BACKGROUND OF THE INVENTION

(1) Field of the Invention

The invention is related to a bracket for connecting a traverse of a landing gear to a cabin of a helicopter. The invention is further related to the application of an inventive attachment with the brackets for connecting a traverse of a landing gear to a cabin of a helicopter.

(2) Description of Related Art

Vibrations or resonance modes are produced, when a helicopter (HC) lands for example on the front part of its landing gear (LG), e.g. when landing on a slope. Those resonance frequencies and resonance modes can cause the HC to become inoperable due to ground resonance. A landing gear assembly comprises typically a pair of cross tubes or traverses and a pair of struts connected at the outboard ends of the cross tubes or traverses.

The document U.S. Pat. No. 4,270,711 A discloses a helicopter landing gear assembly with a pair of cross tubes having a pair of struts connected at the outboard ends thereof. A first of the cross tubes is connected to the helicopter fuselage at a pair of laterally spaced points. The second of the cross tubes is joined by a pivot connection to a structural bridge positioned above the second cross tube. The structural bridge is connected at its outer ends to the fuselage main beams. The structural bridge connected to the second cross tube permits the helicopter fuselage to pivot about a fore-aft axis thereof to lower the natural roll frequency of the helicopter airframe and therefore increase the margin of stability to prevent ground resonance.

The document U.S. Pat. No. 6,244,538 B1 discloses a skid landing gear for a helicopter, in which the directional stiffnesses of the cross members of the skid landing gear have been de-coupled from one another, such that optimization of the longitudinal stiffness of the cross members may be performed independently of the optimization of the vertical stiffness and fatigue life of the cross members. In order to de-couple the stiffnesses in the skid type landing gear, two approaches are employed. In the first approach, the skid landing gear has non-symmetric-section cross members and/or distribution of different materials within the cross-section for de-coupling the vertical stiffness of the cross members from the longitudinal stiffness, such that placement of the ground resonance frequency may be optimized, while retaining the vertical stiffness properties essential for optimizing vertical energy attenuation and fatigue life. In the second approach, mounting devices are employed that provide compliance in selected directions, thereby de-coupling the directional stiffnesses.

The helicopters known from the state of the art require specific adaption of the landing gears and/or cabins for the prevention of ground resonance.

BRIEF SUMMARY OF THE INVENTION

The object of the invention is to provide a helicopter with a landing gear and a cabin with an inherent prevention of vibrations without any or as little as possible constructive modifications of the cabin and/or of the LG.

The solution is provided with an attachment of a landing gear to a cabin of a helicopter with a bracket for connecting a traverse of the landing gear to the cabin of the helicopter and with the application of such a bracket.

According to the invention an attachment of a landing gear to a cabin of a helicopter is provided with a bracket for connecting a traverse of the landing gear to preferably at least one cabin clamp mount fixed to a bottom of the cabin of the helicopter. A longitudinal direction of the traverse is essentially perpendicular to a longitudinal direction of the cabin/helicopter. The bracket comprises a landing gear retainer fixed by clamping rings about the traverse coaxially to the longitudinal direction of the traverse. The landing gear retainer is adapted to be fixed to the preferably at least one cabin clamp mount by means of a pendulum and at least one upper and at least one lower pendulum bolts in at least one upper and at least one lower pendulum bearings of the pendulum.

In some embodiments, the at least one upper pendulum bolt in the at least one upper pendulum bearing is in between the landing gear retainer and the at least one lower pendulum bolt in the at least one lower pendulum bearing. For a rotational degree of freedom about a longitudinal direction of the helicopter/cabin relative to the LG the pendulum is for mobility of the cabin in longitudinal direction of the traverse, the pendulum being hinged to the cabin with the lower pendulum bolts in the lower pendulum bearings; and the pendulum is for mobility in longitudinal direction of the traverse, the pendulum being hinged to the landing gear retainer with the upper pendulum bolts in the upper pendulum bearings.

The inventive attachment with preferred embodiments of the bracket allows prevention of vibrations by upgrading exclusively the connection between the LG and the HC for the prevention of vibrations without constructive modifications of the cabin and/or the LG, such constructive modifications of the cabin and/or the LG being particularly cumbersome. The inventive attachment with the bracket for connection of the cabin to the LG provides an oscillation isolation level between cabin and LG, in which any vibrations and resonance mode of a disturbing oscillation become so “detuned” that the helicopter is out of resonance, for example ground resonance, with the excitation frequencies from the rotors in operation. The pendulum of the inventive attachment with the bracket with its upper end hinged to the LG and its lower end hinged to the cabin provides for a stable equilibrium, as long as the cabin's gravity rests on the LG.

The invention provides the following advantages:

Elements of the cabin and/or the LG remain essentially unchanged for detuning vibration, which would be really expensive, but exclusively the brackets connecting the cabin to the LG are changed. Thus the inventive connection of a landing gear to a cabin of a helicopter is realizable at low cost.

The inventive attachment with the brackets is exchangeable with brackets of the state of the art. Inventive attachments with the brackets can also at any time be upgraded on an existing helicopter without major changes of elements in the helicopter.

The inventive attachment with the brackets is relatively lightweight and compact compared with systems conceived to “absorb” disturbing oscillations by damping.

Optional equipment of the LG, such as a hook for external loads etc., installed on the LG, is not affected by the inventive attachment with the brackets, as the pendulum is very compact in the area of the inventive attachment with the brackets of the LG.

The LG qualities concerning crash remain unchanged with the inventive attachment with the brackets. A new certification of the LG shall therefore not be necessary.

According to a preferred embodiment of the invention the pendulum comprises at least one rod laterally mounted to the landing gear retainer.

According to a further preferred embodiment of the invention the landing gear retainer has a distance ≥0 to the upper pendulum bolts in the respective upper pendulum bearings.

The oscillating motion of the cabin traverse to the longitudinal direction of the cabin is determined in relation to the LG through spring elements and the pendulum bearings of the inventive attachment with the brackets. The spring elements are essentially oriented perpendicular to the pendulum in a neutral position with no deflection of the pendulum relative to the spring elements to decrease transversal movements of the spring elements of the LG once the pendulum moves in direction of the spring elements. The pendulum bearings of the inventive attachment with the brackets with their respective rotation axis are perpendicular to the longitudinal direction of the traverse and thus mobility is provided of the cabin relative to the traverse perpendicular to the longitudinal direction of the cabin.

According to a further preferred embodiment of the invention an equal torque support bolt is provided for fixation of the landing gear retainer to the clamping rings for blocking any rotation of the landing gear retainer about the longitudinal direction of the traverse and for further limitation of the oscillating motion in longitudinal direction of the cabin/helicopter.

According to a further preferred embodiment of the invention compound springs are positioned preferably perpendicular to a plane defined by the pendulum in neutral position, in order to maximize effectiveness while displacements due to rotation of the LG towards and away from the cabin are minimized to an amount <6 mm during pendulousness. Thus the compound springs and the pendulum bearings of the inventive attachment with the brackets implement the oscillating motion of the cabin transverse to the longitudinal direction of the cabin with the stiffness of the cabin-LG assembly.

According to a further preferred embodiment of the invention stops are provided between the cabin clamp mount and the clamp rings to limit the deflection of the spring elements essentially oriented along the longitudinal direction of the traverse of the LG and in order to detour the load transmission while high forces are applied between cabin and LG during flight, e.g. flight with load on a load hook. Preferably each of two inventive attachments with the brackets mounted on a traverse at the right and at the left is provided with two stops pairwise arranged symmetrically with regard to the longitudinal direction of the traverse of the LG. The inventive attachment with the bracket mounted on the traverse at the right limits any movements to the left between cabin and LG while the inventive attachment with the bracket mounted on the traverse at the left limits any movements to the right between cabin and LG.

According to a further preferred embodiment of the invention stop plates with a stiffness >1000 N/mm and friction coefficients between 0.05 and 0.15 are provided between at least one cabin clamp mount and the landing gear retainer of an inventive attachment with the bracket to limit any movements essentially oriented transversal to the longitudinal direction of the traverse of the LG between the cabin and LG. Preferably a tolerance of approximately 0.5 mm is provided between the stop plates in the LG-retainer and the at least one inner cabin clamp mount to avoid friction from pendulousness between cabin and LG at little forces in longitudinal direction of the cabin. In case of higher forces in longitudinal direction of the cabin the stop plates interact at relatively low friction forces due to the friction coefficients between 0.05 and 0.15. The stop plates and the at least one inner cabin clamp mount coordinate with regard to wear and feature emergency operation characteristics.

According to a further preferred embodiment of the invention one of the inventive attachments with one bracket is mounted on a traverse at the front right and another one of the inventive attachments with one bracket is mounted on the front left of the traverse so that through the turning mobile pendulums the cabin can turn mainly about the longitudinal direction of the LG/cabin. It is also conceivable that this pendulum construction is used in each case at the rear right and/or rear left bracket.

According to a further preferred embodiment of the invention in respectively neutral positions a pendulum's plane through a right and a further pendulum's plane through a left bracket on one traverse axis are each oriented to a helicopter's center of gravity, wherein the neutral positions are defined by balanced forces from the compound springs on the respective pendulum and the respective pendulum's planes are defined by passing respectively through the upper and lower pendulum bolts in the upper and lower pendulum bearings of the pendula. According to a further advantage of the invention with these orientations of the pendulum's planes the cabin is restricted to a rotary motion about its longitudinal direction through the helicopter's center of gravity.

