Day 2 of the 2011 Green Flight Challenge had actual flying; very quiet flying. One criterion of the Challenge was a sound check, measuring the low noise levels of the four entrants.
Plane and Pilot reported, “Rules enforced a strict noise ceiling to promote the development of quiet, community-friendly general aviation aircraft:
“Maximum Noise Limit: Participating aircraft were required to stay below a maximum noise level of 78 dBA during full-power takeoff.
(This was a notable goal since Putdue University acknowledged much higher levels for small airplanes,
- “Flyover levels: A typical single-engine general aviation plane (like a Cessna) flying overhead at 1,000 feet measures roughly 88 dBA, though general averages can drop closer to 65 dB depending on distance, engine power, and altitude.
- “Cruise levels: Light aircraft cabins (such as Cessna 172s, Piper PA-12s, or Diamond DA40s) regularly experience high internal noise levels between 88 dB and 106 dB during cruise flight due to minimal sound insulation and proximity to the engine and propeller. “
All were quieter than anything else on the field. eGenius had to make two attempts because its first try was drowned out by a departing Cessna on the main runway.
Organizers came up with a clever way to measure the sound level from each entrant while also evaluating their ability to clear a 50-foot barrier at the end of a 2,000-foot runway.
An extendable cherry picker rig offset 250 feet from Santa Rosa’s runway was flaked by microphones that gave audible evidence of the sound level and visible verification that the aircraft cleared the required height
eGenius won that part of the Challenge quietly. The video below highlights the design philosophy behind eGenius and its predecessor that flew 15 years before, in 1996. Even that 30-year-old airplane still flies and contributes to aeronautical knowledge.
Since a three decibel drop in noise is perceived only slightly even though it cuts the energy level of the sound in half, it takes 10 dB drop to be readily noted by most people. eGenius’ remarkable sonic performance remains a standard for others to approach.
Rhis was our report on Day 2 in 2011: https://sustainableskies.org/green-flight-challenge-day-two/