|Function||Interceptor prototype||Reconnaissance prototype|
|Engines||2*11,200kg R-15B-300||2*12,300kg R-15BD-300|
|Wing Load (kg/m2)||662|
|Speed at 0m||1200km/h|
|Maximum service Speed||3000km/h|
|Turn time (sustained)||40sec|
|Supersonic Range (w/o aux tank)||940km||1600km|
|Supersonic Range (with aux tank)||1285km||2100km|
In the late-50s Soviet design bureaus joined race with their Western partners for Mach-3+ combat aircraft. Main goal was a heavy interceptor, but new design also had to accommodate a reconnaissance role. Interestingly, A.I.Mikoyan was advised by several associates to avoid the program. For example, Anatolij Brunov (many years colleague of Mikoyan) refused to manage the new aircraft.
And they had a reason. Scope and complexity of the project were enormous. Expansion of old facilities and creation of new ones was a must to perform construction and trials of airframe, engines, flight control and other systems.
A.I.Mikoyan took the challenge, and M.I.Gurevich (still active in the bureau) became the chief engineer. It was the last project of M.I.Gurevich, who retired in 1964 at age of 73. His duties were overtaken by Nikolai Matyuk, a competent engineer in his own right. Project was officially initiated on March 10, 1961.
Heavy heat regimes of Mach-3 flight resulted in creation of special creep-resistant nickel steel alloys, as well as heavy duty cooling systems for instrument bays and cockpit. Silver-plated metal mesh combined with glass fiber mats covered the engine bays. Powerplant itself was remarkable. Each of R-15B-300 engines provided 11,215kg of static thrust. To operate convergent/divergent exhaust nozzle of each engine no less than 12 hydraulic rams were installed.
Large variable intakes were equipped with hydraulically actuated ramps, controlled by the central computer. At supersonic speeds those ramps were extended to limit air mass flow into the engines. To gain sub-sonic efficiency of intakes, water-methanol mixture was injected into the intake, increasing density of the air 'swallowed' by the engines. Interestingly, huge intakes played role of canards and improving aircraft stability at supersonic speeds. Canards were considered at early design stage, but found unnecessary - thanks to intakes.
To perform the interceptor task E-155 relied on one of the most capable airborne radars of the time - pulse-Doppler 'Smertch' (Twister) (NATO Fox Fire). This heavy (over 500kg) unit generated approximately 600kW and could burn through any known jamming system at a range up to 80km. Appropriate long-range air-to-air missiles were also developed.
R&D program moved forward on a high pace. By late 1963 the prototype was near-ready. In January-February of 1964 taxi trial were performed, and on March 10, 1964 the first E-155 took to the air with A.Fedorov at the controls. After first flights several changes were introduced. The lack of anhedral was temporary compensated by installing wingtip endplates. Those in slightly modified shape migrated even to the pre-production MiG-25.
Success of the aircraft was not the easy one. First flight revealed insufficient wing rigidity. Resulting control reversal was dangerous, and maneuverability limitations vere imposed. These proved insufficient, and on October 30, 1967 test pilot NII VVS Igor Lesnikov was killed during a world speed record attempt when aircraft was overstressed.
Following changes included new approach to the aircraft control at high speeds. Above Mach 1.5, ailerons were phased out and all controls switched to new slab-type stabilators, providing both pitch and roll control. Refined mass balancing was added to the wingtips as a thin rod (utilized in production aircraft to carry warning receivers and EWF equipment. Those improvements turned to be insufficient, when Oleg Goudkov made another attempt of high speed trials. Aircraft pitched nose at altitude of 500m and killed the pilot in a moment crash. Cause was found in insufficient capacity of hydraulic system, combined with critical center of gravity limits.
Straight-forward approach demanded to replace the hydraulic system. More elegant solution (moving the stabilators closer to the wing) allowed to fix the problem without major rebuilding of the aircraft. All already manufactured airframes were field-modified to the new standard.
Now comes the 'era of records'. First one was set by A.Fedotov on March 16, 1967. Modified variant, referred as E-266, flew 1000km closed circuit at 21000m with average speed 2319km/h. It would not be a remarkable result if it was not performed with 2000kg payload. More records followed (see E-266) after four of those new heavy fighters were presented at Domodedovo on July 9, 1967. One ('3155' flown by G.Vakhmistrov) was later identified as third E-155 built.
In 1970 the E-155R reconnaissance platform was cleared for production as MiG-25R without armament, but with a wealth of photo-equipment and electronic sensors and more powerful and economical engines.