US Air Force tests directed energy weapons in wind tunnels


US Air Force engineers are testing directed energy weapons in wind tunnels that could one day be used by military aircraft to see how aerodynamic disturbances affect their performance.

Researchers at the Aerodynamics Branch of the Arnold Engineering Development Complex (AEDC) at Arnold Air Force Base in Tennessee, have been testing the airborne directed energy (DE) systems.

DE systems use either high-energy lasers or microwaves to degrade or destroy threats and targets. The US Air Force is already testing ground based DE weapons, mainly for use against drones, in the field.

“There is a growing interest for directed energy systems within the DOD for many purposes, especially defending our systems and personnel,” said Dr Rich Roberts, chief of the Aerodynamics Branch Store Separation Section. “There are a number of systems in use and being developed across the DOD. Integrating the DE systems on aircraft has obvious benefits but also creates challenges, especially at higher speeds.”

During flight, an aircraft creates shockwaves in the air and other aero-optics flow disturbances that can affect the beam quality and effectiveness of a DE system. Wind tunnel testing allows test engineers to visualize and measure these changes to the airflow while controlling variables such as Mach number and altitude pressure.

A DE test conducted recently in the 4ft transonic wind tunnel (4T) at the AEDC is part of a research program that has so far run for eight years.

“Simply put, this system transmits a laser to the model, uses a miniaturized optical bench of sorts inside the model, then uses fiber optics to pipe the data to a wave front sensor system,” Roberts said. “From there, we can analyze data that tells us how the laser was impacted by the tunnel flow field around the model.”

AEDC engineers have worked with company MZA Associates to develop the Aero Isolation Measurement System, or AIMS, to enable aero-optical DE testing in the wind tunnels. MZA was also the customer for the recent test.

MZA has been working with the Defense Advanced Research Projects Agency (DARPA) on a supersonic aero-mitigation project with the goal of lessening the impact of high-speed flow over a turret. A prototype of a flow mitigation fence was tested in 4T.

“We are looking at how well this design controls the air flow over the turret to minimize the impact moving air has on the performance of the system,” Roberts said. “We are also comparing tunnel test data to previously generated CFD data to make sure the simulations properly represent actual data. This test in 4T was the first time that this system has been experimentally tested at supersonic conditions, in addition to the first time that the AIMS system has been used at AEDC.

“The test went very well, getting all the priority data over two days of testing. An initial look at the data shows a significant improvement in beam quality using this new aerodynamic fence design.”

A project is now progressing at AEDC to develop the Integrated Directed Energy Aero-Optical Surrogate, or IDEAS, which is a subscale model of an F-15 aircraft with the ability to test laser pods. The IDEAS hardware is scheduled to undergo acceptance testing later this year.

“The ability to perform aero-optical tests of directed energy systems in the wind tunnels represents a new test capability for AEDC,” Roberts said. “As more DE systems are developed and integrated onto aircraft, we’ll be able to help with design decisions, creating employment envelopes, defining adjacent weapons load outs and other things routinely needed by program offices and manufacturers.”

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Ben has worked as a journalist and editor, covering technology, engineering and industry for the last 20 years. Initially writing about subjects from nuclear submarines to autonomous cars to future design and manufacturing technologies, he was editor of a leading UK-based engineering magazine before becoming editor of Aerospace Testing in 2017.

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