« PreviousContinue »
This will result from both the highly competitive situation on aircraft noise and the noise regulations developed by the Federal Aviation Administratinn with the cooperation of the Environmental Protection Agency.
We believe the short-range outlook for the airport neighbor can also be good, but have patience and only if we are willing to allocate the necessary resources to the problem.
The current situation is obviously unacceptable to both the airport neighbor and the aviation industry. Many airport neighbors find the noise exposure higher than they will tolerate and the industry finds itself facing restrictions on both operations and airport expansion.
The problem in this country revolves primarily around two engine types which power the vast majority of the narrow-bodied jet transport aircraft. These are the JT3D engine, which powers most of the four-engine DC-8 and 707 aircraft and the JT8D engine which powers the DC-9, 727, and 737 aircraft. Both these engines are of the low bypass ratio turbofan type and both are manufactured by the Pratt & Whitney Aircraft Co. More than 3,000 aircraft powered by these engines are now in service worldwide.
Perhaps a brief outline of our experience at Douglas Aircraft in seeking ways to reduce the noise of these engines will help provide a better understanding of the prospects for quieting the current fleet. In 1965 we submitted a proposal to NASA to study means of reducing the turbomachinery noise of the JT3D engine. Turbomachinery noise is the noise generated by turbulence associated with blades rotating at high speed within the engine. This noise is mostly of the high frequency type and it contains discrete frequency tones resulting in a whine like characteristic. It is the dominating noise on the JT3D engine at approach power and it is the most noticeable noise of DC-8's and 707's during landing.
A contract was obtained to study means of reducing this noise and the work was successfully completed. It led to further contract work with NASA and finally culminated in flight test demonstration by Douglas on a DC-8 and by Boeing on a 707 in 1968 and 1969.
These demonstrations proved the technical feasibility of making significant reduction in the turbomachinery noise of turbofan engines by replacing the hard wall surfaces of various inlet and discharge ducts with surfaces which were acoustically absorbent. This suppression technique is often referred to as SAM (sound absorbent material).
Noise reductions as high as 10 to 15 EPNdB were obtained under approach conditions in these flight programs. There was a great deal of publicity associated with the results and there was a widespread belief that kits were available to cut the noise of existing aircraft in half. This led to the strong pressures for an immediate retrofit of the fleet.
No retrofit program was launched at that time for two reasons. First, the technical feasibility of the noise reduction had been demonstrated but the devices which were used in the demonstration were not suitable for airline service. Second, an evaluation of the effects of such a retrofit program indicated that the benefits would be quite limited.
Unfortunately, turbomachinery noise is not the only noise generated by the jet engines. The low frequency roar of the jet exhaust is a very important part of jet engine noise. This noise is most noticeable on takeoff because it clearly dominates the engine noise at that condition, but it is present at lower thrust conditions and is often comparable in level to the turbomachinery noise. Jet noise is generated behind the engine where the high velocity exhaust gasses mix with the surrounding air.
This jet noise was not reduced by the devices demonstrated in the NASA program. Thus, the benefits of applying the new technology were limited by the so-called jet noise floor. In cases where the turbomachinery noise is well above the jet noise, considerable reduction can be achieved. If on the other hand, the jet noise is equal to or greater than the turbomachinery noise, there is little or nothing to be gained by reducing the turbomachinery noise.
Of the two engine types being considered only the JT3D at the low engine powers associated with landing approach had the potential for the full 10 to 15 EPNdB reduction by turbomachinery noise suppression. At takeoff thurst, little improvement was possible because of the high level of jet exhaust noise. Turbomachinery noise suppression on the JT8D engine could achieve no reduction at takeoff power because of the relative importance of jet exhaust noise for that engine at all powers.
It became fairly clear that the incorporation of the turbomachinery noise suppression would not offer any real help to the takeoff noise problem. On landing the JT3D noise could be reduced substantially, but only small reductions could be achieved on JT8D powered aircraft. It was noted that the JT3D powered aircraft have higher noise levels than the JT8D powered aircraft on approach but JT8D powered aircraft account for far more approaches than the JT3D powered aircraft and therefore, contribute significantly to the approach noise problem.
An additional argument against the turbomachinery noise retrofit program was that both houses and the atmosphere reduce the turbomachinery noise more readily than the jet exhaust noise. Thus, the noise reduction achieved by turbomachinery noise suppression would be less for people indoors and for people more than 370 feet from the aircraft.
The general conclusion reached in the assessment was that although there would be some noise reductions achieved by the applying of available turbomachinery noise reduction technology to the current fleet, achieving a universal and really meaningful reduction for the problem would require reducing the jet exhaust noise as well. Consequently, several programs were launched to develop practical means of reducing the jet exhaust noise of these engines.
These programs were sponsored by the FAA and revolved around the development of jet exhaust noise suppressors. They were also aimed at providing hardware capable of being certified for the aircraft in the current fleet. They included the development of noise suppression devices both with and without jet noise suppressors for both JT3D and JT8D powered aircraft.
A number of FAA and company sponsored programs are in prog
ress for the DC-9. We have already flown a device which achieved some jet exhaust noise suppression and we are planning to fly a device this summer which we expect to provide a significant amount of jet exhaust noise suppression. There will be some performance penalties associated with this latter device, but we must fly it before we can properly assess its relative merits in terms of the penalties and the benefits involved.
We are also working under NASA sponsorship on the incorporation of the new front fan version of the JT8D engine on the DC-9. This new front fan lowers the jet exhaust roar by increasing the bypass ratio of the engine and reduces the turbomachinery whine by sound absorbent materials. Many people believe this to be the only viable approach to achieving meaningful reductions in the noise of low bypass ratio turbofan engines.
In the meantime, a kit which incorporates only turbomachinery noise suppression, has been developed for the DC-9 for application to future production aircraft. It provides no noise reduction at takeoff thrust, but it does provide reduction of about 6 EPNdB at a distance of 370 feet at approach thrust. The DC-9, in its current configuration, can comply with the takeoff noise limitations of FAR part 36 and with this kit it will also comply with the approach limitations. The kit can be retrofitted to existing aircraft. However, while it improves the noise of the aircraft, we would not expect its application to offer a final solution to the airport community noise problem.
Turning to the DC-8, now, unfortunately, the situation for the DC-8 is less advanced. The FAA has sponsored a program to develop certifiable hardware for the JT3D engine as installed on the 707. The program originally included both turbomachinery noise suppression and jet exhaust noise suppression. The jet exhaust noise suppression approach was not successful. The turbomachinery noise suppression is scheduled for flight tests shortly. While it has been considered by some that the 707 hardware might be applied directly to the DC-8 aircraft, our studies show this to be impractical.
The improved technology and some of the hardware developed on this program can be applied to the DC-8. However, it should be clearly understood that at the present time there is no certifiable kit in existence which can be incorporated on the DC-8 to bring the turbomachinery noise levels down to the jet noise floor. Development of such a kit would take from two to three years depending on the funding available for such a program.
Even if this is accomplished, there is still no reduction in jet exhaust noise of the engines. As indicated above, there would be some benefits on approach, but our studies show that no real benefits can be expected for the takeoff situation.
In 1968 we conducted a study for the NASA to establish the feasibility of incorporating a new quiet engine on the DC-8, assuming one was available in the appropriate thrust class. While such an engine would indeed render the DC-8 quiet, the results were quite discouraging and indicated a cost of around $5 million per aircraft. That approach to the problem has not been very seriously considered since that time.
There was recently a substantial amount of optimism for improving the noise of the DC-8/707 type aircraft with a new front fan program for the JT3D engine. Unfortunately, this program has been dropped due to lack of funds. We would agree that the JT8D new front fan program is probably the more important of the two that were in progress.
However, we see no other program which offers substantial improvements for all neighbors annoyed by DC-8 and 707 operations and would strongly recommend that serious consideration be given to reactivating the new front fan program for the JT3D engine.
The cost of retrofit kits, which will offer a really meaningful reduction in noise for all airport neighbors, are generally quite high. Estimates for the cost of the new front fan are on the order of onehalf million dollars per engine. This would amount to roughly a million dollars for a DC-9 and two million dollars for a DC-8.
This includes the cost of the modifications to the engine and the airframe. If the jet exhaust noise suppression system for the DC-9 proves to be viable, it may provide meaningful reductions at a kit price of around three quarters of a million dollars per airplane. However, the lower kit price may be offset by a greater cost in operating expenses. Incidentally, in round numbers the SAM treatment which obtains no jet exhaust noise, would cost around a million dollars per airplane for a DC-8 and around $125,000 per airplane for the DC-9. While the costs of these kits are considerably lower than those which reduce the jet noise, so, of course, are the benefits to the community.
In terms of schedules, the only kit which we will have available in the near future is the simple kit for the DC-9, which we do not recommend as a truly beneficial retrofit kit. The current program for the DC-9 refan calls for a flight demonstration with certifiable hardware late in 1975, assuming adequate funding is continued. If reactivated, the refan kit for the DC-8 could probably be available in around the same time period.
In summary, we are quite encouraged by the longrange prospects for airport community noise. We are satisfied that when all aircraft in the fleet are at least as quiet as the new widebodied aircraft, such as the DC-10, the airport neighborhood noise problem will be dramatically reduced in scope. It will not necessarily be eliminated, however, and we strongly urge the Government to accelerate basic research efforts to ensure that we have the best possible noise control technology for application to new aircraft types.
We are, on the other hand, quite concerned about the prospects for the near-term noise problem. By near term we mean as long as community noise levels are dominated by the current fleet of aircraft powered by low bypass ratio turbofan engines. While there are strong pressures to incorporate turbomachinery noise suppression kits on these airplanes which will bring them roughly into compliance with FAR Part 36, we believe that such action would lead to bitter disappointment on the part of most airport neighbors. Such a program would, of course, preclude the possibility of a more beneficial retrofit program. In addition, the investment would tend to prolong the life of the older and still relatively noisy aircraft and,
hence, delay the time when new, quiet aircraft types provide a really improved situation.
We do believe that the prospects are good for achieving significant reductions in the noise of the JT8D powered aircraft either by jet noise suppression or by the new front fan program. In a relatively short time, the flight test data can prove or disprove these concepts. In the case of the DC-8 and B-707 we do not see any acceptable solution in the presently active programs. We would urge the Government to consider reactivation of the new front fan program for the JT3D engine.
We should point out that this discussion pertains to what we see as technologically practical. We, as a manufacturer, can develop noise suppression kits for installation on our products and can apply our expertise to minimize the operating cost increase recently-resulting from the modication designs. We can provide the kit costs (assuming we know the quantity required) and the schedule of availability along with the performance penalties and noise reductions that will result from the installation of these kits. However, we cannot establish the total cost associated with a retrofit program, nor can we determine the economic reasonableness of retrofitting these kits.
We believe that such determinations must be accomplished by the Government and the airlines.
One further point. We do have new technology high bypass ratio turbofan engines in the higher thrust class suitable for large aircraft. We do not have any such engine in the 20- to 25,000-pound thrust class. Until such an engine is developed, there will be no new quiet aircraft to replace the existing aircraft in the DC-9, 737, 727 categories. We would urge Government support of the development of such an engine as a prerequisite to reaching the desired improvements in the airport noise situation.
In conclusion, we pledge our continued support and our cooperation with government agencies and other members of the aviation industry in seeking a viable solution to the complex problem of the noise of the current fleet.
Thank you, Mr. Chairman.
Senator CANNON. Well, thank you very much for a very fine statement, Mr. McPike. I think you have helped us very much in pointing out that there is no immediate solution to the entire problem, that this is something that is going to take some time and a lot of effort and in that connection I would like to ask you at what level do you think the JT3D fan research ought to go ahead, dollar wise; do you have a feel for what ought to be going into that program?
My recollection is that it was about $2 million last year, the NASA effort.
Mr. McPIKE. Yes, sir.
It was that order of magnitude. Could I perhaps respond by saying the current program alloted for the JT8D, not just for this year, but it is on the order of $55 million. This would include flight test demonstrations.
I would say that the order of a similar kind of cost would be re