Engineers work off extra engine-blade weight

  • 09-May-2012 04:00 EDT
Image: 10959_13792_ACT.jpg

CTAL’s developmental composite blade incorporates titanium-bonded leading and trailing edges. (Rolls-Royce)

Changing from alloy to composite materials for engine fan blades is an identified path to reducing overall engine weight by a significant amount—typically up to 1000 lb.

Further weight reductions in nacelle structure in turn enable pylon and wing weight reductions that enhance aircraft performance and increase potential profitability. The gains, when spread across large airline fleets, could build into millions of dollars saved each year.

But this switch to composite blades has been tried before and failed initially as a result of insufficient resilience when it came to bird strikes. The technological knowledge about composite blade manufacturing was at a relatively primitive stage.

However, over the years new methods involving the laying up of the multiple crossed layers of composite material sheets have given a far stronger “woven” texture to the material that is far less likely to shatter when hit by birds or other foreign objects.

When combined with titanium tip edges, the composite blade benefits from the best of both worlds, with outstanding lightness along with extreme strength and the ability to resist damage.

The success of the GE90 from GE, currently the only engine option offered on the hot-selling Boeing 777-300ER, which features composite wide chord blades and titanium leading edges, shows that the composite era is now well established as more than a concept, for this stretched version of the 777 has developed a reputation for outstanding reliability.

It achieves its performance (typically carrying more than 300 passengers on 12-h long hauls) and has effectively replaced the 747-400, carrying almost as much payload over a similar distance but using only two engines instead of four.

Earlier this year, a new facility opened on the Isle of Wight, in Southern England, that will be devoted to developing new composite aero engine components. Technology developed under U.K. national and European Clean Sky R&T programs is now being commercialized in a joint venture between Rolls-Royce and GKN Aerospace known as CTAL. GKN is focused on the component and materials level while Rolls-Royce is leading on the system work package, which includes testing and certification. Extreme heat and cold testing is carried out along with impact tests. The big challenge is to get better aerodynamic and weight reduction properties from the composite blades but also reduce weight at a system level.

Rolls-Royce builds advanced production titanium fan blades that are lighter than the best current production composite blades. But the company believes that the development work currently under test has shown that aerodynamic efficiency on composite blades can be as efficient as on titanium blades, with a significant weight saving.

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