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20. Fuel cells (left and right)
21. Electronic component assemblies and associated wire harnesses
22. Instruments
23. Landing gear assembly
SYSTEM DESCRIPTION
57
11.3 NOTAR® ANTI-TORQUE SYSTEM
Greater Safety:
U.S. FAA, NTSB and U.S. Army Studies have shown that 21 percent of all crashes are due
to tailrotor strikes or loss of tail rotor effectiveness. NOTAR® systems eliminate these
problems.
Reduced Noise
Designed and tested to be 50 percent quieter than any other helicopter. This results in
detection distances that are far superior to other aircraft.
Reduced Pilot Workload
Using the Coanda Effect to provide tail boom lift and anti-torque, the system is more stable
and easier to control. This effect reduces the sensitivity to wind direction on helicopter
control, through providing an important tactical advantage during combat operations.
Low Pressure Air System
Since the NOTAR® system uses low-pressure air, it is not sensitive to holes made in the
tailboom by fire from automatic weapons. Studies have shown the NOTAR® system is 60
percent less vulnerable to small arms fire than tail rotor systems on comparable helicopters.
11.3.1 DESCRIPTION OF THE NOTAR® SYSTEM
The NOTAR® system is an anti-torque system made up of an enclosed fan driven by the main rotor
transmission, a circulation control tailboom, a direct jet thruster and a horizontal stabilizer with two
vertical stabilators.
SYSTEM DESCRIPTION
58
11.3.2 NOTAR® System Components
The vertical stabilizers are connected to the pilot’s anti-torque (rudder) pedals. The left
stabilizer moves through approximately 29 degrees of motion and provides sufficient control
power for autorotation. It serves the additional purpose of unloading the thruster during forward
flight to permit optimum cruise performance.
In hover flight, the circulation control tail boom provides the majority of the required main rotor
anti-torque. This is accomplished by two slots along the tailboom that energize the downwash
flow from the main rotor. The result is lift in a horizontal direction that replaces the push of a
conventional tail rotor. The direct jet thruster provides the remaining anti-torque and
maneuverability for yaw control and directional changes. In forward flight, the vertical
stabilators, in conjunction with the direct-jet thruster, provide the required anti-torque and
directional control.
11.3.3 REDUCED AIRCRAFT VIBRATION
The inherent stability of the standard MD 500 is further improved by the elimination of the
exposed tail rotor assembly, which reduces overall helicopter vibrations and increases
passenger comfort while reducing pilot fatigue.
SYSTEM DESCRIPTION
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11.3.4 LOW EXTERNAL NOISE
The elimination of the high-tip-speed tail rotor assembly makes the MD 520N® the quietest turbine
helicopter in the world. Recent comparative FAA tests conducted by MDHI indicate the MD 520N®
is a minimum of 50 percent quieter than comparable helicopters. This lower noise signature makes
the MD 520N® a “good neighbor’ when used in areas where noise is objectionable. Lower noise
levels also increase survivability in hostile operational roles.
SYSTEM DESCRIPTION
60
80% Accidents
Other than Tail
Rotor
6% All Accidents
Avoidable 14% Accidents
Saved with
NOTAR® System
11.3.5 INHERENT SAFETY
The NOTAR anti-torque system eliminates accidents and mishaps caused by the exposed tail
rotor striking objects in flight, and significantly reduces ground incidents with people or
equipment. Potential damage caused by foreign objects is also eliminated. Inherent design
capabilities of the MD 520N® reduces the susceptibility to loss of tail rotor effectiveness and
the problems associated with quartering tail winds. The power and stability of the MD 520N® in
various wind conditions increase operational safety.
11.3.6 IMPROVED HANDLING
The excellent handling qualities of the MD 500 series have been further improved with the
addition of the NOTAR® system. The MD 520N® has high control response provided by the
fully articulated five-blade rotor system. Transient positive load factors of 2.8g’s and negative
load factors of 0.0g’s are attainable with the MD 520N®. The NOTAR® system allows side and
rearward flight speeds above 30 knots, low sensitivity to wind direction, 80 percent fewer pilot
controls inputs and rapid turning rates.
STANDARD EQUIPMENT
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12.0 MD 520N® Standard Equipment
*Required Options Included in Base Price as of 2008
Airframe
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MD500 Series TechDescription Feb09(15)
