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Zveno (Russian: Звено, Chain link or a military unit "Flight") was a parasite aircraft concept developed in the Soviet Union during the 1930s. It consisted of a Tupolev TB-1 or a Tupolev TB-3 heavy bomber acting as a mothership for between two and five fighters. Depending on the Zveno variant, the fighters either launched with the mothership or docked in flight, and they could refuel from the bomber. 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 with good results against strategic targets in Romania during the opening stages of the German-Soviet War. The same squadron afterwards also carried out a tactical attack against a bridge over the River Dnieper that had been captured by advancing German forces.〔Lesnitchenko, Vladimir ''Combat Composites: Soviet Use of 'Mother-Ships' to Carry Fighters, 1931-1941'' Air Enthusiast No.84 November/December 1999 pp. 4-21〕 ==Development== In June 1931, Vladimir Sergeyevich Vakhmistrov of the NII VVS (''Nauchno-Issledovatel'skiy Institut Voyenno-Vozdushnykh Sil'' – scientific test institute of the air force) started work on combinations of fighters rigidly attached to heavy bomber aircraft. The system was envisioned to serve several purposes: # Delivery of fighters beyond their conventional range # Provision of bombers with escort fighters # Use of fighters for dive bombing with heavier bombs than they would be able to take off with on their own # Using the added thrust of parasite aircraft to get a heavily-laden bomber airborne. 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.〔 The fighters were rigidly attached via pyramid-shaped metal frames with bomb latches controlled by the fighter pilots (on Zveno-1, the front latches were controlled by the bomber crew, while the back latch was controlled by the pilot, this was changed to all-pilot control in the next version).〔 The original design included umbilical fuel lines which permitted the fighters to use fuel from the bomber while attached,〔 although this was not fully implemented in practice. The first successful flight of Zveno-1 using a Tupolev TB-1 mothership and two Tupolev I-4 fighters mounted on top of the wings took place on 3 December 1931. An error in the sequence of opening the latches by the bomber crew resulted in one of the fighters prematurely separating, but the TB-1 with an I-4 attached to one of the wings remained in controlled flight and the second fighter was soon uneventfully deployed.〔 After latch control was fully moved into the fighters, the normal launch procedure consisted of pilots opening the tail lock and then pulling on the control stick to open the front locks and separate from the bomber.〔 As predicted, the presence of docked fighters had a minimal impact on performance of the mothership, and Zveno-2 Tupolev TB-3 carrying three Polikarpov I-5 fighters handled the same as an ordinary bomber.〔 To mount the aircraft on the wings, they were pushed up special ramps but the centerline aircraft had to be lifted on top of the fuselage by hand. This was so cumbersome that the centerline I-5 became a permanent fixture on top of the Zveno-2 TB-3 and never started in the air.〔 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 fifth powerplant for the bomber mothership.〔 The Zveno-3 in which TB-3 carried two Grigorovich I-Z fighters under the wings presented a different challenge — the I-Z was a monoplane with fixed landing gear which touched the ground while it was suspended under the mothership. To accommodate the uneven ground during takeoffs, the fighters were attached via a floating frame that permitted vertical movement relative to the TB-3. However, immediately after takeoff the I-Z pilots had to push forward on the control sticks to lock the frame in the fixed bottom position — if the fighter-bomber was not rigid in flight, the bomber became extremely difficult to control.〔 During one of the test flights, I-Z pilot Korotkov incorrectly timed the locking maneuver and the lift generated by his fighter broke the docking frame and crashed him into the bottom of the mothership's wing. As the bomber came in for an emergency landing with both fighters still attached, the slow landing speed of the TB-3 resulted in loss of lift for the I-Z which fell away, killing Korotkov.〔 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.〔 The problem of safe underwing attachment was solved with the appearance of the Polikarpov I-16 fighter with retractable landing gear. This permitted the use of the same rigid mounting frames as for the top-mounted aircraft.〔 The mothership and its fighters were unofficially nicknamed the ''Vakhmistrov's Circus'' (Цирк Вахмистрова). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Zveno project」の詳細全文を読む スポンサード リンク
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