Abstract: An accelerometer with a pivoting beam to accommodate differential thermal effects. The accelerometer measures acceleration along a sensitive axis, and comprises a housing, a proof mass, support means and a coupling assembly. The support means mounts the proof mass with respect to the housing. The coupling assembly is connected to the proof mass and housing, and comprises a beam and first and second force sensing elements. The beam is mounted for pivotal movement about a compensation axis normal to the sensitive axis. The first and second force sensing elements are connected to the pivot member at spaced-apart connection points on opposite sides of the compensation axis from one another, such that an acceleration along the sensitive axis results in respective compression and tension forces on the force sensing elements, and such that differential thermal expansion results in rotation of the beam about the compensation axis.

Abstract: A system for determining angular rate of rotation of a body about a rate axis. In one arrangement, the system comprises first (10) and second (12) accelerometers, movement apparatus and processor. The first and second accelerometers have their sensitive axes (16, 18) parallel to a sensing axis that is in turn perpendicular to the rate axis. The first and second accelerometers produce first and second output signals (a.sub.1, a.sub.2), each output signal having a frequency corresponding to the acceleration experienced by the respective accelerometer along its sensitive axis. The movement apparatus includes a generator (68) for producing a periodic movement signal and a mounting system (14) responsive to the movement signal for periodically moving the accelerometers along a movement axis perpendicular to the rate and sensing axes, such that each output signal includes a periodic Coriolis component.

Abstract: A dual sensor, frequency output accelerometer that does not require either high sampling rates or mechanical matching of the sensors to achieve high levels of accuracy. In one embodiment, the accelerometer comprises a first sensor (12, 14, 16) that produces an output signal S.sub.1 having a frequency f.sub.1 related to acceleration along the sensitive axis, and a second sensor (18, 20, 22) that produces a second signal S.sub.2 having a frequency f.sub.2 related to acceleration along the sensitive axis, the sensors being arranged such that a given acceleration causes the frequency of one output signal to increase and the frequency of the other output signal to decrease. Velocity change .DELTA.V during time interval T is determined according to:.DELTA.V=A[.DELTA..phi.+FT+B.SIGMA..phi.]where A, F and B are constants, .DELTA..phi.is the difference between the phase changes of the output signals over time interval T, and .SIGMA..phi. is the sum of the phase changes of the output signals over time interval T.

Abstract: Prior mounting systems for tuning fork temperature sensors have resulted in unpredictable activity dips within the sensor operating ranges. This problem is eliminated by the mounting and isolation system (32) of the present invention that is adapted to mount temperature sensitive tuning fork (20) to a support structure. The mounting system comprises a mounting member (34) adapted for rigid connection to the support structure, and support means (36) connecting the tuning fork base to the mounting member such that the tuning fork is supported solely by the support means. The support means comprises a low pass mechanical filter that transmits only vibration frequencies that are less than the operating range of frequencies of the tuning fork.

Abstract: A mounting and mounting method for a sensor positioned within a tubular axle of an aircraft undercarriage which will provide an output voltage proportional to the angular deflection of an axle for computation of aircraft gross weight. The sensor is not affected by cross-sectional distortions of the tubular axle under loading, undersirable shear frictional effects at the interface between the sensor mounting and the tubular axle and differential angular deflections of the axle.The cylindrical mounting member for the sensor has a pair of O-rings adjacent opposite ends thereof which are positioned to space the periphery of the mounting member from the bore of the tubular axle and which are under radial compression and act to provide uniform radial compressive forces applied about the full circumferential periphery of the cylindrical mounting member and absorb distortions of the axle by elastic deformation thereof.

Abstract: An accelerometer comprising a proof mass assembly that includes a reed suspended from a support and a cylindrical coil mounted to the reed by a mounting system that minimizes errors due to thermal stress. The mounting system comprises at least three mounting elements. Each mounting element has first and second ends, and a resilient intermediate portion. The first end of each mounting element is connected to the coil, the second end of each mounting element is connected to the reed, and the intermediate portion of each mounting element provides a low resistance to relative movement between the coil and reed in a radial direction, and a high resistance to relative movement between the coil and reed in directions normal to the radial direction. The reed preferably comprises fused quartz, and the mounting system preferably comprises a fused quartz base mounted directly to the reed and connected to the second end of each mounting element.

Abstract: Solid state memory devices employed in crash survivable flight data recorders must be thermally insulated to prevent loss of stored data if the aircraft burns. To provide adequate thermal isolation at minimal size, the solid state electronic memory devices (26) are encapsulated in a synthetic organic wax or pentaerythritol (28) that exhibits a phase transition at a temperature: (a) above the normal operating temperature of the memory unit (10); and below the maximum acceptable peak temperature for the memory devices (26). The synthetic organic wax of pentaerythritol (28) is surrounded by a thermal liner (18) constructed of solid thermal insulating material. A metal enclosure (12) houses and protects the thermal liner (18), the synthetic organic was or pentaerythritol (28) and the memory devices (26).

Abstract: A timing circuit adapted for use in a digital system that includes a raster scanned display device (14) adapted to scan a beam through a series of horizontal scan lines at a rate controlled by a horizontal sync signal. Each horizontal scan line comprises dots that can be individually illuminated. The time required for the beam to horizontally scan one dot is controlled by a dot clock signal. The digital system also includes means for producing row format data indicating the relationship between the horizontal sync signal and the time requried to horizontally scan one character area, and dot per character data indicating the horizontal dot width of one character area. The timing circuit comprises a generator (52) for producing a horizontal reference signal having a frequency corresponding to the desired frequency for the horizontal sync signal, and a phase lock loop for producing the horizontal sync and dot clock signals.

Abstract: An aircraft ground proximity warning system having an excessive terrain closure warning mode and a below glide slope warning mode monitors the glide slope signal and modifies the terrain closure warning envelope to accept a lesser terrain clearance when the aircraft is within the glide slope beam.

Abstract: In a single-frequency precision guidance landing system, the use of a DME interrogator in the aircraft and a DME receiver at the ground installation, each tuned to the same DME channel frequency, to uniquely interrogate a selected ground station and hence identify it by virtue of its replies being synchronous in the aircraft with the interrogations, the interrogations and the replies also being used to obtain range to the ground installation. This technique uses airborne already-installed DME interrogators for selective interrogation of a desired landing installation, thereby to eliminate any need to add additional special purpose equipment to the aircraft to accomplish the desired uniqueness of interrogation and ground installation identification achieved by this invention.

Abstract: An inertial sensor assembly (ISA) includes a cluster of three ring laser gyros, each gyro producing an output signal having a pulse repetition rate representative of the rate of angular deviation of the ISA about one of three coordinate axes X, Y, and Z. The ring laser gyros are synchronously dithered at a relatively constant rate. The ISA also includes a triad of three accelerometers, with each accelerometer producing an output signal representative of the rate of velocity deviation of the ISA along one of the X, Y, and Z coordinate axes. A first processor, P1, accumulates the pulses produced by each ring laser gyro over its dither period. The resultant counts are stored in registers for subsequent sampling by the P1 processor at a periodic sampling rate which is greater than the dither rate. The P1 processor then synchronizes each sampled pulse count to a common sampling interval, thereby eliminating errors otherwise caused by using positional data values taken at different times.

Abstract: A ground proximity warning system utilizes geographic position data to alter the warning criteria as is required by the terrain features of particular geographic areas. To determine whether the aircraft is within a particular geographic area, the world is subdivided into latitude bands that are in turn subdivided into non-overlapping zones by predetermined lines of longitude, with the position of each zone being defined by the latitude and longitude coordinates of one of its corners. The zones are further defined by regions which may overlap other zones. The regions are limited in size, and their positions are also defined by the locations of one of their corners. The regions are further subdivided into one or more geographic areas that are defined by their shapes and locations within the region.

Abstract: A borehole survey instrument has a probe with a polarized light system for transmitting a signal representing the angular orientation of the probe to the surface. Light from a source in the probe is directed through a polarized filter with an axis of polarization orthogonal to the longitudinal axis of the probe. The polarized light beam is transmitted to the surface through an optical fiber light conduit. The angle of polarization is detected with a rotating polarizing filter and provides a measure of the probe orientation. In surveying a borehole, azimuth is determined from inclinometer measurements. The probe orientation in vertical sections of the borehole is measured by the polarized light system. Two measures of borehole azimuth are combined, providing an improved measure of azimuth in boreholes near vertical and near horizontal.

Abstract: A system for determining the closest navigation point to an aircraft utilizes a sphere of influence principle wherein the earth is subdivided into a plurality of geographic areas, for example, one quarter degree squares of latitude and longitude. An identifier such as an index number of the closest navigation point to each square is stored in a look up table. Position information from the navigation system of the aircraft is used to address the look up table to retrieve the appropriate index number which is then used to address a second look up table that contains information defining the closest navigation point.

Abstract: An angular rate sensor comprising a pair of accelerometers that includes means for continuously nulling error signals resulting from misalignment of the accelerometers. The first accelerometer (10) has a first force sensing axis and produces a first output signal (a.sub.1) indicating acceleration along the first force sensing axis. The second accelerometer (12) has a second force sensing axis and produces a second output signal (a.sub.2) indicating acceleration along the second force sensing axis. The accelerometers are mounted by mounting means such that their force sensing axes are both parallel to a common sensing axis and such that the accelerometers can be moved along a vibration axis normal to the sensing axis. A signal generator (76) produces a periodic deive signal having a predetermined frequency, and drive means (80, 82, 84) connected to the mounting means is responsive to the drive signal for vibrating the first and second accelerometers along the vibration axis at the predetermined frequency.

Abstract: Prior power supplies adapted to provide power to the lasers of multiple ring laser gyros were inefficient in that they were required to have power output capabilities far in excess of that required to sustain laser operations. Such inefficiency is greatly reduced by the present power supply comprising a DC power source (30) for producing a firing voltage at a first terminal (40) and a sustaining voltage at a second terminal (42), and interface means (50) associated with each laser (12, 13, 14) for coupling the laser to the first and second terminals. The firing voltage is capable of firing each laser, and the sustaining voltage is capable of sustaining current flow through each laser after firing. Each interface means comprises a resistor (52, 53, 54) connecting the laser to the first terminal and a diode (55, 56, 57) for connecting the laser to the second terminal such that the diode does not permit current flow between the first and second terminals.

Abstract: A data acquisition system for use in an aircraft flight data recorder receives multiple analog and discrete signals representative of various aircraft parameters. A single address command from the flight data recorder central processing unit (CPU) causes a first multiplexer to select a set of analog signals. Each selected analog signal is amplified by a gain factor under CPU control and passed to track-and-hold circuitry which holds a level of the amplified analog signal upon receipt of a suitable command. The held analog signal levels are passed to a second multiplexer which also receives a set of discrete signals selected by a third multiplexer in response to a CPU address command. A control sequencer sequentially passes each signal at the input of the second multiplexer through an analog-to-digital converter, with the resultant digital signal being loaded into memory.

Abstract: An independent test sight is described for a pilot's head-up display (HUD). In one embodiment, the independent test site comprises a collimator assembly and an aligned periscope assembly. The collimator assembly comprises a source of light, a reticle, and a lens for projecting the image of the reticle. The periscope assembly comprises a rhomboid prism housed within the chassis of the HUD in such a manner that it can be pivoted from a stowed position to an erect position where it projects a reticle pattern in the field of view of the HUD combiner.

Abstract: A terrain advisory system utilizes stored data representative of terrain and other obstacles in predetermined geographical areas of interest to provide advisory warnings of the proximity of terrain, obstacles and restricted areas as they are approached. When used in a vehicle such as an aircraft, the system monitors the position, altitude, ground speed, ground track and the vertical speed of the vehicle and provides advisory indications of the position and path of travel of the vehicle with respect to obstacles and terrain. Such advisory indications may take the form of voice warnings describing the nature and position of any obstacles, or a visual display showing the position of the obstacles and terrain with respect to the vehicle.

Abstract: A memory unit for a aircraft flight data recorder system uses an electronically erasable solid state memory for storing the flight data and a memory controller circuit are housed in a penetration resistant, thermally insulated enclosure. Power dissipation within the insulated enclosure is minimized by an external switching circuit that applies operating potential to the solid state memory only when data are being transferred to and from the memory circuit. A data protection circuit, located within the insulated enclosure inhibits memory write and erase operations whenever the system operating potential falls below a predetermined level. In continuously storing flight data, the oldest stored data is overwritten with newly arriving flight data and the memory controller maintains an erased boundary that defines the beginning and end of the recorded data. A power monitor circuit, located outside the insulated enclosure, resets the memory controller to the erased boundary following a power interruption.