News stories related to environmental noise problems are all around us. Some are dramatic, some are not, but a huge effort and great sums of money are often invested in conflicts involving environmental noise.
Sound is defined as any pressure variation that the human ear can detect. Just like dominoes, a wave motion is set off when an element sets the nearest particles of air into motion. This motion propagates to the next particle, then the next particle, and so on. This propagation is about 340 meters/second. As the sound gets farther and farther way from the element that set the particles in motion, the sound level will reduce due to dispersion.
Passengers flying in an aircraft will hear the noise generated by the aircraft they are flying in. It is called cabin noise. Since the passengers are very close to the noise source, it can be very loud.
People on the ground will hear the aircraft passing through their area. This is called community noise. Community noise can vary in intensity a great deal, depending on many factors discussed below.
Here are examples of aircraft noise as compared to other noises you are used to hearing:
Community noise is what causes most of the complaints against airports and airplanes. This noise must travel from the noise source, the airplane, to the listener. Many people have become sensitive to community noise and are particularly sensitive to this type of noise. The most important factors affecting how the listener will hear the noise are as follows:
Although community noise does not cause physical damage to the listener on the ground, this noise can cause poor relationships with the local airport neighbors. It can also upset people and animals in wilderness areas that are distant from an airport. Both the FAA and international standard setting bodies have set up regulations for community noise. The FAA FAR Part 36 sets the standards for the USA.
Cabin noise affects the comfort of the passeners in the cabin and should be less than 85 dB(A). Cabin noise can cause physical discomfort and/or tiredness to the passengers. It can also cause long term and permanent hearing loss. For this reason it is very important that the noise levels are significantly reduced inside aircrafts.
These are the most important factors affecting how the listener will hear the cabin noise:
The cabin noise level may be affected by various regulations and different governmental organizations both nationally and internationally, such as the FAA and OSHA.
There are many different things techniques available for reducing the noise generated by the aircraft. It is of primary importance to reduce the creation of this noise. This can be done with any of these techniques such as:
It is very important to reduce the noise levels generated by an aircraft for both the community surrounding the aircraft, as well as the passengers riding in the aircraft. World wide government agencies have setup regulations to encourage this noise reduction.
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Title |
Author |
Year |
Description |
Size |
| 1 |
A Theoretical and Experimental Investigation of Propeller Performance Methodologies |
K. D. Korkan et al |
1980 |
From AIAA/SAE/ASME. 22 pages on NASA's mathematical prediction of propeller performance compared to actual measured performance, examining the most prevalent blade sections. |
2.7MB |
| 2 |
An Acoustic Sensitivity Study of General Aviation Propellers |
K.D. Korkan et al |
1980 |
A 32 page noise study that examines several methods of reducing prop noise on Cessna aircraft. Good empirical results using metal propellers. Shows the effectiveness of reducing RPM and increasing number of blades. |
2MB |
| 3 |
Noise Control Predictions for High-speed, Propeller-Driven Aircraft |
J. F. Wilby et al |
1980 |
Finds that a double wall cabin structure can effectively reduce noise, with some weight penalty. |
1.3MB |
| 4 |
Noise from a Vibrating Propeller |
H. L. Runyan |
1980 |
An important paper exams the noise contribution of 'tuning fork' action of propeller blades. Engine smoothness is a key factor in propeller noise. |
748KB |
| 5 |
Effects of Acoustic Treatment on the Interior Noise Levels of a Twin-Engine Propeller Aircraft--Experimental Flight Results and Theoretical Predictions |
T. B. Beyer |
1984 |
Looks at passive noise reducing methods for the cabin of a turbo-prop twin. Many methods are explored. |
828KB |
| 6 |
Noise Control Characteristics of Synchrophasing - An Experimental Investigation |
J. D. Jones |
1984 |
Synchrophasing the blade positions of propellers on twin engine aircraft was shown to substantially reduce cabin noise. |
532KB |
| 7 |
Noise Control Characteristics of Synchrophasing - An Analytical Investigation |
C. R. Fuller |
1984 |
High-speed turbo-prop aircraft need synchrophasing to quiet the cabin. This study examines the effects obtained. |
476KB |
| 8 |
Effects of Acoustic Treatment on the Interior Noise of a Twin-Engine Propeller Airplane |
T.B. Beyer |
1984 |
Exams the noise reduction due to placing interior trim panels in a turboprop twin. |
684KB |
| 9 |
Noise Control Characteristics of Synchrophasing, Part 1: Analytical Investigation |
C.R. Fuller |
1986 |
Synchrophasing on a high-speed turbo-prop. Up to 8 dB of quieting. |
764KB |
| 10 |
Noise Control Characteristics of Synchrophasing--Part 2: Experimental Investigation |
James D. Jones et al |
1986 |
Showed 10-34 dB of quieting, depending on location in cabin and frequency band. |
1.4MB |
| 11 |
A Numerical Method for the Design and Analysis of Counter-Rotating Propellers |
S. C. Playle et al |
1986 |
Counter-rotating propellers are numerically analyzed regarding their flow fields and thrust. |
2.3MB |
| 12 |
Validation of an Interior Noise Prediction Model for a Composite Cylinder |
T.B. Beyer |
1987 |
A composite cylinder is used to measure fuselage noise patterns from several sources. |
484KB |
| 13 |
Noise Reduction of a Composite Cylinder Subjected to Random Acoustic Excitation |
F. Grosveld et al |
1989 |
A composite cylinder's interior noise is measured after adding double wall sound-proofing. |
1.3MB |
| 14 |
An Acoustic Experimental and Theoretical Investigation of Single Disc Propellers |
E. A. Bumann et al |
1989 |
2, 3 and 4 blade props studied by a theoretical formula to predict noise. (Succi's) |
738KB |
| 15 |
Determination of Near and Far Field Acoustics for Advanced Propeller Configurations |
K.D. Korkan et al |
1989 |
More theory on propfan noise, with discussion of blade flex as an impediment to predictions. Looks at both near and far measurement. |
1.1MB |
| 16 |
Noise Transmission of a Large Scale Composite Fuselage Model |
T. Beyer et al |
1990 |
Examines the noise absorption/transmission properties of a mock composite fuselage. |
1.3MB |
| 17 |
High-Speed Propeller Noise Prediction—A Multidisciplinary Approach |
Mark H. Dunn and Feri Farassat |
1992 |
Noise prediction theory for high speed propellers by the great Feri Farrassat at NASA. Includes discussion of blade deformation as a noise source. |
1.6MB |
| 18 |
Small Aircraft Propeller Noise with Ducted Propeller |
R. Duane Oleson et al |
1998 |
A ducted propeller noise study indicates that inflow disturbance adds significantly to noise. Paves the way to noise study of ducted propellers. |
1.5MB |
| 19 |
Advanced Turboprop Noise Prediction Based on Recent Theoretical Results |
F. Farassat et al |
1987 |
Computer mathematical analysis of advanced high-speed turbo-propeller noise and performance. |
1.3MB |
| 20 |
The Problem of Noise Reduction with Reference to Light Airplanes |
Theodore Theodorsen |
1946 |
An early paper by the great Theodorsen examines general aviation prop noise and specifically urges use of multiple blades to quiet them. Applies the Gutin Formula, an early predictor of prop noise. |
1.0MB |
| 21 |
Comparison of Sound Emission from Two-blade, Four-blade, and Seven-blade Propellers |
Chester W. Hicks et al |
1947 |
An early look at the noise reducing effect of lowered propeller tip speeds and use of multiple blades. Note: blades used had too much tip chord by today's math. |
1.6MB |
| 22 |
Propeller Loudness Charts for Light Airplanes |
Harvey H. Hubbard et al |
1947 |
A nice collection of charts plotting noise v. RPM and other parameters of GA props. |
2.1MB |
| 23 |
Sound-level Measurements of a Light Airplane Modified to Reduce Noise Reaching the Ground |
A.. W. Vogeley |
1948 |
Noise tests of 150-200 BHP engines and props including a large diameter, slow-turning 5 blade indicated that takeoff thrust suffers as blade number goes up unless a geared engine is used to allow slow-turning props of larger diameter. |
616KB |
| 24 |
Experiments in External Noise Reduction of Light Airplanes |
Leo L. Beranek et al |
1950 |
122 pages on the several ways to reduce noise from a single engine piston aircraft, including multi-blade propellers, RPM reducers and engine mufflers. |
4.5MB |
| 25 |
Experiments to Determine Neighborhood Reactions to Light Airplanes With and Without External Noise Reduction |
Fred S. Elwell |
1952 |
An elaborate survey study showing that reducing aircraft noise substantially improves neighborhood acceptance of GA. |
5MB |
| 26 |
A Theoretical Study of the Effect of Forward Speed on the Free -space Sound-pressure Field Around Propellers |
I. E. Garrick et al |
1953 |
The sound pressure fields calculated around a prop and their sources. Discusses flow separation on the blade as a noise source and uses extensive mathematical analysis. |
2.4MB |
| 27 |
A Method for Calculation of Free-space Sound Pressures Near a Propeller in Flight Including Considerations of the Chord-wise Blade Loading |
Charles E. Watkins et al |
1956 |
An elaborate study of the mathematical model of prop noise. |
2.7MB |
| 28 |
Measurements of Free-space Oscillating Pressures Near Propellers at Flight Mach Numbers to 0.72 |
Max C. Kurbjun et al |
|
Noise measurements of a P51 prop show that tapered tips were quieter and that noise rose rapidly as the blade tip speed exceeded 0.5 Mach. |
808KB |
| 29 |
A Review of Aerodynamic Noise From Propellers, Rotors, and Lift Fans |
Jack E. Marte et al |
1970 |
An extensive review of noise calculation methods for props, fans and heli-rotors, includes a huge bibliography on V/STOL. 58 pages in all |
3.9MB |
| 30 |
Advanced General Aviation Propeller Study |
Rose Worobel et al |
1971 |
204 pages of extensive material on GA prop design, including the full computer program code for designing the prop. |
14.9MB |
| 31 |
Computer Program User’s Manual For Advanced General Aviation Propeller Study |
Rose Worobel |
1972 |
74 pages of User Manual for the Fortran program on propeller design for GA, whose code listing is included here. Developed by Hamilton Standard. |
2.4MB |
| 32 |
Aeroacoustic Wind-Tunnel Tests of a Light Twin-Boom General-Aviation Airplane With Free or Shrouded-Pusher Propellers |
H. Clyde McLemore et al |
1980 |
87 pages on the full scale wind tunnel testing of a Cessna 337 for prop noise using 2, 3 and 5 blade metal props, with duct shrouds. The non-ducted propeller was quieter than the shrouded one. |
4MB |
| 33 |
On the Design and Test of a Low Noise Propeller |
George P. Succi |
1981 |
The M.I.T. low noise propeller design is studied and compared to conventional props. An early attempt at proper span-wise blade lift distribution, but without the full flow field slow-down math of Jack Norris. |
1.1MB |
| 34 |
Experimental Study of the Effects of Installation on Single- and Counter-Rotation Propeller Noise |
P. J. W. Block |
1986 |
A beautiful color 33 page study of the flow fields and noise patterns of counter-rotating propellers. |
18MB |
| 35 |
Prediction of Helicopter Rotor Discrete Frequency Noise |
Kenneth S. Brentner |
1986 |
A computer program named WOPWOP by the great Feri Farassat for predicting heli-rotor blade noise. |
1MB |
| 36 |
An Experimental Investigation of the Interior Noise Control Effects of Propeller Synchrophasing |
J.D. Jones |
1986 |
Virginia Tech examines fuselage quieting by prop synchrophasing. |
2.5MB |
| 37 |
Propfan Test Assessment Propfan Propulsion System Static Test Report |
|
1987 |
A 237 page report on large propfan noise measurement. |
7.6MB |
| 38 |
Aircraft Interior Noise Reduction by Alternate Resonance Tuning Progress Report for the period ending June, 1990 |
Dr. Donald B. Bliss et al |
1990 |
A 41 page study of Alternate Resonance Tuning, alteration of fuselage structure to alter its resonance with sound sources and quiet noise. |
1.1MB |
| 39 |
The Radiation of Sound from a Propeller at Angle of Attack |
Ramani Mani |
1990 |
A study of the radically altered sound propagation from a propeller operating in a non-axis-symmetric flow, as in a positive angle of attack. A valuable 56 page glimpse of the real-world flow streams in which props operate. |
1.4MB |
| 40 |
Computational Methods in the Prediction of Advanced Subsonic and Supersonic Propeller Induced Noise--ASSPIN Users' Manual |
M.H. Dunn et al |
1992 |
The Farassat ASSPIN program for predicting high-speed propeller noise. A pivotal 48 page paper in noise theory. |
2.3MB |
| 41 |
An Assessment of Propeller Aircraft Noise Reduction Technology |
F. Bruce Metzger |
1995 |
128 pages of comprehensive review of the many ways of quieting propeller noise. This is a key paper. Many of the promising methods of noise reduction described herein have not yet been converged into one super quiet prop. |
5.8MB |
| 42 |
General Aviation Interior Noise: Part III Noise Control Measure Evaluation |
James F. Unruh |
2002 |
60 pages of excellent material on the many contributors to cabin noise and how to quiet them. |
4.7MB |
| 43 |
The Noise of a Forward Swept Fan |
James H. Dittmar et al |
2003 |
A multi-blade turbine engine forward swept fan blade shows promise as being quieter. |
8.5MB |
| 44 |
Derivation of Formulations 1 and 1A of Farassat |
F. Farassat |
2007 |
Dr. Farassat's definitive prop noise formulae, derived. Elegant current math in 25 pages. |
616KB |
| 45 |
Advanced Turboprop Noise Prediction Based on Recent Theoretical Results |
F. Farassat et al |
1987 |
Advanced turbo-prop noise prediction. |
1.3MB |
| 46 |
Noise Reduction System for General Aviation Aircraft, Phase II |
Sangvavann Heng et al |
2005 |
A key current paper on GA muffler design, with the promise of a new foam material for silencing higher frequencies. The Ultramet muffler shows great promise for GA piston aircraft. This is the most substantial paper on silencing GA engine noise: 238 pages. |
22.4MB |
| 47 |
Active Attenuation of Propeller Blade Passage Noise |
J. M. Zalas et al |
1984 |
ANR in a fuselage of a turbo-prop. |
2.5MB |
| 48 |
Environmental Noise Measurement |
Brüel & Kjær |
|
A primer on environmental noise. |
628KB |
| 49 |
Basic Concept of Sound |
Brüel & Kjær |
1998 |
Basic concepts of sound and its measurement in 32 pages. |
740KB |
| 50 |
The Connection Between Acoustics and Unsteady Aerodynamics |
Feri Farassat, NASA Langley
|
2008 |
The Connection Between Acoustics and Unsteady Aerodynamics |
101MB |
