INDICADORES DE LIQUIDEZ

Purpose: To evaluate an aeroplane with a wing of variable area.

Design Bureau: NIAI, Leningrad.

In 1936 Grigorii (according to Shavrov, Georgii) Ivanovich Bakshayev, aged 18, joined the UK GVF, the instructional combine of the civil air fleet. He was eager to test his belief that a su- perior aeroplane could be created by arrang- ing for it to have a large wing for take-off and landing and a smaller wing for cruise. As the UK GVF was in Leningrad the NIAI adopted the idea. Called RK (Razdvizhnoye Krylo, ex- tending wing), and also LIG-7 because it was the seventh project of the Leningrad Institute GVF, the aircraft was built quickly and was first flown in August 1937. Remarkably, the

system worked smoothly and reliably (better in the air than on the ground), and it led to the even more unconventional RK-I fighter.

Apart from the wing the RK was a simple monoplane of mixed construction, with en- closed cockpits for a pilot and observer and powered by an uncowled l00hp M-l 1 engine driving a laminated-wood propeller. It had a two-spar wing of constant narrow-chord M-6 profile, braced by pairs of wires above and below to the top of the pilot's hood and to a pyramid truss under the fuselage. At the root was what looked like the root section of a much larger wing, with CAHI (TsAGI)-846 aerofoil profile, but with a span of only 50cm (1ft 7%in). Inside this, nestling tightly like a set of Russian Matroshka dolls, were five further

plywood wing sections each of 50cm span. The observer could crank these out by a cable mechanism, each adding 45cm (1ft 5%in) to the span of the large-chord region. It took 30 to 40 seconds to crank the telescopic sections out to their full extent, covering 60 per cent of the semi-span, and 25 to 30 seconds to wind them back.

Seemingly a 'crackpot' idea, the RK per- formed even better than prediction. It is diffi- cult to account for the fact that it got nowhere. The answer must be that it introduced an el- ement of complexity and possible serious danger, sufficient to dissuade any later de- signer from following suit.

RK, LIG-7

aircraft with the nose engine and rear fuse- lage attached to the thickened centre wing. This central portion contained two pairs of seats, that on the left in front being for the pilot. The entire front and top of this cabin was skinned in transparent panels, those along the sides sloping at 60°, two of them forming doors. The prototype had a ring- cowled engine, spatted main wheels and a broad but squat fin and rudder. Production aircraft had no cowling or spats, but had a re- designed wing root and a narrower rear fuse- lage and completely redesigned vertical tail. Several designers attempted a cabin of this kind, but all the others were very large air-

craft. In fact whether a blended wing/body aircraft can be hyper-efficient is doubtful, though the LK-1 did have useful STOL (short take-off and landing) qualities.

Dimensions (production aircraft) Span Length Wing area Weights Empty Fuel/oil Loaded Performance Maximum speed Time to climb 1 km Service ceiling Range Take-off run Landing speed/ run 12.47m 8.87m 27.6m2 746kg 170kg 1,160kg 154km/h lOmin 3,370m 850km 200m 65km/h 120m 40ft 11 in 29 ft Win 297 ft2 1,645 Ib 375 Ib 2,557 Ib 96 mph (3,281 ft) 11,000ft 528 miles 656ft 40 mph 394ft

N I A I R K , L I G - 7 / R K - I , R K - 8 0 0

Dimensions Span Length

Wing area (minimum) (maximum) Weights Empty Loaded 11.3m 7.34m 16.56m2 23.85 nf 667kg 897kg 37 ft % in 24 ft 1 in 178.25ft2 256.72 ft2 l,4701b l,9781b Performance (small wing)

Maximum speed Time to climb 1,000m to 2,000m Service ceiling Take-off run Landing speed/ run

Performance (large wing) Maximum speed Service ceiling Take-off run Landing speed/

run (both large wing)

156km/h 7.5 min 14.5min 2,900m 250m 105km/h 210m 143km/h 3,100m 135m 68km/h 110m 97 mph 3,281 ft 6,561 ft 9,514ft 820ft 65 mph 689ft 89 mph 10,171 ft 443ft 42 mph 361ft

Two views of RK, LIG-7.

NIAI RK-I, RK-800

Purpose: To create a fighter with variable wing area.

Design Bureau: NIAI, Leningrad.

From the start of his telescopic-wing studies young Bakshayev had really been thinking about fighters. He had regarded the RK mere- ly as a preliminary proof-of-concept exercise. He calculated that a fighter able to retract most of its wing area and powered by the M- 105 engine ought to be able to reach a world- record 800km/h (497mph), overlooking the fact that a fighter with a relatively small wing would have poor combat manoeuvrability. Indeed, as described below, he found a way to make the relative difference between the small and large wings even greater than in the RK, the ratio of areas being 2.35:1. In October 1938 he submitted a preliminary design sketch for the RK-I (Russian abbreviation for extending-wing fighter). After much argu- ment the concept was accepted by CAHI (TsAGI) and the WS. A one-fifth-scale model was tested in a CAHI (TsAGI) tunnel from Jan- uary 1939, but it was difficult to find an indus- trial base capable of building even the prototype. Worse, the RK-I attracted the at- tention of Stalin, who took a keen interest in combat aircraft. Excited, he demanded that this aircraft should use the M-106 engine, the most powerful then on bench test. Under

some difficulty a prototype RK-I was com- pleted in early 1940, but the M-106 engine (later designated VK-106) was still far from ready. The aircraft could have flown with the M-105, but nobody dared to fit anything but the engine decreed by Stalin. In order to do at least some testing a full-scale model was con- structed with the nose faired off, fixed landing gears and a projecting canopy, with no at- tempt to simulate armament or the radiator ducts in the rear fuselage. This mock-up was then tested in the CAHI (TsAGI) full-scale tun- nel. The resulting test report was generally favourable, but noted that sealing between the telescopic wing sections was inadequate. The CAHI (TsAGI) aerodynamicists neverthe- less concluded that with the M-106 the speed might be 780km/h (485mph). Lacking an en- gine the project came to a halt, and after the German invasion in June 1941 it was aban- doned. Bakshayev was appointed to super- vise increased production of the 156km/h (97mph) U-2 (Po-2) at Factory No 387.

The lifting surfaces of the RK-I were unique, and quite unlike anything attempted by any other designer. The aircraft was all-metal, the large fuselage being a light-alloy monocoque which would have housed the 1,800hp M-106 in the nose with the oil cooler underneath and surrounded by two 20mm ShVAK can- non and two 7.62mm ShKAS machine guns.

Behind the firewall were successively the fuel tanks, backwards-retracting single-strut main landing gears, enclosed cockpit and the gly- col coolant radiator with controllable air ducts on each side of the rear fuselage. The amazing feature was that there were two wings of equal span and narrow tapering chord, one in front of the cockpit and the sec- ond, set at a slightly lower level, behind. Each had upper and lower skins of spot-welded SOKhGSA stainless steel, and the rear wing was fitted with three hinged trailing-edge sur- faces on each side serving as flaps and ailerons. These movable surfaces, like the tail, were made of light alloy. The unique fea- ture was that on this aircraft the root of the large wing extended completely around the front wing and back almost to mid-chord of the rear wing. Nested inside it were 14 further wing profiles, which in 14 seconds could be winched out over the entire span by an elec- tric motor and cable track along the rear wing leading edge, which was at right angles to the longitudinal axis. Each section of the large wing comprised a Dural leading edge and rib with a fabric skin, the first section sealing the side of the fuselage in the high-speed condi- tion and serving as a wing end-plate in the ex- tended low-speed configuration. Shavrov gives the weight of all 28 telescopic sections as approximately 330kg (727.5 Ib). Changing

R K - 8 0 0

to the large-area configuration was intended to have no significant effect on the rod-oper- ated flight controls, a fact confirmed by CAHI (TsAGI). Bakshayev left drawings showing that a production aircraft would have had only nine larger telescopic sections, and vari- ous other changes.

Had an M-106 engine been available this aircraft might have flown. Pilots would then have been able to assess whether (as seems doubtful) the ability to fly with much less wing

area than needed for take-off and landing really offered any advantage to an aircraft designed to engage in close combat.

RK-I, RK-800, with lower side view showing full- scale model.

Sketches of RK-I showing its two configurations.

Dimensions Span Length Wing area (large)

(small)

Weights Empty Loaded (estimate)

Performance (estimated) Max speed (small wings) Endurance

Landing speed (large wing) 8.2m 8.8m 28.0m2 11.9m2 not recorded 3,100kg 780 km/h 2 hrs 27 min 115 km/h 26 ft 10s/, in 28 ft 1014 in 301 ft2 128ft2 6,834 Ib 485 mph 7 1.5 mph

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