NOTAR

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NOTAR, an acronym for NO TAil Rotor, is a relatively new helicopter anti-torque system (see the helicopter article for more details} developed by McDonnell Douglas Helicopter Systems which eliminates the use of the tail rotor on a helicopter, yielding quieter and safer operation.

Contents 1 Development 2 Concept 3 Advantages/Disadvantages 3.1 Advantages 3.2 Disadvantages 4 Use 5 References 6 External links 7 See also

[edit] Development

Development of the NOTAR system dates back to 1975 when engineers at Hughes Helicopters began concept development work.^[1] In December 1981 Hughes flew a OH-6A fitted with NOTAR for the first time. A more heavily modified prototype demonstrator first flew in March 1986 (by which time McDonnell Douglas had acquired Hughes).

[edit] Concept

Although the concept, which uses the Coandă effect, took some time to refine, the NOTAR system is simple in theory and works to provide directional control the same way a wing develops lift.^[1] A variable pitch fan is enclosed in the aft fuselage section immediately forward of the tail boom and driven by the main rotor transmission. This fan forces low pressure air through two slots on the right side of the tailboom, causing the downwash from the main rotor to hug the tailboom, producing lift, and thus a measure of directional control. This is augmented by a direct jet thruster and vertical stabilisers.

[edit] Advantages/Disadvantages

[edit] Advantages

• Reduced noise

Benefits of the NOTAR system include greatly reduced external noise (NOTAR-equipped helicopters are among the quietest certified helicopters). This is because up to 60% of the noise from conventional helicopters is produced by the interaction of the tip vortices of the main and tail rotor.^[2]

• Increased safety and reliability

Helicopter accidents may be caused by the tail rotor striking tree branches, power lines, the ground or other obstructions. Eliminating the tail rotor removes this hazard and enables NOTAR helicopters to go where tail rotor layout helicopters cannot i.e. close to trees or buildings.^{[verification needed]}

They are also safer for ground crews to work near as there is no danger posed from a spinning tail rotor.^{[citation needed]}

• Reduced vibration

Since there is no interaction between tip vortices of the main and tail rotor, the operational vibration is reduced.^{[citation needed]}

• Reduced Pilot Workload

The thrust force of the coandă effect caters to the need of antitorque force. As the torque effect requires more antitorque, the coandă effect provides more lift to provide that antitorque.^{[citation needed]}

[edit] Disadvantages

• Efficiency

The NOTAR system is not as efficient as the tail rotor, and NOTAR helicopters sacrifice a few horse power as a result.^{[citation needed]}

• Maneuverability

Although generally agile and stable, at speed the properties of the airflow over the tail boom change, and the Coandă effect fails. The 'H'-shaped tail characteristic of NOTAR helicopters is used to provide anti-torque at speed using conventional moving control surfaces. As a result, the helicopter can be difficult to turn when traveling at speed, and the large control surfaces of the tail inhibit maximum sideways velocity.^{[citation needed]}

• Aerodynamics

The translating tendency and the tail rotor roll forces continue to exist.^{[citation needed]}

[edit] Use

There are three production helicopters that utilize the NOTAR system, all produced by MD Helicopters:

• MD 520N - a NOTAR variant of the Hughes/MD500 series helicopter is seen in the movie Mission: Impossible
• MD 600N - a larger version of the MD 520N, is seen in the James Bond film Die Another Day
• MD Explorer - a twin-engine, 8-seat light helicopter.

Their reduced operational noise means that they are well suited to urban use, and along with the increased safety and the ability to get close to buildings, they are becoming increasingly popular for law enforcement and air ambulance use.^{[citation needed]}

[edit] References

[edit] External links

• MD Helicopters

[edit] See also

• Tail rotor
• Other alternatives to conventional tail rotor
  • Fenestron
  • Tip jet rotor
  • Coaxial rotor
  • Tandem rotor
  • Synchropter