Sukhoi T-4

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, a designation also used by SU-100 tank destroyer of the Second World War.

Development
In 1963, the Soviet government held a competitive tender 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 3200 km/h was favored over the designs submitted by Yakolev and Tupolev and after a preliminary design review in June 1964, the building of a prototype was authorized. Development of the T-4 was fraught with difficulties and required a 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. Some 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, MAI ordered work suspended on the T-4 project, which was officially scrapped on 19 December 1975.

The T-4 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 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 A periscope was used for forward viewing when the nose was retracted, and could be employed at speeds of up to 600 km/h (373 mph). Braking parachutes were used in addition to conventional wheel brakes.

Testing
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, but the program was cancelled before the full performance of the aircraft could be reached. Sometimes it was incorrectly stated that T-4 is the "aircraft 101" that set a 2,000 km circuit speed record of Mach 1.89. In reality, "aircraft 101" was a Tu-144D.

Another reason for cancelling the project was the VVS (Soviet Air Force) issuing the requirement for 250 T-4s. Meanwhile, several other high-ranking officers argued there was a need for more practical and supportive fighters instead of having such a huge flying titanium target in the air. When Marshal Andrei Grechko was made the Minister of Defence, he was told by a staff member, "You can have your enormous MiG-23 order only if the T-4 is abandoned".

Survivors
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.