Russian version

М-50
supersonic strategic bomber

    In 1955, when the Myasischev OKB was still striving to develop the huge 3M subsonic bomber, this design bureau was assigned the additional and much more difficult task of creating a strategic bomber able to make dash attacks at supersonic speed. The need for this had been spurred by the threat of the USAF Weapon System 110, which materialised as the XB-70. The US bomber was designed for Mach 3, but in 1955 this was considered an impossible objective for the Soviet Union. From the outset it was recognized that there could be no question of competing prototypes from different design teams. Even though the Myasishchev OKB was already heavily loaded with completing development of the huge M-4 strategic bomber and redesigning this into the 3M production version, this was the chosen design bureau. In partnership with CAHI (TsAGI), wind tunnels were built for Mach 0.93,3.0 and 6.0. The two partners analysed more than 30 possible configurations, initially in the Izdeliye (product) '30' family (VM-31, tailless VM-32 and VM-34). The basic requirement was finally agreed to specify a combat radius not less than 3,000km (1,864 miles) and if possible much more, combined with a dash speed (with engine afterburners in use) of Mach 2. This demanded an upgraded aircraft, and the result was the '50' series, starting with the M-50. Under chief designer Georgi Nazarov this was quickly accepted, and the initial programme comprised a static-test specimen and two flight articles, comprising one M-50 followed by an M-52. OKB pilots N I Goryainov and A S Lipko flew the M-50 on 27th October 1959. Modified with afterburning inboard engines, it continued testing in late 1960, but was by this time judged to be of limited value, and to be consuming funds needed for ICBMs (intercontinental ballistic missiles) and space projects. The OKB-23 was closed, and its personnel were transferred to V N Chelomey to work on ICBMs and spacecraft. Myasishchev was appointed Director of CAHI. To the protestations of some, the virtually complete M-52 was scrapped, and six later 50-series projects remained on the drawing board. However, for propaganda purposes the M-50 was kept airworthy and made an impressive but rather smoky flypast at the Aviation Day parade at Moscow Tushino on 9th July 1961, naturally causing intense interest in the West. After being photographed with different paint schemes, and the successive radio callsigns 022, 023,12 and 05, it was parked in the nosehigh take-off attitude at Monino.
    Apart from the totally different wing, in overall configuration, size and weight the M-50 exactly followed the M-4 and 3M family. Despite this every part was totally new, to the last tyre and hydraulic pump. The wing was of pure delta shape, with CAHI R-II profile of only 3.5 to 3.7 per cent thickness, and with a leading-edge angle of 50° from the root to the inboard engines at 55 per cent semi-span, and 41° 30' from there to the tip. The tip was cropped to provide mountings for the outboard engines. The leading edge was cambered but fixed, while the trailing edge carried rectangular double-slotted flaps and tapered outboard flaperons. At the time this was by far the largest supersonic wing ever flown. Structurally it was based on a rectangular grid with four transverse spars and seven forged ribs on each side, the skin being formed by forged and machined panels. The enormous fuselage was of almost perfect streamline form, which like the wing was skinned with forged and machined panels. Only a small two-bay section in the nose formed the pressure cabin for the pilot and navigator seated in tandem downward-ejecting seats. These were lowered on cables for the crew to be strapped in at ground level, then winching themselves into place. There was neither a fin nor fixed tailplanes. Instead the tail comprised three surfaces, each with a forward-projecting anti-flutter weight and driven by a quadruple power unit in the twin duplex hydraulic systems. A back-up mechanical control was provided, with rods and levers, but it was expected that this would later be removed. Several possible engines were studied, the finalists being VADobrynin's VD-10 and P F Zubts' 16-17, which was replaced by the 17-18. Construction of the aircraft outpaced both, and in the end the M-50 had to be powered by two Dobrynin VD-7 turbojets on the underwing pylons and two more on the wingtips. As these were temporary they were installed in simple nacelles with plain fixed-geometry inlets. Rated at 9,750kg (21,4951b), these were basically the same engines as those of the 3M. Likewise the main landing gears appeared to be similar to those of the previous bomber, but in fact they were totally new. One of the basic design problems was that the weapons bay had to be long enough to carry the llm (36ft) M-61 cruise missile internally. This forced the rear truck, bearing 63 per cent of the weight, to be quite near the tail, reducing the effective moment arm of the tailplanes and threatening to make it impossible for the pilot to rotate the aircraft on take-off. One answer would have been to use enormous tailplanes, greatly increasing drag, but a better solution was to do what the OKB had pioneered with the M-4 and 3M and equip the steerable front fourwheel landing gear with a double-extension hydraulic strut. Triggered by the airspeed reaching 300km/h (186mph), this forcibly rotated the aircraft 10° nose-up. Another unique feature was that each main gear incorporated a unique steel-shod shoe which, after landing, was hydraulically forced down on to the runway, creating a shower of sparks but producing powerful deceleration, even on snow. For stability on the ground twin-wheel tip protection gears were fitted, retracting forwards immediately inboard of the wingtip engines. All fuel was housed in the fuselage, and yet another unique feature was that to cancel out the powerful change in longitudinal trim caused by the transonic acceleration to supersonic flight fuel was rapidly pumped from Nol tank behind the pressure cabin to No 8 tank in the extreme tail (and pumped back on deceleration to subsonic flight). Over 10 years later the same idea, credited by Myasishchev to L Minkin, was used on Concorde.
    Flight testing of the M-50 at Zhukovskii was remarkably rapid, though the aircraft proved stubbornly subsonic, stopping at Mach 0.99 even in a shallow dive at full power. In early 1960 the M-50 was modified with afterburning VD-7M engines with a maximum rating of 16,000kg (35,275 Ib) on the inboard pylons and derated VD-7B engines rated at 9,500kg (20,944 Ib) on the wingtips. This was considered to offer the best compromise between M-50 in final form available thrust, mission radius and propulsion reliability. The engine installations were redesigned, all four having large secondary cooling airflows served by projecting ram inlets above the nacelle. The outer engines were mounted on extensions to the wing housing new wingtip landing gears which retracted backwards.

References and Credits:

1. V.M.Myasishchev planes / N.V.Yakubovich, V.N.Lavrov, Rusavia, 1999 /
2. «Bombers» / V.Il'in, M.Levin, 1997 /
3. «Supersonic planes» / E.Tsyhosh /
4. Soviet X-planes / Ye.Gordon, B.Gunston, 2000 /