Two European companies team on convertiplane study
By some accounts, riding as a passenger in the Bell Boeing V-22 Osprey military tiltrotor is memorable not for its comfort level but because of the aircraft’s pronounced vibrations.
Probably with this in mind, Eurocopter and AgustaWestland have undertaken a new joint research project in commercial convertiplane technology with the torturously contrived acronym “Nice Trip,” which stands for “novel innovative competitive efficient tiltrotor integrated project.” One major objective of the undertaking, which will leverage the results of previous European research projects, is to study four-blade rotors. This should significantly reduce vibrations and noise associated with the V-22 and the in-development, smaller Bell Agusta BA609, both of which have three-blade rotors.
The project uses the Erica, a conceptual tiltwing aircraft that has been used in European research, as a virtual platform. “We will build a complete one-fifth-scale model with full controls,” Christophe Serr, Eurocopter’s director of research programs for vehicle technology and new concepts, told AIN. The model will be tunnel-tested at DNW in the Netherlands and at Onera’s facility in Modane, in the French Alps. The two airframers plan to begin initial tests in the first half of next year. Evaluations of the complete 15-foot-span model will take place in 2010 and 2011.
The partners will also put together a rotor hub, main gearbox and four blades. These three systems have been or will soon be tested separately as part of ongoing research projects. Testing of the combination will take place in 2011 on Eurocopter’s rotor ground testbed.
The third subproject relates to ATC. Project partners want it to answer questions such as: How can a convertiplane be integrated into the traffic on approach? How can it be integrated into an airport’s taxiing traffic? What should be the procedure in the event of an in-flight engine shutdown?
A previous research project put much effort into the design of a hub for a four-blade rotor. “This makes the rotor diameter smaller but increases its rotation speed,” Serr pointed out. Therefore, the centrifugal force on each blade equals 132,000 pounds. Serr reported that this project provided a good understanding of hub strength and durability. “We made real progress in design methods,” he said.
However, a separate project on main gearbox design did not yield similarly positive results. According to Serr, the current design is too expensive. AgustaWestland will test this main gearbox soon.
Research in the area of fly-by-wire flight controls has been successful, Serr said. Control laws have to be highly sophisticated to optimize wing lift, drag and rotor thrust from engine nacelles and wings that can tilt independently. Wind-tunnel testing has yielded good results, Serr said.
Although many areas of research have shown promise, Eurocopter is not yet considering launching the development of a convertiplane in the future. “First we need to know what kind of certification rules apply; that is why we are closely watching the BA609,” Serr said. Among the open questions, for example, is whether a convertiplane will be subject to the noise standards for fixed-wing aircraft or helicopters.
Serr also questioned the Erica’s specifications. “A suitable engine does not exist for Erica,” he said. The Erica concept uses a growth Pratt & Whitney Canada PW125. Nice Trip would need 30 percent more power, which the engine maker cannot supply. An alternative would be a slower cruise speed of 310 knots. A 10-percent increase of the PW125’s power would then be enough. This increase would be feasible for the engine maker to provide.
Nice Trip is a $44 million (€35.5 million) research project that is scheduled to begin by December and last 4.5 years.