Abstract: The invention is an apparatus which allows selective testing of aircraft or other vehicular components without requiring disassembly of the vehicle or components. The invention consists of a broad-band noise source 11, a guide 12 to direct the acoustic energy, soft sealing insulation 17 to seal the guide to the noise source and to the vehicle component, and noise measurement microphones 13, 14, both outside the vehicle at the acoustic guide output and inside the vehicle to receive attenuated sound. By directing acoustic energy only to selected components of a vehicle via the acoustic guide, it is possible to test a specific component, such as a door or window, without picking up extraneous noise which may be transmitted to the vehicle interior through other components or structure. This effect is achieved because no acoustic energy strikes the vehicle exterior except at the selected component.

Abstract: A rotor blade test apparatus having a striking solenoid to strike a rotor blade to generate an audio signal. A microphone receives the audio signal and applies it to a spectrum analyzer wherein the predominant natural frequencies of the rotor blade are determined.

Abstract: The apparatus comprises one or more acoustical transducers associated with a particular interchangeable rotor blade for monitoring acoustic emissions emitted by the rotor blade under operating stress. The output of the transducers is connected to a computer associated with the particular aircraft. The transducer output signals are processed by the computer and filtered to allow real time stress return level readings so as to accumulate a count of critical acoustic emissions which are indicative of progressive irreversible structural fatigue or damage to the interchangeable rotor blade.

Abstract: A dark-field magneto-elastic non-destructive testing technique for detection of defects in a conductive material by inducing eddy currents or applying an electric current to the material along a path in such manner that the current will be diverted from the path in the vicinity of any material defect, causing the generation of acoustic waves locally from the interaction of the diverted current with a local magnetic field. The resulting acoustic waves are detected as an indication of the presence and location of a material defect. In typical application, a current is induced in the conductive material by the generation of eddy currents in the material along a substantially linear path by coupling from a current excited wire insulated from and applied near the surface of the material. The eddy current will tend to follow substantially the direction opposite of the current excited wire.

Abstract: A vibration monitoring system for aircraft engines includes a nonrecursive digital filter network controlled by a data processor. Digital techniques process tachometer signals to general sampling signals at a frequency which is an integral multiple of the rotating frequency. A novel digital filter can track the rotational frequency of the rotating component and can be accurately centered upon that frequency. The digital filter includes a pair of memories, one of which stores constant coefficients and the other of which stores sampled data. The sampled data storage can accommodate the output of more than one sensor and data from each sensor can be alternatively processed.

Abstract: Workpiece loading, particularly for dynamic testing of aircraft wings, is described. A double ended servo jack is drivably coupled to an upper drive lever which is pivotally mounted for movement relative to the workpiece. The follower end of the upper drive lever is coupled by a tension strap to a lower drive lever. The drive ends of the upper and lower levers are coupled to contour boards provided around the wing by means of whiffle trees so that the single jack applied both upwards and downwards forces to the wing.

Abstract: A variable frequency vibration controller includes a cantilever beam supported from the vibration prone structure whose vibrations are to be controlled. The cantilever beam has selectively shaped hollow interior portions into which fluid can be selectively injected or withdrawn to vary the total mass of the cantilever beam. The cantilever beam natural frequency is thus tuned to match or selectively mismatch the frequency at which the vibration prone structure is vibrating. Thereby, the beam is used to optimally absorb or excite the vibrations of the structure.

Abstract: Acoustic intensity measuring apparatus for determining sound energy intensity utilizing a probe having a pair of microphones and an associated ambient noise shield.

Abstract: A system for measuring resonance frequencies in turbine and compressor vanes and propeller blades in which a vane or blade is excited at its base by a vibration generator and the phase of the excitation signal coming out of an acoustic transducer placed at the base is compared to that of the signal coming from a displacement transducer placed at the blade tip. The resulting phase error signal serves to pilot a variable-frequency oscillator which itself feeds the vibration generator, the frequency of which is noted by a frequency meter.

Abstract: An improved procedure for collecting experimental data reflecting the behavior of a time varying aerodynamic parameter at an airfoil in a cascade of airfoils vibrating harmonically in a fluid stream including the steps of vibrating the center airfoil of the cascade at a selected frequency and amplitude while each of the other airfoils is held rigid, measuring the time varying parameter at the center airfoil and expressing it as a function of the position of the center airfoil in its vibratory cycle, vibrating each of the other airfoils in turn at the selected frequency and any amplitude while maintaining all the remaining airfoils rigid, measuring the time varying parameter at the center airfoil for each individual airfoil vibration and expressing the measurement as a function of the position of the individual vibrating airfoil, expressing the position of each individual vibrating airfoil as a function of the position of the center airfoil, and combining the time varying parameter expressions and position exp

Abstract: Some turbine blades are produced by casting, using the lost wax process. The blades may include cooling air passages and the wall thickness of these is tested ultrasonically i.e. by transmitting and receiving acoustic pulses from and to, a common transducer.Lately the blades, having been cast, are directionally solidified. This process changes the grain structure such that during inspection, pulses received by the blade, have been dissipated. The invention provides ultrasonic testing ability by using a unidirectional pulse transmission system, resulting in pulses which, having passed outwards through the passage wall, still have sufficient energy to effect an indication of wall thickness.

Abstract: A test procedure and test apparatus is described for measuring the degradation in the physical integrity of a structural part by measuring the rate of decay of the amplitude of vibration of the part after it has been set into vibration at its free resonant frequency mode. The presence of invisible imperfections in the part such as may occur as a result of metal fatigue or from the development of tiny flaws or cracks will cause an increase in the rate of decay of the amplitude of vibration of the part. By making periodic measurements of the rate of decay of a structural part which is used in a critical highly stressed application subject to vibration such as a jet engine mount, the periodic degradation due to fatigue can be determined and the part is removed from service at a safe period before the degradation reaches an unsafe limit.

Abstract: A method for controlling the first torsional node line position in a rotatable blade of a turbomachine to improve its flutter stability including the steps of forming a first monolithic blade having a desired airfoil shape with convex and concave side walls; arranging several of the monolithic blades in a cascade array and subjecting the cascade array to an unsteady, supersonic, transonic and subsonic flow condition thereacross and thereafter determining the unsteady surface pressures acting on the monolithic blades; independently determining the first torsional mode vibration node line of each of the monolithic blades and comparing the resultant unsteady pressure force on the monolithic blades and its relationship to the first torsional mode vibration node line to determine whether or not the monolithic blade is absorbing or adding energy to the air flow thereacross; thereafter forming a plurality of first and thereafter modified composite blades by adding dissimilar material to the blade shape of a monolith

Abstract: A method and system for monitoring the angular deformation of structural elements in a composite structure in response to imposed mechanical vibrations in which the structure is part of the monitoring system.A plurality of angular motion signal generating sensors are provided at different selected locations in a composite structure, each sensor being associated to a corresponding structural element. Signals output from the sensors in response to vibrations propagated within the composite structure are detected and a vibration signature for the entire structure is established. The sensor outputs are subsequently monitored and compared with the previously established vibration signature to detect differences therebetween designating changes in the vibration response and potential structural failures.The angular motion sensors employ a magnet and a coil in which a voltage and current are induced in response to angular deflections of the structural member to which the sensor is attached.

Abstract: An improved holographic recording instrument for recording on a holographic recording medium two successive holograms of the structure under differing stress conditions to produce a holographic interferogram containing information defining a deformation fringe pattern representing the deformations in the structure resulting from the change in stress conditions. A holographic recording unit for the instrument and for general holographic recording use.