How The NOTAR System Works

NOTAR stands for NO TAil Rotor. The technology was pioneered by by Hughes Helicopters Inc, now McDonnell Douglas Helicopters in 1975. The first successful flight of an OH-6 (aka MD 500 ) was in the early 1980's. Work progressd at MDH and the final product flew in the form of a MD 530N in December 1989.

NOTAR works by channeling air through the tailboom to the end of the tail. This diagram shows the flow:

James R. Van Horn, chief of NOTAR technology, says that except for the introduction of turbine engines, "the NOTAR system represents the first significant configuration change to conventional helicopters since 1939 when Igor Sikorsky flew the first conventional rotocraft. "The new system uses the Coanda effect of air flowing over or around the surface of the tailboom to create lateral lift. This counteracts the torque of the main rotor. The NOTAR system eliminates drive shafts, gearboxes, and the rotor unit itself. This reduction in the parts count is a distinct advantage over conventional tail rotor craft."

NOTAR has many benefits, not the least of which is safety. Most accidents involving helicopters relate to the tail rotor. It's exposed and very low to the ground. NOTAR complete eliminates this problem. It also eliminates up to 50% quieter than conventional tailed helicopters. This is primarily because over 60% of total noise generated by a helicopter is due to interaction of main and tail rotor tip vortices. By eliminating this you make a very quite vehicle.

Technical Dirt

To operate the NOTAR system draws air in through an intake located at the top of the airframe to the rear of the main rotor shaft. A variable pitch fan pressurises the tailboom to a relatively constant 0.5 psi. The air is then fed to three places- two slots located at 70 and 140 degrees around the tail and a "thruster". The slots generate lift through the Coanda effect.

Stephan a. Hanvey of McDonnell Douglas Helicopter explains: "the main rotor downwash energy (on the OH-6, downwash velocity was about 55 fps) is normally dissipated as essentially symmetric separation on both sides of the tailboom in a hover. The pressurised boom inject low-pressure air at 250 fps onto the Coanda surface (outer surface of the tailboom) which results in the deflection and produces about two-thirds of the required anti torque force. This force is predictable. It is controlled by the appropriate location of the slot and control of the air jet that exits from the slot."

The tail thruster is movable and is used to control the helicopter's yaw attitude.

Very recently, model helicopters have come into this technology as well. Vario, one of the leaders (the leader in my opinion) has developed a MD 520N model that utilizes the NOTAR principal. As I find more images of these I will post them- Vario is not real public with pictures of how it works.... Below are two pictures from their site of an MD 520N. Neither one are full size....