SPL (Hydro-1) by I.V.Chetverikov

The idea of aircraft cooperation with submarine on remote naval theaters developed in few directions:

• employment of long-range land-based recco planes;
• long-range flying boat with possible refueling at sea;
• small short-range aircraft launched from the submarine itself;

Third option was explored in Great Britain (late 20's), but aircraft turned to be oversized for contemporary and projected submarines. In addition, British plane had poor seaworthiness. Soviet designers, in addition, had to rely mostly on the wood and steel tube rather than light alloys.

In 1931 I.V.Chetverikov made a bold effort to overcome the problem by making aircraft fit in a 7.5m long 'hangar' tube (diameter 2.5m). Strict demands were applied to aircraft flight readiness and storage time - 3 to 5 minutes. Those demands could not be fulfilled for no cost. Tail surfaces area was small and its lever arm was quite short, resulting in insufficient stability. Limited engine power demanded to hide crew in deep cockpit to keep airdynamic good and to lower the gravity center. View field for the observer was quite limited. Aircraft carried neither armor, armament or bomb load, and had no provisions for catapult launch.

First prototype (OSGA-101) had no provision for wing folding, but used as a test platform of the aircraft layout. The SPL was finished in December 1934. It was almost identical to the predecessor, but was slightly smaller.

Tail stabilizer was made as a biplane box to provide sufficient surface area within restricted size. Wings could be folded backwards without disconnecting the control wires. Sliding rear engine struts allowed to 'sink' the engine assembly into the tail boom free space - also without disconnecting any controls.

In the beginning of trials SPL was flown with light aluminum Townend ring on the engine, which was later removed without much harm to performance. Trial program was fulfilled on August 29, 1935.

SPL could be prepared for flight in 4...5min and 'packed' into watertight container in 3...4min. As demanded, container size was 7.45mx2.5m diameter. Despite all demands were fulfilled, it was clear that tiny aircraft provides no 'room' for development and as military plane will be obsolete in short time. It was renamed 'Gidro-1' (Hydro-1) and received Aeroflot markings.

In 1936 Gidro-1 was demonstrated at Milan International Airshow.

Small aircraft had a record ceiling for its class - 5400m. Pilot A.V.Krzhizhevskij (who performed trial program on the SPL) established two other records on this plane:

• September 21, 1937: speed 170.2km/h on 100km route
• October 7, 1937: range 480km
SPL (22k b/w) as seen at many sources including "History of aircraft construction in the USSR", Vol.1 p.528



Predecessors	Modifications
OSGA-101	None

References	Links
"History of aircraft construction in the USSR", Vol.1 p.341-342;	....

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Created February 25, 2000

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