Helicopters: High-Speed + Stealth

choi

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Faster helicopters | Racing Rotors; Chop, chop. Economist, May 19, 2011
http://www.economist.com/node/18710100

Note:
(a) The article says, "As the aircraft accelerates, the airspeed of a blade (and thus the amount of lift it provides) increases when that blade is moving forwards and decreases when it is moving backwards. Eventually, the imbalance becomes unsustainable."

This is called "dissymmetry of lift."

Please
(i) BROWSE
helicopter
http://en.wikipedia.org/wiki/Helicopter#Limitations
(section 5.1 Limitations)
(ii) and READ
how Helicopters Work. Start-Flying.com, undated.
http://www.start-flying.com/new%20site/heli1.htm
(Dissymmetry of lift)

I myself could not quite understand what the Wiki said, that is why I ask you to browse (i). The graphic in (ii) is more helpful.

* While on this web page, read on to the next section "Counter-Rotation Vs Contra-Rotation"--for teh Economist article will discuss "contra-rotating: "The X2 uses a pusher propeller mounted at the rear and has a pair of contra-rotating main rotors, one positioned above the other. That arrangement produces an equal amount of lift on each side."

It is stated in (ii): "It [contra rotation] also tends to relieve some of the effects of retreating blade stall as both sides of the aircraft have advancing rotor blades." This is because one propeller moves clockwise while the other, counter-clockwise--rendering an advancing rotor blade (each in a propeller) on each side of helicopter.

(b) X2 TECHNOLOGY™ demonstrator. Sikorsky, undated.
http://www.sikorsky.com/Innovation/Vision+of+the+future/Technologies/X2+Technology

The web page does not say much. Please watch a video clip instead:
Sikorsky X2 Technology helicopter achieves 250kt - Sep 2010. Youtube, Uploaded by theworacle on Oct 6, 2010.
http://www.youtube.com/watch?v=gK7ktLXhq88

(c) X3 flies in the Eurocopter sky in France. YouTube, Uploaded by EurocopterEADS on Dec 17, 2010.
http://www.youtube.com/watch?v=HyAvFCHCYDw&feature=related


(2) Bill Sweetman, Bin Laden Raid May Have Exposed Stealth Helo. Aviation Week, May 5, 2011.
http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=defense&id=news/awx/2011/05/03/awx_05_03_2011_p0-318248.xml

Note: helo (n; by shortening and alteration): "HELICOPTER"
www.m-w.com

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