This is just part of a very intensive effort we have under way to strengthen our working relationship with all of the military services. Our technology will be most useful for their purposes.

Mr. WELLS. The inquiry is directed at the very evident increasing number of joint working arrangements, joint offices with DOT. I am asking, for the committee, if a comparable kind of thinking is going on to see what kind of arrangements can be worked out with the Defense Department which we may not have had in the past.

Dr. DOROUGH. I might make one comment, that on the AACB, which is really a NASA-DOD organization, we invite representatives of DOT and FAA, also. They sit as observers, more than observers; as participants in the AACB meetings. They are completely aware of our negotiations and of the problems that we are attacking. Whenever their interests overlap ours, we try very hard to bring them in. So through the AACB alone, plus all the interactions between NASA and DOT, I think there is coverage. There is a very good arrangement to be sure that we are not going off and building facilities, for example, solely for the DOD that completely ignore the requirements of these other Government agencies.

Mr. WELLS. I think Mr. Anders made a very apt remark in his statement, that one of his jobs as he saw it was to get all organizations in the Government at all levels to "think national.” I think this illustrates the point.

Thank you, Mr. Chairman.

Mr. HECHLER. Thank you, Mr. Wells.

We are glad to get all this concrete evidence that people are not only talking to each other but working together. This is encouraging.

Thank you very much, Dr. Dorough and Mr. Jackson, you and your associates from the Department of Defense.

If there are no further questions or business before the committee, the committee stands adjourned until 9 a.m. tomorrow.

(Whereupon, at 5:50 p.m., the subcommittee adjourned, to reconvene at 9 a.m., Wednesday, January 19, 1972.)

AERONAUTICAL RESEARCH AND DEVELOPMENT

WEDNESDAY, JANUARY 19, 1972

HOUSE OF REPRESENTATIVES,

COMMITTEE ON SCIENCE AND ASTRONAUTICS,

SUBCOMMITTEE ON AERONAUTICS AND SPACE TECHNOLOGY,

Washington, D.C.

The subcommittee met at 9 a.m., in room 2325, Rayburn House Office Building, Hon. Ken Hechler (chairman of the subcommittee) presiding.

Mr. HECHLER. The committee will be in order.

We are very pleased to welcome back again Roy Jackson. Mr. Jackson will you proceed?

Mr. JACKSON. Good morning, Mr. Chairman.

I would like to mention, if I may, Mr. Chairman, that I have here at the table with me Mr. Chuck Foster of the Joint DOT/NASA Noise Abatement Office; Mr. Harry Johnson from NASA who is Director of our propulsion activity in our OAS headquarters organi

zation.

With that I will proceed with my testimony.

AIRCRAFT NOISE ABATEMENT

STATEMENT OF ROY P. JACKSON, ASSOCIATE ADMINISTRATOR, OFFICE OF AERONAUTICS AND SPACE TECHNOLOGY (OAST), NASA; ACCOMPANIED BY CHARLES R. FOSTER, DIRECTOR, OFFICE OF NOISE ABATEMENT, DOT, AND HARRY W. JOHNSON, DIRECTOR, AERONAUTICAL PROPULSION DIVISION, OFFICE OF AERONAUTICS AND SPACE TECHNOLOGY, NASA

Mr. JACKSON. Earlier testimony in this hearing has brought out many aspects of the aircraft noise problem. We have already discussed the reasons which have led both government and industry groups studying the issue to conclude that noise abatement is essential to the continued healthy expansion of our Nation's air transportation systems, and I am sure that most people in this room agree with this conclusion. The many environmental, social and economic benefits of noise abatement have been brought to your attention also. In our earlier testimony, we described the fact that the NASA and DOT are executing an ongoing noise abatement program, while designing and coordinating a total national program of aircraft noise abatement research and technology. We also described a joint office staffed by DOT and NASA personnel set up for this purpose. Following my presentation, Mr. Charles R. Foster, the Director of the Joint Office of Noise Abatement, will explain to you in more detail how we are implementing the required research and technology programs we believe are necessary.

74-827-72- -14

The fiscal year 1972 NASA portion of the national program in aircraft noise abatement includes approximately $17.3 million of R. & D. funds and involves nearly 400 direct man-years of effort at the various NASA centers. Our program can be described in three major categories, which are aircraft source noise reduction, noise abatement through operational flight path control techniques, and human psychoacoustic response studies.

I would like to emphasize that there is other work over and above that included in the $17.3 million whose primary purpose is other than noise abatement, but is of a nature that the results contribute to noise abatement. In a complete accounting for all effort, one would take at least partial credit for that work. A good example is the STOL vehicle research.

I am sure the technical content of our program is of interest to you, and I intend to summarize it. But I believe it will be beneficial to these hearings if I first describe and then use an audiovisual presentation whose primary objective is to acquaint you better with some of the terminology and ideas involved in noise abatement.

By way of introduction to the audiovisual, noise abatement research and application discussions inevitably involve the use of certain technical terms including frequency, sound pressure level, decibels, perceived noise levels, effective perceived noise levels, and others. We recognize that these terms are sometimes not satisfactorily descriptive for people who are not conversant with the field of acoustics or noise abatement, and we recognize the need for improved communication of the ideas they represent. We also feel it is important that you be able to interpret these ideas using your own perceptions, for only then will the significance of some of the noise abatement concepts under discussion become apparent.

You may know that it is quite difficult to reproduce loud noises satisfactorily and accurately, and also that every person in this room will perceive sounds somewhat differently. Sound reproduction equipment limitations, acoustic characteristics of this room, and your own position relative to the loudspeakers are all factors. The aircraft noises you will hear are generally not as loud as those you have probably experienced in the vicinity of actual aircraft. What we have done is to concentrate on comparing noise levels through the representation of noise differences. The sound level differences you will hear are accurately reproduced. I would like to emphasize that point. The sound level differences you will hear are accurately reproduced.

It is these differences that should be kept in mind as you hear noise abatement reductions described in our program discussion.

The audiovisual presentation takes about 26 minutes and must run continuously. With your permission, Mr. Chairman, I will now proIceed with the audiovisual.

Mr. HECHLER. You may proceed.

(Audiovisual presentation given, the text of which follows:)

AIRCRAFT NOISE ABATEMENT

For several years the National Aeronautics and Space Administration has been working on the problem of aircraft noise abatement. Significant progress

has been made in the development of new technology which can be used to alleviate the current problem of aircraft noise pollution and which will also insure that airplane operations of the future will be much quieter. In the next several minutes we shall demonstrate the noise produced by present day aircraft engines and show how the progress that NASA is making can reduce the noise.

Before discussing the progress, it is helpful to know some basic facts about what noise is and to understand some terms used in describing it.

Listen to the takeoff noise of four JT3D engines used on both the Boeing 707 and Douglas DC--8 aircraft.

Noise, by definition, is unwanted sound and the familiar sound we have just heard has come to be annoying and unwanted.

All sounds consist of energy reaching our ears at various pitches or frequencies. What gives each different sound its special identity and, importantly, why it is annoying are the frequencies which it contains and the amount of energy -that is the intensity of each frequency.

One way to describe different sounds is with a graph showing the distribution of frequencies and their intensities. On such a graph we use a vertical intensity scale marked off in appropriate units and a horizontal frequency scale.

The frequency scale goes from 50 cycles per second to 10,000 cycles per second. Essentially all aircraft noise energy is included in this range. A graph of intensity and frequency is called a sound spectrum.

The very simplest sounds called tones contain energy in only one frequency. Listen to a tone at 1,000 cycles per second.

Now listen to another tone at twice that frequency or 2000 cycles per second.

Finally let us double the frequency once again.

All the tones heard had the same intensity as measured with a sound meter. They did not sound equally loud however because the ear is more sensitive to certain frequencies.

Another special kind of sound is one in which all frequencies are present with the same intensity.

The spectrum of such a sound is represented by a level line from low to high frequencies encompassing a broadband of frequencies. Here is an example of such broadband noise.

Now let us hear once again the noise of the DC-8 or 707 airplane at takeoff and observe its spectrum. We see that there is broadband noise over the entire frequency range and that in addition there are some tones which stand out from the rest.

So far we have discussed one aspect of sound-frequency content-which gives each sound its distinct character. One other obvious and important aspect of sound which is related to annoyance is its overall intensity-that is the quality that we change by adjusting the volume control of a radio for example.

The overall intensity of sounds is measured in units of decibels. A good way to get a feeling for the decibel scale is by listening to sounds of different intensity while knowing the decibel difference between them. We shall use the 1,000 cycle tone again and while it is sounding we shall interrupt it momentarily and continue it three decibels lower. Three decibels is a small change so listen carefully.

Now a 10 decibel difference:

A 20 decibel difference:

and finally a 30 decibel difference:

Notice how three decibels is not strongly evident. Listen now to the same differences using DC-8 or 707 airplane noise.

First a three decibel difference:

Ten decibels:

Twenty decibels:

Thirty decibels:

Notice how with this real noise, a three decibel drop is barely perceptible if at all, while a 10 decibel drop is a noticeable improvement. In an aircraft noise demonstration such as this it is not possible to reproduce the decibel levels that would be observed near an airport. However, we are reproducing the decibel differences for comparison so that you can judge the improvement.

There are various decibel scales in use but an important one for aircraft noise is the perceived noise decibel or PNdB. The PNdB is a decibel measure of annoyance which takes into account the overall intensity of the sound, its frequency content and how people respond to these frequencies. The PNdB very simply is a measure of subjective human response. To demonstrate this, listen to three kinds of transportation noise, all played at the same maximum energy level. Since each sound has a different spectrum, the ear will perceive its loudness differently.

Because of the special nature of the aircraft noise problem with whining engines that pass overhead it is appropriate to use one other noise measurement unit. This is called "Effective Perceived Noise Decibel" (EPNdB). It is basically the PNdB unit but which has been adjusted for two additional factors. First, it accounts still further for tones in the noise spectrum, and secondly it accounts for the rise and fall of the sound with time, that is, the duration of the sound. Thus, the EPNdB unit gives a single number which is a measure of the total annoyance a person experiences as an airplane passes over. Federal Aviation Administration noise regulations are written in terms of EPNdB and set maximum limits at specific ground locations near the airport.

The ground locations for which the limits are specified differ for takeoff and approach. For takeoff the ground location is directly under the airplane path 32 nautical miles from the start of takeoff roll. In addition for takeoff, noise limits are specified on a line parallel to the runway called a sideline. For an airplane with three engines or less, the sideline is at .25 nautical miles. For an airplane with four engines or more, the sideline is at .35 nautical miles. For landing noise there is only one ground location directly under the airplane path 1 nautical mile from the touchdown end of the runway.

The noise limits in EPNdB specified for the ground measuring stations vary with the weight of the airplane. For the largest planes like the 747, the limit is 108 EPNdB at all three locations. For a new airplane comparable in weight to DC-8 or 707 long range transports the noise limits are:

For takeoff :

104 EPNdB at 31⁄2 nautical miles and

106 EPNdB on the sidelines.

For approach, 106 EPNdB 1 nautical mile from the end of the runway.

The DC-8 and 707 airplanes entered service long before this noise regulation was in effect and therefore, are not subject to it. Their noise levels are considerably higher.

Listen now to the kind of sound a DC-8 or 707 airplane makes as it takes off.

And now listen to the approach noise of that airplane. The approach noise of the DC-8's and 707's is annoying because of the tone caused by the fan of the engine. More complaints are received from airport neighbors because of the approach noise than because of takeoff noise.

NASA sponsored a program beginning in 1967 to reduce the approach noise by use of nacelle acoustic treatment. In 1969, 707 and DC-8 test aircraft were flown with such nacelles on all four engines. Listen to the original 707 and then a 707 with nacelle acoustic treatment.

The takeoff noise for these aircraft is determined largely by the jet noise. Nacelle acoustic treatment cannot reduce the jet noise because it is generated in the atmosphere behind the engines.

One means of reducing takeoff noise is for the pilot to fly the airplane so that it climbs quickly. Then the airplane is as far from a ground observer as possible. Also he can retract the wing flaps as the airplane accelerates in order to reduce drag. This means that the airplane requires less thrust to climb. When a safe altitude is reached, the pilot can reduce the engine thrust from that required for takeoff to the lower thrust required for climb. Here's what it sound like as a pilot cuts back thrust.

An operational procedure which can reduce landing noise is a two-segment approach. In present day airplane operations aircraft approach the runway for landing on a 3° glide slope. In a two segment approach, the pilot adjusts the airplane controls to descend first on a 6° glide slope. About one mile from the runway he changes the path to a 3° slope. In the final stages there is no difference in the landing procedure. Both the FAA and NASA are working with