Grigorovich I-Z

Purpose: To evaluate a fighter with APK recoilless cannon.

Design Bureau: Team led by Dmitrii PavlovichGrigorovich, inVT(internal prison) run by OGPU (secret police, later NKVD) at Factory No 39.

The story of the development in the Soviet Union of large-calibre recoilless guns, under the leadership of L V Kurchevskii, is outlined in the entry on the Tupolev ANT-23. By the end of the 1920s design bureaux were receiv­ing contracts for experimental fighters de­signed to be armed with such weapons. In late 1929 Grigorovich was sent to Central Construction Bureau 7, which was really Hangar 7 at Factory 39, an OGPU secure prison for designers. Here he led the design of the Z, a secret monoplane to be armed with two 76.2mm (Sin) APK-4 guns. To speed con­struction the powerplant group and forward fuselage of the first prototype were the same as those of the Polikarpov I-5, which was also built in Hangar 7. The complete aircraft, called I-Z (Fighter Z) was flown by Benedikt Bukhgol’ts in (it is believed) early May 1931. It was inspected by Stalin, Voroshilov, Molotov and others on 6th July 1931. Subsequently a small series of21 production I-Z fighters were produced at GAZ No 39. These were still re­garded as experimental. In February/March 1933 aircraft No 39009 was placed on a high
platform and used for firing trials, and in Sep­tember 1933 No 39010 underwent NIl-WS testing. Two of these aircraft were later used in Zveno trials, as described under Vakhmistrov. In 1934-35 Factory No 135 at Kharkov built a further 72, with modifications, designated IP-1. These saw only limited use, partly because of difficult spin recovery, but were not considered as experimental.

At this time monoplanes were still struc­turally difficult, and the wing, though of torch-welded stainless (Enerzh-6) lattice con­struction, still needed underwing bracing to the fixed landing gears. Apart from the semi – monocoque rear fuselage, the covering of the whole airframe was fabric. The prototype had a Bristol Jupiter, in a helmeted cowling, while the first production batch had the same 480hp engine built under licence as the M-22 and cowled in a Townend ring. The second batch, from Kharkov, had the 700hp M-25 (Wright Cyclone). The main landing gears variously had spatted wheels, plain wheels or skis. The guns were suspended from both main spars outboard of the struts (just in­board on the first prototype), and were fed at a slow rate from a seven-round magazine in the wing. A PV-1 machine gun was fitted to right of centre ahead of the windscreen to as­sist aiming using the optical sight. The tailplane was mounted high to avoid the rear blast from the APK-4s.

This neat aircraft did all that was expected of it, but none of Kurchevskii’s big guns ever became operational.