June 2, 2008 Helicopter development is hampered by the fact that for so long it has been a zero sum game, with designers only able to improve forward speed at the expense of hovering ability and low speed control, and vice versa. This, combined with other inherent design restrictions, has kept the top cruise speed for conventional helicopters at roughly 150—170 knots. Looking to overcome these limitations, Sikorsky Aircraft Corp. is working on a coaxial design aimed at realizing a cruising speed of 250 knots. First announced in 2005 and having recently achieved a major ground-testing milestone, the X2 is a scalable technology demonstrator that can hover, land vertically, manoeuvre at low speeds, and transition seamlessly from hovering to forward flight. In the words of Sikorsky’s president, Jeffrey Pino, it could prove to be a real ‘game changer’ for the industry.
Coaxial helicopters incorporate a second rotor above the body of the aircraft, eliminating the angular momentum and dissymmetry of lift caused by having only one rotor. This allows the helicopter to achieve faster speeds with greater efficiency, and without having to compromise hovering ability. Sikorsky is very optimistic about the technology’s scalability, claiming it can be effectively used on anything from Class IV UAVs to high-speed joint heavy lift transports with a 25-ton internal load.
Both rotors on the X2 Technology Demonstrator have four blades, and are powered by a LHTEC T800 turboshaft, which also drives a six-bladed pusher propeller on the rear of the model. The craft is expected to travel as fast as 256 knots, has a range of 1300km and a take-off weight of 3600kg.
The X2 demonstrator will incorporate new rotor blade designs with high lift-to-drag ratio, a fly-by-wire system with advanced flight control laws, transmissions with greater horsepower to weight performance, and active vibration control. The X2 also contains an automatic system that strops the rotor blades from exceeding the speed of sound and shattering from the airflow – a necessary precaution for a helicopter traveling faster than 210 knots.
The recent blades-on ground testing milestone brought the craft within “arm’s reach” of its maiden voyage. "The entire X2 TECHNOLOGY Demonstrator Program Team is extremely pleased that we continue to move our experimental program closer and closer to first flight,” said James Kagdis, Program Manager, Advanced Programs. ”We anticipate that reaching this particular milestone, as with those yet to come, will continue to pique the interest of our military, commercial and international customers regarding the potential that X2 TECHNOLOGY could have on their diverse missions around the globe."
The proof of concept technology demonstrator is scheduled to fly later this year.