Editing NOTAR (section)

==Concept==

Although the concept took over three years to refine, the NOTAR system is simple in theory and works to provide some directional control using the [[Coandă effect]].<ref name="Frawley Civil"/><ref>{{cite web |title=NOTAR Technology |publisher=MD Helicopters |year=2006 |url=http://www.mdhelicopters.com/products.php?id=NOTAR |url-status=dead |archive-url=https://web.archive.org/web/20070312013423/http://www.mdhelicopters.com/products.php?id=NOTAR |archive-date=12 March 2007}}</ref> 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,<ref group=notes>NOTAR is an American-designed system and so this is true for American-made helicopters whose main rotors rotate counterclockwise (viewed from above). Many helicopters made elsewhere, such as France and Russia, have clockwise rotating main rotors and with the opposite resultant torque would require the slots to be on the left.</ref> causing the downwash from the main rotor to hug the tail boom, producing lift, and thus a measure of directional control. This is augmented by a direct jet thruster and vertical stabilisers.

Benefits of the NOTAR system include increased safety (the tail rotor being vulnerable), and greatly reduced external noise as tail rotors on helicopters produce much of the aircraft's sound. NOTAR-equipped helicopters are among the quietest helicopters certified by [[FAA]].<ref name="FAA AC 36-1H">{{cite web |last1=Federal Aviation Administration |title=AC 36-1H - Noise Levels for U.S. Certificated and Foreign Aircraft |url=https://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/22942 |access-date=27 June 2022}}</ref>

<gallery widths="200px" heights="200px">
File:NOTAR System.svg|'''1''' Air intake '''2''' Variable pitch fan '''3''' Tail boom with Coandă Slots '''4''' Vertical stabilizers '''5''' Direct jet thruster '''6'''&nbsp;Downwash '''7''' Circulation control tailboom cross-section '''8''' Anti-torque lift
File:Notar helicopter.png|Diagram showing the movement of air through the NOTAR system
File:Helivectormd.jpg|[[MD Helicopters MD Explorer|MD 900]]
</gallery>