Bell’s XworX studying improved rotor blades

 - December 29, 2009, 9:11 AM
Bell Helicopter’s XworX special projects and rapid prototyping center exists to give customers added value, according to Nick Lappos, senior vice president for XworX. Lappos says XworX can “be more agile and use non-traditional methods” for things such as blueprint release and purchasing to get the job done faster. The facility does not run new programs such as the new twin-engine 429 or BA 609 tiltrotor. Rather, it works with the managers of those programs, as well as the managers of legacy programs, to craft solutions as requested.

“A program manager might come to us and say, ‘I need more capability [on this part of the helicopter].’ And two weeks later we come back with a bunch of possibilities. ‘You know if you swap engines or put this rotor blade on, or how about if we modified the fuel system?’ And then we launch a team with maybe 30 people on it and six months down the road we end up with a flying article that is close to what we could build for a customer.”

XworX also works on short-, medium- and long-term projects and with Bell’s suppliers to develop new technologies. Lappos cited XworX involvement in developing a new line of composite rotor blades and rotor heads as an example of a shorter-term project whose results could find their way onto production helicopters in two to five years.

“We’re creating a new family of rotor blades and heads for Bell that will achieve levels of aerodynamic efficiency that give us great performance in the hover and great forward flight speed,” Lappos said. Performance improvements are expected to translate into modest forward speed improvements, increased useful load, and substantially better high/hot performance. XworX has its own 32-foot-long autoclave and a whirl tower that are speeding this development.

An Alternative to On-aircraft Testing
The 60-foot-tall whirl tower suspends the helicopter’s control and rotor systems and allows the rotor to spin in an out-of-ground effect hover at low speeds with precise measuring. “We used to do it on the helicopter but found that we would get a lot more work done more quickly with a whirl tower,” he explained. The tower also gives XworX the freedom to test new blades to their limits. “You can exercise the rotor through full flapping and enormous thrust ranges. You can take the rotor to a couple of gs of trim capability while standing on the tower. It lets us see its dynamic response and if the blades are stable and strong enough long before we ‘fly’ them,” Lappos said.

Flapping is the range of blade angle up and down relative to the rotor head and it is a key part of the equation in the new rotor heads XworX is developing. “Bell has a great family of rotor heads right now, but going into the future we want to see if we can increase the rotor heads’ control power. We are developing a family of rotor heads that will give us almost twice the flapping of the current Bell product line.” The more you can tilt the rotor head, the more angle of flapping you can get on the rotor disk and the more control you can get on the baseline aircraft,” according to Lappos.

More flapping “gives you the potential for a much larger speed range,” he added. “The cyclic pitch range is really an important determinant of speed. As the rotor goes faster and faster, the pilot has to push the stick farther forward. If you have a smaller degree of flapping you can go only to a certain place before you have to stop because the rotor head would be uncomfortable being at that angle. By having larger flapping range you have a larger speed range. The flapping also determines the center of gravity, so the center-of-gravity range is proportional to the amount of flapping you permit. And that means we have a larger cg and a chance to rearrange the principal masses of a helicopter.”

New rotor heads will not yield significant performance improvements in existing helicopters because it would be cost prohibitive to relocate engines or fuel tanks, but for new designs, improvements could be significant, predicts Lappos. “If the helicopter is designed to serve oil platforms, you could put in a much bigger baggage compartment. Or you could rearrange the fuel cells so they are more easily reached, so there aren’t as many pumps, and check valves and as much plumbing because you have put them all in one place in the fuselage,” he explained.

Lappos says XworX is looking for more than just performance improvements with its new blades and rotor heads; it also wants to design them to be more durable and easier to manufacture. “We think the new family of rotor heads will make a big difference in first-pass quality, which will be nice for the cost of manufacture.”

Similarly, efficient manufacturing is also a big part of XworX new blade designs. “We built a blade design cell with manufacturing engineers and design engineers. We not only had to build the blades; we had to figure out how to build them, to get a good rate of production through a set of production tools,” Lappos said.

XworX is also working on integrated fly-by-wire controls and collaborating with leading suppliers to develop future avionics, hydraulics and electrical systems.

“Manufacturers should be expert in the intrinsic systems of their aircraft such as rotor blades and heads, transmissions and flight control laws,” Lappos said. “But there are a lot of things we would be happy to work on with other folks. We are working with some real pros in the aerospace industry with those types of system, working toward alliances and development of their items on our machines.”