Document
TM X-72675
NASA
TECHNICAL
NASA
COPY NO.
MEMORANDUM
9 2 N75-1 48 NOISE (NASA-TM-X-72675) INTERIOR CONSIDERATIONS FOR POWERED-LIFT STOL (NASA) 19 p HC $3.25 CSCL 01C AIRCRAFT Unclas G3/07 13472 I- FOR NOISE CONSIDERATIONS INTERIOR AIRCRAFT STOL POWERED-LIFT By Kearney Barton C.
April or to provide accelerated is used medium informal documentation This The contents users.
to selected information of technical special release be re- standards, may publiQation editing and NASA formal not meet may in another publication.
incorporated or may be vised,
AND SPACE ADMINISTRATION
NATIONAL AERONAUTICS
VIRGINIA 23665
CENTER, HAMPTON,
LANGLEY RESEARCH
1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.
NASA TM X-72675 4. Title and Subtitle 5. Report Date April FOR POWERED-LIFT CONSIDERATIONS INTERIOR NOISE Organization Code 6. Performing AIRCRAFT 7. Author(s) 8. Performing Organization Report No.
C. Kearney Barton TM X-72675 10. Work Unit No.
9. Pertorming Organization Name and Address 505-02-21-04 NASA-Langley Research Center 11 Contract or Grant No Hampton, VA 23665 13. Type of Report and Period Covered 12. Sponsoring Agency Name and Addresshnical Memorandum National Aeronautics and Space Administration Washington, DC 20546 15. Supplementary Notes 16. Abstract Powered-lift configurations which are currently under development for future use on STOL aircraft involve impingement of the jet engine exhaust onto wing and flap surfaces.
Previous studies have suggested that the impinging jet produces higher noise levels at lower frequencies than does the jet alone.
These higher levels, together with the close proximity of the engine and flap noise sources to the fuselage sidewall, suggest that the noise levels in these aircraft may be high enough to interfere with passenger comfort. To investigate this possibility, interior noise levels were estimated for both an upper surface blown (USB) and an externally blown flap (EBF) configuration.
This paper describes the procedure used to estimate the interior noise levels and compares these levels with levels on existing jet aircraft and on ground transportation vehicles. These estimates indicate high levels in the STOL aircraft; therefore, areas of possible improvements in technology for control of STOL interior noise are also discussed.
17. Key Words (Suggested by Author(s)) (STAR cqtegory underlined) 18. Distribution Statement STOL, Cabin Noise, Interior Noise Unclassified Unclassified Noise Reduction, Octave Band SPL, Unlimited Low Frequency Noise 02 21. No. of Pages 22. Price* 19. Security Classif. (of this report) 20, Security Classifi. (of this page) Unclassified Unclassified The National Technical Information Service, Springfield, Virginia 22151 *Available from STIF/NASA Scientific and Technical Information Facility, P.O. Box 33, College Park, MD 20740 INTRODUCTION use on STOL aircraft development for future are currently under configurations which Powered-lift studies have surfaces. Previous onto wing and flap jet engine exhaust impingement of the involve the jet alone than does at lower frequencies noise levels produces higher impinging jet that the suggested sources to and flap noise of the engine with the close proximity levels, together These higher (ref. 1).
enough to interfere may be high levels in these aircraft that the noise sidewall, suggest the fuselage for both levels were estimated interior noise this possibility, comfort. To investigate with passenger (EBF) configuration.
blown flap and an externally blown (USB) an upper surface these levels and compares the interior noise used to estimate paper describes the procedure This These estimates transportation vehicles.
aircraft and on ground on existing jet levels with levels in technology for areas of possible improvements in the STOL aircraft; therefore, indicate high levels noise are also discussed.
of STOL interior control 0I co ARTIST'S CONCEPTS OF COMMERCIAL STOL TRANSPORTS USING POWERED-LIFT SYSTEMS (Figure 1) Figure 1 shows artist's concepts of commercial versions of aircraft employing externally blown flap and upper surface blowing powered-lift systems. These commercial versions were derived from two STOL aircraft configurations currently under development for the United States Air Force. Figure 1 illustrates the two features of these aircraft that are of interest with respect to interior noise, namely, the forward and inboard location of the engines that brings the noise sources close to the passengers, and the impingement of the engine jet on wing and flap surfaces that generates new noise sources.
Cross sections of the wing-flap systems for each concept illustrate the nature of the engine exhaust impingement on each wing-flap system. These sketches indicate the position of the flaps in the powered- lift configuration and show that the engine exhaust impinges directly on the wing and flaps for both powered-lift concepts. The sketches also indicate that during cruise, when the flaps are retracted, the USB engine exhaust is still located very close to the wing, while the EBF engine exhausts under the wing, much as conventional jets do. The interior noise for these two aircraft configurations was estimated.
ii~iiiiiiiii i !iiiii i . .. ..
FLAP CONFIGURATION(~~
EXERNALLY BLOWN
S8w.: d n WI
00 'i>i i
U
:4 .,iii~i.
® iiliiiliftii~ i
i ! ! ! ! i i i i i i i i i i i i i i i ! ! i i i i i i i i i i i i i !iii~iii~iii~iiiliii~!!~~~i~ic ~iiiiii~iiii!iiiiiiiiiii~iiirn r!i~~iii~i~i~iiiii~iiii~~ii~! ! iiii~~~ ~~ ~~ i ~ i~ii~i~iii~iii~iiii~i iii iii~iiiii~ii ii~iiiiii~~i~i~i!iii~iii!ii~~ii~~iiiiiiiiiiii~iiiii i i!i!!ii ! i~ ~ ~ PROCEDURE INTERIOR NOISE ESTIMATION STOL 2) (Figure essential steps in figure 2. The is outlined interior noise levels used to estimate The procedure the sound levels (2) determine noise, that influence of aircraft parameters the values are (1) establish (NR) associated of noise level the reduction (3) determine the fuselage (SPLoutside), the outside of on and (4) subtract within the cabin, of noise and with absorption through the fuselage noise transmission with that listed indicate aircraft properties level. The estimated interior to obtain the NR from SPLoutside , of the the same as those are about aircraft properties considered. The aircraft is being a large size presented of these aircraft properties development. Geometric now under Air Force aircraft United States and its the engine exhaust was that due to input considered The only forcing 2 were used.
in reference the to dominate is thought this source and takeoff, flaps. For landing wing and on the impingement contri- that an additional speed is high enough design forward cruise, the However, during interior noise.
free from data on were estimated The forcing inputs is to be expected.
layer inputs bution from boundary sources systems. These powered-lift the flaps of pressures on of surface measurements and from recent jets lift were available due to powered on fuselage surfaces pressures data on fluctuating used because no were that measured data obtained based on reduction were sidewall noise Values of published literature.
in the for the larger These data were corrected narrow-body jet aircraft.
in the literature for are available study. Further in this the aircraft considered associated with surface density thickness and values of wall 3.
in figure reduction are presented input and noise of the forcing details
AIRCRAFT
ENGINE EBF
USB, 4
* 2 ENGINE
216 in.
DIAMETER
* FUSELAGE
Ib
z 150 000
WEIGHT
* GROSS
FORCING
INPUT
(SPLOUTSIDE)
EBF
*
JET
FREE
- FROM
CRUISE
FLAP MEASUREMENTS
- FROM
TAKEOFF/LANDING
USB
*
MEASUREMENTS
- FROM FLAP
CRUI SE/TAKEOFF/LANDING
LAYER)
(NO BOUNDARY
ONLY
IMPINGEMENT
AND
ENGINE EXHAUST
*
EFFECTS NEGLECTED
SPEED
* FORWARD
(OCTAVE BANDS)
- 8000 Hz
RANGE 31.5
FREQUENCY
*
(NR)
NOISE REDUCTION
SIDEWALL
BODY JETS
DATA FOR NARROW
* EMPIRICAL
6" THICK)
TO
(INCREASED
FOR THICKNESS
CORRECTED
)
TO 6 lb/ft
FOR MASS (INCREASED
CORRECTED
NOISE
INTERIOR
* SPLINSIDE
. SPLOUTSIDE-NR
procedure.
estimation noise STOL interior 2.- Figure REDUCTION AND SIDEWALL NOISE STOL FORCING INPUT (Figure 3) (NR) used in noise reduction outsid ) and the fuselage spectra (SPL of the external noise e The values 3.
shown in figure this study are During on the fuselage as follows.
obtained for the worst location external noise spectra were The Therefore, the does not impinge on the structure.
the engine exhaust cruise of the EBF configuration, the used to obtain of ref. 3 was The method of the jet alone.
are those sources considered only noise 52 in. and a distance nozzle diameter of ft/sec, an exhaust velocity of 500 an exhaust: values shown, using the fuselage level distributions along fuselage sidewall. Noise engine centerline to the of 98 in. from the takeoff and for the EBF noise spectra external engines. Fuselage ref. 3 for two obtained from length were of models on the flaps pressure measurements made from surface were obtained the USB takeoff configurations levels and fluctuating pressure reported overall 5. These references in references 4 and and reported were USB cruise levels be located. The sidewall would where fuselage locations at flap spanwise spectra ( p) with altitude.
changes in air density levels for the correcting the takeoff obtained by noise levels are highest figure 3 shows the the USB takeoff and cruise, EBF takeoff and for For the 250 and 500 Hz bands.
which is highest in the EBF cruise 63 Hz octave band, in comparison with in the The wing and flap surfaces.
impingement on result from exhaust lower frequencies high levels at the These EBF engine mainly because the lower at the low frequencies, EBF cruise are relatively noise levels for the sidewall the figure is the on the right of cruise. Shown flap surfaces during not impinge on the does reduction The sidewall noise in ref. 5.
data reported based on the narrow-body was noise reduction, which 6 pounds density of about having a surface data to a sidewall the narrow-body by correcting was estimated the noise of ref. 6. As expected, using the method of about 6 inches and a thickness per square foot with the sidewall noise spectra the external Comparing at the lower frequencies.
is the lowest reduction at frequencies highest energy have their powered-lift configurations shows that the STOL noise reduction to be 3 are considered shown in figure Noise reduction values reduction is low.
the sidewall noise where levels interior noise The best current technology.
of the careful application only with high and obtainable in figure 4.
spectra are shown the exterior noise noise reduction from by subtracting the obtained
EXTERNAL NOISE SPECTRA
SIDEWALL NOISE REDUCTION
OCTAVE BAND
NOISE REDUCTION,
dB
160 - , EBF TAKE-OFF
80 -
STIFFNESS
C MASS
CONTROL
CONTROL
USB TAKE-OFF 60---
OCTAVE,
BAND 120
EBF
CRUISE
-
dB
SPL,
31.5 125 500 2K
8K 31.5 125 500 2K 8K
FREQUENCY, Hz
Figure 3.- STOL forcing input and sidewall noise reduction.
SPECTRA INTERIOR NOISE STOL (Figure 4) for the USB (left) in figure 4 are shown cruise conditions for takeoff and noise spectra Interior and are highest levels having the for the seats estimates are the These spectra the EBF (right).
and 5 and (refs.
jet aircraft for conventional noise spectra measured of reference, As a point not averages.
conditions and cruise the USB takeoff levels for the noise shows that The figure 9) are included.
7 to frequencies.
at the lowest are higher and the levels jets, for conventional much higher than are the takeoff EBF aircraft, For the Hz octave band.
in the 125 are indicated 20 to 30 dB of Differences The cruise frequencies.
at the lower CTOL jets dB higher than levels 30 high, with are very levels jets.
found on CTOL the spectra than only slightly higher is the EBF configuration spectrum for and the results condition for the cruise spectra from these were calculated sound levels A-weighted The figure 5.
shown in are
UPPER SURFACE BLOWN FLAP EXTERNALLY BLOWN FLAP
r
TAKE-OFF
/--TAKE-OFF
OCTAVE CRUISE CRUISE
BAND
SPL,
dB90
CTOL CRUISE CTOL CRUISE
iII
50 Ii
31.5 125 500 2K
8K 31.5 125 500 2K 8K
FREQUENCY, Hz
spectra.
interior noise Figure 4.- STOL (estimated) LEVELS COMPARISON OF INTERIOR NOISE (Figure 5) noise levels for both STOL configurations are high Figure 5 shows that the A-weighted interior compared to the OSHA 8 hour limit of 90 dBA.
compared to ground transportation systems as well as dBA range shown for the were obtained from refs. 7 to. 14. The 15 The measured data shown in figure 5 level throughout the fuselage (refs. 13 and 15), with the STOL corresponds to the variation in noise seat shown the top (calculated from the spectra in figure 4), and the quietest noisiest seat shown at cruise for the USB aircraft are higher than those of the EBF aircraft during at the bottom. The levels That is, during (flaps retracted) since exhaust impingement occurs only for the USB configuration.
jet. The are retracted, the EBF configuration functions much as a conventional cruise, when the flaps for about half of the seats for the STOL and diamond marker represents a level estimated to be average are shown in figure 6, similar value for a CTOL jet transport. The three levels marked with diamonds a takeoff and landing.
along with A-weighted sound levels for
110 STOL DESTIMATED
USB L/A
VTOL
O MEASURED
90 - - -O--TYPICAL LEVEL
-
... --
.
-- .
90V
BUS OSHA 8 HOUR
INTERIOR
LIMIT
]
NOI SE
LEVEL, dBAL AUTO
AUTO
RAIL
70 -
noise level.
of interior 5.- Comparison Figure conditions) (cruise WITH FLIGHT TIME VARIATION OF INTERIOR NOISE (Figure 6) with flight time during takeoff, climbout, 6 shows the variation of interior noise levels Figure and represent shown are included as a point of reference cruise, descent, and landing. The CTOL levels noise levels are higher typical narrow body jet aircraft. The STOL the average interior noise for a during powered- but are much higher (by about 30 dBA) those of CTOL not only for cruise conditions, than noise level typically found included for reference is the highest interior lift operations. Also that the to be drawn from this figure are on a CTOL jet. The main conclusions during thrust reversal jets, and significantly higher during all flight conditions than for CTOL STOL interior noise levels are nature of during powered-lift operations. Because of the that the STOL levels are particularly high of flight are expected and descent/landing phases operations of STOL aircraft, the takeoff/climbout flight for of tens of minutes compared to seconds duration for significant time durations (of the order to last with high levels such as those shown CTOL aircraft). These time durations combined thrust reversal on comfort.
detrimental effect on passenger to have a marked in figure 6 can be expected
120 -
110 -
USB STOL
n
INTERIOR 100
NOISE
THRUST II
LEVEL
REVERSAL- I
EBF STOL
dBA 90
II
JET CTOL II
DESCENT/
70 TAKE-OFF/
LANDING
CRUISE
CLIMB-OUT
FLIGHT TIME
6.- Variation of STOL interior noise with flight time.
Figure SUMMARY: STOL INTERIOR NOISE (Figure 7) and that the in powered-lift aircraft will be high, noise estimates show that the levels Interior noise reduction of the best It can be concluded that the problem occurs at low frequencies.
major to control the low these estimates) is not adequate technology sidewall (used in making current exhaust on wing and flap surfaces.
by impingement of jet engine frequency noise generated estimates must be improved so that more precise of acoustic loads on STOL fuselages The definition based on the actual external noise can be obtained and so that control techniques of interior noise acoustic loads program be explored. (NASA-Langley has-expanded its STOL wing and flap characteristics can of low frequency noise reduction fuselage sidewall.) The basic understanding to include loads on the noise reduction of panels ranging from must also be improved and requires investigations of low frequency concepts must be developed aircraft type structures. Finally, new structural simple panels to complex, for use on STOL type vehicles.
to improve low frequency noise reduction
SUMMARY OF FINDINGS
FOR EBF AND USB
* HIGH INTERIOR NOISE LEVELS ESTIMATED
STOL CONFIGURATIONS
* LOW FREQUENCY NOISE PREDOMINATES
* CURRENT TECHNOLOGY SIDEWALL IS NOT ADEQUATE TO CONTROL
LOW FREQUENCY STOL NOISE
RECOMMENDATIONS
* IMPROVE DEFINITION OF ACOUSTIC LOADS
ON STOL FUSELAGE
* IMPROVE BASIC UNDERSTANDING OF LOW FREQUENCY NOISE
TRANSMISSION
*
DEVELOP NEW STRUCTURAL CONCEPTS TO CONTROL LOW
FREQUENCY NOISE
Figure 7.- Summary STOL interior noise.
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72-50, Inter. Council Preprint STOL Vehicles.
Jet-Powered 2, 1972.
September 1975. Aviation Set for First Flight in Final Design; Douglas AMST E.: McDonnell Fink, Donald 2.
7, 1973.
Technology, May Week & Space May 1972.
No. 162, Part 1. AGARDograph Design Data, Fatigue A. G. R.: Acoustic 3. Thomson, on Aircraft Pressures Conrad M.: Fluctuating and Willis, James A.; John S.; Schoenster, 4. Mixson, Inst.
75-472, Am.
Preprint Systems.
Powered-Lift with Surfaces Associated and Flap Wing March 1975.
Aeron. and Astronaut., NASA Fuselage Sidewall.
Through A Transmission T. D.: Acoustic and Scharton, 5. Wilby, J. F.
CR-132602, Press, 1974.
The Fairmont of Noise Control.
K.: Secrets Richard Albert; and Miller, 6. Thumann, NOISE During Flight.
in the Caravelle Noise Levels Beranek, Leo L.: N.; and 7. Miller, Laymon 1958, pp. 19-21.
Control, Sept.
NOISE Control, Transport Airplane.
Levels in a Turbojet Flight Noise Dwight E.: Cruise 8. Bishop, pp. 37-42.
1961, March/April Medicine, Aircraft. Aerospace Environment of Airline B.: Cockpit Noise Stone, Richard 9.
pp. 989-993.
Sept. 1969, Aerospace Light Aircraft.
Fifteen Single-Engle Cockpit Noise Intensity: Tobias, Jerry V.: 10.
963-966.
Sept. 1969, pp.
Medicine, 1969, Sept.
Sound and Vibration, Twin-Engine Aircraft.
Noise in Light Tobias, Jerry V.: 11.
pp. 16-19.
1971.
NASA SP-292, Noise Alleviation.
in Aircraft G.: Trends Morgan, Homer 12.
2, Design Features of Boeing Model 727. J. Aircraft, vol.
13. Gebhardt, George T.: Acoustical no. 4, July/Aug. 1965, pp. 272-277.
in Public Transportation. Sound and Vibration, April 1974, 14. Bray, Don E.: Noise Environments pp. 16-20.
in C.; and Ballard, M.: Cabin Noise Reduction 15. Van Dyke, J., Jr.; Schendel, J.; Gunderson, and Astronaut., June 1967.
the DC-9. Preprint 67-401, Am. Inst. Aeron.