Document
&es Patent 1191 11 13 4,343,447
[45] Aug. 10, 1982
4,168,046 9/1979 Hasquenoph et a l . .......... 244/137 R [54] DECOUPLER PYLON WING/STQRE
4,246,472 1/1981 Sun et al. ............................ 244/137
IFEUTZER SUPPRESSOR [75] Inventor: Wilmer M. Reed, 111, Hampton, Va. FOREIGN PATENT DOCUMENTS
326527 4/1930 United Kingdom ............... 89/15 B
[73] Assignee: The United States of America as represented by the Administrator of Primaly Examiner-Trygve M. Blix the National Aeronautics and Space Assistant Examiner-C. T. Bartz Administration, Washington, D.C.
Attorney, Agent, or Firm-Howard J. Osborn; John R.
Manning; Wallace J. Nelson [21] Appl. No.: 135,057 1571 ABSTRACT [22] Filed: Mar. 28, 1980 This is a device for suspending a store 15 from a support
[51] Hnt. Cl.3 .......................... .B64D 1/00; B64D 9/00
such as an aircraft wing 10, and more specifically for [52] US. C1. ............................. 244/137 R 244A18.1; increasing the flutter speed of an aircraft flying with 89/1.5 G attached store and reducing the sensitivity of flutter to [ 5 8 ] Field of Search ............ 244/137 R, 118.1, 135 R; changes in the pitch inertia and center of gravity loca- 89/13 B, 1.5 G; 267/DIG. 1, 65 D; 280/678, tion of the store. It comprises soft-spring whereby the 714, 112 A store pitch mode is decoupled from support modes and ~561 References Cited a low frequency active control mechanism which main- tains store alignment. In the described embodiment, a U.S. PATENT DOCUMENT§ pneumatic suspension system 30 both isolates the store
1,207,492 12/1916 Buck .................................. 89/15 B
15 in pitch and, under conditions of changing mean 2,974,675 3/1961 Cislo .................................... 280/714 load, aligns the store 15 with the wing 10 to which it is
3,170,371 2/1965 Zimmer et al. .................... 89/13 B
attached.
3,176,939 4/1965 Mard et al. ....................... 244/118.1 3,268,188 8/1966 La Roe et al. ................... 244AlS.l 3,904,156 9/1975 Smith ............................... 244A18.1 12 Claims, 5 Drawing Figures
U.S. Patent Aug. io, 1982
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and theory is least developed; (2) need for high-power, DIECOUPLER PYLON: WING/STORE FLUTTER fast acting control systems; and (3) marginal ability to SUPPRESSOR increase flutter speed in cases of violent-type flutter.
A particular active flutter suppression concept inves- ORIGIN OF THE INVENTION 5 tigated by Triplett et al. and described in “Active Flut- by an em- ter Suppression Systems for Military Aircraft-A Fea- The invention described herein was ployee of the t J S . Government and may be manufac- sibility Study”, AFFDL-TR-72-116, Feb. 1973, uses tured and used by or for the Government for govern- hydraulic actuators as the load carrying tie between mental purposes without the payment of any royalties wing and store. Through feedback control, the actua- 10 tors nullify dynamic loads but transmit steady loads to thereon or therefor.
the wing. By dynamically decoupling the winghtore BACKGROUND OF THE INVENTION system in this way, the flutter mechanism and speed This invention has been designed to alleviate flutter revert to that of the bare wing. Unfortunately, this and suppress vibration of stores suspended from a sup- potentially promising scheme for winghtore flutter port such as an aircraft wing.
l5 control was found to be impractical due to excessive Flutter is a dangerous aerodynamic instability which flow rates required by the actuators.
affects lifting surfaces in a fluid flow. Flutter speed is Some research in helicopter design has focused on the speed at which a given aircraft will begin to experi- carrier pod alignment and vibration transfer. Active ence these self-induced oscillations. The vibrations alignment systems as described in U.S. Pat. No.
which characterize flutter have potentially catastrophic 2o 3,904,156, include Sensors which, when actuated by results; aircraft have literally broken apart because O f angular displacement of the helicopter pod, electroni- flutter.
cally initiate motion of the load arms to damp the dis- Classical bending-torsion flutter involves coupling of placement. one passive vibration isolator, described in at least natural vibration modes, One Or more Of U.S. Pat. No. 3,176,939, adds a pneumatic spring at each which contain torsional deformations of the wing. The 25 point of attachment of the pod to the carrier. These frequencies Of bending and torsion modes with springs, tuned to be soft (with little resistance to exter- airspeed and couple as flutter is approched. nal force), correspond to the tuned pylon arrangements Current fightedattack aircraft are required to carry a Seen in wing-store flutter suppression.
vast number Of external, wing Or mounted The need remains for an effective means of either 30 for or reducing the flutter burden placed stores. With multiple store attachment locations on the wing, each designed to accommodate an array Of store on an aircraft wing by an attached store, allowing re- configurations, some having variable mass (e.g., fuel alignment of the store with the wing after angular dis- tanks and rocket pods), there are literally thousands of placements. The decoupler pylon described herein alle- possible store loading combinations for a single aircraft.
The attachment of a store maSS to a wing alters the 35 viates wing-store flutter using elements of both active and passive suppression. Bending and torsion mode dynamic characteristics of the structure and often frequencies are separated by the arrangement, thus in- causes drastic reductions in the flutter speed, which can creasing flutter speed without performance penalties* result in cabstrophic structural failures. Extensive and An object of the present invention, then, is to Provide costly effort in the form of mathematical analyses, wind flight tunnel mode tests, and flight flutter tests are performed 40 EleanS for suppressing wing-store flutter for conditions within the aircraft’s design envelope.
to assure safety from flutter.
F~~ flutter critical store configurations either the Another object of the present invention is to provide or restric- an attachment, the use of which will reduce the amount flutter speed must be raised by on the aircraft operating envelope. ne of flutter testing and analysis now necessary for aircraft tions flutter speed can be raised by conventional passive 45 that accommodate a large number of wing mounted methods or by more advanced methods involving ac- store configuration.
tive flutter suppression. Some examples of passive meth- Another object of the present invention is to provide ods are: adding mass ballast, tuning the store pylon an attachment, which can make flutter speed insensitive stiffness characteristics or relocating the wing store to variations in center of gravity and store inertia prop- attachment point. Passive schemes of this kind are gen- 50 erties which may change during flight.
erally tailored for a specific store configuration and are Another object of the Present invention is to Provide not readily changed to accommodate the necessary an arrangement wherein aspects of both Passive and broad range of store mass and inertia combinations. active flutter suppression may be employed.
Active flutter suppression concepts have been the Yet another object of the present invention is to pro- subject of considerable research in recent years. In this 55 vide an attachment wherein Soft sPring/dmPer &- approach the flutter mode response is sensed by a trans- ments decouple store pitch motions from the wing.
ducer whose electrical output is modified by an appro- Another object of the present invention is to provide piate control law and fed back to a control surface an attachment, whereby the store is isolated from shock actuator to produce an aerodynamic force opposing and vibration loads, such as buffeting, induced by the flutter. Compared with passive methods, active control 60 wing or other support structure.
of flutter has the advantage of possible weight savings Still another object of the present invention is to plus versatility gains. Although active control of wing provide an attachment wherein a low-power control store flutter has been successfully demonstrated in wind automatically aligns the store with the wing under con- tunnel tests and in flight, there are drawbacks which ditions of changing mean load.
hinder its use in practical applications. Among these 65 SUMMARY O F THE INVENTION drawbacks are: (1) need for accurate knowledge of unsteady aerodynamic control forces, particularly at These and other objects are achieved by a decoupler transonic speeds where flutter is most likely to occur pylon attachment comprising elements of both passive
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and active flutter suppression methods. Passive spring cases. Thus, as illustrated in FIG. 1, the decoupler elements control frequency and damping of the store pylon increases the frequency separation between the pitch mode, by decoupling the store pitch from the flutter critical modes, and as a consequence the flutter support. The support is thus isolated from inertia mo- speed is increased.
ments associated with store pitch. 5 Referring to FIG. 2, there is shown a wing designated generally by the reference numeral 10, with store 15 To avoid large static deflections, a drawback nor- attached by means of a decoupler pylon designated mally associated with soft suspension systems, a low frequency servo control system is used. The control generally by the reference numeral 13. FIG. 3 shows a system maintains alignment of the store relative to the pneumatic embodiment of the decoupler pylon 13. The support under conditions of varying load. 10 wing 10, with upper surface 11 and lower surface 12, A damper may be included in the decoupler pylon includes an air supply line 20 connected to a pressurized arrangement to damp transient oscillations of the store. air source 22. The air supply line 20 divides to yield two 27 and 29. Branch 27 extends forward, with This is especially useful where the store may be sub- branches jected to violent gust loads, as when it is suspended vent passage 31 forking from it and exiting the wing 10 from the wing or fuselage of an aircraft. 15 through an aperture 33 in the lower surface 12. Branch The active control system is triggered by a change in 27 continues beyond the vent passage 31, then turns to alignment of the store relative to the support, as recog- exit the wing 10 through an aperture 35 in the lower nized in compression or expansion of the passive spring surface 12.
elements. The passive and active elements may be inte- Branch 29 extends aft of the wing pivot 59, and, like grated as a pneumatic system, or, among other possibili- 20 branch 27, yields a vent passage 37. The vent passage 37 ties, the passive element may be rubber or metallic exits the wing 10 through an aperture 39 in the lower spring means; the active element hydraulic or electrical. surface 12; the branch 29 continues back, then turns downward to exit the wing 10 through an aperture 41 in BRIEF DESCRIPTION OF THE DRAWINGS the lower surface 12.
The invention will be described in connection with 25 Between vent passages 31 and 37 an arm 4 3 is fixedly the accompanying drawings, in which associated with the lower surface 12 of the wing 10. The FIG. 1 is a graph describing the relationship between lower surface 12 may include, as depicted in FIG. 3, a bending and torsion mode frequencies and flutter speed; panel 14 attached to the body of the wing 10. The exten- FIG. 2 is a perspective view of an airplane wing with sion is provided with a hole 45, shown in FIG. 4. The store attached by means of the decoupler pylon; 30 axis of hole 45 is approximately parallel to the wing FIG. 3 is a schematic cross-sectional view of the elastic axis.
decoupler pylon; A clevis-type arm 53 is fixedly associated with the FIG. 4 is a front cross-sectional view of the pivot upper surface of the store 15. This upper surface may arrangement used in the described embodiment; and be, as depicted in FIG. 3, a panel 51 fixedly or remov- FIG. 5 is a graph describing wind tunnel test results 35 ably attached to the body of the store 15. The clevis- using a model of the described embodiment. type arm 53 is positioned such that wing arm 43 fits into the clevis. Holes 55 and 56 in the clevis arm 53 match DETAILED DESCRIPTION OF ONE the hole 45 of the wing arm 43, as shown in FIG. 4. A EMBODIMENT pin 47 inserted through said holes 45, 55 and 56, com- The concept of the decoupler pylon is based on the pletes the pivot arrangement shown in FIGS. 3 and 4, 4-0 generally accepted premise- that the mechanism of and designated generally by the reference numeral 59. It winghtore flutter is governed primarily by structural will be noted that branch 27 and vent passage 31 lie coupling between the wing and the store and that store forward of the pivot 5 9 branch 29 and vent passage 37 aerodynamic effects are of secondary importance. Anal- lie aft of the pivot 59.
Cylinders 61 and 63 are fixed to the upper surface ysis and wind tunnel experiments indicate that when the 45 store pitch frequency is below the wing bending fre- panel 51 of the store 15. Cylinder 61 lies directly under quency, flutter speed is not only increased above that of the open end 28 of branch 27 of the air supply line 20; the bare wing but also becomes insensitive to changes in cylinder 63 corresponds similarly to the open end 30 of the pitch inertia and the center of gravity location of the the branch 29 of the air supply line 20. Pistons 91 and 93 store. 50 encase branches 27 and 29 from just above their open The rationale behind the decoupler pylon concept ends 28 and 30 to a point below apertures 35 and 41. A may be further discussed with the aid of FIG. 1. Classi- round, convoluted rubber seal 65 fixed to the lower cal bending torsion flutter involves coupling of at least surface of piston 91 and to cylinder 61 forms an airtight two natural vibration modes, one or more of which seal between the two and completes the construction of contain torsional deformations of the wing. The plots in 5 5 an air spring designated generally by the reference nu- FIG. 1 illustrate the characteristic variation with air- meral 62. The rubber seal 65, does not seal the open end speed of frequency of bending and torsion modes, 28 of longitudinal branch 27.
which couple as flutter is approached. The dashed pair A similar round, convoluted rubber seal 67 fixed to of curves represents a rigidly attached store and the the lower surface of piston 93 and to cylinder 63 forms solid pair a decoupler-pylon mounted store. Note in 60 an airtight seal therebetween, completing the construc- both cases that flutter occurs when the bending and tion of an air spring designated generally by the refer- torsion frequencies come close together. Since the de- ence numeral 64. The rubber seal 67 does not seal the coupler pylon isolates the wing from inertia moments open end 30 of branch 29.
associated with store pitch, the wing torsion frequency Leaf-spring type flapper valves 69 and 71 attached to with the decoupled store is substantially higher than 65 the clevis arm 53 are positioned beneath vent passages that for the rigidly attached store, being about the same 31 and 37.
as for the bare wing. The bending frequency with store, The air supply line 20 is provided with a pressure however, is less than the bare wing frequency in both regulator valve 73, located at the pressurized air source
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5 0 22. Flow restrictors 75 and 77 are positioned in the allowed to pitch relatively independently of the air- branches 27 and 29, flow restrictor 75 aft of the vent craft, the store pitch modes are effectively decoupled passage 31 and flow restrictor 77 foreward of the vent from wing bending modes. Because of this increase in passage 37. These valves may be one-way flow restric- frequency separation of the flutter critical wing bending tors. Needle valves 79 and 81 are located in vent pas- 5 and tension modes, the desired increase in flutter speed sages 31 and 37 respectively. is obtained.
A dashpot damper designated generally by the refer- FIG. 5 represents some results from wind tunnel tests ence numeral 87, comprising a cylinder 83 fixedly asso- of a model wing store flutter with the decoupler pylon.
ciated with the lower surface panel 14 of the wing 10 In this graph, the following symbols are used: and a piston 85 fmedly associated with the upper surface 10 q=flutter dynamic pressure panel 51 51 of the store 15 is included in this embodi- Xs=store center of gravity location, measured from ment, and located aft of branch 29 and cylinder 63. In store pivot, positive aft b= wing semichord one experimental embodiment a dashpot damper manu- factured by the Airpot Corporation and described in ra= store radius of gyration around pivot U.S. Pat. No. 3,175,646 was used. 15 From these results, it is evident that, in addition to in- A housing 89 encloses the decoupler pylon 20 as creasing the flutter speed, the decoupler pylon makes above described. flutter relatively insensitive to inertia and center of In operation, the air springs 62 and 64 regulate store gravity location of the store. This feature can greatly pitch stiffness and act by feedback control to align the simplify and reduce the analysis and testing required to store 15 with the wing 10 under conditions of changing 20 flutter-clear aircraft that must carry a large variety of mean load. Air is supplied to the springs 62 and 64 stores.
through the air supply line 20 from the pressurized a i r Aside from winghtore flutter alleviation the decou- source 22 and pressure regulator valve 73. Pressure pler pylon self-alignment feature might also be used as regulator valve 73 and flow restrictors 75 and 77 regu- an aid in aiming aircraft launched missiles. Aeroelastic late the flow of air through branches 27 and 29 and to 25 loads associated with high-g maneuvers can cause elas- pressure release vents 31 and 37. Pitch stiffness is con- tic deformations of the wing tip relative to the root trolled by the supply pressure, and store alignment by which adversely affect aiming or target acquisition for pressure difference in the air springs 62 and 6 4 . This outboard-mounted missiles. To compensate for such pressure difference is achieved through vent passages aeroelastic effects, the decoupler pylon could be used as 30 a means of aligning the missile axis with the wing root 31 and 37. The flapper valves 69 and 71 modulate flow 31 and 37. Stiffness and re- exiting the vent passages or aircraft centerline instead of with the wing structure sponse time of the decoupler pylon 30 are governed by at the store attachment points.
the needle valves 79 and 81 in the vent passages 31 and The decoupler pylon may further be of use in sus- 37, and by the dashpot damper 87. As mentioned before, pending, from any support, a store prone to damage the damper 87 also damps oscillations of the store due to 35 from shock or vibration. A soft pylon suspension system transient loads. effectively isolates the store from vibration and shock The pressurized air source 22 provides a constant loads transmitted from the supporting structure.
supply of air to the air springs 62 and 64. Under steady It must be emphasized that the above specification aerodynamic conditions, the store 15 remains aligned relates to just one of many conceivable embodiments of with the wing 10. Imagine now that due to a changed 40 the invention. The decoupler pitch spring means may be aerodvnamic drag the store 15 has Ditched nose down. metallic, rubber or air spring means; the active controls With the downwird pitch, flapper halve 71 closes and may be hydraulic, pneumatk or electrical, among other 69 opens. Since more air is released through vent pas- possibilities. The pivot arrangement 59 need not be the sage 31 than through passage 37, air spring 64 fills and simple apparatus of FIG. 2 , which apparatus is designed expands; air spring 62 empties and is easily compressed 45 to secure a store for the duration of a flight. The ad- as the decoupler pylon moves about the pivot 59. Pres- vanced and highly specialized ejection attachments of sure regulator valve 73 and flow restrictors 75 and 77 fix modem aircraft may be used, some with slight modifica- the rate of supply of air to the air springs 62 and 64, and tion.
inhibit change in the direction of air flow. They thus The specifications herein discussed are not meant as ensure expansion and compression of the air springs 62 50 limitations on the scope of the invention and its underly- and 6 4 . With the expansion of air spring 62, the align- ing theory. The above description refers to one embodi- 15 is actively changed until it is at the ment of the invention; other embodiments will be obvi- ment of the store desired position with respect to the wing 10. ous to those skilled in the art.
What is claimed is: The decoupler pylon operates in much the same way in response to a tail-down pitch of the store. With such 55 1 . A device for suspending a store from a support, an “upward” pitch, flapper valve 69 closes and 71 comprising: opens. Since more air is released through vent passage an airfoil lifting surface subjected to flutter; 37 than through passage 31, air spring 62 fills and ex- store means; pands; air spring 64 empties and is compressed. The means for suspending said store means from said air- alignment of the store 15 is actively changed to restore 60 foil lifting surface and enabling movement there- it to its desired position with respect to the wing 10.
about; The damper 87 is used to add stability to the store soft-spring means connected between said airfoil lift- ing surface and said store means; and automatic alignment control system and also to reduce the amplitude of store pitch oscillations due to transient control means actuated by movement of said soft- loads such as gusts or maneuvers. 65 spring means; The decoupler pylon apparatus as described in the said soft-spring means and control means maintaining pneumatic embodiment increases flutter speed to a level alignment of said store means about a spanwise axis at or above bare wing flutter speed. Since the store is of the lifting surface and isolating the pitch modes
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of the store means from the torsion modes of the supply of air reaching said air springs by way of air airfoil lifting surface alleviating airfoil lifting sur- supply lines; pressure release vents branching from said face flutter and vibratory loads. air supply lines; and valve means associated with said 2. A device as in claim 1 including damper means pressure release vents, whereby said pressure release whereby transient oscillations of said store are damped. 5 vents are regulated.
3. A device as in claim 1 wherein said support is an 9. A device as in claim 8, wherein said valve means are flapper valve means, attached to said pivot. axis and aircraft wing.
4. A device as in claim 1 wherein said support is an covering said pressure release vents.
aircraft fuselage. 10. A device as in claim 9, wherein said air supply 5. A device as in claim 1 wherein said means for 10 lines have flow restrictor means for regulating the sup- suspending said store from said support is pivot means, ply of air to said air springs.
11. A device as in claim 10, wherein said pressure said pivot means having a pivot axis.
6. A device as in claim 5, hwerein said soft-spring release vents have valve means for regulating the rate of means and said control means are pneumatic means. release of air through said pressure release vents.
7. A device as in claim 6, wherein said soft-spring 15 12. A device as in claim 11 including damper means means include air springs connected between said store whereby transient loads are damped, and whereby re- and said support on either side of said pivot axis. sponse time and stability of said control system are 8. A device as in claim 7, wherein said control means partially regulated.
* * * * *
include a constant supply of air to said air springs, said