Category Soviet x-plenes

Purpose: To create a strategic reconnaissance aircraft.

Design Bureau: OKB-256, Podberez’ye, Director P V Tsybin.

As noted previously, the 2RS was launched as a project in January 1956. It was to be a mini­mum-change derivative of the RS, carried to high altitude under the Tu-95N and subse­quently powered by two RD-013 ramjets. However, it was decided that such an aircraft would be operationally cumbersome and in­flexible, and that, despite a very substantial reduction in operational radius, it would be preferable to switch to conventional after­burning turbojets and take off from the ground. The revised project was called RSR (described later). The Ministry gave this the go-ahead on 31st August 1956, but work on
the 2RS continued until is was terminated in early 1957. As it was no longer needed, Tupolev then stopped the rebuild of the Tu – 95N carrier at Factory No 18 at Kuibyshev.

The 2RS would have differed from the RS principally in having the canard foreplanes re­placed by slab tailplanes. Behind these was installed a braking parachute. Provision was made for large reconnaissance cameras in the fuselage ahead of the wing. Surviving drawings (below) also show provision for a 244N thermonuclear weapon, this time as a free-fall bomb recessed under the fuselage further aft. Carrying this would have moved the main landing gear unacceptably close to the tail.

Though there was much to be said for air launch, the basic concept looked increasing­ly unattractive.

Purpose: To create an improved reconnaissance aircraft.

Design Bureau: OKB-256, Podberez’ye, Director P V Tsybin.

The preliminary project for the revised aircraft, able to take off in the conventional manner, was dated 26th June 1957. Design proceeded rapidly, and in parallel OKB-256 created a sim­plified version, using well-tried engines, which could be got into the air quickly to provide data (see NM-1, next). These data became avail­able from April 1959, and resulted in significant changes to the RSR (see R-020). The basic de­sign, however, can be described here.

Though the RSR was derived directly from the 2RS, it differed in having augmented by­pass turbojet engines (low-ratio turbofans) and strengthened landing gear for convention­al full-load take-offs. A basic design choice was to make the structure as light as possible by selecting a design load factor of only 2.5 and avoiding thermal distortion despite local skin temperatures ofup to 220°C. By this means the use of steel and titanium was almost eliminat­
ed, though some skins (ailerons, outer wing and tail torsion boxes) were to be in alumini – um/beryllium alloy. As before, the wing had a t/c ratio of 2.5 per cent, 58° leading-edge sweep and three main and two secondary spars. The tips, 86mm deep, carried Solov’yov D-21 bypass engines. These bore no direct re­lationship to today’s D-21A1 by the same de­sign team. They were two-shaft engines with a bypass ratio of 0.6, and in cruising flight they were almost ramjets. Sea-level dry and aug­mented ratings were 2,200kg (4,850 Ib) and 4,750kg (10,472 Ib) respectively. Dry engine mass was 900kg (l,9841b) and nacelle diame­ter was 1.23m (4ft 1/2in). The fuselage had a fineness ratio of no less than 18.6, diameter being only 1.5m (4ft 1 lin). All tail surfaces had a t/c ratio of 3.5 per cent, and comprised a one- piece vertical fin with actuation limits of ±18° and one-piece tailplanes with limits of + 10°/-25°. All flight controls were fully pow­ered, with rigid rod linkages from the cockpit and an artificial-feel system. The main and steerable nose landing gears now had twin wheels, and were supplemented by single­
wheel gears under the engines, all four units hydraulically retracting to the rear. A braking parachute was housed in the tailcone. A total of 7,600kg (16,755 Ib) of kerosene fuel was housed in integral tanks behind the cockpit and behind the wing, plus 4,400kg (9,700 Ib) in two slender (650mm, 2ft 1 V-im diameter) drop tanks. An automatic trim control system pumped fuel to maintain the centre of gravity at 25 per cent on take-off, 45.0 in cruising flight and 26.4 on landing. In cruising flight the cock­pit was kept at 460mm Hg, and the pilot’s pres­sure suit maintained 156mm after ejection. An APU and propane burner heated the instru­ment and camera pallets which filled the cen­tre fuselage, a typical load comprising two AFA-200 cameras (200mm focal length) plus an AF A-1000 or AFA-1800 (drawings show four cameras), while other equipment included optical sights, panoramic radar, an autopilot, astro-inertial navigation plus a vertical gyro, a radar-warning receiver and both active and passive ECM (electronic countermeasures) During construction this aircraft was modi­fied into the RSR R-020.

RSR inboard profile

Purpose: To destroy enemy armour.

Design Bureau: A A Arkhangelskiy (Tupolev aide), with G M Mozharovskiy and IV Venevidov, Factory No 32, Moscow.

The idea was that of Mozharovskiy-Venevi – dov, who called their project the Kombain (combine) because of its versatility. They were long-time specialists in aircraft arma­ment, among other things being responsible for all the early gun turrets in the Soviet Union. Arkhangelskiy increased their political power and got them a separate design office and factory for what became called the BSh (ar­moured assaulter, the same designation as the Ilyushin Stormovik) and also KABV (com­bined artillery-bomber weapon). The eskiz – nyi proekt (sketch project) was submitted on 29th December 1940, long-lead materials were sanctioned on 25th January 1941 and the project was confirmed at the NIl-WS by AIFilin on 12th March 1941. Despite being (on paper) superior, it was terminated in the evacuation of the designers from Moscow to Kirov later in 1941, all effort being put into the Ilyushin aircraft (which was built in greater numbers than any other aircraft in history).

The whole emphasis in the M-V project was giving the pilot (the only occupant) the best possible view ahead over the nose. Whereas
the engine of the IL-2 Sturmovik blocked off the view at a downwards angle of 8°, the M-V aircraft gave the pilot a downwards view of 30°. This is because the engine (the l,625hp AM-38, the same as the IL-2) was behind the cockpit. The tail was carried on twin booms and the landing gear was of the then-novel nosewheel type. Many armament schemes were planned, including one Taubin 23mm gun and four ShKAS, or four ShVAK, all mounted on pivots to fire diagonally down. Up to 500kg of bombs could also be carried, mainly to comprise AO-20 or AO-25 fragmen­tation bomblets.

On the basis of written evidence this air­craft would have been a better tank killer than the Ilyushin machine. The drawback was that

BSh-MV

when the Ilyushin suffered heavy attrition from German fighters a backseater was put in to defend it, and this would have been diffi­cult with the BSh/M-V.

Purpose: To test designer’s experimental wing.

Design Bureau: Aircraft constructed by BOK to design of S S Krichevskii.

Sawa Syemenovich Krichevskii, called ‘a tal­ented designer’ by historian Shavrov, spent the early 1930s trying to create the most effi­cient aeroplane wing. He made many tunnel models, eventually settling on a wing of high aspect ratio constructed in front and rear sec­tions. The rear part was hinged to the front
with a small intervening gap acting as a slot. In flight, the intention was that the pilot would select the optimum angle for the rear portion, Shavrov commenting that ‘this wing could al­ways be flown in a drag-polar envelope’.

Krichevskii secured funding to build a re­search aircraft, called RK (Razreznoye Krylo, slotted wing) and designated BOK-2 by the construction bureau. The BOK-2 was complet­ed in 1935 and flew successfully, but Krichevskii died shortly afterwards. Documen­tation on this aircraft has never been found.

The BOK-2 was an extremely neat can­tilever monoplane, with a single M-l 1 engine rated at 11 Ohp. Shavrov comments that ‘The wing skin was polished to mirror brilliance [suggesting all-metal construction]…it is hard to say if its excellent performance was due to its drag-polar envelope or to its perfect aerodynamic shape’.

Despite its apparently excellent perfor­mance the RK appears to have had no impact on the Soviet aviation ministry.

No data available.

Purpose: To create a multirole aircraft with tailless configuration.

Design Bureau: OKB ofK A Kalinin, Voronezh.

In April 1933 Kalinin submitted to the NIl-WS three prelim inary designs for aVS-2 (Voiskovoi Samolyot, troop aircraft) for reconnaissance, bombing, transport, ambulance and other missions. One was conventional, the second had twin tail booms, and the third was tail­less. Kalinin preferred the third option, be­cause of supposed lower weight and drag, better manoeuvrability and ease of Fitting a tail turret for defence. He began with the NACA R-106R aerofoil, with slats, park-bench
ailerons, Scheibe wingtip rudders and a vesti­gial horizontal tail. Tunnel testing of models led to an improved design with a trapezoidal wing ofCAHI (TsAGI) R-II profile, with trailing – edge servo-operated elevators and ailerons of Junkers ‘double wing’ type (as also used by Grokhovskii), the small horizontal tail being eliminated. To test the configuration a half­scale glider (span 10.45m, length 5.2m) was constructed in 1934 and flown over 100 times by V O Borisov. After many problems and ar­guments, the full-scale aircraft was complet­ed at GAZ (State Aviation Factory) No 18 at Voronezh as the K-12, and flown by Borisov in July 1936. Factory testing was completed in 46 flights. The K-12 was then ferried to

Moscow where its Nil testing was assigned to P M Stefanovskii from October 1936. He found severe control problems, and eventu­ally N N Bazhanov, head of the NIl-WS, re­fused to accept the K-12 for official trials. From this time onwards Kalinin was under a cloud. The Director of GAZ No 18 joined with Tupolev, Vakhmistrov (see later) and others to impede progress and get the K-12 aban­doned. Kalinin moved into Grokhovskii’s summer dacha, the K-12 languishing at Grokhovskii’s KB-29. Contrary to the political tide, Voroshilov ordered the K-12 to fly in the 1937 Air Day parade over Moscow Tushino, and Bazhanov had it painted in a fantastic red/yellow feathered scheme as the Zhar

Ptitsa (firebird or phoenix). It made a great impression, and on 12th December 1937 the Assistant Head of the WS, YaVSmushke – vich, signed an order for renewed NIl-WS testing to start on 1st March 1938, followed by series production of modified aircraft at GAZ No 207. Work began, but in spring 1938 Kalin­in’s enemies managed to get him arrested and shot on charges of spying and conspira­cy. As he had become an ‘enemy of the peo­ple’ the contract was cancelled, the K-12 was scrapped and the ten aircraft on the assembly line were never completed.

The structure of the K-12 was almost en­tirely based on welded KhMA (Chromansil steel) tubing. The wing comprised left and right panels bolted to the roots, each having one main spar running straight from tip to tip. The fuselage was in three bolted sections, the front section being mainly skinned in Dl, all the rest of the skin being fabric. The trailing – edge and wingtip controls were all fabric­skinned Dl. The main landing gears were to have been retractable, but the intended M-25 engines and variable-pitch propellers were not available in time, so weight was saved by making the landing gears fixed. The inadequate engines which had to be fitted were 480hp M-22 (Bristol Jupiter licence), in cowlings with cooling gills, and driving 2.8m
(9ft 2%n) two-blade metal propellers with pitch adjustable on the ground. Crew com­prised a pilot in an enclosed cockpit, a navi­gator who also served as bomb aimer in a nose turret with one 7.62mm ShKAS (he was provided with a rudimentary flight-control lever in case the pilot was incapacitated) and a radio operator in a similar tail turret. Bombload of up to 500kg (l,1021b) was car­ried on a KD-2 vertical rack behind the main spar and pilot’s cockpit. Other equipment in­cluded a V SK-2 radio and AF A-12 camera.

At the end of its life, in early 1938, the K-12 was refitted with 700hp M-25 (Wright Cy­clone) engines, driving Hamilton Standard type variable-pitch propellers, but it was never tested in this form. Other modifications included fitting an electrically retractable main landing gear and modified armament. It had also been Kalinin’s intention to replace the wingtip fin/rudder surfaces by rudders above the wings behind the engines, but these were never fitted.

Accounts of this strange tailless aircraft tend either to be strongly positive or strongly negative. There is no doubt Kalinin was the victim of political intrigue, but at the same time the K-12 does not appear to have been a stable or controllable aircraft.

Top: K-12 inboard profile.

Above and right: Two views of Zhar Ptitsa.

Purpose: To boost the speed of a piston – engined fighter.

Design Bureau: The OKB-155 ofAI Mikoyan.

In 1942 the Central Institute for Aviation Mo­tors (often abbreviated as TsIAM) began to develop an unusual method of boosting the propulsive power of fighter aircraft. Called VRDK (from Russian for ‘air reaction auxiliary compressor’) it involved adding a drive from the main engine to an auxiliary compressor for a flow of air rammed in at a forward-fac­ing inlet. The compressed air was then ex­pelled through a combustion chamber and propulsive nozzle. This scheme was worked on by a team led by V Kh Kholshchevnikov. In January 1944 the governments of the UK and USA announced their possession of jet air­craft. In a near-panic response, the GKO (State Committee for Defence) ordered all the main Soviet fighter OKBs to build jet air­craft. Stalin criticised designers for not al­ready having such aircraft. As the only Soviet turbojet (the Lyul’ka VRD-2) was nowhere near ready for use, MiG and Sukhoi were as­signed the urgent task of creating prototype fighters to use the VRDK booster system. Both quickly came to the conclusion that the VRDK method could not readily be applied to any of their existing fighters, and both designed spe­cial (quite small) fighters to investigate it. The MiG aircraft was called N by the OKB, and given the official designation I-250. The pro­ject was assigned to G Ye Lozino-Lozinskii. A mock-up was approved on 26th October

1944, and after frantic effort the ‘N’ Nol was rolled out painted white on 26th February

1945. OKB pilot A P Dyeyev began the flight – test programme on 3rd March. Soon the magic 800km/h mark was exceeded, and Mikoyan presented Dyeyev with a car. VRDK operation was generally satisfactory but deaf­eningly noisy. On 19th May a tailplane failed at low level and the ‘N’ Nol crashed. By this time ‘N’ No2 was almost ready to fly. Painted dark blue, with a yellow nose and horizontal streak, it was restricted to 800km/h to avoid a repetition ofthe failure. Stalin had meanwhile ordered that a ‘regiment’ of ten of these air­craft should fly over Red Square on 7th No­vember, October Revolution Day. ‘N’ No 2 was tested by LII pilot A P Yakimov, assisted by OKB pilot A N Chernoburov. This aircraft was written off in a forced landing in 1946. The hastily built ten further I-250s were tested by IT Ivashchenko. On 7th November nine were ready, but the flypast was cancelled be­cause of bad weather. In late 1946 Factory No 381 was given an order for 16 fully equipped fighter versions, designated MiG – 13. Factory testing of these took place in May-

July 1947,1 M Sukhomlin carried out NIl-WS testing between 9th October 1947 and 8th April 1948, and these aircraft were then deliv­ered to the A V-MF. They served with the Baltic and Northern Fleets until 1950.

Aircraft N bore little similarity to any previ­ous MiG design. Made entirely of metal, with a stressed-skin covering, it was smaller than most fighters, whereas its predecessors had been larger. The straight-tapered wing had a CAHI 10%-thick laminar aerofoil, with two spars and plate ribs. Movable surfaces com­prised two-part Frise ailerons and hydrauli­cally operated CAHI slotted flaps. The fuselage was relatively deep to accommodate the unique propulsion system. The engine was a VK-107, rated at l,650hp for take-off and l,450hp at 3,500m (12,470ft). At the front it was geared down to drive the AV-5B three – blade constant-speed propeller of 3.1m (10ft 2in) diameter. At the back it drove the en­gine’s own internal supercharger as well as a clutch which, when engaged, drove through 13:21 step-up gears to a single-stage axial compressor. This pumped air through a large duct from a nose inlet. Just behind the com­pressor was the engine’s cooling radiator. Be­hind this were seven nozzles from which, when the auxiliary compressor was engaged, fuel from the main tanks was sprayed and ig­nited by sparking plugs. The resulting flame filled the large combustion chamber, from which a high-velocity jet escaped through a two-position nozzle. Downstream of the burners the entire duct was refractory steel, and when the VRDK was in operation its walls were cooled by water sprayed from a 78 litre (17 Imperial gallon) tank, the steam adding to the thrust. At 7,000m (22,966ft) the VRDK was estimated to add l,350hp, to a total of 2,500hp. The oil cooler surrounded the pro­peller gearbox, with flow controlled by gills round the top of the nose. The engine was mounted on a steel-tube truss. Fuel was housed in three self-sealing tanks, one of 415 litres (91.3 Imperial gallons) in the fuselage and one of 100 litres (22.0 Imperial gallons) in each wing. The large central tank forced the cockpit to be near the tail, with a sliding canopy. The metal-skinned tail was repeat­edly modified, the small elevators having a tab on the left side. A unique feature of the main landing gear was that the wheels were carried on single levered-suspension arms projecting forward from the leg. The tail – wheel was fully retractable. Even the first air­craft, called ‘N’ Nol, was fully armed with three B-20 cannon, each with 160 rounds. The MiG-13 batch differed in having a larger verti­cal tail, larger fuel and water tanks, RSI-4 radio with a wire antenna from the fin to a mast projecting forwards from the wind­screen, and (temporarily) strange curved pro­peller blades in an attempt to reduce tip Mach number.

These aircraft performed as expected, but were a dead-end attempt to wring the last bit of performance from piston-engined fighters.

Photographs on the opposite page:

Top: I-250 Nol.

Centre: I-250 No 2.

Bottom: Production MiG-13 (straight propeller blades).

Purpose: To develop the optimum Buran landing profiles and techniques and train Cosmonauts to fly the Buran spacecraft. Design Bureau: NPO Molniya, Moscow, GeneralDirectorGlebELozino-Lozinskii.

In 1976 the various A I Mikoyan spacecraft – Spiral and Epos, and the 105-11 described previously-were terminated and replaced by the Buran (Snowstorm) programme. This was assigned to NPO Energiya for the rocket launch vehicle, with a total thrust at boost separation of4,037 tonnes (8,900,000 Ib), and NPO Molniya for the reusable winged orbiter. Lozino-Lozinskii, then 67, was transferred from the MiG OKB to head the Molniya team. In 1978 work began on a series of BTS (initials from Russian for Big Transport Ship) projects which eventually totalled eight, BTS-001 through BTS-006 plus BTS-011 and BTS-015. Of these BTS-002 was a complete manned air vehicle to explore the landing profiles and handling, and – together with prolonged training on various other aircraft, notably a Tu-154LL – train the future crews. More than 7,000 atmospheric entries, glides and land­
ings had been simulated mathematically, and in tunnel testing of models, but there was no substitute for actually flying a Buran type ve­hicle. In summer 1984 BTS-002 was taken by VM-T carrier aircraft to Jubilee airfield near the Cosmodrome at Baikonur. Here it began taxi testing on 29th December 1984.

Almost a year then elapsed before the first flight, on 10th November 1985 This was a sin­gle take-off, wide circuit and landing, lasting 12 minutes. The Commander was Igor P Volk and the pilot Rimantas A A Stankyavichus. This crew flew many other missions, togeth­er with five other Cosmonauts. An important flight was No 8, on 23rd December 1986, when the Volk/Stankyavichus crew made the first ‘hands off automatic approach and land­ing from a height of 4km.

The last flight of BTS-002 took place on 15th April 1988, just over seven months before the first launch of a Buran in November 1988 made the ‘atmospheric analog’ redundant. It made a final high-speed taxi test on 20th De­cember 1989 and was then retired, but placed on view to the public at MosAero-92 at Zhukovskii.

The airframe ofBTS-002 was geometrically identical to the Buran, and it had the same flight-control system and software. The four large elevens, four sections of rudder (upper and lower left and upper and lower right, which split apart to act as airbrakes) and door-type ventral airbrake were identical. So were the twin-wheel landing gears, K-36L seats and triple cruciform braking para­chutes. On the other hand it was devoid of the 38,000 ceramic tiles and of virtually all the complex on-board systems of the spacecraft.

In particular, the propulsion systems were to­tally different. The orbiter had no main en­gines, relying totally on the mighty launch rocket, but it did have two OMEs (orbital ma­noeuvring engines) and 42 small thrusters for attitude control in space. The BTS-002 need­ed none of these, but instead had four Lyul’- ka AL-21F-3 afterburning turbojets, each rated at 11,200kg (24,800 Ib) thrust. These were arranged one on each side of the rear fuselage and one on each side at the base of

the fin. Of course it also needed a conven­tional kerosene fuel system. The engines were used only for taxying to the runway and for take-off and landing. The important part of the flight had to be a glide, simulating the or- biter. Presence of the four air-breathing en­gines was said to have little effect upon the vehicle’s flight characteristics.

BTS-002 did everything it was designed to do. Unfortunately, the main Buran pro­gramme eventually ran eight years later and
overran its budget severely. Nevertheless, in the opinion of Vyacheslav Filin, Deputy Gen­eral Constructor at NPO Energiya, ‘Had it not been for existence of the Buran system there would have been no Reykjavik meeting where Reagan suggested sharing Star Wars technology and which led to strategic arms reduction’.

Purpose: To create an interceptor with piston engine plus VRDKpropulsion.

Design Bureau: P O Sukhoi, Moscow.

The urgent demand for faster fighters, to meet the competition of German and Allied jets re­vealed in January 1944, is given in the story of the Mikoyan I-250 (N). Apart from Mikoyan Sukhoi was the only designer to respond to this call, and (because the propulsion system was the same) he created a very similar air­craft. Two examples were funded, the second being used for tunnel testing at CAHI (TsAGI). The red-painted flight article first flew – it is be­lieved, at Novosibirsk – on 6th April 1945, a month after its rival. On 15th July 1945 the test programme was interrupted by failure of the main engine, and the opportunity was taken to fit a new wing with CAHI (TsAGI) laminar pro­file. In August the replacement engine failed. As no replacement VK-107A was available, and such aircraft were by this time outmoded, the test programme was discontinued.

The Su-5 was a conventional fighter of its time, notable only for its small size and deep fuselage to accommodate the VRDK duct. The second wing fitted had a 16.5-per-cent CAHI 1VI0 profile at the root, thinned down to 11 per cent NACA-230 near the tip. It was made in three parts, with bolted joints outboard of the landing gears. The split flaps spanned this joint. The Frise ailerons were fully balanced, the port surface having a trim tab. Most of the fuselage was occupied by the propulsion sys­tem. The VK-107A engine, rated at l,650hp, drove a four-blade 2.89m (9ft 5%in) propeller, with a clutched rear drive to a 13:21 step-up gearbox to the VRDK compressor. In the duct were the carburettor inlets, radiator, seven combustion chambers and double-wall pipe of heat-resistant steel leading to a variable propulsive nozzle. The No 2 aircraft had a cir­cular multi-flap nozzle projecting behind the fuselage. In the left inner wing was a broad but shallow inlet for the ducted oil cooler, with exit under the wing. This required a modified upper door to the left landing gear, with 650 x 200 tyres and track of3.15m (10ft 4in). The tail – wheel, with 300×125 tyre, retracted into an open asbestos-lined box in a ventral fairing. The rudder and inset-hinge elevators all had spring-tab drives. The cockpit had 10mm (%in) back armour and a sliding canopy, the No 2 air­craft having a transparent rear fairing. Three tanks housed 646 litres (142 Imperial gallons) of fuel, consumed in lOmin of VRDK opera­tion. Armament comprised one NS-23 with 100 rounds and two UBS with 400 rounds above the engine.

Sukhoi said later this aircraft was a ‘non­starter’ from the outset.

Purpose: To provide full-scale flight data to support the RSR.

Design Bureau: OKB-256, Podberez’ye, Director P V Tsybin.

In autumn 1956 funding was provided for a research aircraft designated NM-1 (Naturnaya Model’, life [like] model). This was to be a sin­gle flight article with an airframe based upon that of the RSR but simplified, with proven en­gines and stressed for lighter weights. It was completed in September 1958. On 1st Octo­ber Amet-Khan Sultan began taxi testing, and he made the first flight on 7th April 1959, with a Yak-25 flying chase. The flight plan called for
take-off at 220km/h, but after a tentative hop Sultan actually took off at 325km/h, and jettisoned the dolly at 40m (131ft) at 400km/h (248mph). The dolly broke on hitting the runway (on later flights it had an automatic parachute). Sultan easily corrected a slight rolling motion, and flew a circuit at 1,500m at 500km/h before making a landing at 275km/h (90km/h faster than planned). Altogether Sultan and Radii Zakharov made 32 flights, establishing generally excellent flying quali­ties (take-off, approach and landing ‘easier than MiG or Su aircraft’) but confirming neu­tral or negative stability in roll.

The five-spar 2.5-per-cent wing had con­stant-chord ailerons and flaps which were unlike those of the RSR. On the tips were two Mikulin (Tumanskii) AM-5 turbojets each rated at 2,000kg (4,409 Ib) thrust, in simple na­celles without inlet centrebodies. The pilot sat in an ejection-seat under a very small canopy; the low-drag RS-4/01 canopy, resem­bling that of the RSR, was never fitted. Along the centreline were a sprung skid, hydrauli­cally retracted into a long box, and a small tailwheel, while hydraulically extended skids were hinged under the nacelles. For take-offs a jettisonable two-wheel dolly was attached under the main skid. A door under the point­ed tailcone released the braking parachute. After the taxi tests, following recommenda­tions from CAHI (TsAGI) small extra wing sur­faces were added outboard of the engines. The fuselage contained two kerosene tanks, a hydraulic-fluid tank and a nose water tank to adjust centre of grravity to 25.5 per cent of mean aerodynamic chord.

The NM-1 showed that the basic RSR con­cept was satisfactory.

Purpose: High-speed research aircraft with fighter-likepossibilities.

Design Bureau: SNII, at Factory No 240.

One of the few aircraft designers to emigrate to (not from) the infant Soviet Union was Roberto Lodovico Bartini. A fervent Commu­nist, he chose to leave his native Italy in 1923 when the party was proscribed by Mussolini. By 1930 he was an experienced aircraft de­signer, and qualified pilot, working at the Central Construction Bureau. In April of that year he proposed the creation of the fastest aircraft possible. In the USSR he had always suffered from being ‘foreign’, even though he had taken Soviet citizenship, and nothing was done for 18 months until he managed to en­list the help of P I Baranov, head of the RKKA (Red Army) and M N Tukhachevskii (head of RKKA armament). They went to Y Y Anvel’t, a deputy head at the GUGVF (main directorate of civil aviation), who got Bartini established at the SNII (GVF scientific test institute). Work began here in 1932, the aircraft being desig­nated Stal’ (steel) 6, as one of a series of ex­
perimental aircraft with extensive use ofhigh – tensile steels in their airframes. After suc­cessful design and construction the Stal’-6 was scheduled for pre-flight testing (taxi runs at increasing speed) in the hands of test pilot Andrei Borisovich Yumashev. On the very first run he ‘sensed the lightness of the con­trols., .which virtually begged to be airborne’. He pulled slightly back on the stick and the aircraft took off, long before its scheduled date. The awesomely advanced aircraft proved to be straightforward to fly, but the en­gine cooling system suffered a mechanical fault and the first landing was in a cloud of steam. Yumashev was reprimanded by Barti­ni for not adhering to the programme, but testing continued. Yumashev soon became the first pilot in the USSR to exceed 400km/h, and a few days later a maximum-speed run confirmed 420km/h (261 mph), a national speed record. One of Bartini’s few friends in high places was Georgei K Ordzhonikidze, People’s Commissar for Heavy Industries. In November 1933, soon after the Stal’-6 (by this time called the El, experimental fighter) had
shown what it could do, he personally or­dered Bartini to proceed with a fighter de­rived from it. This, the Stal’-8, was quickly created in a separate workshop at Factory 240, and was thus allocated the Service des­ignation of I-240. Hearing about the Stal’-6’s speed, Tukhachevskii called a meeting at the Main Naval Directorate which was attended by many high-ranking officers, including heads from GUAP (Main Directorate of Avia­tion Production), the WS (air force), RKKA and SNII GVF. The meeting was presided over by Klementi Voroshilov (People’s Commissar for Army and Navy) and Ordzhonikidze. At this time the fastest WS fighter, the I-5, reached 280km/h. The consensus of the meeting was that 400km/h was impossible. Many engineers, including AAMikulin, de­signer of the most powerful Soviet engines, demonstrated or proved that such a speed was not possible. When confronted by the Stal’-6 test results, and Comrade Bartini him­self, the experts were amazed. They called for State Acceptance tests (not previously re­quired on experimental aircraft). These began

in the hands of Pyotr M Stefanovskii on 8th June 1934 (by which time the fast I-16 mono­plane fighter was flying, reaching 359km/h). On 17th June the Stal’-6 was handed to the Nil WS (air force scientific research institute), where it was thoroughly tested by Ste – vanovskiy and N V Ablyazovskiy. They did not exceed 365km/h, because they found that at higher speeds they needed to exert consider­able strength to prevent the aircraft from rolling to port (an easily cured fault). On 13th July the landing-gear indicator lights became faulty and, misled, Stefanovskii landed with the main wheel retracted. The aircraft was re­paired, and the rolling tendency cured. Vari­ous modifications were made to make the speedy machine more practical as a fighter. For example the windscreen was fastened in the up position and the pilot’s seat in the raised position. Aftervarious refinements Ste­fanovskii not only achieved 420km/h but ex­pressed his belief that with a properly tuned engine a speed 25-30km/h higher than this might be reached. The result was that fighter designers – Grigorovich, Polikarpov, Sukhoi and even Bartini himself – were instructed to build fighters much faster than any seen hith­erto. Bartini continued working on the StaP-8, a larger and more practical machine than the Stal’-6, with an enclosed cockpit with a for­ward-sliding hood, two ShKAS machine guns and an advanced stressed-skin airframe. The engine was to be the 860hp Hispano-Suiza HS12Ybrs, with which a speed of 630km/h (391 mph) was calculated. Funds were allo­cated, the Service designation of the Stal’-8 being I-240. This futuristic fighter might have been a valuable addition to the WS, but Bar­tini’s origins were still remembered even in the mid-1930s, and someone managed to get funding for the Stal’-8 withdrawn. One reason put forward was vulnerability of the steam cooling system. In May 1934 the I-240 was abandoned, with the prototype about 60 per cent complete.

Everything possible was done to reduce drag. The cantilever wing had straight taper and slight dihedral (existing drawings incor­rectly show a horizontal upper surface). The two spars were made from KhMA (chrome – molybdenum steel) tubes, each spar com­prising seven tubes of 16.5mm diameter at the root, tapering to three at mid-semi-span and ending as a single tube of 18mm diame­ter towards the tip. The ribs were assembled from Enerzh-6 (stainless) rolled strip. Ailerons, flaps and tail surfaces were assembled from steel pressings, with Percale fabric skin. The flaps were driven manually, and when they were lowered the ailerons drooped 5°. Barti­ni invented an aileron linkage which adjusted stick force according to indicated airspeed (this was resurrected ten years later by the Central Aero-Hydrodynamic Institute as their
own idea). The fuselage was likewise based on a framework of welded KhMA steel tubes. Ahead of the cockpit the covering comprised unstressed panels of magnesium alloy, the aft section being moulded plywood. In flight the cockpit was part-covered by a glazed hood flush with the top of the fuselage, giving the pilot a view to each side only. For take-off and landing the hood could be hinged upwards, while the seat was raised by a winch and cable mechanism. Likewise the landing gear was based on a single wheel on the centre­line, with an 800 x 200mm tyre, mounted on two struts with rubber springing. The pilot could unlock this and raise it into an AMTs (light alloy) box between the rudder pedals. For some reason the fuselage skin on each side of this bay was corrugated. The wheel bay was normally enclosed by a door which during the retraction cycle was first opened to admit the wheel and then closed. Extension was by free-fall, finally assisted by the cable until the unit locked. Under the outer wings were hinged support struts, likewise retract­ed to the rear by cable. When extended, each strut could rotate back on its pivot against a spring. Under the tail was a skid with a rubber shock absorber. The engine was an imported Curtiss Conqueror V-1570 rated at 630hp, dri­ving a two-blade metal propeller with a large spinner (photographs show that at least two different propellers were fitted). This massive vee-12 engine was normally water-cooled, but Bartini boldly adopted a surface-evapora­tion steam cooling system. The water in the engine was allowed to boil, and the steam flowed into the leading edges of the wings which were covered by a double skin from the root to the aileron. Each leading edge was electrically spot – and seam-welded, with a soldering agent, to form a sealed box with a combined internal area of 12.37m2 (133ft2).

Each leading edge was attached to the upper and lower front tubes of the front spar. Inside, the steam, under slight pressure, condensed back into water which was then pumped back to the engine. The system was not de­signed for prolonged running, and certainly not with the aircraft parked.

Bartini succeded brilliantly in constructing the fastest aircraft built at that time in the So­viet Union. At the same time he knew per­fectly well that the Stal’-6 was in no way a practical machine for the WS. The uncon­ventional landing gear appeared to work well, and even the evaporative cooling sys­tem was to be perpetuated in the I-240 fight­er (but that was before the Stal’-6 had flown). Whether the I-240 would have succeded in front-line service is doubtful, but it was the height of folly to cancel it. The following data refers to the Stal’-6.

Purpose: To experiment with a tailless (so – called ‘flying wing’) design.

Design Bureau: Bureau of Special Design, Smolensk. Design team led by V A Chizhevskii.

The idea for this small research aircraft came from the BOK-2, though the two aircraft were completely unrelated. In 1935 Chizhevskii began studying tailless aircraft, and obtained funding to build a simple research aircraft. This was completed in early 1937, but was then modified and did not fly until Septem­ber, the pilot being I F Petrov. It ‘flew satisfac- torily…but crashed during a landing’. After being repaired and modified its handling qualities were greatly improved. In 1938 the
modified aircraft was tested by the Nil WS (air force flight-test institute), where it was flown by such pilots at P M Stefanovskii and M A Nyukhtikov. Stefanovskii is reported to have said that the BOK-5 could be ‘flown by pilots of average or even below average abil­ity’ and to have been ‘impressed by its acro­batic capability’.

The BOK-5 was a basically simple aircraft, apart from the flight-control system. The air­frame was made of duralumin. The wing was ofCAHI (TsAGI) 890/15 profile (15 per cent t/c ratio), with two spars with tubular booms and sheet webs, and ribs assembled from chan­nel and angle sections, with fabric covering. The short fuselage was a semi-monocoque, with some box-section longerons and
pressed-sheet frames, the vertical tail being integral. The main landing gears were de­scribed as ‘U-2 type’. On the nose was a 1 00hp M-l 1 engine in a Townend-ring cowl, driving a two-blade metal propeller.

Modifications concentrated on the trailing – edge controls. According to Shavrov there were three movable surfaces on each wing, extending over 21 per cent of the chord. The outermost was a rectangular aileron, and the two inboard surfaces acted in unison as ele­vators. Most photographs and drawings show these surfaces as simple one-piece units hinged to brackets below the trailing edge and with a neutral setting of-5°. However, re­cently a drawing (reproduced here) was dis­covered showing the main surfaces operated

by servo action. The pilot’s control cables can be seen to drive a narrow-chord servo control which in turn moves the main surface. The neutral setting of the main surfaces can be seen to be adjusted by a longitudinal-trim wheel with cables to screw-jacks.

The BOK-5 was clearly a safe aircraft which impressed two of the Soviet Union’s best test pilots, but it remained a one-off which was soon forgotten.

Top and centre: Two views of BOK-5.

Bottom: BOK-5 servo control.