Aeromodeling noise
Hello again! By the time you read this, most of the country will be deep in winter and many of you will be enjoying indoor model flying. Those in warmer climates to the south will still be out at the local flying site.
There have been quite a few inquiries at AMA Headquarters concerning model aircraft noise and how it is becoming a problem at many flying sites. Although a large percentage of the model aircraft sold today are electric powered, there remains a number of traditional glow- or gasoline-powered aircraft. I have many and I plan to fly them for a long time to come!
As I tell many club officers, “There are only two types of clubs: those that have lost their flying site, or those that are about to.” I wish that was not the case, but even clubs that own their property still have issues with urban sprawl and new neighbors. Many of these new neighbors are not so charmed by the sound of our model aircraft engines, and have spoken out against the noise created by them.
I want to offer some guidance on how to deal with this issue. Every case is different and there are specific issues that your club will have to deal with, but it is important to deal with the problem and find a solution. Pretending that it will go away will only make matters worse.
So, how should we address model aircraft noise issues and complaints? AMA District I Vice President Andy Argenio sent me some good points that I want to share with you.
First we must understand that the primary objectives are to prevent the loss of a flying site, to continue to fly model aircraft, and to avoid noise complaints. Preventing or excluding certain aircraft that have always flown at the site from flying, based on type, size, engine, or weight, should be a last measure, and only after other methods of noise reduction have been considered, tested, and evaluated.
Next, the club needs to deal with the issue head-on and develop and implement a noise-reduction plan. It is important to understand that dealing with noise emissions from engines is only one component of the plan. The plan must consider a number of factors, all of which need to be addressed to get the best results:
- Create a complaint incident report form. This form should include the date and time of incident, complainant’s name, address, telephone number, email, nature of complaint, persons involved, contacted, and notified as well as what, when, and by whom responses and actions were taken with regard to the complaint. This data is essential in developing action plans to address flying site issues. For example, reducing complaints by limiting flying activity at sensitive times.
- Identify sources and locations of potential complaints. Locate nearby homes, buildings, structures, and any areas where people might be that surround the flying site.
- Create a map of the club’s flying site. Include potential complaint locations and flight boundary lines to limit the potential of overfly. Post the map at the site for member viewing and avoidance of these locations.
- Measure the distances from potential complaint locations to the nearest flight boundaries. These distances can be used to determine whether the decibel (dB) sound level from airplanes at property lines has the potential of being an offensive noise.
- Perform periodic testing of sound levels utilizing a dB meter at potential complaint locations. This should be done at least annually, or when changes have occurred (new homes, buildings, parks, etc.) in the area surrounding the club’s flying site or when noise complaints have been made.
- Involve all members in noise-reduction strategy. Advise members to use good throttle management (lower throttle on downlines), limit the number of aircraft in the air at any one time, and fly at lower altitudes at sensitive times on weekends and holidays.
- Reduce noise emissions. Noise from model aircraft can be divided into four major sources. In the order of their contribution to the total noise output, the sources are propeller, exhaust, airframe, and engine.
Retrofit your aircraft for noise reduction
A) Propeller: Whether we are dealing with a small or large displacement engine, we can lower the noise by selecting a higher-pitch propeller rather than a larger-diameter propeller. This will reduce the rpm and the tip speed of the propeller.
Larger propellers with less pitch can have tip speeds, as they approach the speed of sound (~767 mph), go transonic or supersonic producing a loud snarl or howl (called “ripping the prop”) emitting a significant amount of noise. Propellers that are optimized for less noise can have tip speeds that are close to Mach .7 without transonic effects and noise. Larger displacement engines using three-blade propellers with their reduced diameter will considerably decrease the propeller noise and total dB level.
B) Exhaust: Exhaust silencers that utilize internal baffles will break up the pressure wave that produces the most exhaust noise in the small- to medium-size engines. The larger engines can use a tuned pipe with internal structures to lower the exhaust noise and increase the power and not increase the rpm by using a propeller with more pitch. Canister mufflers will lower a big gas engine’s exhaust noise and boost the engine’s low-end torque.
C) Airframe: Good construction techniques can prevent vibration from the engine to the airframe, which is the source of airframe noise.
D) Engine noise: Large engines, although producing more noise than small engines, run at a much lower rpm. At the lower rpm, they produce lower frequency sounds that are less annoying and irritating to human hearing than smaller displacement, high rpm engines. It is a mistake to think that smaller engines will result in reduced noise problems or fewer noise complaints.
Thanks, Andy! These are indeed good tips for helping clubs deal with sound issues. The AMA has a sound document that explains how noise pressure levels (dBA) are affected by distance. There are some charts to help you develop your own noise levels for your club. You can find the document at: www.modelaircraft.org/files/927.pdf.
See you at the field!
