YB-155M / 99 / Ye-2BGM / Experimental Versions

While confirming the acceptance of the MiG-25RB, the decree signed by the council of ministers in 1972 outlined the path of future updates for the MiG-25 family The WS command was already asking for a range increase at medium and high altitudes, as well as more speed and a higher service ceiling The Mikulin-Tumanskiy OKB proposed the R-15BF-2-300, an upgraded R-15B-300 rated at 13,230 daN (13,500 kg st) with afterburner—an increase of 3,225 daN (3,290 kg st)—that retained the size and connection points of the existing engine and rea­sonable specific fuel consumption

Development of the new aircraft was to happen in two stages First the range and rate of climb would be enhanced without structural mod­ifications The aircraft would be reengined after their operational life expired—a sure way to grow younger. Second, the aircraft structure would be modified, removing the little duralumin still used in the for­ward fuselage and the few non-heat-resisting wing elements so that the aircraft could fly at speeds above Mach 3. The MiG-25’s never-exceed Mach number (Mne) of 2.83 was in fact somewhat theoretical: the later­al stability margin and the structural lifetime were supposed to dimin­ish beyond that figure, but a number of pilots have (more or less inten­tionally) exceeded Mach 3 without causing damage to the aircraft or sending it to the overhaul shop to check for structural yielding.

The first stage was carried to a successful conclusion. The factory designation of the new product was Ye-155M, but the certification doc­uments sent to the FAI after several record attempts in 1975 and 1977 called it the Ye-266M. Unfortunately, the excessive engine develop­ment time and the lack of factory availability delayed the second stage of the upgrade; as a result these modifications either remained experi­mental or did not go beyond the computational phase.

Nevertheless, the results obtained during the first step were very encouraging compared with the MiG-25P or R performance. The ser­vice ceiling increased to 24,200 m (79,375 feet), and the range at super­sonic speed to 1,920 km (1,190 miles)—2,510 km (1,560 miles) if one adds the auxiliary tank’s 5,300 1 (1,400 US gallons). Another R & D channel consisted of powering the Ye-155M with two D-30F turbofan engines rated at 15,190 daN (15,500 kg st) with afterburner. It was developed by P. A. Solovyev out of the core engine of the D-30, the power plant capable of 6,665 daN (6,800 kg st) that had powered the Tupolev Tu-134 twin-jet airliner since 1963.

This engine change led to significant structural modifications that did not, however, change the aircraft’s silhouette drastically; and the fuel capacity was raised to 19,700 1 (5,200 US gallons). Two prototypes were constructed with two D-30Fs. They were used essentially as test beds for developing the engine that would later power the MiG-31. The takeoff weight of this variant reached 37,750 kg (83,200 pounds), the maximum takeoff weight 42,520 kg (93,715 pounds), and the internal fuel weight 16,270 kg (35,860 pounds). Due to the turbofan’s better spe­cific fuel consumption its range on internal fuel reached 2,135 km (1,325 miles) at supersonic speeds and 3,310 km (2,055 miles) at sub­sonic speeds. Its service ceiling topped out at 21,900 m (71,830 feet).

Ye-266M Records

The documents sent to the FAI showed that the Ye-266M was powered by two turbojets rated at 13,720 daN (14,000 kg st). In fact, the aircraft was powered by two R-15BF-2-300 turbojets at 13,230 daN (13,500 kg st). These six world records (including one absolute world record), established more than fifteen years ago, were still standing as this book went to press.

17 May 1975

Time to climb to 25,000 m (82,000 feet), 2 minutes, 34.2 seconds. Pilot, A. V. Fedotov

Time to climb to 30,000 m (98,400 feet), 3 minutes, 9.85 seconds. Pilot, P. M. Ostapyenko

Time to climb to 35,000 m (114,800 feet), 4 minutes, 11.7 seconds. Pilot, A. V. Fedotov 22 July 1977

Altitude with a 2,000-kg (4,400-pound) payload, 37,080 m (121,622 feet). Pilot, A. V. Fedotov

Altitude with a 1,000-kg (2,200-pound) payload, 37,080 m (121,622 feet). Pilot, A. V. Fedotov 31 August 1977

Altitude without payload, 37,650 m (123,492 feet). Pilot, A. V. Fedotov. Absolute world record