NOTAR

NOTAR (No Tail Rotor; German no tail rotor ) is a system developed by McDonnell Douglas for the torque balance in helicopters without the typical tail rotor configuration. The patent is owned by Boeing.

Development

Test vehicle was a Hughes OH - 6, in which the tail boom had been reinforced and a ducted propeller air blew into the boom. This flowed through a longitudinal slot on the right underside of the boom out again. At the rear, an adjustable nozzle was installed to control the thrust. The first flight of this system took place on 17 December 1981.

Similar systems in which most of the exhaust stream of the engine has been used already in the 1940s in the Cierva W-9, the Hiller J -5 or tested in the 1950s at the Aerotecnica AC-12 Norelle.

Principle of operation

In principle, the torque produced by this needs to be balanced in a helicopter having a single main rotor, in order to counteract a rotation of the trunk and to be able to control the helicopter about its vertical axis (yaw axis). Usually this is achieved by the horizontally acting tail rotor, the notary system generates the counter-force, however, by a directed jet of air ( boost ) of the outlet by a variable steering at the end of the boom.

This effect is supported by further placed only along one side of the tail boom outlet nozzles. The air coming out there leads from the main rotor downwash flowing down to the rounding of the boom. Here, the Coanda effect is utilized, the flow around a cylindrical tube with a one- slot-shaped blow-out tangentially to the tube surface. This generates in superposition with the flow around a circulation with suction and pressure side. This creates an additional, the main rotor torque opposing force which stabilizes the body in the longitudinal direction.

The advantages of the NOTAR system are in the lower risk potential for people in the takeoff and landing zone as well as in lower noise levels because the propeller is on the inside and there are no noisy turmoil between the main and tail rotor.