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NFAC wind tunnel testing demonstrates successful integration of refueling, monitoring systems

  • Published
  • By Bradley Hicks

It turns out two systems developed to serve separate purposes were made for each other.

The pairing of an aerial refueling apparatus and instrumentation to boost its functionality was recently tested  in the Arnold Engineering Development Complex National Full-Scale Aerodynamics Complex, effectively combining these two Small Business Innovation Research, or SBIR, projects in simulated flight.

This integrated system, tested this past summer in the 40- by 80-foot wind tunnel at NFAC, located in the NASA Ames Research Center at Moffett Field in Mountain View, California, represents the marriage of two individual Science and Technology efforts originally developed in response to independent needs.

The first of the SBIR projects is an innovative hose and drogue system. This effort was initiated to address the need to provide a more stable aerial refueling platform so that the aircraft receiving the fuel could engage the drogue more safely and efficiently. The drogue, which resembles an open parachute, is attached to the refueling hose and serves to stabilize the hose while the aircraft is in flight and to help facilitate the connection between the refueling hose and the receiving aircraft.

The Actively Stabilized Refueling Drogue System, or ASDRS, was developed by Analytical Mechanics Associates, or AMA. The system is capable of counteracting small-scale disturbances on the aerial refueling drogue in flight.

“NFAC provided a truly unique capability to test this emergent technology,” said Chris Hartley, NFAC test engineer. “The scale of the NFAC provided the space to test a nearly full-length hose and drogue configuration which was not possible in smaller wind tunnel entries. In addition, testing in a controlled environment, as opposed to flight testing, provided the opportunity to show truly side-by-side comparisons of the same turbulence events with the control system on and off. These side-by-side videos conclusively show dramatic improvement on drogue motion under turbulent flight.”

The ASDRS consists of a pair of aluminum shrouds that can rotate and are mounted onto the exiting hose end of the refueling coupling. On these shrouds are pairs of lift and roll strakes, which are devices mounted to improve aerodynamics, driven by onboard direct current motors that, when rotated, produce the lift force and roll moments to counteract the disturbances. When not aerodynamically controlling the position, the strakes generate torque which is stored as power in onboard capacitors to drive the system.

Drogue position is monitored by a closed loop control that was developed over the last 10 years through SBIR contracts with AMA. This test entry was the first application where closed-loop control and position monitoring were demonstrated on a full-length hose and drogue setup.

The first phase of the ASDRS was awarded to a branch of AMA in 2008 to research an innovative controllable drogue refueling system. This research led to the award of a second phase in 2012 and another in 2016 totaling more than $2 million in SBIR funding to continue fine tuning the technology to deliver innovative concepts for stabilization and control.

The other SBIR project, which was eventually joined with the ASDRS, supports future readiness and reliability of the Aerial Refueling Store, or ARS. This effort is an instrumentation package developed to better monitor ARS system performance.

Within this package is the Optical Reference System, or ORS, which was developed by Coherent Technical Services, Inc., or CTSi. The ORS provides real-time hose, drogue and receiver position. It consists of high-resolution cameras, image processing algorithms and data storage.

The ORS is designed to be housed in the fuel plane tanker system. Infrared light emitters onboard the drogue coupling enable position tracking. The system proved effective at giving real-time feedback in the wind tunnel environment in low light conditions at all altitudes under test.

Sponsored by the Office of Naval Research, the first phase of the instrumentation package of which the ORS is a part was awarded funding in 2015 to cover a range of Navy aerial applications. The project was subsequently picked up by Naval Air Systems Command, also known as NAVAIR, and was awarded a second phase in 2018 to continue development for a total of more than $800,000 in first and second phase SBIR funds.

“At CTSi, we are passionate about solving these hard problems for our customer and ultimately delivering these solutions to the warfighter,” said CTSi Managing Director Tom Sanders. “The mission of aerial refueling has always been difficult and dangerous, and our system will not only protect our pilots and aircraft but enable the future of unmanned military aviation.”

Pairing the ORS with the ASDRS has resulted in a more stable aerial refueling platform.

“This integrated test effort was a significant milestone for both the Stabilized Drogue and Optical Reference System SBIR efforts,” said Capt. John Dougherty, program manager for the NAVAIR Precision Strike Weapons program office. “The active stabilization results, using the ORS as a feedback sensor, are impressive and show that these technologies have the potential to transform the aerial refueling mission. We look forward to continued development of these items and will look to transition them as part of our Advanced Aerial Refueling Store program.”

The NAVAIR Precision Strike Weapons office has been awarded a Future Readiness Initiative starting in 2021 to develop the next iteration of the Aerial Refueling Store. These technologies will be key enablers for the future unmanned or automated receiver and are being looked at to transition under this FRI to support readiness and the future automated receivers. Other transition opportunities could include tanker platforms such as the U.S. Marine Corps and U.S. Air Force.

“AMA is proud to bring this enabling technology to the Navy warfighter so they may perform their mission in a more effective and safe manner,” said John Abrams, vice president of Advanced Projects with AMA. “The continuing technology transition is the product of a team effort from innovative engineers, the Navy and its dedicated personnel, key subcontractors, and industry partners.”

The NFAC test team consisted of both DOD employees and Test Operations and Sustainment contract employees from National Aerospace Solutions. The team included researchers, engineers, technicians and mechanics.

“The NFAC and customer team pulled together and pulled out the stops to embody the mantra of a combined test force,” Hartley said. “On a shoestring budget, they provided effective and efficient testing to answer fundamental aerodynamics questions and prove new technology for the ultimate benefit of the DOD. On-the-fly problem-solving is second nature for the NFAC team, and we are truly proud of the work they achieved on this important test program.”