The subject matter disclosed herein generally relates to rotors for aircraft use. More specifically, the subject disclosure relates to flexbeam rotors for helicopters or other rotorcraft.
In typical flexbeam helicopter rotors, a flexbeam extends from a rotor hub and is connected to a torque tube and blade via a bolted joint and a snubber type bearing at an inboard end of the torque tube located between the flexbeam and the torque tube. The snubber bearing positions the torque tube relative to the flexbeam for pitch change and flapping motion of the torque tube and react shear loads on the assembly. Such bearings are often elastomeric bearings with preloaded laminates of elastomeric material placed between the flexbeam and torque tube, and are configured such that the elastomer remains in compression throughout the entire load range. Such rotors are subject to vibrational modes during operation, the vibrational frequencies and mode shapes traditionally are tuned to desired placements by changing stiffness and/or mass of the rotor blades, flex beam, and/or torque tube. This method of tuning is not always particularly sensitive.
In one embodiment, a rotor blade assembly includes a flex-beam member and a torque tube surrounding the flex-beam member and extending at least partially along a rotor blade assembly length. A pitch bearing assembly is supportive of the torque tube relative to the flex-beam member and includes at least two outer bearing members secured to the torque tube and an inner bearing member positioned between the at least two inner bearing members and secured to the flex beam member. A stiffness of the inner bearing member is selected to change one or more dynamic characteristics of the rotor blade assembly.
In another embodiment, a pitch bearing assembly for a blade assembly of a rotary-winged aircraft includes at least two outer bearing members secured to the rotor blade assembly and an inner bearing member located between the at least two outer bearing members to transfer load between the outer bearing members. A stiffness of the inner bearing member is selected to change one or more dynamic characteristics of the rotor blade assembly.
In yet another embodiment, a rotary-winged aircraft includes an airframe, a drive system, and a rotor assembly operably connected to the drive system. The rotor assembly includes a rotor hub and a plurality of rotor blade assemblies operably connected to the rotor hub. Each rotor blade assembly includes a flex-beam member and a torque tube surrounding the flex-beam member and extending at least partially along a rotor blade assembly length. A pitch bearing assembly is supportive of the torque tube relative to the flex-beam member and includes at least two outer bearing members secured to the torque tube and an inner bearing member positioned between the at least two inner bearing members and secured to the flex beam member. A stiffness of the inner bearing member is selected to change one or more dynamic characteristics of the rotor blade assembly.
In still another embodiment, a method of changing one or more dynamic characteristics of a rotor blade assembly includes securing at least two pitch bearing outer members to a torque tube of a rotor blade assembly. A stiffness of a pitch bearing inner member is selected, and the pitch bearing inner member is installed between the at least two pitch bearing outer members. The pitch bearing inner member is secured to a flex beam member of the rotor blade assembly, surrounded by the torque tube. One or more dynamic characteristics of the rotor blade assembly are changed by the selected stiffness of the pitch bearing inner member.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
Shown in
The main rotor assembly 18 includes a hub member 28 located at the main rotor axis 20 and operably connected to the drive shaft 22. A plurality of blade assemblies 30 are connected to the hub member 28.
Referring now to
The pitch bearing assembly 48 includes two bearing outer members 50a, 50b positioned within and secured to the torque tube 40, an inboard outer member 50a and an outboard outer member 50b. In some embodiments. The bearing outer members 50a, 50b are secured to the torque tube 40 by one or more bolts (not shown) at bolt openings 54. It is to be appreciated, however, that the bearing outer members 50a, 50b may be secured to the torque tube 40 by other mechanisms and systems. A bearing inner member 56 extends between the two bearing outer members 50a, 50b into bearing races 58 of the bearing outer members 50a, 50b, and is secured to the flex beam 32 at one or more locations. In some embodiments, the bearing inner member 56 includes interface portions 68, which may be cylindrical, extending into the bearing races 58 of each of the bearing outer members 50a, 50b. Inboard of the bearing outer member 50b, a height 64 of the bearing inner member 56 along the main rotor axis 20 increases to a first peak 72. Continuing inboard, the height 64 lessens to a valley 74, then increases again to a second peak 76. Further, the bearing inner member 56 has a lateral thickness 62 which may be constant along a spanwise length of the bearing inner member 56, or which may vary. It is to be appreciated that the bearing inner member 56 shape described herein is merely exemplary and other shapes are contemplated within the scope of the present disclosure. shape described herein The bearing inner member 56 and bearing outer members 50 are typically metallic elements formed from, for example, a titanium, steel or aluminum material. In other embodiments, the bearing outer members 50 and/or the bearing inner member 56 may be formed from a composite material. One or more bearing elements 66 are located between the bearing inner member 56 and the bearing outer member 50, at an inner member interface portion 68, where the bearing inner member 56 extends into a bearing outer member opening 70. In some embodiments, the bearing elements 66 are elastomeric bearing elements 66, formed from an elastic material such as a rubber or other polymeric material, or nonpolymer elastic material, such as a metal, or combinations of polymer and nonpolymer materials, such as an arrangement of layers of elastomeric material metallic shim material therebetween. In other embodiments, the bearing elements 66 are roller or needle elements made of steel, ceramic, etc moving in a circular pattern between the bearing inner member 56 and the bearing outer member 50 at the interface portion 68. In some embodiments, each blade assembly 30 includes two flex-beam members 32. In such embodiments, as best shown in
Referring now to
Blade assembly 30 response is highly sensitive to slight modifications to bearing inner member 56 stiffness, as the inner member 56 stiffness is the lowest of all the elements in the assembly. This sensitivity minimizes the need to add more complexity and or weight to the blade assembly 30 structure to achieve a selected load share and/or vibratory response.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.