NOTAR

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MD Explorer (German police)
MD Explorer (German police)

NOTAR, an acronym for NO TAil Rotor, is a 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.[1]

Contents

[edit] Development

Development of the NOTAR system dates back to 1975 when engineers at Hughes Helicopters began concept development work.[2] In December 1981 Hughes flew a OH-6A fitted with NOTAR for the first time. The OH-6A helicopter (Serial number 65-12917) was supplied by the U.S. Army for Hughes to develop the NOTAR technology. A more heavily modified version of the prototype demonstrator first flew in March 1986 (by which time McDonnell Douglas had acquired Hughes Helicopters). The original prototype last flew in June 1986 and is now at the U.S. Army Aviation Museum in Fort Rucker, Alabama.

A production model NOTAR 520N (N520NT) was later produced and first flew on May 1, 1990. It later crashed on September 27, 1994 when it collided with an AH-64D while flying as a chase aircraft for the Apache.

[edit] Concept

Diagram showing the movement of air through the NOTAR system.
Diagram showing the movement of air through the NOTAR system.

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.[2] 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.[1]
  • 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.
  • Reduced vibration
Since there is no interaction between tip vortices of the main and tail rotor, the operational vibration is reduced.
  • 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 some power as a result.[citation needed]
  • Maneuverability
Although generally agile and stable, at high forward airspeeds 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 Helicopters 520N NOTAR
MD Helicopters 520N NOTAR

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

  1. ^ a b kulikovair.com
  2. ^ a b Frawley, Gerard: The International Directory of Civil Aircraft, 2003-2004, page 155. Aerospace Publications Pty Ltd, 2003. ISBN 1-875671-58-7

[edit] External links

[edit] See also