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NOTAR is an anti-torque system for helicopters that replaces the tail rotor with fans in the tail boom, using the Coanda effect to create an airflow boundary layer. The system was developed by McDonnell Douglas Helicopter Systems and is used in the MD 520N, MD 600N, and MD Explorer helicopters. It eliminates the disadvantages of a tail rotor and makes helicopters equipped with NOTAR equipment the quietest in the industry.
NOTAR is an acronym for an anti-torque system created by McDonnell Douglas Helicopter Systems for use in helicopters. The actual acronym comes from the words “NO TAIL Rotor,” which describes how the system works. When employed, the NOTAR system completely nullifies the use of a tail rotor and instead uses a system of fans within the tail boom to create an airflow boundary layer; This is made possible by the Coanda effect, which is the tendency for fluid jet propulsion to be attracted to nearby surfaces.
The variable pitch compound blade fan is the driving force behind the NOTAR system, which allows the helicopter to produce simultaneous low-pressure, high-volume ambient air. This air production is what pressurizes and stabilizes the trailing arm. This collected air is expelled through two slits next to the trailing arm, which is what initiates the Coanda effect. Effectively, this turns the rear cabin into a sort of “wing,” giving the plane 60 percent of the lift needed for hovering. In the midst of actual forward flight, the NOTAR system’s vertical stabilizers provide most of the thrust, while directional control is still handled by the helicopter’s standard direct-jet thrusters.
The effects of such a system were recorded for testing and analysis as early as 1945 in the British “Cierva W.9” helicopter. The actual development of what is now known as NOTAR began in 1975 by engineers at Hughes Helicopters. The first aircraft to fly with a modernized version of the NOTAR system was the Hughes OH-6 Cayuse, in December 1981. By the time McDonnell Douglas Helicopter Systems acquired Hughes Helicopters, a modified prototype of the OH-6 Cayuse had also been developed. That historic helicopter now has a place at the US Army Aviation Museum.
The modern application of the NOTAR system is wholly controlled by the company that developed it, McDonnell Douglas Helicopter Systems. The MD 520N, MD 600N and MD Explorer were the only production helicopters to use the NOTAR system in 2011. According to McDonnell Douglas Helicopter Systems, the use of NOTAR completely eliminates the disadvantages of a tail rotor, which includes a long drive axles, suspension bearings and unnecessary gearboxes. Helicopters equipped with NOTAR equipment are said to be the quietest in the industry.
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