Tuesday, November 8, 2011
The Dangers Of Noise Fatigue
Noise fatigue may be an often-overlooked cause of aircraft accidents in general aviation
One almost inevitable result of additional power is more noise, and Power Flow had received some reports that their first generation of tuned exhausts' increased power translated directly to a higher noise level. Company general manager Darren Tilman's demonstrator is a Mooney 201, and he commented that he had flown with a customer in an older, '60s vintage M20E Mooney fitted with the first-generation Power Flow exhaust, and even he was surprised how loud it was—about 114 dB.
Accordingly, the company came up with an improved, super-sound-proofed, stainless-steel, ceramic-coated exhaust. The new pipe mounts in the same location, and Power Flow flight-tested the system and determined there was no cruise loss with the improved exhaust. The Daytona Beach company knew any performance loss could be a critical litmus test that might doom the Quiet Pipe.
The result of the quieting effort was an impressive 13-decibel reduction on Mooney M20E/Fs over the previous system. (The decibel scale is logarithmic, so 13 dB is a HUGE improvement.)
The same Quiet Pipe exhaust may be applied to the later 200 hp Mooney 201, but aircraft designer Roy LoPresti had already reworked the model's exhaust system back in the mid-'70s during the airplane's development process. As a result, the reduced noise level with the new Power Flow pipe is more like three to four dB on the 201, still a substantial improvement, but not as dramatic as the result on older Mooneys such as mine.
The new exhaust is practically indistinguishable from the old. It's about ½ inch larger in diameter and an inch shorter, but from a distance, most people won't be able to tell the difference.
Obviously, the new Quiet Pipe won't do you much good unless you already own a Power Flow tuned exhaust. Fortunately, the company has sold some 3,700 systems, installed in a dozen models powered by four-cylinder Lycomings.
The hush kit is available for 11 models served by Power Flow (only the Cardinal RG is excluded). Price ranges from $650 to $990, and installation time is roughly two hours.
Noise suppression for general aviation is more than a convenience. It's more than being able to hear every transmission from ATC distinctly or listen to your iPod in comfort at 10,500 feet over Omaha. Reducing the dB count can make the cockpit environment less frenetic and the pilot's job easier and safer.
If you're smarter than I am, you won't go flying for 15 hours in one day.
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