NRC Technology Gives a Boost to the Canadian Aerospace Industry

When Bell Helicopter Textron Canada (BHTCL) needed a made-in-Canada solution, they contacted the NRC Institute for Aerospace Research (NRC Aerospace) to manufacture a next-generation wingbox for a tiltrotor aircraft. The NRC team led a multi-partner collaboration that produced the innovative wingbox and expanded manufacturing capabilities within the Canadian aerospace community by transferring the technology to Delastek, a small company in Quebec.

Tiltrotor aircraft combine the vertical lift capability of a helicopter with the speed of a turboprop airplane by using tiltable (rotating) propellers, or proprotors, for lift and propulsion. Angling the proprotors to direct thrust downward provides lift for vertical flight, as in a helicopter. Once the vehicle is aloft, the proprotors are slowly tilted forward to make it fly like a turboprop aircraft.

The Bell Eagle Eye UAV is an example of a tiltrotor aircraft.

BHTC needed a Canadian supplier for the rib chords, which form the skeleton for the wing. Unfortunately, the technology to make these composite rib chords did not exist in Canada. This is where NRC Aerospace lent their expertise. In collaboration with Delastek, a Quebec-based company that serves the aerospace and transportation industries, NRC scientists developed two key processes to enable them to produce the tiltrotor wingbox.

"We ended up reverse engineering what Bell Helicopter was doing in the States," said Dr. Jeremy Laliberté, a Research Officer at NRC Aerospace's Structure and Materials Performance Laboratory (SMPL) in Ottawa. "In the end, what we produced was a generation ahead of what they had developed."

Composites are made from at least two components; a high strength fibre and a resin binder.   Fibreglass is the most common example of a composite. More composite materials are being incorporated into aircraft because they are lighter than metal and have the strength to withstand the stresses of flying. Composite parts are less expensive to operate and maintain than those made of metal because they don't corrode and they contain fewer fasteners. 

Developing the composite manufacturing process is challenging, however. A successful composite part requires a highly precise mould. In addition, the composite 'recipe' has to be optimized to create parts that are consistent, strong and of very high quality.

The NRC Aerospace team used resin transfer moulding (RTM) to make the composite rib chord. In this process, several layers of reinforcing fabric that give the final composite its strength are laid into the mold.

Automated cutting table where rib chord preform material is cut.

Next, the mould is closed and the liquid resin is injected under pressure which pushes the resin into the mould and prevents bubbles from forming. The mould is then heated to cure the resin. Once the resin has hardened and cooled, the mould is opened, the part is removed, and, after some final trimming, the rib chord is ready to go.

Modular mould in which rib chords are formed and cured.

The most expensive part of the process is creating a custom mould for each rib chord in the wingbox. To minimize this expense, NRC Aerospace scientists designed a modular mould with a variety of internal inserts to produce more than one type of rib chord.

"We established ourselves with the wingbox project and gained a lot of experience with RTM," says Dr. Mehdi Hojjati, Group Leader of the composites group at the NRC Aerospace Manufacturing Technology Centre in Montreal.  "We delivered high-quality parts, on time."

Composite rib chord inspected by NRC researchers.

NRC Aerospace scientists also built a fixture to adhere the rib chords to the wing skin. The fixture holds the rib chord and skin in the proper orientation and provides temperature control to ensure a tight, even bond. 

"Our approach was unique in that it included cure monitoring and process control," said Dr. Laliberté.  "We added independent heater controls to ensure even heating along the entire rib and monitored the bond line so that, if anything went wrong during the critical 20 minute processing window, we could stop it, clean things up and start again."

Close monitoring, careful heat application and controlled adhesive bonding meant that very high standards of quality and repeatability were achieved. Overall, the project finished on time with every component passing inspection.

This project won an NRC Outstanding Achievement Award for its 'exceptional technical accomplishments, dedication to quality and commitment to clients.'  The technology was also nominated for a Howard Hughes Award given by the American Helicopter Society to recognize fundamental improvements in helicopter technology. 

Both the composite molding and the adhesive bonding technologies are being used at Delastek. The project team is currently undertaking other projects in which they will further apply their expertise in composite manufacturing, particularly for aerospace applications.

"This project has put Canada on the map in terms of composite technology demonstration," said Robert Fews, Research Director at BHTC.  "This proven technical capability, together with the outstanding working relationships experienced in the execution of this program, bodes well for future collaborative programs and demonstrates the relevance of NRC in generating a competitive edge for Canadian industry."

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NRC's Areas of Research: Aerospace

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