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F-16 Engines Rumble in the Hush House after Renovations

Civilian construction workers perform renovations on the South Carolina Air National Guard’s Enclosed Noise Suppression System Structure, or “hush house,” at McEntire Joint National Guard Base, S.C., March 10, 2016. The renovations occur approximately once every 10 years to keep the structure free of rust and other environmental elements that naturally occur over time. (U.S. Air National Guard photo by Airman 1st Class Megan Floyd)

Civilian construction workers perform renovations on the South Carolina Air National Guard’s Enclosed Noise Suppression System Structure, or “hush house,” at McEntire Joint National Guard Base, S.C., March 10, 2016. The renovations occur approximately once every 10 years to keep the structure free of rust and other environmental elements that naturally occur over time. (U.S. Air National Guard photo by Airman 1st Class Megan Floyd)

Civilian construction workers perform renovations on the South Carolina Air National Guard’s Enclosed Noise Suppression System Structure, or “hush house,” at McEntire Joint National Guard Base, S.C., March 10, 2016. The renovations occur approximately once every 10 years to keep the structure free of rust and other environmental elements that naturally occur over time. (U.S. Air National Guard photo by Airman 1st Class Megan Floyd)

Civilian construction workers perform renovations on the South Carolina Air National Guard’s Enclosed Noise Suppression System Structure, or “hush house,” at McEntire Joint National Guard Base, S.C., March 10, 2016. The renovations occur approximately once every 10 years to keep the structure free of rust and other environmental elements that naturally occur over time. (U.S. Air National Guard photo by Airman 1st Class Megan Floyd)

The South Carolina Air National Guard’s Enclosed Noise Suppression System Structure, or “hush house,” undergoes renovations at McEntire Joint National Guard Base, S.C., March 10, 2016.  The renovations occur approximately once every 10 years to keep the structure free of rust and other environmental elements that naturally occur over time. (U.S. Air National Guard photo byAirman 1st Class Megan Floyd)

The South Carolina Air National Guard’s Enclosed Noise Suppression System Structure, or “hush house,” undergoes renovations at McEntire Joint National Guard Base, S.C., March 10, 2016. The renovations occur approximately once every 10 years to keep the structure free of rust and other environmental elements that naturally occur over time. (U.S. Air National Guard photo byAirman 1st Class Megan Floyd)

MCENTIRE JOINT NATIONAL GUARD BASE, S.C. -- Construction on the South Carolina Air National Guard's Enclosed Noise Suppression System Structure concluded here, May 6, after approximately 12 weeks of renovations.

The renovations began in February and recur approximately each decade due to the slow and continuous oxidation of the metal structure. The nearly 7,000 square-foot structure is large enough to hold three F-16 Fighting Falcon aircraft at once if needed.

The fighter pilots of the 169th Fighter Wing maintain a robust flying schedule, making it necessary for at least two to three aircraft engines to be tested each month.

From baffles to bearings, all of the components of the structure were inspected and rust build-up was removed with wire wheels, grinding wheels and welding tools.

Additional upgrades included; new T5-H0 fluorescent lighting, making the workspace brighter and more efficient, four cameras were installed around the internal perimeter of the structure to safely oversee the engine testing and a voice communication system was installed throughout the structure's interior, allowing for more effective communication between maintainers in different sections of the hush house while engine testing is in progress.

"This will be the first time in the 'hush house' that Airmen will be able to speak to one another without relying solely on hand signals," said U.S. Air Force Senior Master Sgt. Robert Jacobs, the propulsion element supervisor and 32-year Swamp Fox veteran assigned to the 169th Maintenance Squadron.

Before the progression of diagnostic technologies, testing of aircraft engines was performed manually on the runway's "trim pad," located on the north ramp.

"Back in the day, when testing the engine, we used to get up under the engine and make adjustments manually while trouble shooting. This could take a long time and was difficult and dangerous," said Jacobs.

In the hush house, the digital engine tests are electronically controlled and machines adjust and diagnose the engines thrusters, fuel flow and other parameter components to quickly test the jet engine when it is running at its maximum performance, said Jacobs. 

The trim pad has been used since the hush house was built, however, with the completion of the hush house renovations, the trim pad will be closed and no longer necessary because of the efficiency of the electronic diagnostic technologies the hush house provides. 

Each door has an important role to the structure of the hush house, and all have been replaced, including the door of the augmenter tube. The augmenter tube is a reinforced, tube-shaped corridor that allows for rushing air created by the running jet engine to safely expel out of the building. An engine running in the afterburner stage can produce more than 25,000 pounds of air pressure down the augmenter tube. 

"If specific doors are not opened or closed, especially while the F-16's engines are thrust into the afterburner stage, the structure could potentially cave in on itself [because of the extreme pressures produced]," said Jacobs.

Air must be brought in from the outside of the building to balance the pressure of the air that is being pushed out of the tube by the engine. It also keeps the inside of the structure cooled from the heat output of the aircraft's engine, said Jacobs.

Two sets of baffles, located at the front and at the rear of the hush house, mediate the nearly 90 mile-per-hour winds that are generated by the pressure of the engines, said Bill Dorn, the field supervisor of the contracting company employed to complete the renovation project.    

"The baffles near the front of the structure act as an air intake," said Dorn. "The baffles at the rear, or toward the augmenter tube, act as an outlet for excess air pressure to safely exit the building."

The architecture of the baffles also significantly reduces the amount of noise created by the engine that can be heard when standing outside of the building, said Dorn.

Jacobs demonstrated the baffles silencing capabilities by speaking loudly through the baffles from the exterior of the building, and inside, hardly more than a whisper was heard.

"The hush house is one of the most important tools of the Air Force and for McEntire, because the diagnostic testing it provides to keep our jets running," said Jacobs.