The Mil Mi-42 was a projected assault/transport helicopter featuring the NOTAR concept, fit to replace the Mi-40 program. The Mi-42 program was launched in 1985, however the entire Mi-40 program, which include the Mi-42 program, was cancelled because Soviet Union's Collapse.
Starting in 1985 a further development along the lines of these Mil Mi-40 was sought Which would provide higher performance in the "Aerial Infantry Fighting Vehicle" category. Primary roles included landing troops, providing rapid redeployment, escort, close air support and tactical strikes. Its secondary roles would contain transport of equipment, medivac, SAR/CSAR, reconnaissance and communications.
A vectoring NOTAR system would replace the tail rotor. It was hoped that this could be far more durable and increase safety of people working in the vicinity of the tail. Finally, it was planned that, as the aircraft picked up speed and aerodynamic forces began to have a stabilising effect, the vectoring system would angle the NOTAR nozzle so that it faced straight backward - hopefully allowing the Mi-42 to attain its required top speed of 380-400kph.
The design was intended to be heavily armored and carry a mobile forward firing cannon and four hardpoints (equivalent armament to the Mil Mi-28 gunship). because of the complex requirements (essentially mixing those of a truck, transport helicopter, attack helicopter and strike aircraft) the design uncontrollably took on complexity and weight.