Hercules: The Finlet Countdown

25 November 2021
The University of Dayton Research Institute (UDRI)
Reducing drag time for the legendary C-130 Hercules

In flight and service for more than half a century, the C-130 has proven to stand the test of time. This workhorse, while originally designed to transport troops and equipment in the combat zone, is the epitome of a versatile resource with basic and specialized versions have provided services such as airlift support, aeromedical missions, weather reconnaissance, aerial spray missions, firefighting duties for the U.S. Forest Service, natural disaster relief missions, and more.

These vast capabilities come with design features such as a highly upswept afterbody which allows for easy loading and airdrop through a rear cargo ramp, but also results in a massive flow separation that occurs in flight. This upsweep and subsequent flow separation, according to the Mercer Engineering Research Center's (MERC) Computational Fluid Dynamics (CFD) analysis produces two large aft body, counter-rotating vortices. The resulting drag is as much as 11% of the total aircraft drag at cruise. According to their reported findings, reducing the drag would improve the range, loiter times, and payload capacity of Air Force Special Operations Command's (AFSOC) C-130 fleet.

While costly devices are available to reduce the drag and further improve the functionality of the C-130, what if instead the Air Force could design, develop, and manufacture a solution for itself allowing for in-house adjustments for the C-130's variants? In coordination with UDRI, MERC, and the Strategic Enterprise Solutions Corporation (SESC) the Air Force has set out to do just that.

Following MERC's CFD analysis, which projected in late September of 2019 that at least a 6% drag reduction could be achieved, UDRI began concept manufacturing and mounting designs working alongside MERC and SESC throughout the journey. The original part, additively manufactured with aluminum at UDRI on an EOS M290 Metal 3D printer, had a successful fit check in spite of COVID-19 delays on July 20-23, 2020 on the C-130 located in Dayton, OH at the Research Institute. With lessons learned, the part is ready to begin the details design process including a structural analysis. With continued success, the part will move into a new phase including a second fit check and further testing and qualifications to ensure optimal results.