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Looking to the future, a research effort was deemed necessary to determine the potential for further noise reduction. Accordingly, a joint noise reduction program was entered into with P&WA during 1972. Since evaluation of the 747/JT9D noise sources indicated that forward-radiated noise was a very significant component at approach power, the joint program during 1972 was oriented toward control of inlet-propagated noise. To achieve suitable inlet acoustic-geometric relationships, inlet splitters have been tested. A complete assessment of performance, weight, and other installation penalties has not yet been accomplished; preliminary results indicate that the penalties may be less severe than was originally anticipated.
An analytical assessment of the effect of splitter ring diameter on noise reduction indicated a weak dependence on diameter, provided the splitter is at least 65% of the fan rotor diameter. To verify this, splitters were built in two diameter ratios for full scale test. Figure 22 is a photograph of one of the splitter installations. The noise reduction results obtained are shown in Figure 23. These results appear to confirm previous analyses.
Figure 24.-747 Inlet Double Splitter Installation
ATTENUATION AT 60° TO ENGINE CENTERLINE -APPROACH POWER
Figure 22.-747 Inlet Single Splitter Installation
A further investigation of inlet noise control led to the design and fabrication of a set of splitters which could be tested either as a double splitter inlet or, with the innermost splitter removed, as a single splitter inlet. In Figure 24 the double splitter version is shown on a JT9D engine at the Boeing Commercial Airplane Company's Tulalip test site. Figure 25 compares the attenuation of the single and double splitter versions at approach power. These results demonstrate that the double splitter configuration was more effective in attenuating forward-radiated noise than a single splitter; however, both configurations provide significant reductions in engine noise in
Figure 25.-Spectral Attenuation, Inlet Splitters; Ground Test Results
Advances have been made in the technologies of quieter engine design and the acoustic treatment of engine installations to attenuate engine-generated noise. Considerable payoff is expected on future aircraft/engine combinations designed from the beginning for very low noise. This has encouraged predictions that noise at the standard FAR 36 noise measuring points can be reduced 10 dB, or more, per decade starting immediately (2). However, recent studies and flight tests of large commercial airplanes strongly indicate that we now face an airframe noise constraint for at least the approach condition, below which additional noise reduction would be difficult even if the airplane had no engines.
Thus, a new consideration or problem appears to be emerging for future aircraft designers, with little information currently available that would suggest a solution. The complexities of the task can be appreciated by realizing that many of the advanced technology high-lift devices, and other configuration innovations that have done so much to improve airplane performance, may also be noise-generating devices that contribute to aerodynamic or aerophysical noise. Very recent 747 and 727 flight tests identify airframe noise levels for these aircraft (without engine noise) approximately 8 EPNdB below the current FAR 36 standards. Data are shown on Figure 29. Airplane noise level asymptotically approaches a limit as engine noise is reduced, as shown in Figure 30. The asymptote itself represents the airplane noise level without engines. These same tests indicated that flaps and landing gear can contribute as much as 10 to 12 EPNdB to total approach noise.
Far 36 Certified Levels Apparent Aerodynamic Noise
Far 36 Noise Rule
The aircraft industry, the airlines, and federal and local governmental agencies face many problems (2) in continuing to
minimize the effect of aircraft noise and exhaust emissions on the environment. The present costly and time-consuming procedures for making progress demand the early development of significant advances in technology, and in the associated design and operation of quieter, cleaner engines and aircraft. To highlight the technical side of the story, we would like to re-emphasize some key considerations relative to the more serious problems that need urgent attention.
Trained personnel are in very short supply to support the increasing attention being given to all areas of noise reduction, aircraft noise being but a small portion of the whole. It is necessary to recognize applied acoustic engineering as a major technical discipline, and to establish adequate educational curricula and associated research facilities to produce qualified personnel in this field.
Acoustics research laboratory facilities are few and far between. The past development of sophisticated aerodynamic facilities, by government, industry, and educational institutions, is an example of the road we must follow promptly if we are to develop the broad information bank necessary for effective and efficient design of noise reduction concepts.
The field of acoustics research is wide open to improving understanding of the mechanics of noise, and to determining means of defining full-scale flight hardware from scale-model testing. The specific examples covered in this paper(2) demonstrate quite clearly that we have a long way to go in attaining this capability.
There is a critical need for a new high-bypass turbofan engine in the 20,000 to 30,000-pound thrust class, for use both in the continued production of current aircraft, and for
designing advanced technology aircraft of the future. The noise reduction benefits and performance improvements of such an engine are well recognized. However, it is unlikely that industry can proceed with development of such a commercial engine without government help such as that which has resulted in the past from the derivation of commercial engines from military predecessors.
The existence of airframe noise in the absence of engine noise must be given increased attention in establishing attainable noise levels for current and future aircraft. It has become apparent that a limit exists, beyond which quieting the engine installation will be ineffective unless progress is made toward cleaner aerodynamic design and/or cleaner operation of the aircraft.
The aircraft industry needs a reliable measure of noise acceptability for use in the initial planning and design of aircraft and engines. The very subjective nature of noise precludes basing design on the pure physics of noise alone. Yet introducing a new airplane into airline service requires major financial commitments by the manufacturer several years before airplane certification. One of the most important design parameters in future aircraft is its community noise acceptability when it enters service. The high economic penalties resulting from “overkill" in designing to unknown requirements are not tolerable.
EL SEGUNDO DEMOCRATIC CLUB,
DEAR SIRS: We would like to congratulate the residents of Inglewood and Westchester whose coordinated efforts have brought a measure of relief from the constant aggravation of the noise caused by airport operation. In the same vein, the members of the El Segundo Democratic club wish to protest the implementation of the new take off procedures which have caused a much higher level of aircraft noise to be inflicted on our community. Although the change in landing patterns obviously reduces the suffering of the residents of communities such as Inglewood and Westchester, we fail to see the necessity for installing take off procedures which call for steeper take off angles, thus requiring more power and generating more noise. A comparison with the former take off patterns should make the unpleasant consequences quite obvious. Formerly aircraft were quite a bit further down the runway before lifting off. Before lift off, much of the aircraft noise was muffled. After lift off, the aircraft would continue in a gradual climb well out over the ocean before making any maneuvers which would bring them back over our town.
The new procedure results in most aircraft becoming airborne before they reach the eastern limits of our populated areas. El Segundo is becoming more democratic in one respect. We are now all suffering equally from the noise. Furthermore, the altitude most aircraft achieve while flying past El Segundo only serves to distribute the noise over a wider area. Another unfortunate effect of this ability to achieve minimum altitude much sooner is the tendency of most aircraft to make turns in the direction of El Segundo long before they reach the coast, some we suspect, before they reach minimum altitude.
We ask your help to get us relief from this situation. We would like to you to explore the possibility of reinstituting the former take off procedure of gradual ascent out over the ocean before overflying our populated areas.
We have a beautiful park here in El Segundo. Perhaps we could expedite this proposal by making the next meeting of the committee an open air activity in our parks, where the problem which we are describing is all too obvious. EUGENE MOORE, Presdent.
APRIL 28, 1973.
Senator HOWARD W. CANNON: I, Lynn Jane Neumann, do swear under penalty of perjury, that the following letter of declaration is true to the best of my knowledge and wish it to be admitted into the noise hearings conducted by you and Senator Tunney.
LYNN JANE NEUMAN.
RANCHO MIRAGE, CALIF., April 28, 1973.
MY DEAR SENATOR CANNON: I would like to express my appreciation for your acceptance of my uninvited testimony before you, and Senator Tunney, at the "Noise Hearings," conducted at the Inglewood Fire Station. I am just now recuperating from the Easter week, spent in my apartment house under the north runway, in Inglewood, which sends me back to the desert with shattered nerves, upset stomach, and a poorer financial standing.
The personal, and damaging effects of the L.A.X., operations, are becoming more evident with every trip to Inglewood, and if something is not done immediately, we, under the north runway, can, and will become a carbon copy of the South runway environment!
My deluxe split level 2 B/R apt. that became vacant Feb. 1st is still vacant! I have advertised in two newspapers, and find we are at the stage where people aren't even looking in our prime apartment house, and residential area. I have lost $880.00, in income to date on this vacancy, and have no future prospects. While interviewing two girls, on Good Friday, the planes came over so hot and heavy between 6 and 8 p.m. I lost the girls because of the noise, and also the safety element, entered into it! One of the S. runways had been closed Thursday, so we were receiving all that traffic! This was an excellent indication of what will happen if the traffic were increased to that degree. We would be reduced to, "Red-Star Fertilizer!"
I depend upon my building for part of my income, to support myself and my 16-year-old son. I might add, I have never had a vacancy factor of more than two weeks in the four years I've had my building, and I'm sure my ex-husband before me, had none, because I have inherited some well-established tenants who are still there. I lost my ex-tenant, an F.B.I. agent, on the night narcotics division, because he could not sleep during the day because of the planes, and also thought the rent was too high for so much noise.
You can readily see if, L.A.X. is permitted to continue under its present procedure, it will not only pull our rent structure down, but also the quality of our tenants, in our super-deluxe buildings. My rents in some apts. are below what they should be, but retaining good tenants over a period of years, is more important to me. I am now starting to lose some of these old, desirable tenants, and finding it impossible to replace them.
This has happened to Lorraine Gerhardt, my good friend I spoke about that day and she now has lost her apt. house through foreclosure, Its not too late, to save us under the north runway, and these are some of the solutions! 1. Extend all runways out to ocean!
2. Over-ocean approaches and departures!
L.A.X.-F.A.A. and A.L.P.A. stated they would never consider this
With God's, help, and people power, the F.A.A. finally conceded last summer, to give these approaches, "a try," between 12 midnight and 7 a.m.
They proved successful, and will be in effect at the end of April, between 11 p.m. and 7 a.m. except when wind exceed 10 knots.
Just think, Senator Cannon, for the 1st time in the annals of L.A.X. history, people will be able to sleep in Lennox and Inglewood! Our research brought out, these approaches take more gas, and time-a small price to pay for the Health, Welfare, and safety of thousands under the flight pattern.
I have a great deal of respect and admiration for L.A.X., manager Clifton Moore, for initiating this policy, that our Gov. should have done years ago. Its not often today that you see the strength of men shine through, as it did in this instance. These approaches should eventually, be on a full time scale, even tho a few flights may have to be cut out. However, Senator Cannon, more must be done, and I repeat, before its too late. Our Government, has never considered, or protected our rights on the ground, and its long overdue.
I look to you for this strength! 90% of the schools in Lennox and 80% in Inglewood, are under the flight pattern. It is criminal and unjust, what is happening, not only to the education of our children, but their hearing!
An all time and permanent solution to the L.A.X. problem, is the "OFF-SHORE AIRPORT." I will be more than happy to send you these plans upon request. To go one step further, is to build a nuclear plant underneath the airport, that would provide us with the first failsafe plant ever to be built. Safety devices could be built in to flood the chamber where that golf-ball size of energy is placed, in case of earthquake or explosion.
At present, San Orfro is not only endangering Nixon's life while he is at San Clemente, but hundreds of thousands of lives within a 50-mile radius of the fallout, if anything should happen at that location. There is NO working model of San Orfro, so wouldn't it be wise, as well as economical, to kill two birds with one stone rather than have another Hiroshima?
The Edison Co. could share the cost of building the off-shore airport and gain a new plant that they have been pleading for.
You, Senator Cannon, now have a choice to go down in history as a great man of decision, as a few men who have changed the course of history have, or you can make a non-plus decision that will keep the people's interest on a diminishing basis.
An airport, and people, can and will live compatibly, only if directed on the right course.
May God direct you in all your decisions.
LYNN JANE NEUMANN, Advisor to S.T.O.P. Committee, "Stop the Overhead Planes."
STATEMENT OF HIGHLINE PUBLIC SCHOOLS, SEATTLE, WASH.
Schools located in the vicinity of airports, and particularly those which are more or less directly underneath air traffic paths, suffer repeated intrusion from aircraft noise. These intrusions have been found to be interruptive and
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