Eurocopter says its hybrid X3 helicopter has attained its “Step 1 speed objective: attaining a true airspeed of 180 knots (333 km/h) in level flight at a reduced level of engine power” ahead of schedule. The European rotorcraft manufacturer Friday said the feat was achieved at the French DGA Flight Test centre at Istres late last month.
The company reminds the X3, a converted AS365 Dauphin, made its maiden flight on September 6. The top speed of a standard Dauphin is 165 knots (306 km/h). Eurocopter in a statement says “Step 2” of the project is aiming at sustained cruise speeds in excess of 220 knots. This compares to the 250 knots achieved by the Sikorsky X2 in mid-September using a single pusher propeller at the end of its tail boom.
The X3 is equipped with two turboshaft engines that power a five-blade main rotor system, along with two propellers installed on short-span fixed wings. “This hybrid configuration creates an advanced transportation system that offers the speed of a turboprop-powered aircraft and the full hover flight capabilities of a helicopter. It is tailored to applications where operational costs, flight duration and mission success depend directly on the maximum cruising speed,” Eurocopter says in a statement.
The X3 will seek to combine “excellent vertical takeoff and landing capabilities with fast cruise speeds of more than 220 kts,” the company adds. Eurocopter envisions a wide range of applications for this concept, including long-distance search and rescue (SAR) missions, coast guard duties, border patrol missions, passenger transportation and inter-city shuttle services. It could also be well-tailored for military missions in Special Forces’ operations, troop transportation, combat SAR and medical evacuation – benefitting from the hybrid aircraft’s combination of higher cruise speeds with excellent vertical takeoff/landing performance.
In the flight testing performed thus far, the flight envelope has been opened with and without autopilot to validate the basic hybrid demonstrator aircraft’s stability and handling characteristics and the X3 has reached an altitude of 12 500 feet (3810 meters). It also performed manoeuvres with left and right turns at bank angles of up to 60 degrees.
X3 flights, to date, were performed by Eurocopter test pilot Hervé Jammayrac and flight test engineer Daniel Semioli. “The X3 has performed extremely well, demonstrating handling and flight qualities that are exactly in line with our ground-based simulator evaluations,” Jammayrac said. “This helicopter is really built for speed, and our test team looks forward to taking the X3 to the next steps of its flight regime.”
Jane’s Defence Weekly last month reported Eurocopter, Sikorsky and others are “all struggling against laws of physics to increase helicopters performance,” which according to British Army Major General Barney White-Spunner “have reached a limit.” The French ADIT agency’s newsletter recently reported that to counter this statement, “engineers are struggling to make progress on fundamental challenges such as retreating-blade stall, advancing-tip Mach drag, and reverse-flow region disappear, in order to achieve higher performance.”
On the high-speed front, ADIT notes the US Defence Advanced Research Projects Agency (DARPA) is sponsoring Boeing and the Virginia Polytechnical Institute in developing an aerodynamic disc that contains retractable blades to be used for the hover. Once retracted the disc will provide lift, with propulsion coming from variable thrust ducted propfans to reach cruise speed between 300 and 400 knots.