« PreviousContinue »
NOISE-REDUCTION RESEARCH AND DEVELOPMENT
V. L. Blumenthal
W. S. Huntington
BOEING COMMERCIAL AIRPLANE COMPANY
NOISE REDUCTION RESEARCH AND DEVELOPMENT, 1972 PROGRESS
V. L. Blumenthal, W. S. Huntington, and J. M. Streckenbach
Boeing Commercial Airplane Company
Renton, Washington A January 1972 paper(1) summarized 15 years of activity aviation industry. Currently, over three-quarters of the com by The Boeing Company in noise reduction research and mercial airlines seats are on airplanes powered by JT8D or JT3D development. It also discussed work that was in progress at that engines. There is no way open for these airplanes to be replaced time, and plans for future work. It is the objective of this paper with new aircraft or be retrofitted with new engines in the near to update the January 1972 paper, reporting progress made future, even if funds were available. The current wide-body jets during 1972. Problems that still need solutions will also be with new high-bypass engines are too large for many airline highlighted.
routes, both present and future. In addition, no high-bypass-ratio replacement engines in the 20,000- to 30,000-pound thrust class
are in production or likely to be in production in the near THE LOW-BYPASS-RATIO TURBOFAN FLEET
To re-emphasize the importance of the noise reduction research and development Boeing has been conducting on the low-bypass-ratio turbofan fleet, a brief discussion of the current and future importance of this fleet to the world's airlines is in order.
The JT3D and JT8D engines powering the current low-bypass-ratio fanjet fleet of commercial airliners have been continually improved and uprated, such that today they are well-proven engines that incorporate significant technical advances over their predecessors. Although these engines may be noisier than desired, their well-established reputation for reliability deserves careful consideration of means by which they can be quieted.
In the world today there are over 2,840 JT3D and JT8D powered commercial aircraft. Comments are frequently made that these are old aircraft and engines, and should be retired. This is not only completely unrealistic, it is also far from the truth. Both the engines and aircraft have been continuously improved such that those now coming from production lines are generally considered modern in every respect.
The fleet is not old in terms of accumulated years, as seen in Figure 1. About half of the JT3D and two-thirds of the JT8D fleets are less than 5 years old. Furthermore, as indicated in Figure 2, these airplanes are fulfilling an essential role in the 2000 1849
The expenditure of over $60 million in Boeing funds alone over the past 8 years on noise reduction research and production development is indicative of the importance the company has placed on improving community noise. During the same period of time, this expenditure has been supplemented with over $30 million in government funding. Our earlier paper(1) went into considerable detail in discussing the specific noise problems of each of the JT3D/JT8D powered airplanes in the low-bypass turbofan fleet, and reported progress made up to the end of the 1971 calendar year. The following discussion will serve to update these efforts through 1972 for each airplane type.
The 727 Airplane
Early tests on the 727 airplane and its JT8D engines showed that noise reduction was dependent on lowering both jet noise roar and the higher frequency rotating machinery noise. The first immediate step taken was to reduce the fan-generated noise levels as far as possible with sound-absorbent linings without waiting for a solution to the more complex and less-understood jet noise problem. This effort resulted in development of the production quiet nacelle illustrated in Figure 3, which has been certified by the FAA as fully meeting the Appendix C noise levels of Federal Air Regulation Part 36 specified for new airplane type designs.
PRODUCTION STANDARD NACELLE
300 NUMBER OF PASSENGERS
-707 120/720 STID ENGINES
RANGE, 1000 NMI
Figure 4 is an indication of both the continuing popularity of the 727 for future domestic and foreign airline routes, and the importance placed by the airlines on purchasing quieter aircraft. Since mid-1971, when the quiet nacelle was first offered as an option, 185 model 727 airplanes have been ordered. The airlines have voluntarily ordered the majority of these with quiet nacelles. This is significant, since there is currently no regulation that requires older aircraft types such as the 707, 727, and 737 to meet the noise levels required of new types.
A lengthy Boeing program aimed at the development of a JT8D jet noise suppression concept for the 727 was reported previously. (1) A subsequent FAA/Boeing co-funded program culminated in flight testing in late 1972 of the configuration illustrated schematically in Figure 5. Two views of the flight test ejector-suppressor installation are shown in Figures 6 and 7. The concept included a 20-lobe jet noise suppressor enclosed in an acoustically lined ejector shroud, in combination with an acoustically treated, ringed inlet to suppress forward-radiated fan noise, and fan duct treatment to reduce aft-radiated fan noise. The objective was a balanced design that would work equally well in reducing jet-dominated takeoff noise and fan-dominated approach noise.
Although the final flight test results confirmed earlier predictions that significant reductions in community noise were attainable using this configuration, the performance losses were much greater than was expected or considered reasonable. Figure 8 summarizes the noise and airplane performance values of the in-production quiet nacelle (fan noise treatment only) and the ejector-suppressor concept (fan treatment and jet suppression), both related to the baseline 727 airplane.
JASONDJEMAMJ JASONDJEMAM J JASON DJEMAM J J A SOND 1972 1973 1974
Figure 9 illustrates the range penalties associated with operating ejector-suppressor-equipped airplanes from limited field lengths and high-altitude airports. A detailed discussion of the ejector-suppressor development program is covered in References 2 and 3.
Figure 4.-727 Quiet Nacelle Delivery Status (Firm Orders and Options, 8 June 1971 Through 24 January 197
MIXED HOT ENGINE AIR ANO SECONDARY AIR
Figure 8.-727-200 Retrofit Data Summary (JT8D-9 Engines)
An alternate means of reducing noise is to increase the
Increment bypass ratio of current engines in a direction toward the new
high-bypass engines powering the 747, DC-10, and L-1011 Operating Weight
airplanes. This bypass ratio increase results in a reduction of jet Empty, Lb.
velocity, thereby reducing jet noise. Studies started by Boeing,
and under NASA sponsorship since August 1972, are aimed at Unlimited Field Length
determining the feasibility of noise reduction on JT3D and JT8D Takeoff Weight, Lb.
powered airplanes by replacing the two-stage fans with larger 172,500 172,500
diameter single-stage fans. The new fans extract more work from Required Field Length,
the turbine, resulting in reduced jet velocity and jet noise. Pratt Sea Level, 840 8,400 9,000+600 (+7.1%)
& Whitney and McDonnell-Douglas are also participating in the Range, Nautical Miles 1,565 1,290
-275 (-17.5%) NASA-sponsored program. Work accomplished to date indicates
that this fan replacement concept is potentially very attractive. 7000-Ft Field Length, Sea Level, 84°F Takeoff Weight, Lb. 165,000 160,300
Along with reduced primary jet velocity, the refanned
engines also experience improvements in specific fuel consumpRange, Nautical Miles 1,220 760 -460 (-38%)
tion, and in takeoff and cruise thrust. 11,500-Ft Field Length, 5000 Ft, 59°F
Figure 10 is a schematic comparison of the refanned and Takeoff Weight, Lb. 160,000 151,900
production JT8D engines and their treated nacelles. Range, Nautical Miles 990 385 -605 (-61%)
The data comparisons shown in Figure 8 indicate con
siderable noise reduction for the refanned engine installation includes Ballast for Typical 727-200 airplane.
(next to the last column), but the weight of the installation results in a high range loss when operating at the basic airplane
gross weight. By taking advantage of the higher thrust rating of Figure 9. -Effects of Ejector Suppressor on Airplane Performance the refanned engine, allowing the takeoff weight to increase so as