1. Field of the Invention
This invention relates to a helicopter rotor of the bearingless type, having an airfoil shaped blade attached to a flexible spar, specifically designed and fabricated to accommodate the torsion deflections of pitch change, and the bending requirements due to lead/lag and flap/droop blade excursions. This invention is specifically directed to the group of bearingless rotors wherein the flexible spar is rotatably driven by suitable attachment to the rotor hub and rotor drive shaft. The specific geometric shape of the spar is not important to this invention, and is shown in the accompanying figures as rectangular. Likewise, it is not important whether the spar be continuous across the rotor axis to attach to opposed blades, or whether each spar be unitary and joined only to one blade. For the latter configuration there may be an odd number of blades.
2. Description of the Prior Art
Prior art patents familiar to the inventors and pertaining to hingeless rotor blade attachments and controls have generally been directed to tail rotor applications where pitch, lead/lag and flapping motions are less than those of main rotors. In attempting to transfer rotor technology developed for tail rotors to a main rotor application, concern had to be addressed to the adverse influence of these larger excursions, and especially to the pitch coupling effect due to inplane or lead/lag blade motions. The longer, wider, and heavier main rotor blade undergoes significant bending in first advancing into the direction of flight and then retreating from it as it completes it cycle of rotation at a constant driven rotor speed and undergoing commanded cyclic pitch changes as well as being impinged upon by wind gusts at any point on the azimuth. Starting and stopping produces still further inplane bending. The concept of using blade motions to introduce a proportional blade pitch change in a direction to stabilize the blade is known, as well as the concept of elimination or prevention of such pitch coupling.
A specific rotor configuration to which our invention may be applied is shown in U.S. Pat. No. 4,008,980 to Noehren et al, which is used in the UH-60A helicopter. The specific "snubber bearing" of that rotor head is depicted as FIG. 5 in U.S. Pat. No. 4,087,203 to Ferris.
The main objective of the teaching of this latter patent is similar to that of our invention; namely to provide structure that accommodates pitch change relative motion (torsion) between the flexible spar and rigid torque tube, minimizes the pitch coupling effect of the blade flapping wherein relative bending takes place between the spar and torque tube, and prevents pitch change motions due to lead or lag excursions when blade spar inplane motion occurs relative to the torque tube.
In an embodiment wherein blade pitch change is introduced by means of a torque tube enveloping a flexible spar, and wherein the attachment to the rotor hub follows the teaching of the U.S. Pat. No. 3,874,815 to Baskin, use of this invention also appears beneficial, provided the linkage is suitably mounted at the virtual hinge axis of the blade spar such that the root end of the torque tube can be restrained from vertical motion.