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.
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.
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?
CF is shiny black with a very high surface tension means it really doesn't like to wet out throughly and because of the color, can't tell when it is completely wet out. With FG it is white and turns clear when fully wet out.
Even one area like this can down a helicopter/plane or in my case million $ racing sailboats in the FasnetForce10 race in the UK losing their pricy CF rudders .
Which really come down to do CF corectly one needs pressure resin feed very well designed or better, pultrusion forcing an much higher CF/resin ratio be squeezing it.
Or prepreg is great or very labor intensive of many thin layers I normally do.
And 1 small slipup and the 10% advantage CF gives disappears leaving one with a 10-20x's cost underspec piece.
For spars/wings, blades pultrused CF rods should take 90+% of the forces with the rest for shape, stiffness and hold the CF in columm is the lowest cost, weight, is the winning app.
And I just finishing details on a contract to build Composite 2kw wind generator blades of 16' dia which in many areas will power an eff home at costs well under coal for a customer and do my own design as well. Cost complete is about $3k/kw installed and they should work 50 yrs.
Customers blade like normal ones and mine is a variable pitch one without moving parts be tayloring the fibers, area, etc to make it twist as, when I want it too. This alone increases eff 25% while being lighter, easier to build.
Jerry, thanks for the detailed reply. It sounds like you're saying it's tough to avoid delam during the CF composite manufacturing process--or perhaps during the process of making components out of the composites?--compared to FG. It's interesting that something as simple as the presence of absence of a color change can make such a big difference! It also sounds like the specific process method for making composites can make a big difference.
It's mostly a QC problem as Boeing had with the Italian 787 parts they just couldn't build so they had to move the factory IIRC
You can make very good part with CF but you need people with experience and constant QC or your reject pile becomes very costly.
When I'm sailing new waters I always sek out local knowledge can make the difference in a pleasent cruise or losing the boat on some uncharted rocks. Same really in most fields, real life intrudes, things one would never expect, on carefully laid plans. This is especially true with CF where experience counts.
Sadly too many armchair quarterbacks and few who actually make things.
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?
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.
This is a really a great move. With the advancements in the field of SHM ( Structural Health Monitoring) systems it is possible to explore the possiblilties hitherto a bit cumbersome. Aircraft manufacturers are incorporating more and more composite materials into their new aircraft structures. Airbus' giant A380 is made of 25 percent composite materials, while about 50 percent of the weight of the Boeing 787 Dreamliner is composite, a dramatic increase over the approximate 12 percent used for B777.
Composites have already taken over the small plane and kitplane industry. Now just eating it's way up the size chain.
A really good thing about most composites is they can be made from renewable or extremely common materials like sand and various biomass from fat to celulose with RE.
CF was and maybe still is made from carbonized Rayon thread which is made from celulose IIRC. Most if not all plastics, resins can be made from biomass.
With it's other advantages like lightweight, easy start up costs, doesn't oxidize and flexibility means it will be the future of transport and many things now done with metals which will become increasingly costly.
For instance starting up a Car production line in steel is about $1B vs one in Composites $10M. Sadly if 4wheels the legal is $15M so I'll build 2 and 3wh EV subcars legally motorcycles with almost no legal costs.
Jerry, thanks for all the detailed info. It's interesting to hear about composite use for awhile in small aircraft, since the other "root" of their use has been in military aircraft going back several decades.
Re delam, Boeing is having ongoing problems with this, although they claim it's minor and won't slow production this time:
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