Abstract: A Coriolis rate sensor for determining both angular rate and linear acceleration with respect to three orthogonal axes. A first embodiment of the rate sensor (10) includes three pairs of accelerometers (26, 28, and 30) mounted on counter-rotating frame members (20, 22). The accelerometers are mounted with their sensitive axes antiparallel with each other, forming an acute angle with the common axis (40) about which the upper and lower frame members are counter-rotated back and forth in a dither motion. The upper and lower frame members are connected to a baseplate (12) by flex links (32), which are aligned radially about the axis. The flex links provide a relatively rigid support (in compression) between the frame members and the centrally disposed baseplate, yet readily permit counter-rotation of the two frame members. A link (56) prevents all but relative rotational movement between the frame members and baseplate.

Abstract: A warning system for rotary wing aircraft compares the accumulated altitude loss after take-off of the aircraft with its altitude above ground, and generates a warning if the altitude loss is excessive for the altitude above ground at which the aircraft is flying. The position of the landing gear, the speed of the aircraft and its altitude enable the system only during the take-off and missed approach phases of operation in order to minimize nuisance warnings during other phases. The relationship between radio altitude and altitude loss required to generate a warning is optimized for rotary wing aircaft such as helicopters.

Abstract: The apparatus includes a parallelogram frame (50) including two accelerometer support surfaces (24, 26) on which are mounted two accelerometers (20 and 22) having their sensitive axes in parallel alignment. The accelerometer support surfaces are connected to opposite ends of a flex member (52), which includes six flexures (32, 34, 36, 38, 40, 42) having parallel bending axes. Two of the flexures (34, 38) are disposed at opposite ends of one side of each flexure member, and have a "long" axis that is substantially parallel to the sensitive axes of the accelerometers and aligned with a line connecting their centers of percussion. The centers of mass of the accelerometers and their associated supporting surfaces are coincident with the centers of percussion, and are rigidly connected by the two flexures and by one side (30) of each flex member. This solid metal path between the centers of percussion minimizes common mode errors.

Abstract: Disclosed is a borehole survey system that utilizes strapdown intertial navigation techniques for mapping a borehole while the system probe (10) is continuously moved along a borehole (12) by means of a cable (14) that is wound on a cable reel (16). Signals representative of the acceleration of the probe (10) relative to the three axes of a probe body coordinate system (34)) and signals representative of angular rotation of the probe (10) about the three axes of the probe body coordinate system are processed within a signal processor (24) to obtain signals that represent probe velocity and probe position in a level coordinate system (36) that is fixed in orientation relative to the geographic location of the borehole (12).

Abstract: A crystal controlled oscillator in which changes in damping are compensated and a method for decoupling the output signal of such an oscillator from damping changes. The damping decoupled oscillator includes a quartz crystal (10), which produces a periodic signal, connected in series with a variable gain amplifier (18) and a variable phase shift circuit (22). Feedback from the output of the variable phase shift circuit is provided to sustain oscillation of the crystal. Unity gain in the loop is maintained by adjusting the gain of the variable gain amplifier in accordance with the DC value of the output signal, provided by a precision rectifier (34). As the DC value of the output signal changes due to changes in damping or energy loss of the crystal, an absolute value circuit (38) responds by providing a phase control signal for adjusting the phase of the periodic signal to compensate for changes in damping.

Abstract: A Coriolis rate sensor comprising first and second accelerometers mounted with their force sensing axes parallel to a common sensing axis. The accelerometers are vibrated along arcs in response to a periodic drive signal at a first frequency, each arc being tangent to a vibration axis normal to the sensing axis. The accelerometer output signals are demodulated to determine angular rate, as well as to detect the phase shift between the drive signal and the periodic compounds of the output signals. In one arrangement, the detected phase shifts are used to drive a phase servo that tends to reduce the bias error caused by interaction between the phase shifts and misalignments of the accelerometers with respect to the sensing axis. In another arrangement, the phase shifts are used to calculate a bias term for correcting the measured angular rate. A single accelerometer embodiment is also described.

Abstract: A system and method for precisely and continuously estimating the path length between the entrance of a borehole and a probe (10) which is supported by an elastic cable (14) and carries a gyrocluster (42) and accelerometer cluster (40). The precise estimate of borehole path length is used to aid the inertial navigation performed within the survey system and is selectively determined by integration of either the rate at which the probe (10) moves along the borehole or a compensated cable feed rate that is based on the rate at which the cable (14) passes into or out of the borehole with correction being made for changes in temperature and gravity induced cable stretch. Selection of the rate to be integrated at any given time being determined by whether the rate at which probe (10) moves along the borehole exceeds the compensated cable feed rate by a predetermined amount.

Abstract: A ground proximity warning system especially adapted for a tactical aircraft provides the pilot with a warning in the event that the closure rate is excessive for the altitude above ground at which the aircraft is flying. The descent rate of the aircraft is monitored and used to bias the closure rate warning signal to reduce nuisance warnings when the excessive closure rate is part of an intentional maneuver such as a dive during a tactical mission.

Abstract: An aircraft performance instrument which provides a first indicator which represents the line of level flight of the aircraft and a second indicator representative of the maximum permissible angle of attack of the aircraft.

Abstract: A device and method for measuring the frequency of an input signal by measuring the number of cycles of the input signal that occur in a sample interval between successive sampling times t.sub.n. An integer counter determines an estimated integer number of input signal cycles, and fraction counters determine fractional counts by counting cycles of a clock signal during time intervals between a first measurement time before the sampling time and a second measurement time after the sampling time. A correction circuit refines the fractional counts by determining the phase relationships between the clock and input signals at each measurement time. The correction circuit includes a constant current source, a capacitor, a first switch connected between the constant current source and a reference potential, a second switch connected between the constant current source and the capacitor, and a control circuit for the switches.

Abstract: An apparatus for producing signals indicative of both a Coriolis rate and an acceleration along a preferred axis while decoupling extraneous vibration and motion that would introduce errors into the signals, and a driving mechanism for vibrating the apparatus at a dither frequency. The apparatus includes a parallelogram frame (50) including two accelerometer support surfaces (24, 26) on which are mounted two accelerometers (20 and 22) having their sensitive axes in parallel alignment. The accelerometer support surfaces are connected to opposite ends of a flex member (52), which includes six flexures (32, 34, 36, 38, 40, 42) having parallel bending axes. Two of the flexures (34, 38) are disposed at opposite ends of one side of each flexure member, and have a "long" axis that is substantially parallel to the sensitive axes of the accelerometers and aligned with a line connecting their centers of percussion.

Abstract: Disclosed is an inertial navigation borehole survey system wherein the signals supplied by accelerometers (40) that are contained within the borehole survey system probe (10) are corrected for gravitational gradients encountered as the probe (10) travels through a borehole (12). The gravity correction is effected in the survey system signal processor (24) and is based on a gravity gradient signal that mathematically corresponds to: ##EQU1## where f represents the specific force due to gravity; f.sub.o represents the specific force of gravity at wellhead (20) of borehole (12); R.sub.o represents the average radius of the earth; .rho.(H) represents the local density of the geological formation penetrated by the borehole as a function of depth H; and .rho..sub.ave represents the means density of the earth. In utilizing the gravitational gradient to generate a gravity correction signal, the signal processor (24) effects a summation process that mathematically corresponds to: ##EQU2## where (.DELTA.H).sub.

Abstract: A system for warning the pilot of a rotary wing aircraft such as a helicopter of a flight condition that, if left uncorrected, would result in the tail of the aircraft striking the ground monitors the altitude above ground, descent rate, pitch and pitch rate of the aircraft and provides a warning if the relationship between the aforementioned parameters is such that a tail strike is imminent.

Abstract: An accelerometer comprising a support (52) and a proof mass (40) mounted to the support by a flexure (50) or the like, such that the proof mass can rotate about a hinge axis (HA) perpendicular to sensitive axis (SA). An isolator (42) is also mounted to the support by an isolator suspension system (60, 62) that is relatively compliant for isolator movement parallel to a transducer axis (TA) normal to the hinge axis, and relatively noncompliant for isolator rotation about the hinge axis. Force transducers (80, 82) are connected between the isolator and the proof mass. The force transducers are parallel to the transducer axis, and positioned on opposite sides of the hinge axis from one another, such that rotation of the proof mass about the hinge axis puts one force transducer in tension and the other force transducer in compression.

Abstract: Prior vibrating beam accelerometers are subject to errors caused by differential thermal expansion between the vibrating beams and other accelerometer components. This problem is overcome by the present accelerometer that comprises a housing (32), a proof mass (30), a support (34,36) for mounting the proof mass with respect to the housing, and first and second force sensing elements (38,40). The force sensing elements are connected between the proof mass and the housing such that differential thermal expansion or contraction between the force sensing elements and the proof mass, support and housing results in rotation of the proof mass about a compensation axis (CA) normal to the sensitive axis (SA).

Abstract: A circuit (62, 64) for receiving a periodic input signal at frequency f, and for producing a pseudosinusoidal staircase output signal at a fundamental frequency f from which predetermined harmonics of the fundamental frequency are absent. Also provided are an oscillator in which such a circuit forms the drive circuit for a piezoelectric crystal, and an accelerometer in which such an oscillator is used as the force sensing means. In the accelerometer, the reaction force of a proof mass (40) is sensed by a resonator that comprises a drive circuit (44) for producing a drive signal and a piezoelectric crystal (42) connected between the proof mass and support (46). In response to the drive signal, the crystal undergoes mechanical vibration at a frequency f that varies with the force applied to the crystal. A resonator signal corresponding to the mechanical vibration is produced and input to drive circuit.

Abstract: Disclosed is a combined flight data recorder data aquisition circuitry (10) and airborne integrated data circuitry (12) that can be variously packaged to supplement and update existing aircraft systems or serve as a standalone flight data recording and/or airborne integrated data system. The flight data recorder system circuitry (10) and airborne integrated data system circuitry (12) are separately programmed microprocessor based systems that are capable of processing aircraft parametric signals provided by a variety of aircraft signal sources. In the disclosed arrangement, the airborne integrated data system circuitry (12) is arranged and programmed to automatically monitor engine start and shutdown procedures, aircraft takeoff and cruise and to provide a landing report that indicates fuel consumption and landing weight.

Abstract: An accelerometer with improved resistance to errors due to thermal stress. The accelerometer comprises a proof mass assembly (44), a stator (40), and an interface member (90) that includes a plate-like body positioned between the proof mass assembly and the stator. The proof mass assembly includes a reed (72) suspended from a support (70), and a reed capacitor plate positioned on the reed. The body includes a body capacitor plate (94) positioned to form a capacitor with the reed capacitor plate. The interface member includes first mounting member (110) for securely mounting a first area of the stator with respect to a corresponding first area of the support, and a mounting element (126) extending between a second area of the stator and a corresponding second area of the support. The mounting element is relatively compliant along a first axis, and relatively rigid along all other axes. The first axis lies in the plane of the body and passes approximately through the first mounting member.

Abstract: A wind shear detection and alerting system (30) compares inertially derived accelerations with air speed rate to provide a wind shear warning signal. Inertially derived accelerations are used instead of purely inertial accelerations because purely inertial systems generally require a vertical gyro. By utilizing angle of attack (.alpha.) and flight path angle (.gamma.) instead of pitch angle (.theta.) in the calculation, no vertical gyro signal is required and the system will be responsive to vertical as well as horizontal shear conditions. An enhanced version of the system is also compensated for roll angle (.phi.), with the roll angle being derived from the rate of change of heading (.PSI.) to avoid the need for a vertical gyro. The alerting system is capable of providing visual and aural warnings for a variety of wind shear conditions, such as, head shear, tail shear, head shear followed by tail shear and wind shear trend.

Abstract: The invention provides independent guidance and monitoring integrated into an MLS landing system and a scaled-down MLS take-off or missed approach guidance system useable at small airports. An added fixed beam precision guidance system is integrated into the MLS time sequence format. The fixed beam guidance system is based upon the concept of using paired fixed overlapping beams, sequentially radiated by different fixed antennas (80 and 81), oriented to left and right of a prescribed guidance path. The paired beams overlap at the prescribed guidance path in such a manner that an aircraft departing or making a missed approach on such path will intercept equal signal intensities to indicate an on-course condition.