Zveno project

The definitive Zveno-SPB using a TB-3 and two Polikarpov I-16s, each armed with two 250 kg (550 lb) bombs, was used operationally as a strategic weapon system with good results against targets in Romania during the opening stages of the German-Soviet War.

The system was envisioned to serve several purposes: In all Zveno configurations, all aircraft were piloted and all had their engines running — it was expected that the combined thrust would more than offset the weight and actually improve the performance of the mothership compared to conventional bombers.

[3] At one point, the centerline I-5, still with a pilot at the controls to operate the engine, had the wings and the tail surfaces removed and was used purely as a fifth powerplant for the bomber mothership.

[3] During one of the test flights, one I-Z pilot, Korotkov, incorrectly timed the locking maneuver and the lift generated by his fighter broke the docking frame and he crashed him into the underside of the mothership's wing.

[3] This was the most serious accident of the entire Zveno program despite the inherent complexity of carrying as many as five aircraft, performing mid-air launches and dockings, and damage to the motherships by propellers and landing gear of the fighters.

Tests with various combinations of aircraft determined that top-mounted configurations presented the most difficulty in docking due to turbulent airflow coming off the mothership's wings.

[2] The problem of safe underwing attachment was solved with the introduction of the Polikarpov I-16 fighter with retractable landing gear, permitting the use of the same rigid mounting frames as for the top-mounted aircraft.

[4] The military ordered 40 carriers to be split between the navy and army, but the Soviets were worried of an invasion by the Germans, and production was shifted toward proven weapons.

[5] In 1938, Vakhmistrov devised the 'Zveno-SPB (Sostavnoi Pikiruyuschiy Bombardirovschik, "Combined Dive Bomber") which consisted of a Tupolev TB-3-4AM-34FRN mothership and two Polikarpov I-16 Type 5 fighters.

The three-aircraft Zveno-SPB had a total takeoff weight of 22,000 kg (49,000 lb), a top speed of 268 km/h (145 knots, 165 mph),[2] and a range of 2,500 km (1,350 NM, 1,550 mi).

[4][page needed] By 1939, government support for the project had waned, the Navy canceled all of its orders, and the Air Force reduced the number of fighters from 40 to 12.

[4][page needed] However, Soviet military observers noted the success of the German Junkers Ju 87 Stuka dive bombers in the opening stages of World War II.

All were attached to the 2nd Special Squadron of the 32nd Fighter Regiment of the 62nd Aviation Brigade of the Black Sea Fleet Air Force stationed in Yevpatoria, western Crimea.

[4][page needed] Mirroring the nickname of the Zveno experiments, the squadron was dubbed 'Shubikov's Circus' (Цирк Шубикова) after its commander Arseniy Shubikov.