to fan-jet suppression. We achieved about a 1512 EPNdB reduction. This is the side-line noise level here. In this case what we have been able to achieve so far has been very minimal, and what we can do with jet-suppression is still much in the questionable stage.

money

We have been working the noise problem quite aggressively for a number of years. This table is an indication of the amount of that we have put in in the form of either Boeing research funds or Government contract funds in working noise reduction. You can see that between 1958 and the end of this year that it will total approximately $60 million.

I think you can appreciate the health of the Boeing Co. won't permit. us to continue expenditures of that nature very long.

This is a summary of the airplane types that we have under consideration. We have about 2,000 airplanes in the commercial fleet today. About 160 of those are pure jets and are not shown on this tabulation. We consider that they are too old for consideration of retrofit. Furthermore, we have nothing to suggest in the form of retrofit.

You will notice these broken into three distinct groupings, although there are in the neighborhood of seven different types of airplanes. Here are 707-120B airplanes at about 258,000 pounds, the 720B at 235,000 pounds, running up to the 320B at 336,000. These use JT3D engines. We think that one configuration would take care of all three of these types of airplanes.

I must point out, however, that in tuning an airplane-by that I mean arriving at a final configuration of an airplane-flutter is a very critical point in a design consideration. It is the first thing to be tested when an airplane is in its initial flight-test stages, and the postioning of the nacelle on the wing is quite critical as far as flutter is concerned. We think that we will be flutter-free on all three of these. We have, however, only checked it out on the 320B to any detail. In both the other two groupings here, there is a short body and a long body airplane. Particularly in the case of the 727, additions to the weight of the nacelle installation at the back end of the airplane begin to create balance problems that in many cases involve ballast on the front end of the airplane in order to make it operational.

The three types of nacelles, then, that we are looking at are, one with the JT3D engine, and two with the JT8D. This picture shows the one JT8D mounted on the side of the body on the 727. There is another one in the center of the body on the tail-end, but it poses no particular problems in addition to those that would be encountered in mounting the ones on the side.

The JT8D on the 737, whereas it is the identical engine, does pose completely different problems, however, in mounting the engine up close to the wing relative to the mounting on the side of the body. So, they must be handled as individual design problems.

Now, with respect to the 707 airplane in more detail, this graph is an indication of the noise levels broken into components versus engine thrust. The most important point to notice is the component of noise contributed by the jet. It is down for both the takeoff and the approach conditions. It is significantly down from the noise exhibited oy the fan-inlet or the fan-exit.

This suggests, then, that considerable noise reduction can be obLained, particularly at the approach conditions with fan-treatment

only before we run into a jet-floor. If you keep this chart in mind when we get to the JT8D, you will find that the characteristic is considerably different on the JT8D and the jet noise is predominant.

This upper chart represents the current production nacelle with short fan ducts; the fan air exhausting here; the primary air exhausting at this point.

The contract we had with NASA involved lengthening the fan duct to make it a full length duct, putting treatment in the fan duct to absorb the fan noise, and significant treatment in the inlet in the form of inlet rings to absorb the noise coming out of the front end of the engine.

About 70 square feet of treatment was added to the front end, and in the order of 207 square feet at the back end.

We were not particularly pleased with the performance results from this configuration and have continued research in an effort to improve the overall quality of the airplane that could result with better treatment aboard.

I will show some of the configurations that have been examined since 1969. Recently we have had on our test stand at Wichita, a configuration similar to the one shown here. Whereas the NASA cowl had a long duct that extended coplanar with the primary duct, we have foreshortened the duct, we have made use of advancements in treatment technology, such that we can get the same noise reductions but with lesser square feet of treatment involved in the fan duct. The inlet is the same as we tested in the NASA program previously. That is still associated with fan-treatment only.

This particular configuration here is one that we have been examining with an eight-lobe jet suppressor attached to the back end of the previous configuration. This is an effort to quiet the jet noise and to reach an overall noise level somewhat lower than we could achieve with fan-treatment alone.

In addition to an eight-lobe nozzle, we have included a variable area primary nozzle which would permit further noise reductions on power cutback after takeoff.

All of these designs that I am describing, involve a complete new nacelle, approximately 25 inches added to the length, some increase in diameter, and the most costly portion of it is that it does involve a new fan-thrust reverser. We would retain the current primary thrust reverser.

Senator CANNON. What does it weigh?

Mr. BLUMENTHAL. You are a good, straight man, Mr. Chairman. The weight increases that we ascribed to the NASA configuration were on the order of 800 pounds per nacelle, about 3,100 pounds per airplane. This means that we would either reduce the fuel aboard or reduce the payload by that amount.

In our effort to improve the performance losses, the second configuration that I have shown reduced this weight penalty to approximately 2,200 pounds. By the time we put the jet suppression on, the penalty increases to approximately 2,700 pounds.

Now, associated with the weight penalties, however, are some drag increases and some changes in fuel consumption, such that the resulting range degradation that we had estimated for the NASA program

was in the order of 200 miles, for the improved configuration about 175 miles still fan-treatment alone-and with the multi-lobe nozzle, about 340 miles. This is a very important point to consider because most of the analyses involving direct operating costs that we have seen referred to in the press and other places do not reflect the reductions or potential reductions in city pairs involved in performance losses of this magnitude, and they certainly need to be taken into consideration.

As far as the noise reductions, this is shown in the upper portion of the chart. At full takeoff power, the basic airplane creates an EPNdB in the order of 115. As shown on the NASA contract, this was reduced to 111.5 or a reduction of 32 EPNdB. As you heard on the tapes earlier by Mr. McPike, that amount is hardly discernible. Our improved configuration had the same takeoff noise reduction. We would increase that to 412 with the jet suppressor.

At the cutback power, the airplane basically is 113 EPNdB. We can reduce it by 6 with fan-treatment alone, or by 9 when we put a jet suppressor on.

The approach noise, which is much more responsive to fan-treatment, is reduced 151⁄2 EPNdB, and that is something that you can clearly notice. The same exists with the jet suppression.

On sideline we get 412, 412, and 712.

Incidentally, the costs that we had estimated for the NASA configuration were in the order of a million dollars per ship set. The improvements in the foreshortened cowl brought this down to $750,000 per ship set. When we put jet suppression on, our estimate is that it would be in the order of $1.25 million per ship set based upon a 400 airplane modification program.

We have recently been awarded an FAA contract to further develop this configuration. Work is going on in our Wichita facility. Go ahead was July 1 of this year. We expect to complete the ground demonstrations in 15 months. This will include flight-worthy hardware and include the development of a thrust reverser. Assuming production go ahead immediately upon completion of this contract, we believe we can complete the entire retrofit at the end of an additional 60 months. This means the fleet of 400 airplanes, 707's in this case, would be accomplished about the end of 1977.

Now, I would like to turn to the 727 airplane. Based upon the information that we picked up in our NASA contract earlier and were able to incorporate into the 727 program, we have successfully designed, tested and we believe flight-certified a new advanced 727-200 airplane. It has only been announced within the last couple of months. In doing that, we were attempting to pay attention to the problem that is illustrated on this chart wherein you can see that the jet noise has risen considerably from that shown on the JT3D engine.

There is only a modest amount that we can do with fan treatment alone this area here and only a small amount in this area.

The configuration that I spoke of that we have recently certified is shown on this chart. Here is the basic production version that exists on the majority of our 727 airplanes to date. This is the configuration that is on our new advanced 727 airplane. It involves treatment in the inlet, treatment in the Pratt & Whitney engine fan ducts, and treat

ment on the tailpipe. In spite of the fact that we have every expectation of being able to certify this airplane configuration to meet FAR Part 36 rule levels, it is very clear from listening to the airplane and from looking at the resulting noise levels that reduction in jet noise is very highly desirable if the effect is going to be noticeable and provide relief to the community.

For the past several years, we have been tackling this problem agressively. This is a listing of full-scale ground and flight test hardware that we have built and tested in an effort to achieve some sort of a breakthrough in the reduction of jet noise. Unfortunately, there is very little known today about the mechanism of jet noise and what to do about it, and we have been faced with a cut-and-dry procedure that is very time-consuming and very costly.

We have had probably more failures than we have had successes, but we think we are making progress. The pictures that I want to show you here indicate some of the things we have tried in an effort to find something, regardless of how practical it is, that could make a dent in the jet noise. Then we could begin to focus our attention on something more practical.

One of our earlier trials was a configuration shown here on the back end of a JT8D engine involving 19 tubes. That didn't give us anything noticeable as far as reducing the jet noise. We went to the next step, and on the back end of each of those 19 tubes, we put 10 lobes. That began to make some noise reduction. It still was far from being satisfactory. Incidentally, we don't know how we would handle anything like that on an airplane.

The next piece of hardware that we built involved 12 lobes. The idea was to bring air in from the outside from around the nacelle, get it down deeply into the primary core, generate mixing, and reduce the shear noise between the primary jet and the ambient air. This looked god enough to us on ground tests that we put it on a 737 and actually made flight tests. I stood in the center of the runway listening to the airplane fly over. Unfortunately, if I closed my eyes, I could not tell which engine had the throttle forward. We did not accomplish much. The next thing we tried was a six-lobe suppressor, again attempting deep penetration. This one we put onto, again, the 737 airplane and flight-tested it. It looks like a very normal kind of installation, something that could be hung on an airplane. It did provide some reduction in sideline noise and a modest amount of reduction in takeoff noise. Unfortunately, at the same time the approach noise went up. It didn't appear very satisfactory.

There had been some discusion of directional nozzles, the idea being that if you stood off to the side of an oval nozzle, you might get less noise reaching you than if you were standing off in this direction from the nozzle. This we found to be true, but the differences were in the order of 1 EPNdB and certainly not worthwhile hanging on an airplane.

You will recall that the JT8D engine has the primary exhaust and the fan exhaust both exhausting through a common exit nozzle. We thought that perhaps we would make some dent in the noise if we separated those two. So, we extended the primary nozzle that is normally buried within the engine exit. We extended it aft to be coplanar with the fan nozzle exit. All this did was to increase the noise.

So, although we laugh at these things now, I had to defend the funds on every one of these, and we were serious. We had something going for each when every one of these things was tested.

This one is an internal mixing nozzle where we were attempting to get more mixing within the nacelle prior to exhausting through the primary exit. What we found from this was that the nozzle, as it is currently constructed, does a very excellent job of mixing, and we couldn't improve on it.

The next thing we tested was a 48 lobe suppressor, this time behind a J75 engine. We began to get some impressive noise reductions. In this case, a J75 being a pure jet, had only high velocity, high temperature gas coming out through the tail pipe and exhausting through these small lobes, peripheral to a large center plug.

This looked interesting enough to us that we took that installation, separated the fan air on a JT8D from the primary air, extended the primary air through a long duct and tested that to see if the characteristics of slower, lower temperature primary air would still give some noise reduction. In addition, we put a silencer or shroud around the lobes such that we could put treatment inside the shroud, and absorb noise that might be generated within the shroud.

The chart here indicates why we were doing that. This is a chart showing noise versus frequency. The primary nozzle of a JT8D exhibits this sort of a spectrum. When we put the 48-lobe nozzle on the back end of the JT8D primary duct, it brought the noise level down in the low frequency level significantly; it increased the high frequency noise, and this is roughly what we would have expected.

Then, by putting a shroud around the nozzle, we were able to absorb the high frequency noise. This showed, virtually across the entire. spectrum, an ability to reduce the noise on the order of 20 decibels. Bear in mind, this was on the primary only, and we still didn't have anything that we felt we could hang on to an airplane, but we thought we were opening the door to at least an avenue of further investigation. The next step, then, was to build a 36-lobe nozzle designed sperifically for a JT8D where both the fan air and the primary air went through the lobes. Here you can see the 36 lobes. This is the shroud, not in place.

This is a picture showing the shroud around the lobes and showing an avenue for air ingress to essentially surround the lobes with external air. You will hear this type of a configuration referred to as an ejector-suppressor.

These were tested full-scale, so we have some appreciation, from ground test at least, as to what noise levels could be accomplished. Here is the basic airplane showing 100 EPNdB at cutback thrust, 109 at approach and 108 at sideline. Those are noise levels that the majority of the 727 fleet exhibit today.

With the fan treatment alone that I showed on the earlier chart and the one that we have flight tested on the advanced 727 airplane, we can get a reduction of one EPNdB at cutback, six at approach, and nothing at sideline. You can see that that is really not much to write home about.

When we put the jet suppressor on, we got five reduction at cutback, 10 at approach, and eight at sideline. And more significantly, we got a