May 3, 2008
By Ian J. Twombly
By Ian J. Twombly
Airplanes are nothing if not loud. In the case of piston-engine general aviation airplanes, the noise usually penetrates straight to the interior. That might be cool if you’re flying a P-51 Mustang, but on a long cross-country flight in a four-seater, the quieter the better.
AOPA’s Get Your Glass Sweepstakes Piper Archer is one of those loud four-seaters. Considering that it was built before pilots wore headsets in small cockpits, it means scores of pilots have endured the noise over the years. Fatigue is also a factor. Pilots who fly with active noise-attenuating headsets will tell you they arrive more refreshed. When you consider the Get Your Glass Archer has seats that took 50 hours apiece to construct, all in the name of comfort, why would we not address the sound issue inside the airplane?
According to Oxford Aviation president and founder Jim Horowitz, small airplane insulation had one original purpose: “Most factory insulation is for thermal purposes,” he said. Though it generally keeps the pilot and passengers warm, it does a poor job at keeping out sound. In most cases the material is not unlike fiberglass home insulation, he said.
Oxford does things a bit differently. When an owner decides to have new sound-proofing material installed, the first step is to rip out the old stuff. Horowitz said most owners would be amazed at the condition of their airplane. If the insulation isn’t damp or full of mold, it’s piecemeal, or in some cases, completely missing. After removing the old material, Oxford coats the inside of the skin with an impregnated vinyl. Horowitz said it helps to distribute the sound waves. Oxford will sometimes illustrate this to customers by putting them inside the airplane and tapping on the fuselage. Without the vinyl, the tap will ring through like a bell. But after the vinyl, said Horowitz, the tap is more like a thud.
Next comes Oxford’s special sound-proofing material. The workers take a layer of fiberglass made specifically for sound attenuating, a dense layer of foam for low-frequency sound waves, and then another layer of the fiberglass. That sandwich of materials is then heat-sealed in Mylar to make what resembles a pillow or a couch cushion. The entire inside of the airplane is filled with the custom material, which is numbered for easy removal and reinstallation later.
After the sound-proofing material, the sidewalls are addressed. Though each manufacturer does it a bit differently, the Archer’s sidewalls were made of cardboard. The flimsy material retained moisture really well—something it wasn’t designed to do. So Oxford took the initiative and created custom plastic sidewalls that will be much more durable for the sweepstakes winner. That plastic is also covered with an extra layer of foam to help with sound attenuating, and let’s face it, the sidewalls will look better too.
In addition to the sound proofing, there are a few other steps an owner can take to reduce the amount of noise in the cabin, many of which Oxford installed for the winner. Windows probably make the biggest improvement in cabin noise reduction. We outfitted the Archer with all new glass, thanks to LP Aero Plastics in Jeannette, Pa. LP Aero is a frequent contributor to the sweepstakes projects, so we were confident the windows would be a nice addition. The new windows are a quarter-inch thick—double the thickness of the factory glass. Extra thickness means more sound damping. To bring in the “Get Your Glass” theme and hopefully help to protect the black leather seats, the windows are tinted a light gray and provide 100 percent UV protection.
New door seals are a common method to keep noise outside the airplane. Horowitz said some owners will complain about hearing new noises inside the cabin after the sound-proofing process. “That is usually a sound that was just masked before,” he said. Often, the “new” noise is a leaky door seal. Thanks to Aircraft Door Seals, that won’t be a problem in the Get Your Glass Archer. The company provided us with new door seals for the main cabin door and the baggage door. And instead of the old metal-door-to-rubber-door seal connection, Aircraft Door Seals sent us material for a new STC. Just like in fine luxury cars, the new cabin door will seal rubber to rubber, removing all the air gaps that would otherwise manifest themselves as annoying whistles.
Between good sound-proofing material, new windows, and new door seals, our new glass platform should be one quiet, comfortable ride. Of course, we don’t know how much quieter it is, because we haven’t had a chance to fly the new glass platform away from the shop. But when we do, we’ll pass on the new decibel level, as well as information on how these modifications have affected the empty weight of the airplane.
Next week: A look inside our new engine
E-mail the author at email@example.com
Flight Training Editor Ian J. Twombly joined AOPA in 2003 and is an instrument flight instructor.
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