Landing Gear Door Liners for Airframe Noise Reduction

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(12) (1o) Patent

United States Patent No.: US 8,708,272 B1

(45) Date of Patent: Apr. 29, 2014

Jones et al.

(54) LANDING GEAR DOOR LINERS FOR 3,821,999 A 7/1974 Guess et al.

3,853,428 A 12/1974 Hayden et al.

AIRFRAME NOISE REDUCTION 4,240,250 A 12/1980 Harris 4,836,469 A * 6/1989 Wagenfeld .................... 244/1 N (75) Inventors: Michael G. Jones, Newport News, VA 5,543,198 A * 8/1996 Wilson .......................... 428/116 (US); Brian M. Howerton, Newport 6,454,219 B1 9/2002 Moe News, VA (US); Thomas Van De Ven, 6,948,906 132 9/2005 Leishman et al.

7,458,542 132 * 12/2008 Chow et al ................ 244/102 R Savannah, GA (US) 7,484,930 132 2/2009 Hutcheson et al.

7,637,462 132 12/2009 Pal (73) Assignee: The United States of America as 7,866,939 132 * 1/2011 Harper et al . ..................... 415/9 represented by the Administrator of 7,954,757 132 * 6/2011 Moe et al . ................. 244/100 A National Aeronautics and Space 7,967,108 132 * 6/2011 Harper .......................... 181/292 8,033,510 132 10/2011 Shmilovich et al.

Administration, Washington, DC (US) 8,056,850 132 11/2011 Lin et al.

8,096,513 132 1/2012 Mau et al.

(*) Notice: Subject to any disclaimer, the term of this 20 04/0 197 194 Al 10/2004 Leishman et al.

patent is extended or adjusted under 35 2007/0020099 Al 1/2007 Hutcheson et al.

U.S.C. 154(b) by 0 days.

2008/0179448 Al* 7/2008 Layland et al . ............... 244/1 N (Continued) (21) Appl. No.: 13/417,349 OTHER PUBLICATIONS (22) Filed: Mar. 12, 2012 Tony L. Parrott, et al, "Parallel-element liner impedances for Related U.S. Application Data improved absorption of broadband sound in ducts." Noise Control Engineering Journal, Nov. -Dec. 1995, pp. 183-195, vol. 43(6).

(60) Provisional application No. 61/451,730, filed on Mar.

11, 2011, provisional application No. 61/451,727, (Continued) filed on Mar. 11, 2011, provisional application No.

61/451,735, filed on Mar. 11, 2011, provisional Primary Examiner Tien Dinh application No. 61/597,282, filed on Feb. 10, 2012.

Assistant Examiner Keith LDixon (74) Attorney, Agent, or Firm Andrea Z. Warmbier (51) Int. Cl.

B64C1140 (2006.01) (57) ABSTRACT (52) U.S. Cl.

USPC .......................................................... 244/1 N A landing gear door for retractable landing gear of aircraft (58) Field of Classification Search includes an acoustic liner. The acoustic liner includes one or more internal cavities or chambers having one or more open- USPC ........................... 244/1 N, 100 R, 102 R, 133 See application file for complete search history. ings that inhibit the generation of sound at the surface and/or absorb sound generated during operation of the aircraft. The (56) References Cited landing gear door may include a plurality of internal cham- bers having different geometries to thereby absorb broadband U.S. PATENT DOCUMENTS noise.

3,612,146 A 10/1971 Klein 3,779,338 A 12/1973 Hayden et al. 17 Claims, 5 Drawing Sheets I t6

US 8,708,272 B1

Page 2 to Slat Trailing Edge Noise," NASA/TM-2003-212416, May 2003, (56) References Cited pp. 1-14.

U.S. PATENT DOCUMENTS Mehdi R. Khorrami, et al., "Novel Approach for Reducing Rotor Tip-Clearance-Induced Noise in Turbofan Engines," AIAA Journal, 2009/0084905 Al 4/2009 Mau et al.

Aug. 2002, pp. 1618-1528, vol. 40, No. 8.

2010/0133378 Al* 6/2010 Lidoine ......................... 244/1 N Meelan Choudhari, et al., "Computational Study of Porous Treat- 2010/0294883 Al 11/2010 Trich, Jr. et al.

ment for Altering Flap Side-Edge Flowfield," AIAA 2003-3113, 9th 2013/0062143 Al* 3/2013 Ichihashi ...................... 181/292 AIAA/CEAS Aeroacoustics Conference, May 12-14,2003, pp. 1-15, OTHER PUBLICATIONS Hilton Head, South Carolina.

W. Clifton Horne, et al., "Measurements of 26%-scale 777 Airframe L. S. Wirt, "Analysis, Testing, and Design of Lined Ducts," The Noise in the NASA Ames 40-by 80 Foot Wind Tunnel," AIAA 2005- Journal of the Acoustical Society of America, May 1972, pp. 1448- 2810, 11th AIAA/CEAS Aeroacoustics Conference (26th AIAA Aerocoustics Conference), May 23-25, 2005, pp. 1-19, Monterey, 1463, vol. 51(5), Part 1.

California.

Tony L. Parrott, et al., "Effect of Resonator Axis Skew on Normal D. Angland, et al., "Measurements of Flow around a Flap Side-Edge Incidence Impedance," AIAA 2003-3307, 9th AIAA/CEAS with Porous Edge Treatment." AIAA 2006-213. 44th AIAA Aero- Aeroacoustics Conference, May 12-14, 2003, pp. 1-8, Hilton Head, space Sciences Meeting and Exhibit, Jan. 9-12, 2006, pp. 1-22, Reno.

South Carolina.

Nevada.

Brian M. Howerton, et al., "Validation of an Acoustic impedance D. Angland, et al., "Measurements of Flow around a Flap Side Edge Prediction Model for Skewed Resonators," AIAA 2009-3143, May with Porous Edge Treatment," AIAA Journal, Jul. 7, 2009, pp. 1660- 2009, pp. 1-21.

1671, vol. 47, No. 7.

M. G. Jones, et al., "Assessment of Soft Vane and Metal Foam Engine Noise Reduction Concepts," AIAA 2009-3142, May 2009, pp. 1-20.

Mehdi R. Khorrami, et al., "Application of Passive Porous Treatment * cited by examiner

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LANDING GEAR DOOR LINERS FOR angles that are typically in the range of about 30° to about 90° AIRFRAME NOISE REDUCTION relative to other portions of the chambers. One or more of the internal acoustic chambers may be partially or completely CROSS-REFERENCE TO RELATED tilled with an acoustic bulk material such as foam or other APPLICATIONS 5 suitable material to provide the desired propagation and absorption of sound within the internal acoustic chambers.

The chambers may have closed inner ends, or the chambers This application is related to co-pending U.S. patent appli- may have open opposite ends whereby sound entering one of cation Nos. 13/417,347 and 13/417,351, filed on Mar. 12, the openings is transmitted through the chamber, and a por- 2012. This application claims the benefits of U.S. Provisional tion of the soundthat is not absorbed inthe chamber is emitted Application Nos. 61/451,727, filed on Mar. 11, 2011; 61/451, from the other opening. The chambers thereby form passage- 730 filed on Mar. 11, 2011; 61/451,735 filed on Mar. 11, ways whereby sound can thereby be transmitted between 2011; and 61/597,282, filed on Feb. 10, 2012, the entire inner and outer surfaces of the landing gear door, or between contents of all which are incorporated by reference.

different locations on the same surface of the landing gear 15 door.

STATEMENT REGARDING FEDERALLY These and other features, advantages, and objects of the SPONSORED RESEARCH OR DEVELOPMENT present invention will be further understood and appreciated by those skilled in the art by reference to the following speci- The invention described herein was made in part by fication, claims, and appended drawings.

employees of the United States Government and may be manufactured and used by or for the Government of the BRIEF DESCRIPTION OF THE DRAWINGS United States of America for governmental purposes without the payment of any royalties thereon or therefore.

FIG.1 is an isometric view of an aircraft including retract- able landing gear and landing gear doors according to one FIELD OF THE INVENTION 25 aspect of the present invention; FIG. 2 is a partially fragmentary enlarged view of the main The present invention relates to reduction of aircraft noise, landing gear of the aircraft of FIG. 1; and specifically to acoustic liners to reduce airframe noise FIG. 3 is a cross-sectional view of the landing gear door of during takeoff and landing.

FIG. 2 taken along the line III-III; BACKGROUND OF THE INVENTION FIG. 4 shows a landing gear door according to another aspect of the present invention; and Aircraft noise is a significant issue with economic and FIG. 5 is a cross-sectional view of the landing gear door of public health implications, especially for communities near FIG. 4 taken along the line V-V.

airports. As a result, increasingly stringent international con- 35 DETAILED DESCRIPTION OF EMBODIMENTS straints are being placed on aircraft companies to reduce this noise. Aircraft noise is generally divided into two categories.

For purposes of description herein, the terms "upper," The first has to do with noise generated by the propulsion "lower," "right," "left," "rear," "front," "vertical," "horizon- system, while the second is related to noise generated by the tal," and derivatives thereof shall be related to the invention as interaction of mean flow over the airframe as it traverses 40 oriented in FIG. 5. However, it is to be understood that the through the air.

invention may assume various alternative orientations, except BRIEF SUMMARY OF THE INVENTION where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated One aspect of the present invention is a landing gear door of in the attached drawing, and described in the following speci- the type that covers retractable landing gear of an aircraft 45 fication are simply exemplary embodiments of the inventive when the landing gear is retracted during flight. The landing concepts defined in the appended claims. Furthermore, refer- gear door shifts outwardly when the landing gear is deployed. ences to specific items or features (e.g. a wing structure, The landing gear door includes a door structure defining first leading edge slat, and slat cove filler) shall not be construed as and second opposite sides. The first and second opposite sides limiting the item or feature to one-piece or multi-piece items have first and second opposite surfaces, respectively. The 50 or features. Hence, specific dimensions and other physical door structure further includes edge surfaces extending characteristics relating to the embodiments disclosed herein between the first and second sides, and the door structure are not to be considered as limiting, unless the claims defines an internal structure disposed between the first and expressly state otherwise.

second opposite sides. The door structure defines a porous An aircraft 1(FIG.1) includes a fuselage 2, wings 3, and a surface on at least one of the first and second opposite side 55 propulsion system such as jet engines 4. The primary aircraft surfaces, and the internal structure defines at least one internal structure including the fuselage 2, wings 3, and engine 4 may acoustic chamber or passageway defining a first end that is comprise a known design and these parts of aircraft 1 will not acoustically connected to the porous surface such that at least therefore be described in detail herein.

a substantial portion of sound entering the elongated acoustic With reference to FIG. 1, Aircraft 1 includes a retractable chamber or passageway at the first end thereof is absorbed by 60 landing gear system 10 including a nose assembly 12, and two the internal structure of the landing gear door. The internal main assemblies 14. The main assemblies 14 include tires 15, acoustic chambers or passageways may be elongated. The struts 16, and doors 20. During takeoff and landing, the land- landing gear door may include a plurality of internal acoustic ing gear is in a deployed position as shown in FIG. 1. During chambers, each having the same length, or one or more of the level flight, the landing gear is retracted such that the tires 15, chambers may have a different length than one or more of the 65 struts 16, and other related components are received in land- other chambers. The internal chambers may be substantially ing gear bays or cavities 18. When the main assemblies 14 are linear, or they may include angled portions that extend at retracted, outer surfaces 22 of landing gear doors 20 are flush

US 8,708,272 B1

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with outer surfaces 6 of the fuselage 2 and/or wings 3. The opposite side 28A of door 20A or at a different location on the tires 15, struts 16, and associated powered actuators (not same side 26A or door 20A. Porous surface 44A of acoustic shown) and other such components are generally known, and liner 8A comprises a sheet of material 46 having a plurality of will not therefore be described in detail herein.

perforations 47 such that the ends 52A of acoustic chambers With further reference to FIGS. 2 and 3, landing gear door 5 50A are acoustically open at the surface 30A of door 20A.

20 includes a door structure 24 defining first and second One or more of the acoustic chambers 50A may include an opposite sides 26 and 28. The opposite sides 26 and 28 open end 60A on opposite side 28A of door 20A to thereby include first and second opposite surfaces 30 and 32, respec- foiin a passageway that permits sound to travel through the tively. Edge surfaces 34, 36, 38, and 40 extend between the door 20A from first side 26A to second side 28A, and vice- first and second sides 26 and 28 of door structure 24. It will be io versa. One or more of the acoustic chambers 50A may alter- understood that the landing gear door 20 and door structure 24 natively include an open end on the same side 26A of door may have a variety of different shapes and sizes as required 20A to thereby form a passageway that permits sound to for a particular aircraft design.

travel through the door 20A from first side 26A to another The door structure 24 also defines an acoustic liner 8 com- location on the same side. Similarly, one or more of the prising an internal structure or body 42 disposed between the 15 chambers may alternatively include two open ends within the first and second opposite sides 26 and 28. The door structure second side 28A suchthat sound is permitted to travel through 24 includes a porous surface 44 on at least one of the first and the door 20A from one location to another on the second side second opposite side surfaces 30 and 32. The internal struc- 28A.

ture 42 defines at least one internal acoustic chamber 50. The The acoustic treatment embedded within the volume of the internal acoustic chambers 50 have first ends 52 that are 20 acoustically connected to the porous surface 44 such that at landing gear doors 20 and 20A changes the boundary condi- least a substantial portion of sound entering the acoustic tion at the surface(s) 30 (and 32) such that sound is absorbed chambers 50 at the first end 52 is absorbed by the internal within the door 20 or 20A. The internal acoustic chambers structure 42 of the landing gear door 20. 50A and porous surface 44 of liners 8 and 8A also change the Referring again to FIG. 3, acoustic chambers 50 of acoustic 25 boundary conditions of the door 20 to inhibit the generation of liner 8 may include an outer end portion 54 that extends noise at the surface 30 and/or 32.

substantially transverse or perpendicular to porous surface As discussed above, the lengths of internal acoustic cham- 44, and an inner end portion 56 that extends transverse to the bers 50A of the liner 8A of door 20A (FIG. 5) are varied. If the outer end portion 54. The inner end portion 56 may extend partitions between adjacent internal chambers are impervious substantially parallel to porous surface 44. The acoustic 30 and sufficiently close together, this provides a local-reacting chambers 50 may have inner closed ends 58, such that open- liner configuration, and each chamber in this embodiment ings 52 comprise the only openings that permit sound to enter behaves as a quarter-wavelength resonator (sometimes called the acoustic chambers 50. Alternately, one or more of the an organ-pipe resonator). In this embodiment, the different acoustic chambers 50 may extend all the way through the lengths of the chambers 50 are selected for optimal absorp- internal structure 42 to thereby form an internal passageway 35 tion of different frequencies. By proper selection of the com- with openings 52 and 60 on opposite sides 26 and 28, respec- bination of lengths of the chambers 50, a broadband sound tively, of door structure 42. absorber can be achieved.

The internal chambers 50 may have circular cross-sec- If the internal volume defined by chambers 50 is filled with tional shapes, and the cross-sectional area of the internal foam 48 or the like, sound that enters through the porous chambers 50 may be substantially constant along the length 40 surface 44 of the liner 8 of door 20 travels in multiple direc- of the internal chambers 50. Alternately, the chambers 50 may tions within the foam. If configured in this way, the sound can have non-circular cross-sectional shapes (e.g., quadrilateral travel in multiple directions, and exit the liner 8 of door 20 via shaped), and/or the cross-sectional area of the chambers 50 different portions of the porous surface 44. The chambers 50 may vary. may include openings at opposite ends at surface 30 and 32, Also, as shown in FIG. 3, different internal chambers 50 of 45 or the acoustic chambers 50 may have multiple openings at acoustic liner 8 may have different lengths defined between surface 30 or multiple openings at surface 32. Surface 32 may ends 52 and 58. The differences in lengths provide for absorp- also comprise a porous surface 44 having a sheet 46 with tion of sound at different frequencies. Thus, acoustic liner 8 of perforations 47.

door 20 may be configured to absorb a broad spectrum of It will be understood that the specific acoustic liner con- sound utilizing internal acoustic chambers 50 of different 50 figurations and door geometries discussed above in connec- lengths and/or different shapes. tion with FIGS. 2-5 are examples of suitable geometries, but Porous surface 44 of acoustic liner 8 may comprise a thin the present invention is not limited to these configuration sheet of metal or other suitable material having a plurality of and/or geometries. There are many designs that could be used perforations therethrough. Alternately, porous surface 44 to achieve similar surface acoustic impedance boundary con- may comprise a mesh or the like, ortheporous surface44may 55 ditions. This can be done by suitably varying the geometry of be formed by the internal structure 42 itself, Acoustic filler the internal cavities 50 and the surface face sheet 46.

material 48 such as foam or other suitable material may be The sound-absorbing liner and landing gear door discussed positioned in one or more of the internal chambers 50, and the above are utilized for main landing gear assemblies 14 (FIG.

filler material 48 may partially or completely fill the cham- 1). However, it will be understood that acoustic liners and bers 50. The internal structure 42 may comprise a metal 60 doors according to the present invention may be utilized in material, fiber composites, or other suitable material. connection with a variety of different retractable landing gear With further reference to FIGS. 4 and 5, a landing gear door configurations. Thus, the shape and size of the acoustic liners 20A according to another aspect of the present invention and doors may therefore vary significantly when utilized for includes an acoustic liner 8A having an internal structure different applications.

42A, and a plurality of internal acoustic chambers 50A. Each 65 It is to be understood that variations and modifications can chamber 50A has a first or outer end/opening 52A, and an be made on the aforementioned structure without departing inner end 36A that may optionally be open at the second from the concepts of the present invention, and further it is to

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be understood that such concepts are intended to be covered 7. The landing gear door of claim 6, wherein: by the following claims unless these claims by their language at least one of the inner and outer portions is substantially expressly state otherwise, linear.

The invention claimed is: 8. The landing gear door of claim 7, wherein: 1. A landing gear door that covers retractable landing gear s at least a portion of at least one of the acoustic chambers of an aircraft when the landing gear is retracted during flight, has a circular cross-sectional shape.

and shifts outwardly when the landing gear is deployed, the 9. The landing gear door of claim 8, wherein: landing gear door comprising: the inner and outer portions of at least one of the acoustic a door structure defining first and second opposite sides chambers are both substantially linear whereby the having first and second opposite surfaces, respectively, io chamber is L-shaped.

and edge surfaces extending between the first and sec- 10. The landing gear door of claim 1, wherein: ond sides, the door structure further defining an internal at least a first one of the internal acoustic chambers is structure disposed between the first and second opposite substantially linear along its length and at least a second sides, wherein the door structure defines a porous sur- one of the internal acoustic chambers is substantially face on at least one of the first and second opposite side is non-linear along its length.

surfaces, and wherein the internal structure defines a 11. The landing gear door of claim 1, wherein: plurality of internal acoustic chambers each defining a the plurality of internal acoustic chambers is further first end that is acoustically connected to the porous defined as first and second internal acoustic chambers, surface such that at least a substantial portion of sound each having an outer end at the porous surface defining entering the acoustic chamber at the first end is absorbed 20 a sole external opening to each of the internal acoustic by the internal structure of the landing gear door; chambers and wherein each chamber further includes an wherein each of the plurality of internal acoustic chambers opposite inner end that is closed whereby sound cannot defines a second end disposed in spaced relationship to escape from the inner ends of the internal acoustic cham- the porous surface, with a length extending between bers.

each of the first ends and second ends and wherein at 25 12. The landing gear door of claim 11, wherein: least one of the plurality of internal acoustic chambers at least one of the plurality of acoustic chambers extends includes first and second portions that extend transverse substantially linearly from the outer end to the inner end.

relative to each other at an angle in the range of about 30° 13. The landing gear door of claim 1, including: to 90°; and, acoustic filler material disposed in at least a portion of the wherein the lengths of at least two of the plurality of inter - 30 plurality of at least internal acoustic chamber.

nal acoustic chambers are different from one another.

14. The landing gear door of claim 1, wherein: 2. The landing gear door of claim 1, wherein: the first opposite surface of the door structure comprises a the porous surface is disposed on the first side of the door smooth, generally planar aerodynamic surface that tends structure, and wherein at least two of the internal acous- to permit non-turbulent airflow over the surface.

tic chambers have first ends that are acoustically con - 35 15. The landing gear door of claim 1, wherein: nected to the porous surface.

the internal structure defines at least one internal acoustic 3. The landing gear door of claim 2, wherein: chamber having first and the porous surface comprises a thin sheet of material hav- second ends that are open at the porous surface whereby ing a plurality of perforations therethrough.

sound can enter at the first end and exit 4. The landing gear door of claim 3, wherein: 40 at the second end.

the perforations are arranged in a repeating pattern.

16. The landing gear door of claim 15, wherein: 5. The landing gear door of claim 4, wherein: the first end is disposed on the first opposite side of the door the thin sheet of material comprises metal.

structure, and the second 6. The landing gear door of claim 1 wherein: end is disposed on the second opposite side of the door at least two of the internal acoustic chambers have closed 45 structure.

second ends and wherein at least one of the two acoustic 17. The landing gear door of claim 15, wherein: chambers defines an outer portion adjacent the first end the first and second ends are both disposed on one side of that extends transverse relative to the porous surface, the door structure.

and an inner portion at the second end that extends transverse relative to the outer portion.