RE: Flying Field Airplane noise
The part of the law that makes it suspect is the "above ambient" clause. When is the ambient noise level determined? Who determines it? If cited, I would use that as a basis for a challenge in court.
The second thing I would do is conduct an ambient noise survey at the property line. Buy, rent, or borrow a noise meter with a graphic recording capability. Then over the period of a week, take average sound levels and keep the graphs as a club record.
Based on the "average" abient noise levels you determine, establish a maximum noise level that planes may not exceed. For example, our local noise ordinance restricts noise during the daytime to 65db at the recieving property line (not relative to ambient). For reference, 65 db is a normal conversational tone at 1 meter/yard. For a plane that reads 90 db at 9 feet, the sound must spread 165 feet to be below 65 db (assuming spherical spreading and no other attenuation). We therefore established a 90db at 9 feet rule. For the typical pilot, they are generally high enough when near the field boundary to be more than 165 feet from the property line. Factor in careful throttle management, as well as encouraging distance from the boundary, and we can demonstrate that we are not exceeding the noise restriction.
We found that most two stoke engines in the 40-60 size came in well under 90 db if propped to keep the tip speed below .7 mach. Four strokers can be very quiet. I've had times where I couldn't hear my Magnum 91 over the ambient traffic noise.
Keep your records of the ambient survey, records (such as a sticker) that you have checked the planes, and keep the meter and its calibration records. If someone complains, you now have evidence that you can present in court to challenge the complaint.
Admittedly its more effort, but you may be able to keep the field open.
Brad