Patent Application
20140286691
The invention relates to a fuselage structure for a means of transport, to a means of transport comprising a fuselage structure, and to a method for producing a fuselage structure for a means of transport.
Noise perceptible by passengers in a cabin of a means of transport is caused by sound sources inside and outside the cabin. In the case of aircraft, systems that are installed in the fuselage, for example hydraulic systems, an air conditioning system and vacuum systems for toilets, and outside the cabin, for example boundary layer sound and engines, significantly contribute to the sound level in the cabin. Some new drive systems, for example engines with counter-rotating propellers, may generate very high sound levels for which targeted additional measures for reducing the noise on the fuselage structure are of great importance because at that location locally-introduced sound power in the form of structure-borne sound-waves propagates along the fuselage structure, and along this sound path emits airborne sound to the cabin. This results in identical noise nuisance due to high sound levels, in particular near a sound-input location of the engines.
Presently employed measures to reduce structure-borne sound, for example in aircraft, relate to installations in a predetermined aircraft structure; these measures comprise, for example, sound-absorbing glass wool insulation packages, customized cabin wall elements and acoustically decoupled suspension elements. Sound waves emanating from external sound sources thus first impinge on the primary structure of the aircraft fuselage where they excite structural vibrations that propagate along the aircraft fuselage in the form of structure-borne sound-waves. Along the propagation path of these structure-borne sound-waves airborne sound waves are emitted into the aircraft cabin, and cabin equipment elements are excited to vibrate by way of their points of attachment to the fuselage structure, which also results in sound radiation into the cabin. High sound excitation levels, which in the case of engines with counter-rotating propellers at the surface of the aircraft fuselage may be in the magnitude of up to 150 dB, correspondingly high sound levels transmitted into the aircraft cabin result, because generally speaking the loss mechanisms occurring during structure-borne sound-transmission through the aircraft fuselage and during local transmission of airborne sound into the aircraft cabin are significantly below the required extent for a cabin sound level that corresponds to the present state of the art. Because such aircraft propulsion systems are not used in civil passenger aviation, in the state of the art no effective devices exist for reducing structure-borne-sound-induced noise in the cabin.
An aspect of the invention proposes a fuselage structure for a means of transport, in which fuselage structure as little structure-borne-sound-induced noise arises within the fuselage structure.
Proposed is a fuselage structure comprising at least two interconnected fuselage segments, wherein the fuselage segments in each case comprise an outer skin with at least one end edge, wherein in a connecting region between two fuselage segments the end edges of the outer skin of the relevant fuselage segments are spaced apart from each other, and wherein at least one connecting means establishes a mechanical connection of the relevant fuselage segments.
It is thus a core idea of the disclosure to stop direct structure-borne sound-conduction between two interconnected fuselage segments by way of the outer skin. Complete interruption of the outer skin in the connecting region and producing a mechanical connection by way of connecting elements arranged on the structure requires multiple redirection or deflection of structure-borne sound emanating from a fuselage segment. Overall, this results in a significant reduction in the extent of cabin noise that arises as a result of structure-borne sound. By the spacing apart of the end edges of facing fuselage segments, in particular waves of low frequencies or large wavelengths are reflected at the end edges. Sound-wave reflection results, furthermore, also from a mass discontinuity due to the mass of the connecting elements on the structure when compared to that of the outer skin.
The connecting elements should be designed and used in such a manner that the lowest possible number of connecting elements is sufficient in order to ensure a space at the end edges of the outer skin. In means of transport such as aircraft, trains, ships or boats etc. fuselage segments or body segments are lined up in axial direction. The space to be set between the fuselage segments to be connected should thus preferably occur in the axial direction. The term “axial direction” refers to a main direction of extension, and particularly preferably to the longitudinal direction parallel to the longitudinal axis of the particular fuselage segment. In the case of an aircraft the direction is, for example, the direction of the aircraft fuselage, which direction coincides with the “x” axis according to DIN 9300 that applies to aviation. If the means of transport has a fuselage structure comprising several fuselage segments or body segments that are interconnected in the lateral direction, spacing-apart in this direction is thus required.
The active total cross-sectional area, which results from the connection of two fuselage segments, of conventional connecting elements, which are for example designed as screw bolts, screw rivets or similar positive-locking or non-positive-locking connecting elements overall causes a reduction in the sound-transmission cross-section when compared to a conventional connection of the outer skin of two facing fuselage segments in a connecting region. Apart from this, due to the design according to an embodiment of the invention, multiple changes in the direction of the sound propagation path from the outer skin by way of the connecting elements also result in sound reflections. Each change in direction is always followed by coupling existing sound wave propagation forms to other forms, accompanied by a reduction in strength.
In an advantageous embodiment at least one of the fuselage segments comprises stringers that end in the region of the end edge of the outer skin so that stringers of two interconnected fuselage segments are spaced apart from each other in a longitudinal direction. Such stringers are used together with frame elements and the outer skin to produce a dimensionally-stable fuselage structure. By separating the stringers the structure-borne sound-transmission at this position may also be eliminated, which even more significantly reduces noise induced by structure-borne sound. It is not mandatory for the stringers to end so as to be flush with the end edges of the outer skin; instead, said stringers may project beyond said end edges, provided spacing to the stringers and to the outer skin of the fuselage segment to be connected may be ensured. As an alternative, it is also possible for a stringer to be interrupted within the fuselage segment before it reaches the end edge of the outer skin. Of course, it is also possible for the stringers to be arranged so as to be offset in the circumferential direction, alternating between the fuselage segments, wherein in this case for reasons of symmetrical force distribution a regular equidistant circumferential arrangement is to be preferred.
In an advantageous embodiment each fuselage segment comprises a structural connecting element that is arranged on the end edge of the outer skin and that is designed to receive the at least one connecting element for connection to a structural connecting element of another fuselage segment. Each structural connecting element should thus have a mechanical strength that is sufficient to take up all the structural loads. It should be pointed out that the structural connecting elements in a connecting region are of course also spaced apart from each other in order to prevent onward-transmission of contact-induced sound.
If the fuselage structure comprises stringers, in the relevant fuselage segments said stringers may be mechanically firmly connected to the structural connecting elements so that a precise flux of force becomes possible by way of this mechanical ending. It may thus be advantageous if the structural connecting elements comprise a strap-like flange that extends in the circumferential direction, by means of which flange the stringers are connectable. This strap-like flange may be an integral component of an annular frame, for example a frame-element-like component, which comprises a strength-optimized cross section with one or several projections.
In an advantageous embodiment the interconnected fuselage segments in a connecting region comprise differently-shaped structural connecting elements. Consequently, the latter have different resonance frequencies so that in this manner a resonance that otherwise would occur in both facing structural connecting elements may reliably be prevented.
Apart from the geometry, in an advantageous embodiment the masses of the structural connecting elements may also differ. If no pressure differentials inside and outside the fuselage segment are to be expected, for example if the particular fuselage segment is arranged outside a pressurized cabin region, in addition perforated regions are imaginable, taking into account the required structural strengths in the structural connecting elements in order to reduce transmission of airborne sound between parallel surfaces of facing structural connecting elements.
In a particularly advantageous embodiment a structural connecting element is designed as a frame element that comprises, for example, an annular shape with a cross section that is singly or multiply angled in order to provide circumferential stiffening of the fuselage structure in order to absorb radial forces. A frame element is usually a single-part or multi-part body, which radially extends on the inside of the outer skin, which body is used to take up forces acting in the radial direction, wherein frame elements are arranged on the fuselage structure at regular axial spacing. In the fuselage structure according to the invention this frame element, which serves as a structural connecting element, comprises in particular an end face situated in a region of the end edge of the outer skin of the particular fuselage segment so that the end faces of structural connecting elements of facing fuselage segments extend parallel to each other in a connecting region, thus making it possible to optimally receive connecting elements and optional components situated in between.
The structural connecting elements may comprise the same material as all the remaining parts of the fuselage structure; as an alternative to this they may, however, comprise some other adequately strong material so that each structural connecting element may fully take up the structural loads occurring during operation of the means of transport.
To bridge the space between facing end edges of fuselage segments it is advantageous to use at least one cover element that extends at least between the facing end edges. The cover element is preferably flexible and covers the gap between the end edges or completely fills said gap. The cover element may comprise a strap-like flat shape that may be made to conform to the outer skin contour so that sleeve-like encompassing of the interconnected fuselage segments results. To achieve a fluid-dynamically improved transition between the outer skin contour and the cover, the outer skin in the region of the end edge may comprise an indentation or a heel to which the cover element may conform and with a matching material thickness may produce an even outer contour. The cover element may either be mechanically firmly connectable to the outer skin, or it may be displaceable at least to one side, in order to allow compensation for movements of the fuselage structure, be it as a result of thermal effect or mechanical effect. However, opening the gap to the environment must be prevented in particular in the case of aircraft with a fuselage structure according to an embodiment of the invention so that an adequately positionally-fixed arrangement of the cover element is to be aimed for. In the choice of the material to be selected it should be taken into account that in particular in the case of aircraft greatly different temperatures are experienced during flight operation, for example with the aircraft on the ground on a hot day or during cruising at high altitude, or in takeoff and landing operations with varying fuselage deflection. For this reason it may make sense to consider elastomers.
In order to seal fuselage segments that contain a pressurized cabin, sealing elements are particularly advantageous. Accordingly, the fuselage structure further comprises at least one sealing element, preferably situated in the interior of the fuselage structure in a connecting region between two fuselage segments, for producing a fluid-proof transition between the two fuselage segments. If these comprise, for example, a radially interior delimitation, the sealing element is particularly preferably to be arranged on this radially interior delimitation. The sealing element must be designed so as guarantee a permanent seal, wherein permanent flexibility is required, in particular taking into account the expected instances of deformation of the fuselage structure. This may be achieved by bellows-like structures comprising an elastomer, or by a mixture of an elastomer, metals and/or fiber-composite materials.
Pressurized bellows constructions or tube constructions that adapt to locally continuously changing gap geometries are possible, as are slidable or deformable flat cover elements.
In order to maintain a minimum space between facing end edges of fuselage segments, the use of spacers may make sense. Such spacers may be implemented in various ways, wherein a simple form could comprise adjusting shims or washers in combination with bolt-type connecting elements. A spacer may also be implemented by a section of a connecting element, which section comprises, for example, a projection, a heel or similar that is designed to rest against an end surface of a structural connecting element or the like.
In an advantageous embodiment at least one spacer comprises a piezo element that is designed to reduce structure-borne sound-conduction by means of external excitation. The anti-phase excitation of the piezo element or causing a force against mechanical excitation may reduce the conduction of structure-borne sound.
In an advantageous embodiment the piezo element, by way of a control unit connected to it, may be used to carry out active reduction of structure-borne sound-transmission. The piezo element comprises a piezo-active material that may be excited to vibrate when a voltage is applied. Compensation takes place by the anti-phase application of contraction or extraction of the piezo-active material. Efficient control requires acquisition of the structure-borne sound-waves to be compensated, a process that may be carried out by an acceleration sensor attached to the fuselage structure. For example a structural connecting element may be equipped with an acceleration sensor. By means of the signal obtained in this manner the control unit may generate the control signals for anti-phase vibration generating on the piezo element, and may provide control by way of an optional additional amplifier. Expediently, in terms of the sound path the acceleration sensor is arranged sufficiently far from the controllable spacer so that the control unit has enough time to generate control signals and to then transmit these signals with correct timing, in other words phase-effectively in terms of sound cancelling, to the piezo element.
In a likewise advantageous embodiment the piezo element is connectable to an electrical resistor which in the case of mechanical excitation of the piezo element generates heat and counteracts the mechanical excitation of the piezo element. In this arrangement the piezo element forms a vibration damper. The electrical power arising at the piezo element during movement is converted to heat by way of a resistor connected to the piezo element.
In a furthermore advantageous embodiment at least one structural connecting element comprises at least one vibration absorber that is used as a pendulum-like oscillator to compensate for vibrations. A vibration absorber may be of an active or a passive design. While active excitation in principle functions in the same manner as in the piezo element described above, a passive vibration absorber is connected relatively “softly” to the relevant structural connecting element so that the vibrating mass of the vibration absorber follows the local, structure-borne-sound-induced, movements of the structural connecting element with some delay so that compensation takes place.
The invention also relates to a means of transport with at least one fuselage structure presented above. The means of transport may be used for transporting a sizeable number of passengers present in a cabin formed in the interior of the fuselage structure or body structure. The means of transport may be an aircraft, a rail-bound vehicle, a terrestrial vehicle or a water craft. As a result of the design according to an embodiment of the invention of the fuselage structure, a particularly advantageous reduction in structure-borne-sound-induced noise may be achieved. The aircraft may, furthermore, comprise engines with propellers, for example in each case two counter-rotating propellers.
The invention further relates to a method comprising, in particular, the arrangement of two fuselage segments relative to each other, each fuselage segment comprising an outer skin in each case with at least one end edge, in such a manner that facing end edges in a connecting region are spaced apart from each other. Preferably the resulting gap is covered by means of at least one cover element.
Further characteristics, advantages and application options of the present invention are disclosed in the following description of the exemplary embodiments and of the figures. All the described and/or illustrated characteristics per se and in any combination form the subject of the invention, even irrespective of their composition in the individual claims or their interrelationships. Furthermore, identical or similar components in the figures have the same reference characters.
The connecting elements 16 may be designed in the form of elongated positive-locking and/or non-positive-locking elements that allow complete transmission of structural forces and at the same time ensure spacing between the end edges 8 of the outer skin 6 of the fuselage segments 2 and 4 in the connecting region 10. For example, the connecting elements 16 are designed in the form of bolts, each comprising at least one end with a thread and a middle section that preferably has a larger diameter and serves as a spacer between the structural connecting elements 12 and 14. The middle parts of the connecting elements 16 may therefore extend between facing surfaces of the structural connecting elements 12 and 14, while the thread extends through the structural connecting elements 12 and 14 or may be reached from the side of the fuselage segment. Thus by way of the arrangement of screwing devices on the side of the fuselage segment into the connecting elements 16 reliable connection of the two fuselage segments 2 and 4 may be achieved.
Optionally (not shown in
The gap between the first structural connecting element 12 and the second structural connecting element 14 is covered by means of a cover element 19 in order to harmonize the external surface that is subjected to an airflow. Said cover element 19 may, in particular, comprise a flat cross section with a smooth outer contour. A number of different exemplary embodiments exist for implementing the cover element 19.
The connection principle according to an embodiment of the invention between two fuselage segments is suited in particular to reducing structure-borne sound of engines with propellers, and in particular with counter-rotating propellers. Such engines may be arranged at different fuselage sections directly adjacent to a passenger region or aft, and consequently different requirements in terms of the tasks to be achieved result.
As an example, two engines 30 with counter-rotating propellers 30 are arranged on the second fuselage segment 34; in operation they transmit structure-borne sound into the second fuselage segment 34. As a result of the de-coupling connection, according to an embodiment of the invention, to the adjacent fuselage segments 32 and 36 structure-borne sound-conduction may be significantly reduced. The noise nuisance to passengers present in the adjacent fuselage segments 32 and 36 is thus significantly reduced.
In
A certain mass discontinuity may be achieved by different radial extensions of the structural connecting elements 12 and 14, which becomes apparent from the different height of the frame element heads 52 and 54. The geometry may be optimized both in terms of structural mechanics and acoustics, a task that could also include the use of different materials.
The connecting element 58 may also be arranged in an elastic/damping sleeve 68 in order to mechanically separate the connecting element 58 from the structural connecting elements 12 and 14. Of course, it is also possible, as shown for example in
In a further exemplary embodiment according to
In a diagrammatic view
Apart from flat sealing elements 84 made from an elastomer, bellows constructions comprising an elastomer or a composite comprising elastomer materials and metals, fiber-composite materials and/or other plastics may be considered. The necessary characteristics of this sealing element 84 are a corresponding flexibility even at low operating temperatures, taking into account, for example, conventional flight altitudes with low temperatures at the outer skin of, for example, −30° C., adequate tensile strength, in particular in view of the expected deformation of the fuselage during takeoff and landing, a corresponding tear strength and tensile strength, resistance to alternating pressure, and of course adequate pressure tightness.
In order to improve the sealing effect, active pressurization of the sealing element 86 may be caused, be it by means of a source of compressed air, by a bleed-air line, a connection with a component of an air-conditioning system or the like. As an alternative, the sealing element 86 may be supplied at regular intervals with compressed air, by way of a valve, and may autonomously keep this compressed air.
In addition, it should be pointed out that “comprising” does not exclude other elements or steps, and “a” or “one” does not exclude a plural number. Furthermore, it should be pointed out that characteristics or steps which have been described with reference to one of the above exemplary embodiments may also be used in combination with other characteristics or steps of other exemplary embodiments described above. Reference characters in the claims are not to be interpreted as limitations.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2013 102 812.8 | Mar 2013 | DE | national |
