Patent Application
20170121015
Aircraft landing gear shimmy is a dynamic instability that results from torsional instability of the gear in combination with lateral instability. During taxiing, the landing gear of an aircraft is subject to various vibrations due to ground features, tire dynamics, and a variety of other factors. If the frequency of the vibration to which the landing gear is exposed is close to the natural frequency of the landing gear, a potential vibration resonance can occur, which can cause the landing gear to experience undesirable shimmy. In addition to causing vibration that can be felt by passengers, such shimmy can cause premature wear to landing gear components, and in extreme cases, can cause landing gear failure.
Known solutions for landing gear shimmy are typically driven by the relative motion or displacement between two landing gear components. One known configuration uses a fluid damper to reduce relative motion between landing gear components. For example, a cylinder may be connected to an upper torque link, and a piston may be connected to a lower torque link. Movement of the upper torque link relative to the lower torque link moves the piston within the cylinder to force damping fluid through an orifice to create a damping force that suppresses oscillation.
In another known configuration, the relative motion of the landing gear parts generates a frictional force between two or more frictional surfaces. This frictional force in turn dissipates the oscillation of the landing gear parts to reduce shimmy vibration.
Known shimmy damper systems suffer from several disadvantages. The relative motion that drives the dampers requires more complicated mounting features. This motion also requires that the dampers themselves be more complex, adding cost and weight to the designs. Further, known dampers are prone to wear, requiring more frequent service and replacement. Thus, there is a need for a simplified damper to counteract shimmy vibration in landing gear.
A first representative embodiment of a disclosed shimmy damper is suitable for use to reduce vibrations in aircraft landing gear. The shimmy damper includes a housing with an internal cavity, and a weight slidingly disposed within the cavity. The weight is positioned between a first pneumatic spring and a second pneumatic spring. The shimmy damper further includes at least one mounting feature to fixedly mount the housing to a component of the aircraft landing gear.
A second representative embodiment of a disclosed shimmy damper includes a housing comprising an internal cavity. A weight is slidingly disposed within the cavity and sealingly engaging a wall of the cavity to divide the cavity into a first chamber and a second chamber. A passageway is formed between the first and second chambers to provide a fluid connection therebetween. The shimmy damper further includes a fluid disposed within the first and second chambers such that the fluid provides a resistive force in response to movement of the weight within the cylinder.
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
The foregoing aspects and many of the attendant advantages of the disclosed subject matter will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
The detailed description set forth below in connection with the appended drawings wherein like numerals reference like elements is intended as a description of various embodiments of the disclosed subject matter and is not intended to represent the only embodiments. Each embodiment described in this disclosure is provided merely as an example or illustration and should not be construed as preferred or advantageous over other embodiments. The illustrative examples provided herein are not intended to be exhaustive or to limit the claimed subject matter to the precise forms disclosed.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of representative embodiments of the present disclosure. It will be apparent to one skilled in the art, however, that many embodiments of the present disclosure may be practiced without some or all of the specific details. In some instances, well-known process steps have not been described in detail in order not to unnecessarily obscure various aspects of the present disclosure. Further, it will be appreciated that embodiments of the present disclosure may employ any combination of features described herein.
A first lug 14 extends longitudinally from one end of the housing 12, and a second lug 16 extends longitudinally from an opposite end of the housing. The lugs 14 and 16 are sized and configured to allow the housing 12 to be mountable to a cooperating component of the aircraft landing gear. In this regard, a component of the landing gear includes corresponding devises to allow the housing 12 to be coupled at each end to the landing gear component with pins, bolts, or other suitable fasteners so that the housing is fixedly secured to the landing gear component. It will be appreciated that the illustrated lugs are exemplary only, and the size, position, and orientation of the lugs may vary within the scope of the present disclosure. It is further contemplated that the attachment of the housing is not limited to lugs, but can include any other known configurations suitable to secure the housing 12 to the landing gear component. It will also be appreciated that that the exterior shape of the housing is exemplary only. In this regard, the illustrated cylindrical shape of the housing should not be considered limiting.
Referring now to
A weight 30 is slidingly disposed within the cavity 20. In the illustrated embodiment, the weight 30 is sized and configured to sealingly engage the cylindrical surface 22 of the cavity 20 as it slides within the cavity 20. More specifically, the outer surface of the weight 30 has a generally cylindrical shape having a slightly smaller diameter than the diameter of the cylindrical surface 22 of the cavity 20. One or more seals 36 are disposed between the weight and the surface 22 to provide an airtight or substantially airtight seal between the weight and the cylindrical surface. In the illustrated embodiment, the seals 36 are elastic O-rings partially disposed within annular grooves formed in opposite ends of the weight 30. The O-rings are sized to provide a seal between the weight 30 and the cylindrical surface 22, while allowing reciprocating movement of the weight 30 along the length of the cavity 20. A lubricant 38, such as a light oil, facilitates movement of the weight 30, ensures an airtight seal, and reduces wear on the seals. Alternate embodiments are contemplated in which piston rings or other suitable sealing configurations are utilized. When disposed in the cavity 20, the weight 30 creates first and second volumes 42 and 44 on opposite sides 32 and 34, respectively, of the weight 30.
A transfer conduit 50 is provided with the housing 10. In the embodiment shown, the transfer conduit 50 is integrally formed in the body 12 such that one end of the conduit is in fluid communication with the first volume 42, and a second end of the conduit is in fluid communication with the second volume 44. A valve 52 is mounted to the housing in fluid communication with the transfer conduit 50. The valve 52 allows for selective introduction and release of a fluid into and out of the first and second volumes 42 and 44 of the damper 10. The fluid is preferably an inert gas, but can alternatively be a combination of inert and/or non-inert gases, such as air.
In use, the damper 10 is mounted to a landing gear component to reduce vibration that would otherwise be experienced by the landing gear. In one representative embodiment, the damper 10 is mounted to the torque link of either the main landing gear or the nose landing gear. Although not required, the damper 10 is preferably mounted at a location on the landing gear most likely to have the largest vibration amplitude. Mounting the damper 10 at such a location, for example at the torque link apex joint, optimizes the effectiveness of the damper. It will be appreciated, however, that the damper 10 can be mounted to any part of the landing gear by any suitable attachment configuration.
In use, the landing gear experiences vibration during takeoff, landing, and taxiing. With the damper 10 mounted to a component of the landing gear, the landing gear vibration causes the damper to vibrate as well. As the damper 10 vibrates, the housing 12 moves with the landing gear component, and the inertia of the weight 30 causes the weight to move relative to the housing 10 in a direction opposite to the vibration, i.e., out of phase with the vibration.
As the weight 30 moves relative to the housing 10, the gas inside each of the first and second volumes 42 and 44 act as pneumatic spring that biases the weight 30 toward the middle of the housing 12. In this regard, movement of the weight 30 toward the first end surface 24 reduces the size of the first volume 42, thereby compressing the gas in the first volume. The compressed gas in turn applies a biasing force to the weight 30 that tends to move the weight toward the second end surface 26. Similarly, movement of the weight 30 toward the second end surface 26 compresses the gas in the second volume 44, which applies a biasing force that tends to move the weight toward the first end surface 24.
The damper has a natural frequency that is determined mainly by the mass of the weight 30 and the spring rate of the compressed gas within the first and second volumes 42 and 44. In order to optimize the performance of the damper 10 to a particular landing gear, it is desirable to be able to adjust the natural frequency of the damper 10. To a produce a damper 10 having a suitable natural frequency, the weight 30 can be selected to have a mass that provides a desired natural frequency. While varying the mass of the weight 30 is an effective way to adjust the natural frequency of the damper 10, it is not ideal due to manufacturing considerations.
The presently disclosed damper 10 allows for adjustment of the damper's natural frequency by selectively modifying the pressure of the gas within the first and second volumes 42 and 44. Referring to
It is generally known that the spring rate (stiffness) K of a pneumatic spring varies with the pressure of the gas within the spring. In this regard, pneumatic springs typically have a progressive spring rate wherein the spring rate increases when the pressure of the gas within the spring increases. As a result, the spring rate of the pneumatic springs (the gas within the first and second volumes 42 and 44) and, therefore, the natural frequency of the damper 10 can be adjusted by increasing or decreasing the amount of gas within the damper, i.e., by adjusting the pressure of the gas within the damper. Accordingly, the presently disclosed damper 100 allows for tuning the damper 10 to optimally damp the shimmy vibration of a particular landing gear configuration.
While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the claimed subject matter.
