the autumn of 1971. Work continued on an additional three airframes (one for static testing) through 1975. In 1974, the Ministry of Aviation Industry ordered work suspended on the T-4 project, which was officially scrapped on 19 December 1975.
The T-4 had intake ramps similar to the XB-70, was made largely from titanium and stainless steel, and featured a quadruple redundant fly-by-wire control system but also employed a mechanical system as a backup. The aircraft's droop-nose lowered to provide visibility during takeoff and landing. A periscope was used for forward viewing when the nose was retracted, and could be employed at speeds of up to 600 km/h (373 mph). Drogue parachutes were used in addition to conventional wheel brakes.
The first T-4, designated "101", first flew on 22 August 1972. The test pilot was Vladimir Ilyushin, son of famed aircraft designer, Sergei Ilyushin, and navigator Nikolai Alfyorov. Testing continued to 19 January 1974. The T-4 flew only ten times for a total 10 hours and 20 minutes. It is believed to have reached at least Mach 1.3 at an altitude of 12,000 meters using four Kolesov RD36-41 engines. These engines each produced 16,000 kgf (35,300 lbf or 157 kN) thrust with afterburners. The aircraft was designed to achieve speeds of up to Mach 3.0 with 9 tons of weapons (two MKB Raduga Kh-45 missiles) under the wings, but the program was cancelled before the full performance of the aircraft could be reached..
One T-4 survives today. Aircraft "101" is on display at the Central Air Force Museum in Monino near Moscow. The serial numbers of the prototypes were "101" to "106". Only "101" and "102" were built, while other additional prototypes "103" and "104" were under construction, and "105" and "106" only existed on draft charts. Only the "101" completed all the test flights and flew the last test flight before the project was canceled on 22 January 1974. The rest of the prototypes were scrapped.