AFRL’s Advanced Power Technology Office helps ‘lighten’ C-5 energy footprint with composite technology

WRIGHT-PATTERSON AIR FORCE BASE, Ohio --  Finding ways to integrate technologies that are cleaner, lighter, multifunctional and energy efficient to reduce fuel costs and maintain the force’s aging fleet is a primary mission driver of work by the Air Force Research Laboratory’s Advanced Power Technology Office, based out of the AFRL Materials and Manufacturing Directorate. 

And, once again, the APTO team is proving that novel advances in aerospace material can make a big difference in aircraft fuel savings, maintenance and durability.

A new, lightweight composite RAM Air Inlet system for the C-5M Super Galaxy Transport Aircraft is set to begin a six month operational flight demonstration test in May, as a two year APTO-led project draws to a close.

The new air inlet pieces, designed to replace legacy aluminum honeycomb air inlets on the C-5, weigh less, cost less to manufacture and have a greater corrosion resistance than traditional inlet systems, increasing part life and aircraft availability while reducing maintenance costs.

“Novel advances in materials and technology today can save the Air Force money over the long term,” said Capt. Randall Hodkin, Aviation Project Manager for APTO. “This is a small part that alone may not affect overall fuel savings, but there are about 1000 (aluminum panels) on a C-5. We’re demonstrating a proof of concept for technology that can make a big difference.”

During aircraft periodic depot maintenance (PDM), typically four to five C-5 aircraft are taken out of service for complete servicing that includes everything from calibration of landing gear to specific part maintenance, application of new paint coatings and beyond. Depot maintainers noticed a trend towards corrosion in a number of the traditional aluminum RAM air inlets on the C-5 during the maintenance cycle.

Though aerospace grade aluminum has excellent corrosion resistance properties, the C-5 fleet is aging. As an aircraft is continually subjected to atmospheric conditions that may include corrosives such as oxygen, water vapor and salt, the material used on the aircraft may start to corrode, with pitting and etching appearing on the surface. If left untreated, this corrosion can eventually lead to cracks or a material failure.

The APTO team was approached to design a more corrosion resistant air inlet piece that could mitigate the corrosion issue and also be lighter, more durable and cost efficient to produce and maintain. This would also help address a shortage in the number of spare legacy air inlet pieces on hand to replace corroded parts. If these run out, an aircraft might be out of service even longer as maintainers would need time to repair versus replace the damaged parts.

Working in collaboration with the C-5 Systems Program Office, the Air Mobility Command fuel efficiency office, the University of Dayton Research Institute (UDRI), Applied Composites Engineering (ACE) and others, an air inlet comprised of a fiberglass honeycomb core with a carbon shell was designed to replace the corroded parts. Fiberglass lines the aerodynamic surfaces on the new inlet to mitigate potential galvanic corrosion that can occur when bonding an incompatible metal to aluminum parts. Stainless and titanium fasteners complete the inlet package, aimed at preventing corrosion in areas of installation.

Since the design data for the original parts did not exist since the pieces were manufactured so long ago, engineers reverse-engineered a legacy part to make sure they could develop this equivalent, if not better, air inlet. Legacy inlet components were 3-D scanned and modeled to develop baseline technical data for a new part, which the Air Force now has on record.

The newly engineered composite inlets were subject to significant testing ranging from material coupon tests to bird strike, hail impact and weather and corrosion testing in the laboratory environment to make sure they would meet the same stringent standards of the old parts.

“This new part is as strong, if not stronger. It’s a well-made part,” said Hodkin.

The resulting piece is 19 percent lighter than legacy inlets, weighing only 34 pounds versus 42. Moreover, the new air inlet costs almost $100,000 less per part to produce—a significant savings over the lifecycle of the aircraft.

This is a small part, but you are still saving a significant amount of money per part,” said Hodkin. “So not only can you cut weight and improve corrosion durability, but you can do it economically as well.”

Once flight testing is complete, the composite air inlet will be analyzed for performance. A determination will be made for either further improvement of the part or approval to transition the inlet for installation on other aircraft in the fleet.

Either way, the APTO team views this as a success for demonstrating the ability of state-of-the-art materials and technologies to augment the Air Force effort towards increased energy resilience.

“This is a demonstration of how advances in materials and technology can save the Air Force money,” said Hodkin. “The Air Force is focused on improving operational energy, and we’re helping to meet that need.”