The Bratukhin B-11 was a prototype Soviet twin-rotor transport helicopter and the last design of the Bratukhin aircraft design bureau to be built.[1]
Development
The B-11 was similar to the design bureau's earlier B-5, a twin-rotor helicopter, with each rotor driven by an Ivchenko AI-26 radial engine.[1] Each engine was housed in a pod on an outrigger with the related rotor above.[1] Designed for a 1947 air force design competition for a general-purpose helicopter. Two prototypes were built and flown in June 1948, test flights showed a problem with rotor-blade stall at high speed and high resonant vibrations in the whole helicopter.[2] In August 1948 the first prototype was grounded for investigation, but limited testing carried on with the second to find the causes of the problems.[2]
On 13 December 1948 a blade on the right-hand rotor of the second prototype broke, and the subsequent crash killed the two crew.[2] The prototype was then re-designed and re-built to overcome the problems, but when flying resumed in 1949 the stall occurred again.[2] Bratukhin further modified the helicopter in May 1950 with new rotor blades, but development was soon abandoned, and soon after the design bureau was closed down.
