Airbus Helicopters X3 (X Cubed) Experimental Compound Helicopter
The compound Eurocopter X3 helicopter development combines a traditional mast-mounted main rotor with side-mounted propeller units.
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The Eurocopter X3 (or simply as the "X-Cubed") is an developmental rotary-wing platform intended to validate a helicopter design at speeds exceeding 250 miles per hour (typical operating speeds for modern helicopters range from 150 to 160 miles per hour). The design is based on a highly-modified Eurocopter EC155 model yet differentiated by the addition of side-mounted propeller units and highly noticeable fuselage protrusions not common to the EC155 design. As of this writing, the X3 is currently undergoing flight testing with the prospect of the design being used in a future commercial- or perhaps military-minded rotary-wing platform (weapons placement could prove problematic in the X3's current engine arrangement). If successful, the X3 will usher in something of a new age considering high-speed rotary-wing flight. First flight of the Eurocopter X3 was completed on September 6th, 2010. On May 12th, 2011, the X3 completed a recorded flight with speeds in excess of 267 miles per hour. Naturally, the X3 is being billed as the "World's Fastest Helicopter" though there are other similar competing helicopter designs in the works elsewhere (the Sikorsky X2 demonstrator is one such competitor). All told, the X3 has proven a sound concept with excellent agility and impressive speeds during its presentation flights meaning that its application in the real world could be rather limitless as helicopters go.
The overall design of the X3 features pleasing and well-contoured lines from nose to tail. As in the EC155, the X3 sports a finely sharpened nose assembly with the two-person cockpit just aft. A passenger compartment is located directly behind the cockpit seats. The main powerplant is fitted within the engine compartment mounted atop the fuselage. The twin engine arrangement powers the main rotor installation as well as a pair of propeller-based systems and there is no conventional tail rotor as seen on contemporary helicopters (the portside propeller spins at less RPMs than the starboard mounting, countering the inherent torque effect from the main rotor). As such, energy is not wasted along a long shaft to the tail rotor but instead added to the forward speed output. The empennage is smooth and rounded to the extreme aft end to which a pair of horizontal fins are affixed. The undercarriage is completely retractable.
Power for the X3 comes from the 2 x Rolls-Royce Turbomeca RTM322 series turboshaft engines each delivering 2,270 shaft horsepower. These powerplants rotate a five-bladed main rotor atop the fuselage as well as a pair of five-bladed tractor propeller systems fitted to wingstubs along the fuselage sides. Cruise speed is expected to be in the vicinity of 252 miles per hour. A service ceiling of 12,500 feet is estimated.
Only a single prototype form of the X3 has been completed. Some sources state that EADS intends the X3 to be a true production-ready helicopter and not a technology demonstrator or "proof of concept" design. Only time will tell for sure.
In 2014, the sole X-3 example was given to the Musee de l'Air for display.