Abstract: A system and method for monitoring a structure for damage is provided. The method includes stimulating a sensor in a sensor array to generate a plurality of waves. The sensor array includes one or more quadrants, wherein each quadrant includes one or more sensors. Sensor data from all sensors are acquired in each quadrant in parallel. The sensor data wave characteristics is processed for analysis. The processed sensor data wave characteristics are compared with threshold values to determine the presence of damage to the structure. If the presence of damage is determined, a corrective system is notified for corrective action.

Abstract: An apparatus for inspecting samples that may include a curvature that varies from sample to sample comprises a scanning element, a feed mechanism, and a pivot mechanism. The scanning element transmits and receives a signal to and from the sample as the sample passes by, thereby building an image or profile of the sample. The feed mechanism includes a drive motor coupled to a series of pulleys and belts that form an open-ended chain. The pulleys rotate when driven by the drive motor and are coupled to an array of rollers that rotate as well to propel a inspection sample past the scanning element. The pivot mechanism includes a series of primary and secondary links that also form an open-ended chain. The primary links are coupled to the rollers and the combination pivots in unison to form an arc that matches the curvature of the sample in order to maintain a fixed distance between the sample and the scanning element.

Abstract: A non-conductive composite doubler is fabricated for application to an electrically conductive surface of a structure by: forming the composite doubler; placing an array of capacitive gap thickness sensors between the doubler and the structure surface; measuring the gap thickness between the doubler and the structure surface in a plurality of areas over the surface of the structure; using the gap thickness measurements to shape a layer of adhesive to essentially match the contour of the structure surface; and, applying the layer of adhesive to the doubler.

Abstract: A device for use in detecting structural damage includes at least one piezoelectric wafer that has a sensor, and an actuator in-plane with the sensor. At least one of the sensor and the actuator at least partially surrounds the other of the sensor and the actuator such that the piezoelectric wafer provides radial detection of structural occurrences in a material.

Abstract: A simulation arrangement is used for laboratory testing of enclosed partial cabins to be installed as resting cabins in commercial aircraft. The partial cabin is outfitted with vibration generators for simulating the excitation of structure-borne noise corresponding to noise that will be caused by the later connection to the aircraft fuselage. Elements for exciting airborne noise are also allocated to the partial cabin. The vibration generators and the elements for the airborne noise excitation are adjustable via control and regulating devices. The signals are generated via a computer unit with an input data file of knowledge-based information and/or by extrapolation of the acoustic values at the installation location and of the details of the construction of the partial cabin.

Abstract: A solution for monitoring a property of an object and/or an area using a Micro-ElectroMechanical Systems (MEMS)-based monitoring device is provided. In an embodiment of the invention, the MEMS-based monitoring device includes a MEMS-based sensing device for obtaining data based on a property of the object and/or area and a power generation device that generates power from an ambient condition of the monitoring device. In this manner, the monitoring device can operate independent of any outside power sources or other devices. Further, the monitoring device can include a transmitter that transmits a signal based on the property. The monitoring device can be used to monitor a moving component of a machine, and can be integrated with a health monitoring system of the machine using one or more relay devices.

Abstract: Soft support systems and methods for dynamically testing structures are disclosed. In one embodiment, a soft support system adapted to decouple a structure from a support surface for dynamic testing includes a containment bag, an inflatable chamber disposed at least partially within the containment bag and adapted to engage with a portion of the structure, the inflatable chamber being further adapted to exert a lifting force on the portion of the structure during inflation of the inflatable chamber, and an inflator module coupled to the inflatable chamber and adapted to facilitate inflation of the inflatable chamber within the containment bag. In one embodiment, the inflatable chamber comprises a toroidally-shaped inflatable member defining a central opening adapted to at least partially receive a portion of the structure during inflation of the inflatable chamber.

Abstract: The invention relates to a device that is used to analyse the structure of a material. The inventive device comprises: probe elements (5) which are used to (i) emit a wave, in the material, with emission delay laws that correspond to several simultaneous deviations and (ii) receive, on the different probe elements (5), signals from the refraction of said wave by the material; detection channels, each detection channel being connected to a probe element (5), in order to collect the refraction signals and to transmit same to data processing means (4); and delay circuits that apply a delay on each detection channel according to the reception delay laws which are predetermined and which correspond to the different deviations of the wave emitted. The invention also relates to an analysis method which can be used, in particular, on said device.

Abstract: A method and apparatus for detecting the defects of at least one rotor of a rotary wing aircraft, in particular a helicopter, in order to adjust the rotor. In the method, in a preliminary step, a reference aircraft is used corresponding to a particular type of aircraft and having a rotor (6, 10) without defect and adjusted so that the level of vibration is at a minimum, a series of measurements are taken on the aircraft (1), and a neural network is deduced therefrom illustrating the relationships between accelerations representative of vibration, and defects, and adjustment parameters. Thereafter, in a later step, for a particular aircraft (1) of the same type, measurements are taken on the particular aircraft (1) and on the basis of said measurements and on the basis of the neural network, the defects, if any, are detected and values for the adjustment parameters are determined that will enable the level of vibration of the aircraft (1) to be minimized, which parameters are applied to the rotor (6, 10).

Abstract: A defect detection system for thermally imaging a structure that has been energized by a sound energy. The system includes a transducer that couples a sound signal into the structure, where the sound signal causes defects in the structure to heat up. In one embodiment, the sound signal has one or more frequencies that are at or near an eigen-mode of the structure.

Abstract: A method is used for checking the air noise of a motor vehicle, particularly of a passenger car, which air noise is generated by air flowing onto an outer skin of a vehicle body of the passenger car. In order to optimize this method, targeted air currents are applied by means of a blower to a stationary passenger car in areas where sealing devices extend between stationary vehicle body structures and movable vehicle body elements of the vehicle body, and the air noise occurring as a result of the air currents is measured subjectively and/or objectively. For the implementation of the method, a device is used in the case of which the blower comprising the outflow cross-section is a component of a flow device which is equipped with a blast nozzle for acting upon measuring points on the outer skin.

Abstract: A method is disclosed for nondestructively examining airfoils for defects without removing them from the turbine machines of which they are a part. The method uses phased array ultrasound technology, which can be used with all types of airfoils. The angle of entry of the ultrasonic beam is varied by using phased array ultrasound technology. The phased array ultrasound allows an inspector to steer the ultrasonic beam toward an area of interest within the airfoil. The phased array allows an inspector to monitor multiple angles at once. So long as the scan angle does not exceed a calibrated range, an inspector can monitor an area of interest, no matter what the sound beam entry surface angle is. The ultrasonic beam is steered or phased to inspect different orientations with one scan. The method uses a phased array transducer that is a linear array probe that is comprised of a series of transducers.

Abstract: A system for identifying a signal source in a predetermined space, the system including multiple sensing units arranged at different locations to detect signals in the predetermined space. The system also includes one or more recording units arranged to separately and simultaneously record a detected signal at each of the sensing units that detects the signal. The system further includes a processing unit including a first storage area configured to store a set of identified signatures corresponding to multiple signal sources in the predetermined space, and a second storage area configured to store parameters related to the conditions under which the recordings of the signal are made. The processing unit also includes an identifying unit that is programmed to identify a signal source by comparing a determined signal spectrum with some or all of the signatures included in the set of identified signatures.

Abstract: In a method of identifying a source of a signal, the signal is recorded and then analyzed in order to determine its spectrum. The method includes the following steps: in parallel with recording the signal, storing parameters significant of the conditions under which the recording is made; after analyzing the signal and determining its spectrum, detecting lines emerging from the background noise of the signal, using a predetermined emergence threshold; comparing each line detected with some or all of a set of signatures of sources identified and inventoried in a database established prior to the recording; and for each line, and where applicable, selecting signatures that may correspond to the line and, as a function of the resulting signature/line pairs, consolidating, resolving ambiguity of, or quantifying the source corresponding to said line.

Abstract: A method for identifying a signal source in a predetermined space, the method including inventorying a set of identified signatures corresponding to a plurality of signal sources and recording a signal simultaneously at different locations of the predetermined space. Parameters related to the conditions under which the recordings are made are then stored, and a spectrum of the signal is determined. The method also includes detecting a line emerging from background noise of the spectrum by using a predetermined emergence threshold. The line is then compared with some or all of the signatures included in the set of identified signatures, and at least one signature corresponding to the line is selected to create at least one signature/line pair. Finally, a source of the signal is identified based on the selecting step.

Abstract: The apparatus and method for moving a sensor over a workpiece includes a sensor, and an actuating member. The sensor, such as a non-destructive test sensor, is carried by the actuating member, and the actuating member is at least partially disposed within a housing. The actuating member is adapted for automated movement in one direction, and the housing may be configured to be grasped by an operator and manually moved in another direction. As such, the sensor may automatically move in one direction with respect to the workpiece without manual intervention, and manually move in another direction, such that the sensor is moved by the combination of automated and manual movement. In addition, the actuating member may have at least two substantially parallel arms extending from near the sensor, which permits the sensor to slide along the workpiece while maintaining a substantially normal relationship to a surface of the workpiece.

Abstract: A method according to the present invention calculates a performance function for a structural system (10) that can be used to determine system dynamics at points of interest on the structural system (10). A test input force is applied to an input subsystem (12) and an output subsystem (14) while the motion in response to the test input force is measured to determine a drive point transfer function. A test relative force is applied to the input subsystem (12) and output subsystem (14) at interface points in all degrees of freedom while the motion in response to the test relative force is measured in all degrees of freedom to determine the interface transfer functions. A performance function for the structural system (10) is mathematically calculated based upon the measured drive point transfer functions and interface transfer functions.

Abstract: A self-aligning turbine disc inspection apparatus (30) for positioning a non-destructive examination sensor (38) proximate the disc web surface (20) of a turbine rotor assembly (10). The apparatus supports the sensor at a proper height above a support surface (34) while simultaneously providing passive freedom of movement in X, Y and theta directions so that the sensor is free to follow the slight movements of the web surface as the rotor assembly is rotated on a test stand. The freedoms of movement are provided by a first sled (52) rolling on a base (42), by a theta alignment assembly (62) rotating on the first sled, and a second sled (54) sliding on the theta alignment assembly. A vertical drive assembly (48) attached to the second sled provides a selectable height. The sensor may be moved across the disc web surface by a motorized slide (82) attached to a head assembly (46) attached to the vertical drive assembly.

Abstract: A non-destructive inspection, testing and evaluation system and process is provided for the review of aircraft components. The system provides for a structure configured to contain an inspection and testing apparatus and the aircraft components under inspection. The structure is lined with shielding to attenuate the emission of radiation to the outside of the structure and has corbels therein to support the components that constitute the inspection and testing apparatus. The inspection and testing apparatus is coupled to the structure, resulting in the formation of a gantry for supporting a carriage and a mast is mounted on the carriage. The inspection and testing equipment is mounted on the mast which forms, in part, at least one radiographic inspection robot capable of precise positioning over large ranges of motion. The carriage is coupled to the mast for supporting and allowing translation of the equipment mounted on the mast. The mast is configured to provide yaw movement to the equipment.

Abstract: A support system for ground vibration testing of a large flexible structure. The system includes a plurality of light weight lifting mechanisms that impart an upward force sufficient to lift the flexible structure off the ground. The system also includes a plurality of lift beams coupled to the lifting mechanisms in a pendulous manner. Each lift beam attaches to the flexible structure at one of a plurality of designated jack points, and lifts the flexible structure off the ground when the upward force is imparted by the lifting mechanisms. Thus, the flexible structure is thereby pendulously suspending above the ground such that rigid body mode test data is decoupled from first flexible mode test data.

Abstract: Thermoplastic welding is an emerging technology targeted at significantly reducing the manufacturing cost of aerospace structure by eliminating fasteners and the touch labor associated with fasteners to prepare, install, and inspect the assemblies. Quality welds are highly dependent upon achieving appropriate temperatures everywhere along the bond line. The present invention is a system that evaluates the quality of the welds involving inputting an EM pulse to the embedded susceptor and listening to the acoustic response that the pulse generates to determine weld quality from the sound.

Abstract: A method of ultrasound inspection is provided. The method comprises providing a composite first part, introducing ultrasound to the part, receiving reflections of the ultrasound introduced in the first part, and predicting a residual strength of the first part using an amplitude of the received reflections.

Abstract: A smart skin structure has vibration energy managing and steering capabilities. The skin can be used to managing vibrations in the skin or shell of a system, subcomponent, device, or structure. The skin has sensors coupled to the skin to obtain a response to vibrations. Actuators integral with the skin can be selectively activated to apply forces to the skin to confine or redirect vibration energy to one or more predetermined skin regions. The forces applied by the actuators can be controlled to create confinement power flows. Further, the skin actuators can be controlled using spatial derivatives of the vibration forces. The structure can be used in, but is not limited to, watercraft, aircraft, space vehicles, automobiles, marine devices, industrial machinery, machine tools, home appliances, buildings, bridges, and offshore oil platforms.

Abstract: Disclosed is a noise source visualizing system used in a wind tunnel test to measure generated sounds, the system comprising an acoustic mirror for converging sound waves of sounds generated on a surface of a vehicle during a wind tunnel test; a microphone measuring the converged sound waves; an image-photographing unit photographing locations on the vehicle at which the sounds are generated; a first display unit displaying the sounds measured by the microphone as colors that vary according to characteristics of the sounds; a movable traverse to which the acoustic mirror is connected for enabling the acoustic mirror to collect the sounds; a workstation for analyzing the converged sound waves measured by the microphone, the images photographed by the image-photographing unit, and the signals displayed through first display unit; and a second display unit overlapping then displaying image signals photographed by the image-photographing unit and the colors displayed on the first display unit.

Abstract: A device for generating an acoustic stress wave in metal structures in real-time. A cylindrical housing includes a chamber, a piezostack actuator inside the chamber, and a support ring for relieving strain. The actuator has a high tensile strength block extending therefrom for contacting the surface. A pulse wave generator drives the actuator in accordance with a predetermined frequency to cause microindentation and generate an acoustic stress wave in the surface. The stress wave is transmitted to a signal transformer for producing a signal for use in systems for interpreting the signal. In a preferred embodiment, the high tensile block has a ceramic tip for engagement with the surface. The preferred piezostack actuator includes a poled element.

Abstract: An acoustic rotor monitor that is an autonomous self-powered measurement instrument which can detect embedded and hidden fatigue cracks in remotely inaccessible devices such as helicopter rotor system components. A predictive maintenance-related problem for rotor craft is the detection of fatigue cracks as a continuous real-time monitoring process under dynamic rotor system loading conditions. The rotor monitor focuses on the embedding an acoustic emission-based smart sensor directly into the rotor system to measure the high frequency stress waves indicating that a structural crack has propagated as a “self-powered” measurement without reducing structural integrity.

Abstract: A damaged turbine rotor wheel dovetail is repaired by cutting off the annular dovetail and welding a new forged ring onto the remaining wheel body. Fine-line welding is accomplished by inserting welding apparatus into grooves opening through axial faces of the wheel body and ring and rotating the rotor to provide multiple welding passes. Periodic ultrasonic inspection of the welds is provided by applying an ultrasonic transducer to the periphery of the ring to detect defects in the weld. To enable the transducer to operate at high welding temperatures, a manifold is disposed about the transducer defining a coolant cavity. Cooling medium is supplied the coolant cavity to maintain the transducer operable within predetermined temperature operating limits.

Abstract: An acoustic rotor monitor that is an autonomous self-powered measurement instrument which can detect embedded and hidden fatigue cracks in remotely inaccessible devices such as helicopter rotor system components. A predictive maintenance-related problem for rotor craft is the detection of fatigue cracks as a continuous real-time monitoring process under dynamic rotor system loading conditions. The rotor monitor focuses on the embedding an acoustic emission-based smart sensor directly into the rotor system to measure the high frequency stress waves indicating that a structural crack has propagated as a "self-powered" measurement without reducing structural integrity.

Abstract: An active damage interrogation (ADI) system (and method) which utilizes an array of piezoelectric transducers attached to or embedded within the structure for both actuation and sensing. The ADI system actively interrogates the structure through broadband excitation of the transducers. The transducer (sensor) signals are digitized and the transfer function of each actuator/sensor pair is computed. The ADI system compares the computed transfer function magnitude and phase spectrum for each actuator/sensor pair to a baseline transfer function for that actuator/sensor pair which is computed by averaging several sets of data obtained with the structure in an undamaged state. The difference between the current transfer function and the baseline transfer function for each actuator/sensor pair is normalized by the standard deviation associated with that baseline transfer function.

Abstract: An apparatus and method for determining the dynamic response of a physical structure is disclosed. A single sheet of a piezoelectric polymer film, preferably polyvinylidene fluoride, or PVDF, is coated on one side with a thin layer of conductive material to serve as a ground electrode. The other side of the sheet is coated with a thin layer or conductive material in a non-contiguous pattern of individual electrodes defining an array of discrete piezoelectric transducers. Sensor leads are connected to each individual electrode and lead to a signal processor which includes associated software for determining from the processed electrical signals relative strain amplitudes of the surface area of a physical structure onto which the sheet is attached. The resulting output can be used to record strain time histories for later processing or, more simply, to show the time-averaged, steady state strain response of a structure.

Abstract: A method and apparatus for evaluation and inspection of a composite-repaired structure generates a frequency-varying electrical signal to test and evaluate the composite-repaired area. The electrical signal is converted into a mechanical signal and transmitted through the composite-repaired area of the structure. The transmitted mechanical signal is received and converted into an electrical signal for processing. The processed signal is compared with a baseline reference signal to determine whether the composite-repaired area is damaged or undamaged. The baseline reference signal is obtained at the time of the composite repair of the structure.

Abstract: The present invention is directed towards an aircraft engine testing tool which facilitates the visual inspection of aircraft internal engine blades by permitting the automatic repositioning of the internal engine blades to an inspection orientation. The aircraft engine testing tool includes a power driver structured to selectively and in a precisely controlled manner turn internal engine and which includes a gear down assembly that produces substantial amounts of low speed torque, and a gear spline connected to the gear down assembly and structured to rotate at substantially low speeds in accordance with the low speed torque produced by the gear down assembly. A mounting plate secures the gear spline operatively within an aircraft engine gear socket such that the low speed rotation of the gear spline results in a corresponding rotation of a plurality of the internal engine gears of an aircraft engine's constant speed drive and therefore the internal engine blades.

Abstract: A method and apparatus for non-destructive inspection of complex structures employs a portable laser based ultrasonic transducer 600 output to rapidly detect and size flaws in such structures, including the radii of composites, laminates, and complex skin/substructure assemblies, such as airplane wings. A fiber optic delivery system 610A is employed with the laser based ultrasonic transducer 600 and a thermoelastic medium to rapidly and accurately access the radii of complex structures in the field without the need for liquid or gel couplants, with the thermoelastic expansion of the test piece 680 producing mechanical stresses that initiate detectable sound waves regardless of the angle of the laser based ultrasonic transducer 600 output with respect to the test piece 680. A MAUS III scanning device may be employed to detect these sound waves and provide accurate information as to the detected flaws.

Abstract: A method and apparatus for evaluation and inspection of a composite-repaired structure generates a frequency-varying electrical signal to test and evaluate the composite-repaired area. The electrical signal is converted into a mechanical signal and transmitted through the composite-repaired area of the structure. The transmitted mechanical signal is received and converted into an electrical signal for processing. The processed signal is compared with a baseline reference signal to determine whether the composite-repaired area is damaged or undamaged. The baseline reference signal is obtained at the time of the composite repair of the structure.

Abstract: Operability of aircraft mechanical components is monitored by analyzing the voltage output of an electrical generator of the aircraft. Alternative generators, for a turbine-driven rotor aircraft, include the gas producer turbine tachometer generator, the power turbine tachometer generator, and the aircraft systems power producing starter/generator. Changes in the peak amplitudes of the fundamental frequency and its harmonics are correlated to changes in condition of the mechanical components.

Abstract: A force-generating actuator connected at or across points of a structure capable of relative motion at an exciting frequency is operated to input a predetermined load into the structure and the response of the structure is measured for analysis. In one form of the invention the actuator is one of a plurality of actuators of an active vibration control system which is isolated and operated independently in a shake test mode. Advantageously, especially in a helicopter application, the remaining actuators can continue to be operated to reduce background vibration.

Abstract: This invention monitors data produced by a vibration reducing system relating to the vibration of a structure, compares the data against a predetermined value and provides a warning if the predetermined value is exceeded to provide an integrated vibration reducing and structural health monitoring system.

Abstract: A system for locating a fatigue point on a structure (10) employing a smart sensor patch (12) having three triangularly adjacent acoustic sensors (40 a,b,c). The smart sensor patch (12) has a local processor (34) associated therewith, which triangulates the location of the fatigue point.

Abstract: A method and device for measuring higher mode vibrational energy is provi. The device includes a plurality of sensors placed with uniform spacing around the circumference of a structure and a processing unit. The sensor placement may be either on the inside or the outside of a structure depending on the structure and on the experiment. In operation, signals from individual sensors, preamplified if required, are fed to processing equipment. The processing equipment performs a double Fast Fourier Transform. The first transform is done on temporal data thereby providing an output representing a frequency spectrum. The second transform is performed on simultaneous data readings from all sensor locations thereby providing an output representing a spectrum of mode numbers. The combining of these outputs provides a three-dimensional plot of amplitude versus frequency and mode number.

Abstract: A system is disclosed for monitoring a structure and detecting disturbances and faults associated with such structure. The system includes an actuation device for mechanically exciting the structure, a sensing device for transducing vibrations experienced by the structure, and digital signal processing means for processing signals output by the sensing device. The response of the structure due to the mechanical excitation is analyzed and a baseline or normal response is determined. Vibrations of the structure are then analyzed and compared to the normal response of the structure and the nature of disturbances identified. Another aspect of the invention relates to a system for monitoring cracks, strains and the like and includes a continuity/strain sensor having a piezoelectric layer, and first and second low resistance layers. By suitably monitoring sensors in accordance with the invention, the magnitude as well as the location of a force can be determined.

Abstract: A vibration monitoring system employing a capacitive accelerometer determines the energy associated with one or more frequency components within the frequency spectrum of the vibration signal. The capacitive accelerometer operates as a mixer due to its time varying capacitance which provides a measure of the vibration. When the accelerometer is excited by an AC signal the output from the accelerometer comprises beat frequencies due to the mixing of the time varying capacitance and the AC signal. By changing the frequency of the AC signal the location of the beat frequencies in the frequency domain of the accelerometer output can be shifted. Subsequent bandpass filtering to attenuate frequencies except those associated with the frequency component and demodulation to bandshift the energy of the filtered signal energy to DC, creates a DC value which provides a measure of the energy present at the frequency component.

Abstract: So as to control parts of any form, such as panels made of a composite material, a control head (10) is used comprising a small bar made of an elastic material, aligned ultrasonic transducers (18) being placed in said control head which functions by reflected light. The small bar bears contact blocks (22,24) which are brought into support on the surface of the part to be controlled, which has the effect of deforming the small bar and orientating each of the transducers perpendicular to the surface. As regards parts having a non-uniform shape, a uniform quality of the control is thus ensured, the same applying for a reduction of the control time. A precise control of the evolution of the structure of parts during production is also rendered possible. Advantageously, the transducers are mounted on the small bar so as to be disassembled, said mounting being effected by means of wedging members, such as screws and metal wire clips.

Abstract: Vibrational data is compressed about 8.5 to 18 times by isolating a low frequency component from the signal, frequency analyzing the signal to obtain important frequency/amplitude data, and recombining the low frequency component with the analyzed information for efficient transmission.

Abstract: A novel system for determining the magnitudes of loads on rotating helicopter components from signals remotely measured on the helicopter fuselage is characterized by a processor which decomposes the measured signals into corresponding Fourier components and extracts selected components therefrom. A programming module performs a multiplication on the respective Fourier components to correlate the measured components with corresponding determinative parameter values. The parameter values are established in a calibration process which is characterized by determination of the independent values of a measured signal set using a Jones orthogonalization process. The signals output from the coefficient programming module are provided to a multiplying resolver which receives synthesized reference sinusoids from a digital processor and generates time dependent signal components therefrom. These signals are ultimately summed in an analog summer circuit whose output signal corresponds to the desired parameter signal.

Abstract: The present disclosure describes an apparatus and a method for inspecting the degradation of a gas nozzle. The nozzle is of the type that can produce a whistle when a gas is blown through the nozzle. The method comprises the steps of detecting an acoustic signal emitted by the nozzle when the gas is blown through the nozzle, the gas having a pressure selected to produce an acoustic resonance at a certain frequency; generating an electrical signal responsive to the detected acoustic signal; band pass filtering the electrical signal at the frequency; and detecting the amplitude of the electrical signal at the frequency. The method also comprises the steps of comparing the amplitude of the electrical signal with a reference amplitude corresponding to a reference nozzle; and displaying a signal indicative of the degradation of the nozzle according to the signal resulting from the comparing step.

Abstract: A flutter exciter induces vibration either for actual aircraft flight testing or for wind tunnel model testing. The basic flutter exciter unit is a pair of rotatable concentric cylinders mounted on either a fixed vane or an aircraft wing or a tail surface. Each cylinder has a slot which allows the air flow to pass therethrough. By rotating the cylinders together, oscillating air pressures are induced on the fixed vane or the aircraft surface to which the cylinders are attached. The cylinders may be mounted at a trailing edge of either the fixed vane or the aircraft wing, to any tail surface, or on any other lifting surfaces of the aircraft itself. Thus, because the flutter exciter can be made as a completely self-contained unit, it may be simply mounted to any suitable hard point on either the test model or the aircraft. The power required to rotate the slotted cylinders is minimal, thus allowing the use of a low wattage motor.

Abstract: It is common practice to pass an ultrasonic probe over a workpiece so as to enable examining of the material for faults such as flaws within the material thickness. Known apparatus for achieving this has a drawback in that the probe supporting structure is such that the probe oscillates about some point within its length, as the structure passes over curved or undulating surfaces. Control over the position of the focal point is thus lost. The invention involves ensuring that the pivot point of the probe coincides with its focal point which in turn enables control of the position of the focal point to be maintained.

Abstract: Apparatus for continuously orienting an ultrasonic transducer so that the emitted ultrasonic waves remain at a normal angle of incidence to the opposing surface of an object while the transducer is being moved laterally across the surface in order to inspect the subsurface composition of the object. The sensor casing which contains the ultrasonic transducer pivots about one end of a tubular support arm, while the other end of the support arm pivots about a gearbox casing. A drive shaft passes through the support arm and has a miter gear on each end. One miter gear is engaged with a miter gear attached to the gearbox casing, and the other is engaged with a miter gear attached to the sensor casing so that the rotation of the drive shaft causes the simultaneous rotation of the support arm about the gearbox casing and, in the opposite direction, the rotation of the sensor casing about the support arm. The gearbox casing is attached to a carriage and has the freedom to roll relative to it.

Abstract: A portable acoustic impedance measuring device 10 is provided for measuring the impedance properties of a panel 12. The device 10 includes a horn section 14 having a flexible plate 18. The plate 18 can assume the curvature of the duct panel 12. The horn section 14 is supported adjacent the panel's surface by a spindle shaft 28 which spans or bridges the inside diameter of the duct 12. The curvature of the plate 18 may be locked to hold the curvature of any of a variety of different panels having various sizes and shapes.

Abstract: A signal classifier system is disclosed that includes an on-line apparatus for monitoring various electrical signal inputs derived from vibration signals without data interruption, and providing an output from each of several levels of classifications. Classification is by a three-level classification algorithm. A first level of classification provides for the independent processing without structural or operational information of each signal input. The output of the first level is stored according to a strain gauge in a spatial file. The second level of classification provides a combination of the output of the spatial file with structural information (such as compressor structural information) and on-line operational information to provide an output indicative of event probabilities which are stored.