601,051. Turn sensitive devices. SPERRY GYROSCOPE CO., Inc. Nov. 13, 1942, No. 16111. Convention date, April 10, 1941. [Class 97 (iii)] [Also in Group XXXVIII] An instrument for providing information concerning the angular movement of its mounting such as an aircraft comprises an element maintained in continuous vibration constant in direction or pattern in the absence of the disturbing effect of force or movement and means for detecting and indicating departure of the vibratory motion of the element from the constant direction responsive to said force or movement. Figs. 1 and 2 show a directional indicator comprising an outer casing 1 having secured to it a base 27 to which is clamped a vertical rod 2 the upper end of which is free to vibrate. The rod 2 is enclosed in an evacuated glass envelope 4 which at the lower end is surrounded by pick-off coils 6, 7, 8, 9 having cores 10, 11 &c. An axial iron cored coil 5 fed with alternating current of twice the natural frequency of the rod causes the rod to vibrate continuously. Change of direction of the aircraft to which the casing 1 is pendulously fixed causes the base 27 to turn and impose a distorting force on the plane of vibration of the rod 2 causing its end to vibrate in an elliptical path. Voltages will be generated in the pick-off coils 6 ... 9 according to the direction of the vibration plane with respect to the coils and these voltages after passing through amplifiers 12, 13 operate a repeater motor 14, 15, 16, 17 with the armature 17 of which a spindle operating a dial 18 and hand 18<1> is frictionally engaged. The rod 2 is magnetically polarized. Fig. 7 shows another form of directional indicator in which the vibration member is in U -form carried at the base by spokes 54 on a member freely rotatable about the axial spindle 45. A compass card 46 is secured to the rotatable base. Alternating current fed to the coils 41 maintains the vibrations of the rods 40 in a plane parallel to the arms. The case 42 is carried on the aircraft since the plane of vibration of the rods 40 tends to remain fixed in space the rotation of the case 42 about the axis 45 due to the turning of the aircraft permits the new bearing of the aircraft to be read on the compass card 46 through the window 47. Fig. 9 shows the instrument adapted for use as an artificial horizon. The round magnetically polarized rod 2 is clamped at one end in the casing 58 in a horizontal position and is vibrated by an alternating current sent through the coil 5. The plane of oscillation is normally maintained horizontal by electromagnets 61 which are maintained in position by pendulum 63 ... 67. Pick-off coils 59, 60 are provided. Vibration of the rod 2 when the instrument is upright under normal conditions would cause no signals to be generated on the coils 59, 60 but on the support being tilted, due to the tilting of the aircraft, in such a way that the coils 59, 60 are no longer normal to the plane of vibration of the rod signals will be generated and may operate an indicator. The instrument may indicate pitching or rolling according as the instrument is mounted transversely or longitudinally of the aircraft. Fig. 9A shows the means employed to produce on the screen of a cathode ray tube 96 a line 108 whose position in the vertical direction depends on the angle of pitch and whose angle to the horizontal index line 114 marked on the face of the tube indicates the angle of roll of the aircraft. For indicating pitch and roll respectively two instruments 106, 105 similar to that shown in Fig. 9 are employed with their axes in appropriate direction. The pitch indicating instrument 106 is provided with vertical pick-off coils 59<11>, 60" while the roll indicating instrument 105 is provided with both horizontal and vertical pick-off coils 93<1>, 94<1> and 59<1>, 60<1> respectively. The vibrating rods are driven from a generator 104 through frequency doubler 92<1> to exciting coils 5<1>, 5<11>. From the roll instrument 105 the alternating voltages which appear in the pickoff coils 59<1>, 601 are applied to the vertical plates of the cathode ray tube 96 through amplifier 95. The voltages which appear in the pick-off coils 93,<1>, 94<1> are applied, through amplifier 94, to the horizontal plates of the cathode ray tube. The angle which the trace 108 makes with the index mark 114 indicates the angle of roll. To denote pitch the signal from instrument 106 through coils 59<11>, 6011 is, by means of the electronic phase detector 109, compared in phase with a signal from generator 104 through transformer 103 by means of diodes 97, 98. Whenever the aspect angle of the aircraft alters a direct current signal appears in the wires 111, 112 amplified in amplifier 95 and applied to the vertical plates of the cathode ray tube. The position of the trace above or below the index mark 114 indicates the pitch attitude of the aircraft. Fig. 15 shows a rate of turn instrument in which the rod 2, vibrated by the coils 20, 21 from generator 121, is provided with a plate 122 forming with plates 123, 124 capacitances which are equal when the rod 2 vibrates in a straight line parallel to the plates 123, 124. These capacities form a bridge with capacities 127, 128. To one set of mid points of this bridge is applied an alternating current of frequency f (of the order of 10,000) generated by oscillator 125. On the aircraft turning the rod end 2 opens into an ellipse so that the capacity ratio of the plate 122 with the plates 123, 124 varies with a frequency equal to that of the rod 2. The frequency f modulated by the frequency of the rod appears at the other mid points of the bridge and is placed across the resistors 129, 130. The signal is amplified by triodes 132, 133 and fed to a detector circuit 135 which removes frequency f leaving the low frequency voltage, the magnitude of which depends on the rate of turn of the craft and its phase upon the direction of the turn. The phase detector 136 operates in a similar manner to that shown in Fig. 9A and the indicator 137 may be of any known suitable form. Fig. 4A shows an indicator wherein the end of the vibrating rod 2 is directly observed preferably at the point at the end of its minor axis by the use of a neon lamp 24<1> connected to the pulsating supply circuit leads 20<1>. The lamp is provided with a phase adjusting circuit 25<1> to adjust the point in the path at which the lamp will illuminate the end of the rod 2. The end of the rod may be coloured by white pigment so that it may be readily seen through the slotted window 26<1>. In operation when the aircraft makes a turn to the right the end of the rod 2 will appear to move from opposite the central index 28<1> to the right and the distance of the spot indicating the end of the rod from the central index 28<1> is a measure of the rate of turn.