Two prototype helicopters that will be evaluated by the US Army deploy carbon-fiber-reinforced composite materials in both the aircraft structure and the blades. The light tactical S-97 RAIDER helicopters are the successors to Sikorsky Aircraft's award-winning X2 Technology demonstrator aircraft, which achieved twice the average cruise speed of a conventional helicopter at more than 250 knots in a 2010 demonstration.
UK-based Hexcel Composites' HexWeb honeycomb core composite and HexPly prepreg composite technologies will give the aircraft's structure and blades light weight and extreme strength.
Composite structures and prepegs will help give the super-fast S-97 RAIDER demonstration helicopter strength and light weight. (Source: Sikorsky Aircraft)
Hexcel is one of 35 companies that are members of the team self-funding the design and build of the demonstrator helicopters. Sikorsky announced its supplier team recently during the Association of the US Army's ILW Aviation Symposium and Exposition in National Harbor, Md. Other team members include BAE Systems, Garmin, General Electric, Goodrich, Honeywell, Lockheed Martin, and Northrop Grumman.
The S-97 RAIDER program will demonstrate the potential military applications of Sikorsky's breakthrough X2 rotorcraft design, which was also used in the X2 Technology demonstrator aircraft. To provide significant improvements in maneuverability, hover efficiency, high/hot climate performance, and speed, X2 rotorcraft design features coaxial counter-rotating main rotors, and a pusher propeller, which yields cruise speeds of up to 220 knots (253mph), with dash speeds of up to 240 knots (276mph) or higher. In 2010, the National Aeronautic Association awarded Sikorsky the Robert J. Collier Trophy for the helicopter's speed achievement, and for its potential as a future rotorcraft technology.
I would imagine composites will play a really important role in defense aircraft and these prototype models are just a starting point. I would also think there are some real synergies between these military helicopter blades and the work being done to deploy carbon-fiber-reinforced composites for wind turbine blades. Perhaps some cross-industry IP sharing is in the cards, particularly between those wind turbine projects with government backing.
One of the great collateral benefits of this is that we'll get a broader database of how composites perform over time -- i.e., more hours in the air. This will play into the experiential information we need on delamination risk, which is something that everyone's wondering about as composites move into primary structures on commercial aircraft (e.g., the wings on the Boeing Dreamliner).
Wind turbine use of composites in their blades may well provide some information for defense use of composites. In the computer area, it was use of commercial components that allowed an incredible expansion of the use of comuters on the battlefield. Of course there are adaptations that have to be made. One difference between wind turbine blades and helicoters is the speed with whcih the blades spin. Another is the size. On the other hand, there are lots of wind turbine blades out there in lots of operaitonal environments. There should be some good information that can be shared.
It's interesting that the material suppliers are sharing a significant part of the cost of these prototypes. Of course, the advantage to them is obvious; not only do they benefit if the Army decides to buy the helicopter, but they also benefit from having a high-profile showcase application of their material, which may help them to get into other applications. Is this kind of arrangement common?
As Pederson said, the main difference is that the scale of use in military (and early commercial) applications was way below what's being considered for commercial aircraft today. That change in volumes manufactured also changes much about the processes, their monitoring requirements, and the nature of the risks for failure. The last is also affected by the fact that we're talking primary structures, and these are commercial planes.
I think the points Beth and naperlou make about wind turbine blades are good ones: yes there are differences between the uses in size and rotation speed. But the similarities should allow us to increase the database, as Alex says.
Dave, that's a really intriguing question. I've been wondering the same thing. I think there's a growing trend, but the trend may be a little broader. We've got these suppliers here coming together and self-funding. We've got aerospace component companies buying composite makers, as I report here, although I've seen similar announcements since:
Funny, this talk of partnerships and cross-collaboration got me thinking about a composites design tool I wrote about recently. Collier Research, which makes a composites structural sizing and analysis tool and it actually was born out of NASA, and the now commercial tool, HyperSizer, helps engineers determine the best structural layup for composite materials used in everything from space crafts to wind turbines.
Finally a place where CF can earn it's keep! The skin and core of a helicopter rotor have little bearing on it as everything almost is in the capspar or whatever they call it. Most are made up of CF pultruded rods to take the forces.
Heli and windgen blades have very different roles and not much in common other than materials. WG blades and aircraft wings, bodies is another story with much in common.
Windgen and heli blade speeds are similar as both are limited by the speed of sound/drag. Also why they turn so slow rpm to keep the tips from getting close to mach1. Otherwise higher rpm would be much cheaper to work with.
And about time they went to twin rotors which is about 15-20% more eff/ payload plus the added speed plus more stable.
Delam is mostly a process/QC problem which extremely hard with CF. Prepreg and pultrusion are best way to make CF work. If you screw up just 10% then your advantage over FG is gone.
Jerry, could you expand a bit on your comments regarding CF composite delam: "Delam is mostly a process/QC problem which extremely hard with CF." What's hard--having the problem in the first place? Catching it?
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