In the summer of 1940 S.A. Kochierigin developed a new assault aircraft project called MMSh, short for Small Modification of the Sh (ММШ – М алая М одификация Ш турмовика) based on a Shvetsov M-81 powerplant.
The Kochierigin MMSh (Russian: Кочеригин ММШ) development of the Kochierigin Sh-2 appeared in 1940 in order to improve performance and lower construction costs.
The basis for the development of the MMSh was the Kochierigin Sh-2, but with the replacement of the M-87A engine by the 1,280 hp M-81. In an installation under the hood some enlarged oil radiators were located. The fuel was regrouped in 4 protected tanks.
The wings were wood and with a reduction in area to 18 m² (instead of the 24.15 of the Sh-2). There was the same ratio of decrease to the area of the tailplanes and the empennage.
The planned armament included only four ShKAS machine guns and a bomb capacity of 200 kg (which could reach 400 kg in overloaded version).
The preliminary drawings were analyzed in the NII VVS and generally received a positive evaluation. The project was approved by Ya. V. Smuskievich on June 27, 1940. In the analysis report of the preliminary drawings it was verified: – ” taking into account that the aircraft is practically built, it is necessary to prepare and test it… “.
The MMSh was actually completed, tested and recommended for series production as a light bomber. With the designation BB-21 it was assigned to Factory No. 292 for serial production. Soon the preparation was stopped to guarantee the Yatsenko I-28 and later the Yakovlev I-26.
Powerplant: One 1,280 hp M-81
Wingspan: 12.00 m
Wing area: 18 m²
Length: 10.00m
Take off weight: 3800 kg
Wing loading: 211 kg/m²
Power load: 2.97 kg/hp
Speed at sea level: 450 km/h
Speed at 5000 m: 520 km/h
Landing speed: 140 km/h
Time 6000 m: 11 min
Take-off run: 400 m
Landing run: 300 m
Range at top speed: 685 km
Maximum range at economic speed: 905 km/h
Accommodation: 2 crew
All Aero 