Aircraft engine inlet ducts provide the engine compressor with a constant supply of air to prevent the compressor from stalling. Since the inlet is directly exposed to the impacting airflow, it must create as little drag as possible. The smallest gap in airflow supply can cause major engine problems as well as significant efficiency losses.
Part of the Air Force 2030 Science and Technology strategy includes the deployment of low-cost Unmanned Aerial Systems in mass to assist in future near-peer engagements. In order to realise this vision, new manufacturing strategies need to be identified which can support the rapid manufacturing of high-quality aerospace components at costs that are lower than what is currently available using legacy manufacturing processes.
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 pre-impregnated 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 over-braid process which applies dry fibre to a mandrel. The very heavy multi-piece steel mandrel was replaced with a light-weight single-piece shape-memory polymer mandrel and the dry braided carbon fibre was processed with low-cost epoxy resin using a vacuum-assisted resin transfer moulding process.
One of the primary goals of this program is to understand the part cost and production time benefits from introducing the new tooling and processing solutions.
The team completed element analysis finalisation of the over-braid architecture, fabrication of a shape memory polymer-forming tool and construction of the SMP mandrel that will serve as the tool during the preform over-braid process.
We believe that the introduction of a reusable shape memory polymer mandrel together with the automated over-braid process and an oven based VARTM composite cure will lead to significant cost and cycle time reductions
Mr. Craig Neslen, manufacturing lead for the Low Cost Attritable Aircraft Technology Initiative
Because of inlet duct geometrical complexity, multiple iterations were necessary to optimise the over-braid machine settings and thus minimise 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.
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.