Ilyushin's concept to meet the 1947 requirement for a superior aircraft to the Il-10 in performance and firepower was a heavily armored, single-engine, all-metal, low-wing monoplane powered by the newly developed M-47—also known as the MF-45Sh or M-45Sh—liquid-cooled engine, which developed at takeoff. The design's most notable feature was the pilot's cockpit mounted directly above the engine, reminiscent of the
Blackburn Blackburn and
Blackburn Cubaroo. Furthermore, the cockpit was situated directly behind the four-bladed propeller to maximize pilot visibility. The
windshield extended down to the propeller hub and provided the pilot with a 37° downward field of view; in a medium dive he could view targets directly underneath the aircraft. As was traditional with Ilyushin's ground-attack aircraft the Il-20 used a load-bearing armored shell to protect the pilot and gunner as well as the engine, fuel, lubrication and cooling systems. The thickness of the armor varied between and weighed a total of . The pilot's canopy used armored glass thick for the main windshield and for the
quarterlights. The obliquely-mounted fuselage cannon were thought to be too difficult to aim and were not included in the prototype; the weight savings allowed the ammunition for the four 23 mm Shpital'nyy Sh-3 wing-mounted guns to be increased to 900 rounds. One additional innovation in the prototype was that they could be adjusted on the ground to fire at a 23° downward angle in addition to the normal level position. The prototype was completed on 27 November 1948 and its first flight was shortly afterwards on 4 December. The best speed that the Il-20 could manage was only at an altitude of , slower than the Il-10 at the same altitude, possibly a consequence of the increased drag and weight penalties inherent in the greater fuselage cross-section and area as a result of the placement of the pilot above the engine. The new M-47 engine proved to be defective with severe vibration problems. Other problems were that the Air Force was not satisfied with the armament and that access to the engine for routine maintenance was severely hampered by the placement of the cockpit over the engine. Another concern was the close placement of the cockpit to the propeller; this was believed to increase the risk to the pilot if he had to bail out or make a
belly landing—in which case the bent propeller blades might hit the canopy. These issues, coupled with emerging jet engine technology, led to the cancellation of the Il-20 program on 14 May 1949. ==Specifications (Il-20)==