Abstract: An apparatus and a method for measuring one or more acoustic parameters in a duct are described. The method includes arranging at least one pair of microphones in an array on a microphone support device, disposing the microphone support device including the array of microphones in the duct, generating an acoustic signal in the duct such that the acoustic signal propagates toward the array of microphones, and receiving by the array of microphones, the acoustic signal to provide a microphone output signal. The microphone support device is configured to fit within an inner diameter of the duct.

Abstract: Methods and apparatus to control pitch and twist of blades are disclosed. An example apparatus includes a twist input assembly driven by a drive shaft that drives a rotation of blades of a rotorcraft, the twist input assembly comprising a twist shaft, a first gear set driven by the drive shaft, and a first frequency controller to create a first rotational speed difference between a first gear of the first gear set and the drive shaft, the first rotational speed difference to cause the twist shaft to oscillate. The examples apparatus includes a pitch input assembly driven by the drive shaft, the pitch input assembly comprising a pitch link in communication with a first one of the blades of the rotorcraft, a second gear set driven by the drive shaft, and a second frequency controller to create a second rotational speed difference between a second gear of the second gear set and the drive shaft, the second rotational speed difference to cause the pitch link to oscillate.

Abstract: An apparatus and a method for measuring one or more acoustic parameters in a duct are described. The method includes arranging at least one pair of microphones in an array on a microphone support device, disposing the microphone support device including the array of microphones in the duct, generating an acoustic signal in the duct such that the acoustic signal propagates toward the array of microphones, and receiving by the array of microphones, the acoustic signal to provide a microphone output signal. The microphone support device is configured to fit within an inner diameter of the duct.

Abstract: Methods and apparatus to control pitch and twist of blades are disclosed. An example apparatus includes a twist input assembly driven by a drive shaft that drives a rotation of blades of a rotorcraft, the twist input assembly comprising a twist shaft, a first gear set driven by the drive shaft, and a first frequency controller to create a first rotational speed difference between a first gear of the first gear set and the drive shaft, the first rotational speed difference to cause the twist shaft to oscillate. The examples apparatus includes a pitch input assembly driven by the drive shaft, the pitch input assembly comprising a pitch link in communication with a first one of the blades of the rotorcraft, a second gear set driven by the drive shaft, and a second frequency controller to create a second rotational speed difference between a second gear of the second gear set and the drive shaft, the second rotational speed difference to cause the pitch link to oscillate.

Abstract: A rotational actuator assembly employs a drive torque actuator having a shape memory alloy (SMA) tube with a first trained twist direction and a return actuator having a SMA tube with an opposite trained twist direction collinear with the drive torque actuator with abutting proximal ends. A central fitting joins the proximal ends. A control system employs a position sensor for the drive torque actuator and the torque sensor for the return actuator for combined antagonistic rotation of the central fitting.

Abstract: A torsion lock may include a clutch, a spring, and a shape memory alloy (SMA) member. The spring may cause the application of pressure on the clutch for engagement thereof. The SMA member may linearly contract when heated in a manner to relieve the pressure on the clutch for disengagement thereof.

Abstract: An actuator assembly may comprise a housing, a shaft, a shape memory alloy (SMA) torque tube, and first and second unidirectional bearings. The SMA torque tube may rotate the shaft. The first unidirectional bearing may limit rotation of the shaft relative to the SMA torque tube to a first direction. The second unidirectional bearing may prevent rotation of the shaft relative to the housing along a second direction opposite the first direction.

Abstract: An actuator assembly may comprise a housing, a shaft, a shape memory alloy (SMA) torque tube, and first and second unidirectional bearings. The SMA torque tube may rotate the shaft. The first unidirectional bearing may limit rotation of the shaft relative to the SMA torque tube to a first direction. The second unidirectional bearing may prevent rotation of the shaft relative to the housing along a second direction opposite the first direction.

Abstract: A torsion lock may include a clutch, a spring, and a shape memory alloy (SMA) member. The spring may cause the application of pressure on the clutch for engagement thereof. The SMA member may linearly contract when heated in a manner to relieve the pressure on the clutch for disengagement thereof.