Abstract: A passive device is provided for reducing vibration and noise in a hydraulic system. The passive device includes a tubular element having an open end and a closed end. The open end of the tubular element is adapted to be attached to a fluid conduit carrying pressurized fluid in the system so that the tube fills with the pressurized fluid. The area and length of the tube are such that the fluid within the tube has a resonant condition at a frequency that is the same as at least one frequency of the vibration and noise that is to be reduced or removed in the hydraulic system. A helicopter is also provided having a hydraulic system of pressurized fluid for reducing the transfer of vibrations from the transmission to the airframe including the passive device. Several such passive devices may be applied at selected locations in a hydraulic system for effectively reducing high frequency vibration and noise due to, for example, helicopter transmission gear clashing.

Abstract: An active mount is provided for use in a rotary wing aircraft between each of the gearbox and airframe mounting locations for mechanically suspending the airframe from the gearbox. The active mount comprises first and second linear hydraulic actuators each having a principal axis. The length of the actuators is variable along the principal axis for providing relative movement between the airframe and the gearbox. The principal axes of the actuators are adapted to lie in the directional planes of the primary forces necessary for supporting the airframe and acting on the transmission gearbox mounting locations for providing movement of the gearbox relative to the airframe in the planes at a frequency for reducing the transfer of vibration through the active mount to the airframe. A system for reducing vibration in the rotary wing aircraft further comprises a hydraulic system for supplying a controlled flow of pressurized hydraulic fluid to the actuators.

Abstract: A seal assembly is provided for use in a hydraulic actuator of the type including a cylinder, a piston movably disposed in the cylinder, and a piston rod connected to the piston and extending from an end of the cylinder. The seal assembly comprises a seal member formed of a material impervious to hydraulic fluid and having an inner edge and an outer peripheral edge. The inner edge of the seal member defines a central opening which is larger than the outside diameter of the piston rod for receiving the rod. The outer edges of the seal member are attached adjacent the end of the cylinder so that the inner edge of the seal member is radially spaced from the outside diameter of the piston rod and the seal member forms a fluid impervious wall for preventing hydraulic fluid from contacting the elastomeric portion of the bearing assembly.

Abstract: A motor has a rotor for controlling a parameter of an instrumentality, such as a blade or a blade flap. The rotor is positioned about the drive shaft of the instrumentality and rotates at the same average angular velocity of the drive shaft. The instrumentality is controlled by applying to the instrumentality a physical displacement signal that is generated by the phase relationship of the rotor of the motor with respect to the angular position of the drive shaft. A plurality of permanent magnets proximate the periphery of the rotor cooperate with a plurality of stator polepieces and electromagnetic coils. The current flowing through the coils is reversed each time that the rotor advances by the angular space of one permanent magnetic pole. The strength and polarity of the current flowing through the coils controls the direction and displacement of the rotor with respect to a neutral phasing of the rotor with respect to the drive shaft.

Abstract: An active mount is provided for use in a rotary wing aircraft between each of the gearbox and airframe mounting locations for mechanically suspending the airframe from the gearbox. The active mount comprises first and second linear hydraulic actuators each having a principal axis. The length of the actuators is variable along the principal axis for providing relative movement between the airframe and the gearbox. The principal axes of the actuators are adapted to lie in the directional planes of the primary forces necessary for supporting the airframe and acting on the transmission gearbox mounting locations for providing movement of the gearbox relative to the airframe in the planes at a frequency for reducing the transfer of vibration through the active mount to the airframe. A system for reducing vibration in the rotary wing aircraft further comprises a hydraulic system for supplying a controlled flow of pressurized hydraulic fluid to the actuators.

Abstract: A seal assembly is provided for use in a hydraulic actuator of the type including a cylinder, a piston movably disposed in the cylinder, and a piston rod connected to the piston and extending from an end of the cylinder. The seal assembly comprises a seal member formed of a material impervious to hydraulic fluid and having an inner edge and an outer peripheral edge. The inner edge of the seal member defines a central opening which is larger than the outside diameter of the piston rod for receiving the rod. The outer edges of the seal member are attached adjacent the end of the cylinder so that the inner edge of the seal member is radially spaced from the outside diameter of the piston rod and the seal member forms a fluid impervious wall for preventing hydraulic fluid from contacting the elastomeric portion of the bearing assembly.

Abstract: A passive device is provided for reducing vibration and noise in a hydraulic system. The passive device includes a tubular element having an open end and a closed end. The open end of the tubular element is adapted to be attached to a fluid conduit carrying pressurized fluid in the system so that the tube fills with the pressurized fluid. The area and length of the tube are such that the fluid within the tube has a resonant condition at a frequency that is the same as at least one frequency of the vibration and noise that is to be reduced or removed in the hydraulic system. A helicopter is also provided having a hydraulic system of pressurized fluid for reducing the transfer of vibrations from the transmission to the airframe including the passive device. Several such passive devices may be applied at selected locations in a hydraulic system for effectively reducing high frequency vibration and noise due to, for example, helicopter transmission gear clashing.

Abstract: A hub mounted actuation system for providing control of a portion of a rotor blade, such as a flap, on a rotorcraft. The rotor blade is attached to a rotor shaft that rotates with respect to an airframe. The hub mounted actuation system includes a stationary support mounted to the airframe and a rotary support attached to the rotor shaft for concomitant rotation therewith. At least one hub actuator rotates in combination with the rotor blade and includes a piston which is slidable within a housing. The piston and housing define a pressure chamber within the actuator which contains a fluid to be pressurized. A displacement control device is disposed between the stationary support and the rotary support for controlling movement of the piston within the housing. A linkage connects the hub actuator to the portion of the blade to be controlled. The linkage is adapted to displace the blade portion as a function of the movement of the piston within the housing.

Abstract: In many uses of electrical motors, the interaction of a tool being powered, e.g., a milling machine, and the workpiece being worked on by the motor induces mechanical vibrations which adversely affect the functioning of the tool as well as inducing wear producing vibrations in the motor rotor shaft. Damping of such vibrations is achieved by deliberately inducing internal unbalanced forces on the motor rotor shaft for counteracting the externally induced vibrations. Such internal unbalanced forces are produced by the use of additional currents in the main stator coils for generating additional, unbalanced force generating magnetic fields. A mathematical analysis of the process is provided.

Abstract: An eddy current sensor comprises a generally E-shaped core having three parallel legs joined together by a bridge. Current carrying coils are mounted on each of the outer legs and a signal coil is mounted on the central leg. Identical a.c. currents are caused to flow through the two outer coils for generating two magnetic fields which combine to form a sensing magnetic field extending outwardly from the ends of the legs for sensing purposes but which cancel one another within the central leg. The sensor is disposed within an E-shaped, hollow shield of an eddy current producing, electrically conductive material. The sensor fits within the shield as fingers in a glove with the parallel legs of the sensor magnetically separated from one another by walls of the shield. Only the ends of the sensor legs are exposed through apertures through the shield for emergence of the various magnetic fields. The shield cancels unwanted fringing fields and better guides the magnetic fields in desired directions.