EC-130 Posted April 4, 2008 Report Share Posted April 4, 2008 Firstly, specifics have been given on the A160T's optimum-speed-rotor whisper-mode technology. Most helicopters' blades spin at a predetermined rate, set for best performance at full forward speed. This means that they waste energy - and produce unnecessary racket - when hovering or moving slowly. Not so the A160T, which can vary its rotor rate to suit its speed, and so lurk or sneak about relatively quietly - not unlike the black helicopters in the film Conspiracy Theory, for instance. It seems that the A160T is "roughly four times quieter" than comparable conventional choppers. -- http://www.theregister.co.uk/2008/04/01/a160t_back_in_black/ However, it is the patented Optimum-Speed Rotor (OSR) concept and its accompanying two-speed transmission that Boeing believes represent the game-changing aspects of the A160T design in terms of performance and low noise. In conventional helicopters, the RPM of the rotors is normally set for a maximum forward speed at a maximum weight at a certain critical altitude. At maximum forward speed, the tip of the advancing blade is traveling at speeds just below Mach 1, which avoids the drag, vibration and noise encountered at higher transonic speeds. But this means that at any other flight conditions, particularly low-speed forward flight, the rotor RPM is higher than needed, creating additional drag and consuming extra fuel. Several ways of getting around this conundrum have been developed successfully and tried in a few vehicles. These include the Lockheed XH-51A compound helicopter, which used both a fixed-wing and propulsive engine to enable rotor RPM to be reduced, and the more recent Bell-Boeing V-22, which tilts the rotor itself. Other attempts have been made to improve helicopter maximum forward speeds by using two-speed gearboxes that allow the rotor to rotate at two RPM values while maintaining a constant engine RPM. However, Boeing believes the OSR goes beyond these attempts because it allows the RPM to be reduced for lower-speed flight conditions, substantially cutting fuel consumption and therefore increasing range and/or payload. The key breakthrough in the OSR concept is the design and construction of the A160T's rigid, but extremely light composite rotors. These overcome the structural dynamics problems normally associated with significant changes of rotor RPM by having a continuously decreasing flap, lag and torsion stiffness, as well as mass, from the root to the tip. Weighing around 52 lb., each blade is constructed of a carbon-epoxy spar/shank and a leading edge made from the same material. The trailing edge is a lightweight section made of thin carbon-epoxy top and bottom skins and a full-depth honeycomb core. The blades are mounted in a steel, hingeless rotor system and move only in pitch through a beefed-up bearing system designed to resist moments that are substantially greater than those for an articulated rotor system. Due to the blade stiffness and lightness, the OSR is able to operate over a wide RPM range at full rotor lift load, close to the rotor excitation frequencies. This is possible because of the rigidity of the blades in relation to the feathering or pitch axis. -- http://"http://www.aviationweek.com/aw/generic/story_generic.jsp?channel=awst&id=news/aw033108p1.xml&headline=Boeing%20Rotary%20UAV%20Aims%20To%20Set%20Records%5b/ In simpler terms: The Hummingbird features a unique optimum speed rotor technology that significantly improves overall performance efficiency by adjusting the rotor's speed at different altitudes, gross weights and cruise speeds. -- http://www.boeing.com/ids/news/2007/q3/070928a_nr.html This also saves on the amount of fuel used. The helo they compared noise signatures with was a Bell 407. Very intersting stuff ,if you ask me. Quote Link to comment Share on other sites More sharing options...
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