Tail rotors have been a necessary evil on conventional helicopters with single, main rotors. They help counter the torque, or twisting force, applied
to the airframe by the engine drive as it proceeds through the transmission to the main rotor blades. Without a counter force, especially when
hovering, the airframe, or body, would tend to spin in the opposite direction to the drive rotation
The NOTAR system
Glendale PD NOTAR
Two Special Enforcement Detail deputies riding on the skids of a LASD MD 530 NOTAR helicopter
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.
20% of Helicopter accidents involve the rear rotar blade damage. The Notar system is also quieter then convential tail rotors.An important by-product
of the NOTAR system is the elimination of the medium - to high - frequency vibrations and the noise caused by a conventional tail rotor. Inside the
cockpit, pilots report that the absence of vibrations is noticeable both in the pedals and the surrounding cockpit area.
The Notar helicopters are the only helicopters allowed to fly over the Grand Canyon thanks to their less noise pollution.
In operation, the NOTAR system draws low-pressure air in through an air 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 fed to two starboard side slots and a direct jet thruster.
The slots provide the necessary antitorque force. The rotating jet thruster provides direction control.
Russian Helicopters have gotten rid off tail rotors through another method of using two main rotor blades. This method comes at the price
Twin-rotor helicopter have more complicated transmissions compared to single rotor machines.The maintenance costs of all aircraft are roughly
proportional to the number of moving parts.This leads to greater design and production costs. For similar reasons, the maintenance costs of a
twin-main rotor system will also be higher than a single main rotor system.
Another major disadvantage with twin-rotor machines (tandems and coaxials), is the high parasitic drag of the rotor hubs and controls in forward
flight. Generally, the parasitic drag (quantified in terms of equivalent flat-plate area) of tandems and coaxials is higher than a single-rotor
helicopter when compared at the same gross weight. This means that single-rotor helicopters generally have the edge when it comes to climb and forward
The NOTAR seems to gets the best of two worlds with little if any draw backs.
Is this the future of Helicopter design? The system is safer, easier to fly, with less noise.
Could this be one reason the Comanche was scrapped? Perhaps in favor of a redesign with a NOTAR system?
[edit on 5-9-2004 by ShadowXIX]