JP2788914B2 - Aircraft configured to prevent wing flutter and methods for reducing flutter in aircraft - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an apparatus and method for reducing flutter on an aircraft lifting surface by vibrating the left and right lifting surfaces at different natural frequencies. More specifically, the present invention relates to an engine nacelle attached to a right wing and a right wing when a component such as an engine nacelle is attached to the left and right wing surfaces when a time-varying excitation force is applied. For vibrating at a different natural frequency than the left wing and the nacelle attached to the left wing, thereby reducing wing flutter.

BACKGROUND OF THE INVENTION When temporary forces are applied to an aircraft wing while the aircraft is in flight, the aircraft wing vibrates between a bent state and a straight state, but one of the purposes of aircraft design is When the force disappears, the vibration is no longer attenuated, and the wing returns to a stable and straight state.

On the other hand, “wing flutter” refers to a phenomenon in which the vibration of a blade between a bent state and a straight state is not attenuated. Rather, in this case, the amplitude of such oscillations is constant or increases over time.

Wing flutter is an aeroelastic instability caused by the in-phase matching of two or more structural vibration modes of a flying aircraft. The flutter mode usually involves both bending and torsion types of movement, but the torsional type of movement draws energy from the airflow to increase the amplitude of the bending mode. In other cases, these may be slightly attenuated over the operating speed range of the aircraft, but persist and may make the aircraft uncomfortable.

The position of the engine nacelle relative to the wing, the mass characteristics of the engine, and the stiffness of the struts that attach the nacelle to the wing are factors that affect the wing's flutter characteristics. More specifically, the natural frequency of the nacelle and the mounting state of the struts affect the mode in which the blade vibration becomes unstable (flutter) and the airspeed.

In the past, the natural frequency of the nacelle and the nacelle strut was limited to a certain narrow range to avoid wing flutter. For example, in earlier versions of the Boeing 747 aircraft, the outer engine nacelle could oscillate laterally at a natural frequency of about two cycles per second. If the lateral frequency of the outer engine nacelle is well above or below two cycles per second, wing flutter will occur at unacceptably low speeds.

However, modern aircraft with stronger and less rigid wing surfaces flutter at speeds below the airspeed required by government regulations. in this case,
To avoid wing flutter, flutter cannot be avoided unless a frustrating solution is taken, such as reducing the maximum operating speed of the aircraft.

Other methods have been disclosed for avoiding wing flutter, such as by adding material for damping or by changing the relative position of the mass and / or center of pressure of the components. For example, Younger
U.S. Pat. No. 2,124,098 to r) relates to an auxiliary airfoil that is mounted on a main airfoil to create a fluttering force within the main airfoil.

In addition, U.S. Patent Number by Bockrath
No. 3,327,965 discloses a damping device for distributing the amount of vibrational energy transmitted from an aircraft wing to an attached engine nacelle to prevent unwanted movement of the engine nacelle.

Other systems for preventing wing flutter include U.S. Patent No. 3,734,432 to Low. This patent relates to a system for attenuating wing flutter using leading and trailing edge control surfaces under the control of a stability enhancement system.

An air spring system to suspend storage tanks from the wings to reduce wing flutter has been developed by Reed III (Re
ed III) in U.S. Patent No. 4,343,447.

U.S. Pat. No. 4,502,652 to Breitbach also relates to a spring device for suppressing wing flutter when transporting external loads.

SUMMARY OF THE INVENTION The present invention relates to a method and apparatus for preventing wing flutter in aircraft having left and right lifting surfaces such as wings. The method includes providing a first element of the left wing, such as an engine null and a strut, and a second element of a right wing, such as another engine nacelle and a strut, having different lateral natural frequencies from each other. Including. The difference in the lateral natural frequency is
It is large enough to increase flutter speed when exposed to time-varying disturbances.

Objects and advantages of the present invention will become apparent to those skilled in the art by reference to the following detailed description when taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION The present invention relates to an apparatus and method for preventing flutter on a lifting surface, such as an aircraft wing, by causing the left and right wings of the aircraft to vibrate at mutually different frequencies. As described in the detailed description below, the wings may have suspended objects such as, for example, engines or external storage tanks. In an exemplary embodiment, the present invention will be described with reference to mounting one or more engine nacelles on both the left and right wings of the aircraft in such a manner as to reduce wing flutter. However, it is clear that the scope of the invention is not limited to this embodiment.

Further background must be added that the aircraft is designed to fulfill a certain mission within the maximum operating speed envelope (maximum operating speed range) and at a reasonable cost to the operator. To get a margin above the maximum operating speed in case of emergency maneuver,
The structure of the aircraft must survive until it reaches a higher planned dive speed (V _D ). The federal government minimum flutter speed of the aircraft has to be 20% higher than at least V _D. That is, at least 1.2V
_D is required.

Early aircraft operated at low speeds, usually with overdesigned wings, resulting in large flutter margins. As speed increased and wing design became less conservative, flutter margin decreased. Material strength tolerances have been increased and the structural dimensions of the wing have been reduced to reduce weight. However, as a result of the reduced dimensional specification, the stiffness of the wing was reduced and the wing became more flexible. Since wing flutter is generally proportional to the stiffness of the wing, this result decreases, even relative to the wing that meets all aspects of strength design, it may be insufficient margin of the portion exceeding the often V _D is predicted . In many of these cases, dimensional specifications had to be increased beyond that required for strength purposes in order to obtain acceptable flutter speed margins. This increased dimensional specification has the disadvantage of increased weight, which has diminished aircraft performance. More recently, methods for optimizing the distribution of rigid materials, such as aeroelastic adjustment methods, have been used to reduce the aforementioned disadvantages.

Other passive means of reducing the disadvantages of flutter described above have also been used, including, but not limited to, aspect ratio, swept angle, taper ratio, blade thickness ratio, and dihedral angle. Including changing the wing geometry.
When mounting an engine or other storage tank on the wing, its location is carefully selected to increase flutter speed. However, these design choices can result in reduced aircraft performance.

Referring first to FIG. 1, a conventional method of attaching an engine nacelle, indicated at 10, to a wing 12 by a conventional post assembly, indicated at 14, is shown. As shown in FIG.
The post assembly 14 has a cross-sectional shape similar to a trapezoid. Prop
14 (FIG. 1) is an upper linking rod 16 extending rearward.
The linking rod 16 is connected at its front end to the upper part 20 of the column by a connector 18 and at its rear end by a connector 22 at the wing spar.
Connected to 21. To further connect the strut 14 to the wing,
A pair of connectors 26 (only one is shown in FIG. 1) are provided, which are located at the upper rear end of the post and are attached to wing fittings 28. The lower rear end of the column 14 is attached to the wing by a connector 30, the connector 30 is attached to a place 32 extending upward and backward, and the other end of the place 32 is attached to a wing attachment 34. . Further, the engine nacelle 10 is connected to the strut 14 in a conventional manner by a front fitting 36 and a rear fitting 38.

The strut 14 (FIG. 1) is formed by a plurality of vertical, spanwise partitions 40, the partition 40 being formed by a lower girder 42 extending at its lower end in the front-rear direction, and a central section being formed by a central girder 44.
The upper end is joined by an upper spar 46. The plurality of rear partitions 40 are smaller in height than the front partitions. The lower partitions include a rear partition 40a and the higher front partitions include a rear partition 40b.

Referring now to FIG. 2, a partition 40b of the
A portion extending from just forward to the rear and ending at the partition wall 40a is shown. In this manner, the portion of the strut 14 connected to the wing 12 is shown. The center girder 44 is formed by a pair of beams 48 extending to the nose side and the stern side, respectively, and these beams 48 are joined to each other by a horizontal beam 50 at the partition wall 40a. At the tail end of each beam 48,
At the position of the side 50, a female portion 51 of the connector 26 is attached. The female portion 51 is connected to a male portion (not shown) of the connector, and the connector is attached to the wing. The male and female portions of the connector are held together by lateral pins (not shown) that extend through openings in the male and female portions.

An end 53 of the connector 30 is attached to the rear end of the lower spar 42 to connect the strut 14 to the brace 32 (FIGS. 1 and 2). Additionally, a male portion 55 of the upper fixture 22 is attached to the rear end of the upper spar 46 to further secure the strut to the wing. The struts are further formed by an enclosure spar including a pair of beams 59 extending downwardly and rearwardly from bulkhead 40b and connected to the rear end of center spar 44. The fairing skin 60 surrounds the struts to reduce aerodynamic drag.

Having described the conventional struts for mounting the nacelle to the wings, attention is now directed to the load forces generated in response to the lateral (between one and the other) movement of the engine nacelle. Referring now to FIG. 3, there is shown a simplified view of the wings 12 of the connector 26 that support the engine nacelle 10 with conventional struts 14. When a lateral force F _L is applied to the nacelle 10, a vertical force F _V and −F _V are applied to the connector.
Generated through 26 and struts 14, forming a couple. Similarly, when the lateral force -F _L (FIG. 3B) acts in the opposite direction on the nacelle, the vertical forces -F _V and F _V act on the wing 26 via the connector 26. In this way, the exciting force acting on the nacelle is transmitted to the wing.

The lateral natural frequency of the nacelle vibration is determined to some extent by the stiffness of the column. The stiffness of the strut is controlled by careful design of the structural components of the strut, such as beams and bulkheads. The importance of the lateral frequency of the nacelle is apparent with reference to FIG. FIG. 4 is a graph showing flutter speed as a function of nacelle lateral frequency for an aircraft having all of the above-described conventional structures. That is, the lateral frequency of the nacelle and strut on the left wing is configured to be the same as a similarly positioned nacelle and strut on the right wing (referred to as a "symmetric design"). According to federal regulations, the wing flutter speed must be at least 1.2 times the guaranteed dive speed of the aircraft. The exemplary graph shown in FIG.
Between about 1.8 to 2.0 cycles per second (Hz) of the nacelle lateral bending frequency, there are areas where the airspeed of the aircraft can reach 1.2 V _D and wing flutter can be avoided. In this case, the previously described conventional struts can be "tuned" so that the lateral bending frequency of the nacelle falls within this region.

In some engine nacelle configurations using the conventional struts shown in FIGS. 1 and 2, this flutter region is essentially closed. As shown by the graph in FIG. 5, the onset of wing flutter occurs at an airspeed below 1.2 V _D , with maximum airspeed being obtained at a side bending frequency slightly below 1/9 Hz. In this conventional configuration,
To avoid flutter, it is necessary to reduce the maximum operating speed of the aircraft. Alternatively, the wing stiffness can be increased to achieve flutter speeds above 1.2V _D. However, increasing the stiffness of the wing has the disadvantage of adding weight to the aircraft.

The strut design of the present invention can also reduce speed,
This problem is overcome without increasing the weight of the wing without increasing the rigidity of the wing. The nacelle mounting struts are configured such that the nacelle mounted on the left wing has a different lateral bending frequency than the nacelle mounted on the right wing (assuming that the nacelle is located at the same relative position with respect to both wings). (Asymmetric strut design) and found to be flutter-free or at least stretchable to fairly high airspeed. The concept of providing such right and left wing columns that the nacelles on both sides of the fuselage may have different lateral bending frequencies is the same as in the past, where the left and right columns have a common lateral bending frequency. It is completely different from adjusting the mounting. More broadly, the present invention operates to eliminate wing flutter by configuring the aircraft so that the left and right wings oscillate at different natural frequencies.

This concept is illustrated in the graph of FIG. In FIG. 6, the left outer nacelle of the four-engine aircraft is caused to oscillate at a natural frequency of 1.76 Hz, and the right outer nacelle is adjusted within the experimental range of several different lateral bending frequencies. . As shown in Figure 6, when the right outer nacelle having a lateral bending frequency of at least 1.9 Hz, airspeed flutter begins exceeds 1.2V _D.

In order to achieve an asymmetrical strut design, the mounting struts shown in FIG. 7 are provided. In FIG. 7, elements common to the conventional struts described with reference to FIGS. 1 and 2 are identified by common numbers with a prime ('). FIG. 7 shows a part of a support column 70 for attaching the engine nacelle to the wing. A portion of this column extends rearward from the partition 40b 'to the rear partition 40c. In this design, the first to connect the struts to the wings
A pair of parallel spring beams 72 are provided in place of the connector 26 shown in the figure. That is, each spring beam 72
Extend in the front-rear direction so that the front end 74 of each spring beam is fixed to the partition wall 40b '. The center girder in FIG.
It is formed by left and right parallel beams 75 extending rearward from the partition 40b '. Outside each beam 75, one of the spring beams 72 is located. At the rear end of each spring 72 is a female portion of a connector 78 attached to the wing in a conventional manner.

In the present invention, the natural lateral bending frequencies of the nacelles on the left and right wings are different. This different lateral bending frequency is obtained by the spring beams 72 having different stiffness of the left and right nacelle struts. In the preferred embodiment, the spring beam in the right outer nacelle post of the Boeing 747 (FIG. 8) is larger than the height h 'of the cross section of the spring beam 72' (FIG. 9) in the left outer nacelle post. It has a sectional height dimension h. Here, the primed numbers refer to the right spring beam component, and the unprimed numbers refer to the left component. In this way, the right outer nacelle strut has higher rigidity than the left outer nacelle strut. Of the left and right wing nacelle struts,
The difference in the vertical flexibility along each longitudinal axis of the spring beam is a unique feature of the present invention.

Referring now to FIGS. 7-9, a rotary bearing 79 is disposed between the forward end and the rearward end of each spring beam 72. The rotating bearing 79 is supported in the trunnion 80 by a pin (not shown), which passes through a lateral hole in the trunnion and passes through the central opening of the bearing 79.
It passes through 81. The left and right trunnions 80 are attached to the rear ends of the beams 75 forming the central girder. In this way,
A portion of each spring beam extending between the bearing 79 and the connector 78 is cantilevered, and the cantilevered portion is slightly rotatable within the bearing 79. Support for each trunnion 80 is provided by a septum 40d. The partition 40d has its lower end attached to the lower girder 42 'and its upper end attached to the bottom of each trunnion 80. The upper end of the partition 40d is also attached to the rear end of the center beam 75.

In the present invention, the horizontal force applied to the engine nacelle F _L (Figure 7) is the FIGURE 3A and with reference to F _V and -F _V similar force components mentioned the Figure 3B produce. These forces act vertically in opposite directions, causing the cantilevered portion of the spring beam to move up and down. By controlling the flexibility of the spring beam in this way, the natural frequency of vibration of the engine nacelle can be controlled. That is, by controlling the material configuration of the spring beam and the vertical dimension and / or thickness dimension of the spring beam, the exact stiffness of the beam is controlled in a known manner. In this way, the lateral bending frequency of the engine nacelle is a function of the spring beam stiffness.

In an exemplary embodiment of the present invention, the conventional struts 14 shown in FIGS. 1 and 2 are used to attach the inner engine nacelle to the left and right wings of a Boeing 747 while using the present invention. The strut 70 is used to attach the outer engine nacelle to the left and right wings. The inner struts are adjusted so that each nacelle lateral bending frequency is the same. The left outer strut is adjusted so that the nacelle has a lateral bending frequency of 1.76 Hz, and the opposite outer strut is adjusted so that the nacelle has a lateral bending frequency of 2.11 Hz. Wind tunnel experiments with this configuration have shown that flutter has been avoided up to speeds above 1.2V _D. While not wishing to be bound by theory, it is speculated that the difference in vibration frequency between the left and right wings may have suppressed wing flutter from each other.

The foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description. This description is not exhaustive and is not intended to limit the invention to only the precise form disclosed by this description.
It will be apparent to those skilled in the art that many modifications and variations are possible.

[Brief description of the drawings]

FIG. 1 is a side view showing a conventional support for mounting an engine nacelle on an aircraft wing. FIG. 2 is a partial isometric view of a portion of the conventional strut shown in FIG. Figures 3A and Figure 3B, when the lateral force is applied to the nacelle, which is a simplified diagram showing a reaction force generated in the conventional strut (F _D). FIG. 4 shows flutter (unstable) with respect to the conventional support structure.
3 is a graph showing the boundary between motion and non-flutter (stable) motion as a function of aircraft speed and nacelle lateral bending frequency. FIG. 5 is similar to the graph of FIG. 4 and shows that flutter occurs before reaching the required maximum operating speed of the aircraft for a conventional strut configuration. FIG. 6 is similar to the graph of FIG. 4 and is for an aircraft incorporating the apparatus and method of the present invention. FIG. 7 is a partial isometric view of the nacelle mounting column of the embodiment of the present invention. FIG. 8 is a side view of a spring beam member having a first sectional height dimension. FIG. 9 is a side view of another spring beam member having a second cross-sectional height smaller than the first cross-sectional height. In the figure, 14 and 70 are columns, 40b 'and 40c are partitions, 75 is a beam, 73 is a connector, and 80 is a trunnion.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor John Thomas Rogers 1416 (56) Reference: Snow Homish Seattle Hill Road, Washington, United States of America 4917331 (US, A) U.S. Patent 4437627 (US, A) U.S. Pat.

Claims (22)

(57) [Claims] 1. An aircraft having first and second lifting surfaces, each having a first element and a second element, wherein the method comprises reducing flutter on the first and second lifting surfaces. Applying a force to the first element of a surface and the second element of the second lift surface; and responsive to the force, moving the first and second elements in an oscillatory manner; Vibrating the first and second lifting surfaces in response to vibrations of the first and second elements; and the first and second lifting means so that the first element vibrates at a different frequency than the second element. Adjusting the element; and responsive to the first and second elements vibrating at different frequencies, the first and second lifts at different frequencies. And a step of vibrating the surface, a method of reducing flutter in an aircraft. 2. The method of claim 1, wherein the adjusting step comprises: moving the first element to the first lift surface and the second element to the second lift element in a manner such that the first element vibrates at a different frequency than the second element. 2. The method according to claim 1, comprising connecting each to a second lifting surface. 3. The aircraft according to claim 1, wherein said first lift surface is a first wing of said aircraft and said second lift surface is a second wing on an opposite side of said aircraft.
3. The method of claim 2, wherein the wings are. 4. The adjusting step wherein the first element is connected to the first wing by a first mounting element, and the second element is connected to the second wing by a second mounting element. Between the first element and the second element is defined by adjusting the stiffness of the first mounting element and the second mounting element such that the stiffness of the second mounting element is different. 4. The method of claim 3, wherein 5. The method of claim 4, wherein said first and second elements are engine nacelles suspended from said first wing and said second wing. 6. An aircraft configured to prevent wing flutter, comprising: a first wing means and a second wing means; a first wing element and the second wing element; a first wing element and a second wing element. First mounting means for mounting the first element to the first wing means and the first mounting means so that the first wing element oscillates at a different frequency than the second wing element when a force is applied to the wing element. Aircraft mounting means for attaching a two-wing element to the second wing means. 7. A means for transmitting vibrations of said first wing element to said first wing means such that said first wing means oscillates at a different frequency than said second wing means; Means for transmitting vibration of a two-wing element to the second wing means. 8. The first mounting means includes a first member, the second mounting means includes a second member, wherein the first member is configured to apply a force to the first and second wing elements. The aircraft of claim 7, wherein the first wing element has a different stiffness than the second member such that the first wing element oscillates at a different frequency than the second wing element. 9. The first mounting means includes first support means for suspending the first wing element from the first wing means, and the second mounting means includes a first wing element for suspending the second wing element. Second
Second strut means for suspending from the wing means, wherein the first strut means comprises the first wing element and the first
A first member connected between the second wing element and the second wing element;
A second member connected between the first wing element and the second wing element when a displacement force is applied to the first and second wing elements. The aircraft of claim 8, wherein the aircraft has a different flexibility than the second member to vibrate at different frequencies. 10. An aircraft having a fuselage and configured to prevent wing flutter, wherein the first lifting surface means and the second lift surface means are mounted on opposite sides of the fuselage.
Lifting surface means; a first object and a second object; wherein when a force is applied to the first object and the second object, the first object has a different frequency from the second object. The first object is moved to the first
First mounting means for mounting on the lifting surface means and second mounting means for mounting the second object on the second lifting surface means, the first mounting means further comprising the first lifting surface means But means for transmitting the vibration of the first object to the first lifting surface means in a manner to vibrate at a different frequency than the second lifting surface means to reduce flutter; and
An aircraft, comprising means for transmitting vibrations of said second object to said second lifting surface means. 11. The first mounting means includes a first mounting member disposed between the first object and the first lifting surface means, and the second mounting means includes a second mounting member and the second object. A second mounting member disposed between the second lifting surface means and the second mounting member, wherein the first mounting member is configured to move the first object to the second object when a force is applied to the first and second objects. 11. The aircraft according to claim 10, wherein the aircraft is different from the second mounting member in such a manner as to vibrate at a frequency different from that of the object. 12. The apparatus of claim 11, wherein the first and second objects are engines, the first and second mounting means are columns, and the first and second lifting surface means are wings. Aircraft. 13. The first mounting means includes first beam means disposed between the first object and the first lifting surface means, and the second mounting means includes a first beam and the second object. Second beam means disposed between the first and second objects, wherein the first beam means is configured to move the first object into the second state when a force is applied to the first and second objects. 11. The aircraft according to claim 10, wherein said aircraft differs from said second beam means in such a way as to vibrate at a different frequency than the other object. 14. The first beam means has a different flexibility than the second beam means such that when a force is applied, the first object vibrates at a different frequency than the second object. 14. The aircraft of claim 13. 15. The first mounting means includes first suspension means for suspending the first object from the first lifting surface means, and wherein the second mounting means includes means for suspending the second object. A second suspension means for suspending from the second lifting surface means, wherein the first suspension means causes the first object to move when the first and second objects are subjected to a force. An aircraft according to claim 10, wherein said aircraft is different from said second suspension means in such a way as to vibrate at a different frequency than the second object. 16. The method of claim 15, wherein said first and second objects are engines, said first and second suspension means are columns, and said first and second lifting surface means are wings. The aircraft mentioned. 17. The first mounting means includes first column means for suspending the first object from the first lifting surface means, and the second mounting means includes a first column for suspending the second object. A second strut means for suspending from the second lifting surface means, wherein the first strut means includes a first strut member disposed between the first object and the first lifting surface means; The second strut means includes a second strut member disposed between the second object and the second lifting surface means, wherein the first strut member applies a force to the first and second objects. 11. The aircraft of claim 10, wherein the first object has a different flexibility than the second strut member such that the first object vibrates at a different frequency than the second object when the first object vibrates. 18. A method for reducing flutter in an aircraft, comprising: providing an aircraft having a fuselage and first and second lifting surfaces mounted at different locations on the fuselage; providing first and second objects. When a force is applied to the first and second objects, the first object vibrates at a different frequency than the second object, and the vibration of the first object is transmitted to the first lift surface. The first object is moved to the first lift surface in such a manner that the vibration of the second object is transmitted to the second lift surface.
Attaching the second object to the second lifting surface, respectively; and further responsive to vibration transmitted from the first and second objects, at a different frequency than the second lifting surface. A method of vibrating a first lifting surface. 19. The first mounting means, wherein the first object is mounted on the first lifting surface by first mounting means, the second object is mounted on the second lifting surface by second mounting means, 19. The method of claim 18, wherein the first mounting means differs from the second mounting means in a manner such that when a force is applied, the first object vibrates at a different frequency than the second object. 20. The method of claim 19, wherein the first and second lifting surface means are wings, the first and second objects are engines, and the first and second mounting means are columns. the method of. 21. The method according to claim 19, wherein said first mounting means comprises first beam means and said second mounting means comprises second beam means. 22. The first beam means has a different flexibility than the second beam means such that when a force is applied, the first object vibrates at a different frequency than the second object. 22. The method of claim 21, comprising: