Sound of silence

  • Published
  • By Airman 1st Class Daniel Phelps
  • 20th Fighter Wing Public Affairs
SHAW AIR FORCE BASE, S.C. --  If a jet engine is running and no one hears it, does it still make a sound?

One of the key tools to community relations and ensuring the 20th Fighter Wing's F-16 Fighting Falcons are able to take the skies is the 20th Component Maintenance Squadron's engine test facility, also known as the "hush house."

"The hush house shows the Air Force knows the noise that it creates and is striving to reduce that noise," said Gary Hallmark, 20th Civil Engineer Squadron base community planner.

Hush houses are where jet engines go to be tested after the engine back shop has completed its work.

The building, which is also considered a piece of equipment and a deployable asset, is sized to allow aircraft to be safely installed and restrained while running through a full performance test. There is a 20-foot long cylindrical tunnel at the back of the test facility to allow space for the 30-foot afterburner flame shot out from the engine. The tube is designed to absorb the expelled gas and flames to almost instantly cool.

"It is the last step to ensure the engine is running properly before it is put in a jet," said Tech. Sgt. Michael Sierra, 20th CMS engine test facility assistant section chief.

However, the main reason for having the hush house is community relations, said Master Sgt. Tony Hyatt, 20th CMS engine test facility chief. The noise of jets while they are flying is overbearing enough.

"The community doesn't need to hear our engines while they are just being tested," Hyatt remarked. "The hush house helps cut down on the noise emitted from the base tremendously. If people who live over 10 miles away can hear the jets taking off, imagine what it would be like if they could hear all of our testing."

The 20th Fighter Wing's F-16s use the F110 General Electric-129 engine because of its proven record and heritage of high reliability. The engine weighs 3,980 pounds and can produce 29,000 pounds of thrust.

When the engine runs at full afterburner, it creates a 139 decibel roar. The loudest sound that is safe to be around with hearing protection is 140 decibels.

To put this into perspective, normal conversation is generally around 60 decibels, a home lawn mower is 100 and the loudest possible sound on the scientific chart is 194.

Hush houses are designed and built like giant car mufflers and suppress the noise of a jet engine running at full afterburner by about 40 to 50 percent at 250 feet away, said Todd Abrahamson, ASE Holdings marketing and sales vice president, the company that makes and distributes the engine test facilities. So, if the F110 produces 139 decibels at full afterburner in open air, 250 feet outside the house you would only hear about 80 decibels, which is about the sound level of an electric shaver.

By having the hush house, we are able to continue our mission on into quiet hours, said Master Sgt. Joshua Varney, 20th CMS engine test facility section chief. They can continue running tests on the engines until 1 a.m. and start up again at 6 a.m.

The engine test facility tests an average of about seven to 10 engines a month and spends an average of six hours on each one.

In the hush house, engines are checked for leaks after they have been taken apart and put back together by the back shop, said Harvey. We ensure that it has been properly fixed. Sometimes the aircraft maintenance units will bring an aircraft in, and we'll troubleshoot it in the hush house without pulling out the motor.

The engine testing process will depend on the unit, Harvey added. When an engine comes from the back shop, we review the work to see what we need to look for. Then we load the engine on a rack and ensure all safety precautions are taken. Once everything is safe, the motor is started and put through test runs and follow-up inspections.

Once the engine has been brought to full afterburner, the main things the maintainers check for are leaks, odd temperature variations and discrepancies in the core speed, and listen for unusual noises, said Sierra. Everything must operate within certain parameters before it can be released.

If the mechanics come across issues with the engine, they may or may not take care of the issue there depending on what the issue is, he added. If it's an external engine problem, they can fix it at the hush house; if it's internal, they'll return it to the back shop.

"There is nothing that the original shop can do that we can't do," Hyatt said. "They just have more tools and equipment available."

All of this work could be done without the hush house, but the hush house allows for us to continue our work through almost all hours and weather without creating a lot of noise, Sierra said. It gives the surrounding community another reason to want us to stay here.