I-7U and 1-75 Series

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The I-7U interceptor equipped with the Uragan-1 was developed once it became apparent that the I-3U would be grounded for lack of the right engine. The preliminary plans were completed in August 1956. The structure of the new aircraft was entirely reworked so that it could be powered by the Lyulka AL-7F turbojet, which delivered a dry thrust of 6,155 daN (6,240 kg st) and a reheated thrust of 9,035 daN (9,220 kg st). Except for a few standardized parts, the only piece of equipment common to both the I-3U and the I-7U was the Uragan-1 system Everything else was completely modified.

All of the main airframe assemblies were redesigned after recon­sideration of their basic principles. The fuselage diameter was increased, the wing sweepback С/4 was reduced to 55 degrees, and the gear kinematics were modified (the main gear retracted into the fuse­lage, their legs folding up inside the wing between the integral fuel tanks and the Fowler-type flaps). Many stamped panels were required for the wing and the tail unit The ailerons and other movable surfaces contained no ribs but rather a solid core. Armament comprised two NR-30 cannons located on either side of the fuselage alongside the wing root ribs and four optional automatic rocket pods under the wing with a total of sixty-four ARS-57M rockets.

The aircraft was moved to the test center on 26 January 1957 and on 17 April performed its first taxiing tests, during which the aircraft was lifted a few feet. The I-7U made its first flight on 22 April with G. K. Mosolov at the controls. On the thirteenth flight the landing gear on the right side collapsed as the aircraft landed, damaging the right wing. The aircraft was returned to the workshop for repairs and later made six more flights, the last one on 24 January 1958. On 12 February tests were canceled by the general designer. The aircraft was once more returned to the workshop; fitted with the AL-7F-1 engine, it became the 1-75F.

The tests had demonstrated the aircraft’s quick acceleration as well as its outstanding climb rate on either dry or reheated thrust, a distinc­tive feature of the 1-7U. On the other hand, the deflection travel of the stabilator proved to be sufficient at landing. When the aircraft reached Mach 1.6-1.65 it had a tendency to bank to the left, but its yaw stability remained satisfactory.

The resemblance between the 1-7U and the I-3U was quite superficial. The I-7U was in feet an entirely new machine.

The weapons system was the only common feature of the I-7U and I-3U The cone housing the Almaz ranging radar is centered on the I-7U.

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Specifications

Span, 9.976 m (32 ft 8.7 in); overall length, 16.925 m (55 ft 6.3 in); fuse­lage length (except cone), 15.692 m (51 ft 5.8 in); wheel track, 3.242 m (10 ft 7.6 in); wheel base, 5.965 m (19 ft 6.9 in); wing area, 31.9 mz (343.4 sq ft); empty weight, 7,952 kg (17,525 lb); takeoff weight, 10,200 kg (22,480 lb); max takeoff weight, 11,540 kg (25,435 lb); fuel, 2,000 kg (4,410 lb); wing loading, 319.7-361.7 kg/m2 (65.5-74.1 lb/sq ft); max operating limit load factor, 9.

Performance

Recorded max speed with engine dry rating, 1,420 km/h (767 kt) (not recorded with reheated thrust because the Pitot-static probe readings were not corrected at high speeds; the max speeds that follow are design specifications); max speed with reheated thrust, 1,660 km/h at

5.0 m (896 kt at 16,400 ft); 2,200 km/h at 10,000 m (1,188 kt at 32,800 ft); 2,300 km/h at 11,000 m (1,242 kt at 36,080 ft); climb to

5.0 m (16,400 ft) in 0.6 min; to 10,000 m (32,800 ft) in 1.18 min; ser­vice ceiling, 19,100 m (62,650 ft); landing speed, 280-300 km/h (150-162 kt); endurance, 1 h 47 min; range, 1,505 km (935 mi); takeoff roll, 570 m (1,870 ft); landing roll, 990 m (3,250 ft).