If the inlet duct is to retain its function of providing sufficient air with minimum turbulence, it must be clean and flawless.
The Air Force Research Laboratory’s Manufacturing and Industrial Technologies Division and the contractor team of Cornerstone Research Group, A&P Technology and Spintech LLC conducted research to quantify the benefits of replacing legacy manufacturing processes with novel processes for the fabrication of an 11-foot-long, S-shaped engine inlet duct.
The legacy fabrication process for the inlet duct consists of composite material preimpregnated with a synthetic resin, applied by hand, to a multi-piece steel mandrel. The mandrel is packaged and placed in an autoclave for processing. An autoclave is essentially a heated pressure vessel which supplies heat to activate resin curing and pressure to ensure there is minimal absorbency in the fully cured composite part.
The approach replaces the hand applied composite prepreg with an automated overbraid process that applies dry fiber to a mandrel. The heavy, multi-piece steel mandrel was replaced with a light-weight, single-piece shape-memory polymer mandrel. The dry braided carbon fiber was processed with a low-cost epoxy resin, using a vacuum-assisted resin transfer molding process.
One of the primary goals of this program is to understand part cost and production time benefits from introducing the new tooling and processing solutions.
The team completed element analysis finalization of the overbraid architecture, fabrication of a shape memory polymer forming tool and construction of the SMP mandrel that will serve as the tool during the preform overbraid process.
Because of inlet duct geometrical complexity, multiple iterations were necessary to optimize the overbraid machine settings and thus minimize composite material wrinkling. A total of four inlet ducts will be fabricated and legacy part cost and production time will be compared to the new design.
“We believe that the introduction of a reusable shape memory polymer mandrel together with the automated overbraid process and an oven based VARTM composite cure will lead to significant cost and cycle time reductions,” said Craig Neslen, manufacturing lead for the Low Cost Attritable Aircraft Technology Initiative in the Manufacturing and Industrial Technologies Division. “Quantifying the manufacturing benefits and validating structural integrity will be critical to establishing a positive business case and convincing designers and manufacturers that the new materials and processes should be incorporated into future low cost engine inlet duct designs.”
The final inlet duct will be delivered to the government for further integration into the Aerospace System’s Directorate’s complementary airframe design and manufacturing program. Personnel at the Aerospace Vehicles Division will conduct static ground testing of the integrated braided fuselage and inlet duct structure.
“While we have yet to define all of the implications of attrition tolerance on design criteria and the resulting manufacturing materials and processes utilized, we do have a baseline with threshold requirements for strength and stiffness which we will assess via full-scale airframe ground tests,” said Ray Fisher, aerospace engineer in the Aerospace Vehicles Division.
The Air Force Research Laboratory is the primary scientific research and development center for the Air Force. AFRL plays an integral role in leading the discovery, development, and integration of affordable warfighting technologies for our air, space, and cyberspace force. With a workforce of more than 11,000 across nine technology areas and 40 other operations across the globe, AFRL provides a diverse portfolio of science and technology ranging from fundamental to advanced research and technology development.
For more information, visit www.afresearchlab.com.
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