Helicopter is now a common mean of transportation in all hard-to-reach for other modes of transport areas. Mountains and desert terrains, areas with poorly developed motor roads and without airfields are essentially for helicopters.
A lightweit 2-7 seater helipcopters with takeoff weight up to 2500 kg have become extremely popular in recent years.Their share on the global helicopter market has reached 75% during the last 10 years.For example, American firmcompany "Robinson" produced and sold 896 lightweight helicopters (2-seater R22 and 4-seater R44) in 2009. It is explained by their relatively low costs, compactness, the possibility of being located close to the owner's residence (the roof of the house or a small-sized platform next to it), simplicity and low maintenance costs. But almost all currently existing light serial helicopters, including R22 and R44, are powered by a single engine - either with an outdated piston type "Lycoming", "Franklin" (on helicopters with a takeoff weight up to 1500 kg), or or gas turbine type "Allison", "Turbomeca" (on helicopters with a takeoff weight more than 1500 kg). It is unreasonable to install 2 gas turbine engines on a light helicopter with weight up to 1500 kg, as it needs no more than 350-400l to fly, and this is the lowest power limit for gas turbine engines.
Currently, there is only one lightweight helicopter with 2 gas turbine engines: French
6-seater ECU-2 helicopter with a takeoff weight of 2600 kg and costs $ 2 500 000. The high cost of the helicopter is due to the fact that gas turbine engines are about five times more expensive than piston ones. Due to the above mentioned reasons, all existing lightwtght serial helicopters on the market (except for the "Ekurei-2") have one engine. Engine failure is leading to immediate landing in the auto-rotation mode of the bearing screw. Thus, such helicopter can not be used to perform transport tasks, for example, in the mountains or above the city due tosafety reasons.