USRE25756E - Visual cue generator - Google Patents

Description

A ril 6, 1965 s. H. BALDING 25,756

VISUAL CUE GENERATOR Original Filed April 11, 1958 12 Sheets-Sheet 1 INVENTOR GEORGE H. BALDING April 6, 965 G. H. BALDING Re. 25,756

VISUAL CUE GENERATOR Original Filed April 11, 1958 12 Sheets-Sheet 2 INVENTOR GEORGE H. BALDING (A1 A la ATTORNEY 12 Sheets-Sheet 3 ATT'Ys A ril 6, 1965 G. H. BALDING VI SUAL CUE GENERATOR 12 Sheets-Sheet 4 RADAR SAMPLER CLIPPER AMPL F ER REcEwER swncu cm: CliTf i I73 T I74 175 L I77 loo-H (FIG. I)

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u s I668 COMPUTER ALTITUDE PROGRAMMED FoR cuRvEo AaovE 3E52 SPEED PATH cm. a BELOW CILLATOR 4 [66A 4 I68 4 I69 170 PHASE mv. 275 (FIG. [4)

mom PATH GENERATOR I60 FIG. [3

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GEORGE H. BALDIN G ATT'YS April 6, 1965 G. H. BALDING 25,756

' VISUAL CUE GENERATOR Original Filed April 11, 1958 12 Sheets-Sheet 5 ATT'YS April 6, 1965 s. H. BALDING VISUAL CUE GENERATOR Original Filed April 11, 1958 12 Sheets-Sheet 7 April 6, 1965 s. H. BALDING VISUAL CUE GENERATOR Original Filed April 11, 1958 3! En W s mob-20! .P I m & m .H m N- I T. m a #m A V on? m H i M" u" E M QT 33' n? nnnc m v m Pu! ak n" G a v. F B in avnrx v n x x nwv 2.1 v1 .31 P10 0! v m2 A wvn NR. Own; w H H 8.. m2 1 mm H 8 2 k2 5.1305, :350 wzxaju .2: 056 E2316 VA" 225? zocofihmo at g u m9. 3h Em nwv R ulll ov In 4 R m 3! 2w XI .2 !v N m2 Aprilfi, 1965 G. H. BALDING VISUAL CUE GENERATOR Original Filed April 11, 1958 12 Sheets-Sheet 8 G N S t 2. m m T M 1 W A m H I a m fi E .2 6 m be End" M 3 M M M w 22 i u u.\ 2:1 num mu? omnk u a P #2 n 2 Q? n En kn lil H MM. 3 u fin I: BR 31 Rn nR G? 55128 2 *1 Swan QC 22.26 9505 O mwm 92k 92 v nuwmm m v: mPEfiGwo owumm l 1E 5 an mrwwm ww v! J F con 2 April 6, 1965 a. H. BALDING VISUAL CUE GENERATOR 12 Sheets-Sheet 10 Original Filed April 11, 1958 s. H. BALDING VI SUAL CUE GENERATOR Original Filed April 11, 1958 12 Sheets-Sheet 12 VIDEO ROLL CLIPPER CKT. 137 (CAP 392) 6NDu MIXER SENSOR E ECTR |c CLIPPER I64 L w L145 (ANODE 566) PATH-D6645 I ,424

AMPLIFIER 623 POWER CLOUD MlX-b663 P657 SUPPLY HORIZON GEN. I38 (ANODE I04) SKY-b 666 66! 655i sss Jr MIXER |oo-v,7 MM [3 MM 0 DEFLECTION 55/ 653 66 1,33% CIRCUITRY 1 J (FIG. l4) L COLOR PRESENTATION 650 FIG. 23

HORIZ. VARIABLE SAWTOOT H DELAY TR'ANGLE CLIPPING AMPLIFIER GENERATOR CIRCUIT 4 cmcun' CKT.

Tbs/9 T 620 621 $22 s23 IO0H+20O I ms. l4)

WEATHER X-Y AMPLIFIER RADAR POSITIONER L624 25 L (FIG. l6)

CLOUD GENERATOR 6!? FIG. 22

imam AMP. :45 (FIG. l6) lOO-V M v. (FIG-l4) -642 L HORIZON GEN. CKT. I38 647 (FIG. I6)

PITCH VERT. SAWJ'OOTH F 43 If? 645-4 644 4r SKY TEXTURE GENERATOR 640 INVENTOR.

GEORGE H. BALDING & %z/ M( aw ATT'YS United States Patent 25,756 VISUAL CUE GENERATOR George H. Balding, Los Altos, Calif., assiguor, by mesne assignments, to Kaiser Aerospace & Electronics Corporation, Oakland, Calif., a corporation of Nevada Original No. 3,093,822, dated June 11, 1963, Ser. No. 728,019, Apr. 11, 1958. Application for reissue June 24, 1964, Ser. No. 390,252

- 111 Claims. (Cl. 34311) Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

The present invention relates to a visual cue generator for providing an integrated display of information relating to the flight condition of an aircraft, and particularly to an all electronic system for generating such display.

With the rapid advancement in the development of aircraft in recent years there has been an increasing need for a visual cue generator apparatus which is capable of providing to the pilot in an integrated manner, the information relating to the flight condition of the aircraft. The instrumentation in existing aircraft installations now known in the art generally comprise a large number of individual meters and indicators which are mounted in tandem or side-by-side relation on an instrument panel for viewing by the pilot. Although the readings on the instruments are relatively simple, the act of scanning, choosing and integrating the numerous bits of information for the purpose of determining the maneuver to be executed by the pilot frequently requires a split second reaction. In the newer, faster flying aircraft now appearing in the field, the time for pilot response has been even further reduced, and the time for integrating the metered information is also decreased. Such factors are of serious concern from the standpoint of the safety of the pilot and the aircraft.

Extensive research studies have indicated that the overall response time of a pilot to a situation consists of the data acceptance time plus the reaction time of the pilot to initiate corrective action. Since the reaction time is the property of the individual pilot, such time cannot be materially decreased once the individual has been selected and trained. The data acceptance time, however, depends upon the number of separate inputs, the time required for the integration thereof, and the nature of the integrated display presented to the pilot. Each of these time factors may be decreased by the provision of integrated instrumentation in a single display unit, and particularly by the provision of an instrumentation which presents such information in a form which is compatible with and related to the same information in the real World.

More specifically, studies have indicated that the basic cues essential to such presentation include cues which display a sky texture, a horizon, and a ground texture, the sky texture and ground texture being readily distinguishable from each other, and the horizon being a distinct and recognizable line. In a preferred display, the texture of the ground is comprised of symbols which vary in size with the altitude of the aircraft and which move across the ground texture to create the illusion of movement of the aircraft relative to the ground. The rate of movement of the symbols is preferably related to the speed of the aircraft, and the positions of the symbols on the display should change with a change in heading of the aircraft. The horizon in straight and level flight should extend laterally across the display, and the position of the horizon on the display should vary relative to the horizontal with movement of the plane about the roll axis of the craft, as for example, in the banking Re. 25,756 Reissued Apr. 6, 1965 of the plane and the execution of a turn. Further, the position of the horizon should change in an upward or downward direction with changes in pitch of the aircraft, the texture of the ground pattern changing in perspective in accordance with the degree of change of pitch of the aircraft. With the incorporation of these basic visual cues into a common display, the pilots reaction time to an existing flight condition may be materially decreased.

It is a primary object of the invention, therefore, to provide apparatus which is capable of presenting such visual cues in a single integrated display, and particularly to the provision of a system which generates such cues electronically and effects incorporation of such cues into a single display with equipment which requires a minimum of space and weight whereby the inclusion of the equipment in an aircraft is more readily accomplished The study has further indicated that the presentation of additional symbols on the display, and particularly the presentation of a flight path for the guidance of the pilot would prove of further aid to the pilot in the maneuvering of the aircraft. In one conventional system (commercially known as an ILS system), now used in the art to assist the pilot in landing during periods in which visual contact with the ground cannot be made, the system sends out control impulses to the aircraft which are indicative of a preferred approach path, and which are reproduced for the pilot on a meter having a pair of crossed pointers. If the aircraft is on the proper path, the crossed pointers will intercept at the midpoint; and the pilot therefore attempts to maintain the aircraft on the approach path by maintaining the pointers in such relative position. If the plane descends or rises above or below or moves to the right or left of the path, the pointers are correspondingly displaced from such relative position. Thus in making approach the pilot must maintain a careful surveillance of the relative position of the two pointers (while simultaneously noting the information on a number of other related meters), and take such corrective action as is necessary with the departure of the plane from the desired flight path. It is apparent that the maintenance of the two cross pointers in an intersecting relation, and the maneuvering of the aircraft in the proper direction responsive to the departure of the needles from such relation, while simultaneously watching a number of the meters is an arrangement which is extremely susceptible to human error. In addition, there is always the danger that the pilot, in attempting to effect a change in the planes position relative to the guide path responsive to departure of the needles from their intersecting position, will over-compensate in his adjustment of the position and thereby place the aircraft in a dangerous flight condition.

It is an object of the present invention, therefore, to provide a flight path in the display which guides the pilot along the approach path directly to the point of touchdown. One particularly novel path taught herein comprises a flight path which during a normal approach is superpositioned over the ground texture of the display in the direction of the horizon, such flight path being presented in perspective to simulate true world conditions. highway in the sky" wherein a white ribbon [extended] extends from the lower margin of the display in the direction of the horizon, the ribbon path having a center line and a series of cross-grids spaced along the path length in the manner of a conventional highway.

In use, the pilot may follow the center line of the path, or if desired, the path may be assigned to represent two lanes in which case the pilot follows a preassigned one of the lanes. If the aircraft descends below the approach path of the system, the flight path presented on the dis- In one embodiment, the flight path appears as a play is inverted and extends downwardly from the sky portion of the display towards the horizon to provide the illusion of flight below the approach path. If the pilot maneuvers to the right or left of the path, the flight path is adjusted laterally from the middle of the display in a related direction and distance, and the pilot maneuvers the craft in the direction of the path displacement to regain the desired on-course position. Thus, during the approach,the pilot is only required to maintain the aircraft on the flight path in the manner in which one drives a vehicle on a highway. -Ostensibly, such arrangement eliminates the complicated throught process and integration required in systems in which meter presentations of information are used, and constitutes an important step in the provision of a more safe display system for flight conditions.

In one specific embodiment of the device, a program speed computer provides an input signal into the system indicative of a safe speed along the flight path for existing conditions. Such speed is displayed on the path by symbols spaced at increments therealongv If the proper speed is maintained, the symbols are stationary. If the speed of the aircraft deviates in either direction, the symbols move along the path in a related direction to indicate to the pilot the need for speed adjustment. Thus each condition critical to the safety of the aircraft in a guided landing is integrated into a single display.

The novel flight path of the arrangement is readily adjusted to present a linear path which is related to the normal path of flight of the aircraft, and also to provide a curvilinear path in perspective which indicates a particular path which must be followed in order to reach an intended destination. Thus, in use in conjunction with a radar system, a memory device or a computer, a display of the contour of the terrain which lies in the flight path of the plane may be coupled to the system, and data computer equipment may provide signals to the system to adjust the path to a shape which is indicative of the obstacle-free course for the plane to a desired destination or target.

In one novel arrangement set forth herein, the system is operative to provide a presentation of the terrain contour in the path of the aircraft, and a curved flight path on the display which guides the pilot from his given course around the obstacles detected in such contour, and back to the course which extends to the desired destination. Such equipment, of course, provides an extremely safe operating system for aircraft, and substantially minimizes the possibility of collision with other aircraft, mountain ranges, buildings and other similar types of obstacles.

The provision of such flight path also has particular value in its adaptation for use with military aircraft. That is, modern jet military aircraft operate at a speed which permits a minimum, if any, response time for effecting firing at a second jet aircraft which is approaching the first aircraft at a like speed. Accordingly, by superposing the opposing aircraft as detected by the radar on the display target, and coupling the output of a data computer system to the flight path control equipment, the pilot need merely direct his craft along the flight path, fire at the target which appears thereon at the time indicated, and maneuver the aircraft along the indicated escape course to prevent collision with the target subsequent to firing.

The novel flight path also permits maximum utilization of the operating characteristics of the aircraft. That is, each aircraft has a predetermined operating envelope at which safe operation of the craft at different altitudes and speed may be effected. However, there is presently no known way of indicating to the pilot when the relative speed and'altitude safety maximums are being approached other than by training the pilot to feel or sense such condition. ostensibly, most pilots will therefore allow a substantial safety margin in flight, and as a result, the aircraft are frequently operated below the limits of their safe performance curves. In the present arrangement, the envelope representative of the operating characteristics of the plane may be coupled into a data computer, and such information continually fed into the flight path being projected on the display device to indicate to the pilot the maximum path which may be flown in any maneuvering position without exceeding the operating capabilities of the aircraft.

According to a feature of the invention, a pulse shaping circuit and a readout circuit are operatively coupled in a-novel manner to a mixingcircuit to generate cue symbols which include the contour of the shaped pulse or the readout pulse. In this manner, cue symbols having the shapes of ships, aircraft, submarine mines, etc. are readily incorporated into the display.

Further features disclosed in a preferred embodiment of the invention include means for providing a visual cue of adverse weather conditions andterrain contours in conjunction with the flight path, and in one embodiment the system provides the different information cues in different colors. Other similar applications and uses of the novel display system will be evident to parties skilled in the art, and such are considered to be within the scope of the present teaching.

The foregoing objects and features of the invention, and others, which are believed to be new and novel in the art are set forth in the following specification, claims and drawings in which:

FIGURE 1 is a showing of the presentation of the novel display device with the aircraft at a relatively high altitude;

FIGURE 2 is a showing of the presentation of the display device with the aircraft at a relatively low altitude;

FIGURE 3 is a showing of the presentation of the display device with the airplane executing a bank to the right;

FIGURE 4 is a showing of a presentation of the display device with the aircraft in the attitude of a dive;

FIGURES 5 and 6 are pictorial representations of the manner in which the path and guide circle patterns are provided in the successive stages of the device;

FIGURES 7-10 are illustrations of the novel flight path as superposed in different positions on the basic cue display of the device; a

FIGURE 11 sets forth a presentation of a display device including each of the visual cues relating to the aircraft flight condition, as well as the terrain condition and the optimum flight path for such conditions, bad weather clouds, and two lane traflic;

FIGURES l2 and 13 set forth, in block representations, the component parts of the novel visual cue generator system including the flight path generator equipment;

FIGURES 14-19 set forth a specific set of circuits for effecting cue generation of the basic sky horizon and ground cues including cues of speed, pitch, azimuth,v altitude, roll; and also the novel flight path including cross grid lines, a center line, and program speed;

FIGURES 20 and 24 set forth schematically a circuit for a terrain cue generator;

FIGURE 21 sets forth a sky texture cue generator;

FIGURE 22 sets forth a circuit for a cloud cue generator;

System Components In a preferred embodiment, the novel display generator is adapted to present an integrated display of the basic visual cues relating to the speed, altitude, pitch, roll and azimuth of the aircraft. Such presentation includes a sky pattern, a horizon, and a ground texture to relate the cues to true visual conditions. With reference to FIG- URES l-6, the photographs thereat set forth the manner in which the diflerent cues in the display of one embodiment are changed in size, shape and position to represent changes in the aircraft flight condition.

As there shown the display in level flight basically comprises a sky portion of comparatively light intensity, a sharp black horizon line and a ground portion of varied intensity. The ground portion of the display as it extends from the dark horizon to the bottom of the display is of a successively lighter intensity, and a series of rows of elliptical mounds and holes (three major rows and twominor rows in the present illustration) are superposed on the portion of the display which represents the ground surface. Motion of the aircraft relative to the ground is represented by movement of the symbols across the ground portion of the display, the symbols increasing in size during such movement to provide the illusion of motion. More specifically, small symbols emerge from a point immediately below the horizon and move in the direction of the lower margin of the display, each one expanding in size as it approaches the lower edge of the display. Thus the showings in FIGURES 1-11 are stopmotion photographs of an animated display. The emission of the guide circles from the horizon is at a rate which is related to the speed of the aircraft, the guide circles being emitted at a comparatively high frequency as the speed is increased and at a comparatively low frequency as the speed of the plane is decreased.

The altitude of the aircraft is represented by the relative position of the symbols, the symbols being farther apart as the aircraft is closer to the ground, and being closer together as the aircraft is at a higher altitude. Thus, with reference to FIGURE 1 the showing thereat illustrates the smaller symbols which are presented on the display when the aircraft is at a comparatively high altitude, and FIGURE 2 is illustrative of the manner in which the size and number of the holes in the ground pattern are altered to represent a comparatively low altitude of the aircraft.

During the maneuvering of the aircraft about its roll axis, as for example banking of the aircraft in the execution of a turn, the horizon line is displaced from the horizontal through an angle which is consistent with the degree of bank of the aircraft. The nature of the changein the horizon line of the presentation on the display during banking of the plane to the right is illustrated in FIG- URE 3. The position of the line in other conditions of roll will be obvious therefrom.

In a similar manner, the horizon line must be displaced along the vertical axis responsive to changes in pitch of the aircraft. It is apparent that as the aircraft is maneuvered into a dive of increasingly steeper attitude, the horizon will move progressively towards the top of the display. At such time as the plane is in a true vertical dive, the nature of the presentation on the display device will be as shown in FIGURE 4. As the heading of the aircraft is changed, the sets of circles are displaced laterally across the target display in a direction consistent with the direction of the change so that with the arrival of the plane at a new heading, a row of guide circles extends down the middle of the display in the ground texture.

As disclosed hereinafter, the apparatus may be readily adjusted to provide symbols other than guide circles, such as for example, small diamond-shaped symbols or square shaped symbols which, in the manner of the guide circles, appear to emanate from the horizon and to expand in size as they proceed across the face of the screen in the direction of the lower margin thereof. Such apparatus is also readily adjustable to provide symbols which are not aligned in row formation as shown, whereby a more random ground pattern is obtained.

The basic cues relative to speed, altitude, pitch, azimuth and roll are supplemented in a preferred embodiment by the superpositioning of a flight path on the display to indicate a preferred course of flight to the pilot The flight path in one embodiment shown in FIGURE! 7-11, comprises a ribbon-like path having a center lin which extends coextensively down the length of the path and a series of spaced crossline markings which are dis posed on the path at successive increments therealong The cross line markings appear to emanate from the hori zon in the manner of the guidecircles to thereby provid the illusion of movement over the path in the directio' of the horizon. It is noted that in the present embodi ment, the guide lines on the path move across the displa at a rate which is faster than the rate of movement c the guide circles to thereby simulate closer proximity c the aircraft to the path than to the ground surface. A flight path comprised of a dotted line, a solid line, a serie of symbols, etc., may be incorporated in the display wi-ti out departing from the scope of the invention.

The nature of the flight path superpositioned on th visual cue display will vary in accordance with the ir formation to be portrayed by the flight path. In a systei which is adapted, for example, to provide a flight pat indicative of the preferred approach path for a landin; the flight path is projected on the display device in tt manner shown in FIGURE 7, and the pilot guides tl plane along such path. In the event of deviation fro] such path, the flight path will be angularly shifted to ind cate such deviation. The position of the flight path 1' FIGURE 8, for example, indicates that the aircraft flying to the left of the guide path, and that the aircra should be maneuvered to the right for the purpose of oni more positioning the aircraft on the flight path.

In each of the illustrations of FIGURES 7 and 8 tl aircraft is on, or slightly above, the guide path. In tl event that the aircraft descends below the guide path, tl flight path is inverted in the manner of FIGURE 9 to i dicate to the pilot the need for increasing altitude to r gain the path indicated by the system.

The center line shown in each of the illustrations 7- may be utilized as the intended line of flight of the pat or alternatively may be used to divide the path into tv lanes, whereby one lane of trafiic would fly along the la: to the right of the centerline, and the second set of tr: he would be assigned to use the lane to the left of ti centerline. The cross line members which appear FIGURES 7-9 emerge from the horizon and proceed the direction of the lower margin of the display at a spe which is, in the illustrated embodiment, of a higher It than the movement of the holes across the ground te ture, to thereby indicate closer proximity of the aircr: to the path than to the ground.

In one embodiment of the device, a second set of 1' formation symbols (not shown in FIGURES 9-11) 2 incorporated in the flight path display for the purpose providing a guide to the pilot as to the preferred spe of the device for a given situation. In the arrangeme described hereinafter, a set of guide circles appear travel along the center line of the flight path to indic: the most desirable speed of the plane for such COIldltlt In the event that the aircraft is moving faster than 1 desired speed, the guide circles will move in the directi of the bottom margin of the display. In the event that 1 plane is moving at a rate slower than the optimum rate 1 such condition, the guide circles on the center line of 1 path will move in the direction of the horizon. In 1 event that the optimum speed is being obtained for st condition, the guide circles will remain stationary.

In certain embodiments it may be desirable to prov. a flight path which extends around certain obstacles a which requires a change in altitude. The manner in wh the flight path may be adjusted to portray such change course and altitude is set forth in FIGURE 10. The s; cific manner in which such arrangement is operable provide a flight path in an integrated display includ' terrain contours and undesirable weather conditions is forth in FIGURE 11, the contour of the terrain be BASIC CUE GENERATION The electronic visual cue generator 10 basically comrises an electronic generator set which is operative reponsive to the application of information representative ignals thereto to provide an integrated presentation of uch information on a suitable display device, such as for xample, a cathode ray tube. The more basic cues may iclude aircraft speed, altitude, pitch, roll and azimuth ues which are integrated in and displayed in superposed elation to an electrorically produced set of background ues including a sky, horizon and ground pattern.

The electronic generator 10 for providing such basic isplay cues is schematically shown in FIGURE 12, and s there shown, includes a azimuth sensor 111 for provid- 1g azimuth representative signals, an altitude sensor 113 or providing altitude representative signals, a pitch sensor 09 for providing pitch representative signals, a speed ensor 142 for providing speed representative signals, and

roll sensor 148 for providing roll representative signals.

The sensor devices 109, 111, 113, 142, 143 may comrise conventional aircraft sensing equipment, examples f which were set forth in the copending application which Ias filed by Aid and Balding on June 30, 1958, and was rsued Serial No. 745,472, and which was assigned to the ssignee of the present application. These and other pes of sensor devices and systems adapted for use in ircraft equipment are well known in the art and corniercially available. In the use of the display unit with imulator equipment, for example, each of the sensor cleices may be replaced by a manually adjustable means, uch as a variable potentiometer, having a control knob djustable to different positions to provide different outut potentials indicative of different flight conditions, such s altitude, pitch, etc. Alternatively, data computer or iernory equipment may be connected to the potentiomters to adjust the input signals representative of the diferent conditions to different values. Other types of signal enerating equipment for providing signal inputs to the isplay system in its diilerent uses will be apparent.

Generation of the different cues into a common dislay is basically controlled by a timing genenator ltlt) FIGURE 12), which is operative to provide horizontal y-nc pulses at the rate of 15,750 cycles per second and 'ertical sync pulses at the rate of 60 cycles per second, uch type timing generator being commonly used in comaercial television transmitter equipment. The horizontal ync output pulses of the timing pulse generator 100 are oupledto the input side of a set of variable delay pulse ii'cuits 101, 102, 103, respectively, the number of variable .elay pulse circuits being determinative of the number of ets of circle guide paths which are provided in the ground exture of the final display. In the illustrated embodiment be three circuits sets 101-103 provide the illustrated isplay comprised of three major guide rows and two minor guide rows as shown in FIGURES l-ll.

The sensor signal output of sensor devices 109, 111, .13, is coupled over a cue symbol positioner 104 to the 'ariable delay pulse generators 101-103 to control such nits in the generation of cue signals. More specifically, ach of the variable delay pulse circuits 101-103 is opertive to generate a square pulse, the trailing edges of the quare pulse output of the respective circuits 101-103 veing different in time as determined by the azimuth, itch and altitude sensor signals coupled thereto by the no symbol positioner 104 and sensor units 109, 111, and

113. That is, as the sensors 109, 111, 113 couple signals of different values to the cue symbol positioner 104 with changes in the azimuth, pitch and altitude of the aircraft, the time diiterence between the trailing edges of the output of the generator circuits 101-103 is correspondingly varied. As shown in more detail hereinafter, with a change in the azimuth, the signal output of the generator circuits 101-103 is modified in time to adjust the circle guide paths laterally in a direction consistent with the direction and degree of the turn; with a change in altitude the signal output of the generator circuits 101-103 is modified in time to cause the guide circles to move apart or closer together, and simultaneously to adjust the angular relation of the outer guide circle rows relative to the center circle row to thereby vary the perspective pattern on the ground surf-ace; and with a change in pitch, the signal time is adjusted in a similar manner to alter the perspective showing.

The output pulses of the variable delay pulse circuits 101-103 is coupled, respectively, to the input sides of the triangle generators 105-107 which are controlled to operate in response to the trailing edge of each square pulse input thereto, and in such operation to generate a triangular-shaped pulse for coupling over the circuit 136 to the clipping circuit 137. As indicated by the wave form adjacent the input to the mixing circuit 136', and the Wave forms adjacent the output sides of triangular generators 106-107, the output triangles of each of the successive stages 105-107 generated during each horizontal line trace of the raster are spaced relative to one another in time, the spacing between the pulses being determinative of the. spacing between the rows of guide circles on the display device.

It is apparent from the foregoing description that variation of the time distance between each of the three pulses of the successive pulse generators 101-103 varies the spacing between the guide circle rows on the display screen, and that the perspective representation may be varied by providing an increased time spacing between the signals as successive lines of the raster are scanned. The sensor input signals which indicate a change in altitude and pitch are operative to effect such adjustment of the time spacing between successive signals in successive time scans. Variation of the duration of each pulse of each set of three pulses will manifestly vary the position of the circles on the display, and the signals indicating a change in altitude are coupled to the pulse delay circuits 101-103 to effect such adjustment. The lateral positions of the guide circle rows relative to the vertical edges of the display screen are manifestly determined by the time of initiation of each successive pulse [or pipe] of a waveform of three pulses during each horizontal scan, and signals indicating a change of heading are coupled to the generator 101-103 to efiect lateral adjustment of the guide circles in a direction consistent with the direction of the heading change (i.e., right or left). This adjustment of the time of generation of each pulse relative to each horizontal trace, and the duration of each pulse during each successive horizontal trace determines the relative location and size of the guide circles on the display screen, and adjustment of the amplitude of the pulses of each set in turn determines the size of the circles.

The output signals of the pitch sensor 109 are coupled directly to a mixing circuit 136 and clipping circuit 137 and also over the vertical sawtooth generator 274 of the cue symbol positioner 104 to the mixing circuit 136 and clipping circuit 137. The output signal of the vertical sawtooth generator 274 is controlled by the pitch sensor signals and comprises a positive going sawtooth Waveform, which is generated at the vertical rate of the raster trace and, which varies in amplitude with a change in pitch to efiect a corresponding change in the size of the guide circle. The pitch sensor output signals directly coupled to the mixing circuit 136 adjust the vertical positioning of the first symbol. As shown hereinafter, the output signals of the cue symbol position-er are also operative to adjust the skew angle of the circle rows relative to the center row with a change in pitch to thereby effect a cor responding change in the perspective display. This is done by changing the amplitude of the vertical sawtooth.

The positive going sawtooth waveform output of the vertical sawtooth generator is mixed with the symmetrical triangular waveform output of the generators 105-107 in the mixing circuit 136' for coupling of the clipping circuit 137, the signal output for the mixing circuit 136- comprising a plurality of groups of impulses, each group being comprised of three triangular impulses, the amplitude of the three triangular impulses in each successive group during a raster scan increasing incrementally as the vertical sawtooth changes in value. Thus the width of the guide circle increases as the scan progresses in the manner shown in FIGURES 1-11, and a change in pitch automatically effects a further adjustment of the circle symbol sizes.

The sets of signals are clipped in a clipping circuit 137 and are coupled to an amplifier 139 to provide a signal of an increased amplitude for coupling to a mixer circuit 140, which is controlled in its operation by the output signals of a horizon generator 138 and additionally by the output signals of a speed sensor 142 and a sine wave oscillator unit 144.

As shown in more detail hereinafter, if the output of the clipping circuit 137 were coupled directly to the display device, the display would consist of three paths as shown in FIGURE 5. In order to obtain separate symbol elements having relative motion to indicate movement of the aircraft over the ground pattern, the signal output of the amplifier circuit 139 is modulated by the pulses of an oscillator 144, the shape of the oscillator pulses determining the shape of the symbols which form the paths. Thus in the disclosed embodiment, the clipping circuit pulses as modulated by the sine wave shapes result in the generation of circle symbols on the display screen, as shown in FIGURES 1-4 and 6. If a triangle generator were used in lieu of the sine wave generator, the symbols on the display device would be triangular shaped, and if a square wave generator were used, the symbols would be square shaped; etc.

As the speed sensor equipment 142 couples signals of different values to the oscillator 144, the rate of oscillation of the oscillator 144 is correspondingly altered, and as a result thereof the repetition rate of the sine wave signals input to the mixer 140 are correspondingly adjusted to different values. Such change in frequency results in a corresponding adjustment of the rate of movement of the symbols across the display device, and accordingly provides a visual cue of the relative increases and decreases in speed of the aircraft. Adjustment of the output of the oscillator frequency to a value less than a multiple of the frequency of the vertical sweep will cause the symbols to apparently move from the bottom margin of the display in the direction of the horizon to thereby create the illusion of backward flight. Such use has especial application in helicopter installations which are frequently operated in such manner.

The horizon generator 138 is controlled in its operation by the pitch sensor 109, and is synchronized with the system by the vertical sync output pulses of timing generator 100. The horizon generator 138 basically provides a pulse having a sharp leading edge, the time of occurrence of the leading edge in a raster scan determining the location of the horizon line on the display, and, in turn, being controlled by the pitch sensor output. The trailing portion of the output wave of the horizon generator 138 is mixed with the output signals of amplifier 139 and coupled to a video amplifier 145, and the video gun of display device 146.

Roll sensor equipment 148 is operative with rotation of the aircraft about its roll axis to couple signals indicative of the change in roll attitude to control equipment 10 for the deflection yoke of the display device 146, to control same to mechanically effect a corresponding rotational adjustment of the yoke and thereby rotation of the horizon line from the horizontal. Such adjustment may also be effected electronically, if desired.

It is seen from the foregoing description that the novel visual cue generator system provides an integrated display of the cues which set forth the relative pitch, altitude and speed of the aircraft, as well as changes in the roll and heading attitude thereof.

FLIGHT PATH GENERATION In the preferred embodiment of the disclosure, a flight path is superposed on the display presented to the pilot as a further aid to the provision of safe flight conditions. As shown in FIGURE 13, the flight path generator 160 may include a horizontal sawtooth generator 161 which is controlled in its operation by the horizontal sync output of the television timing pulse generator (FIG- URE 12), and which in turn controls a variable delay pulse generator 162 (of the type similar to the variable delay pulse circuit generators 101-103) to control a triangle generator 163 (similar to triangle generators 105- 107), in the provision of timed triangle impulses for each horizontal sweep. The output of the triangle generator 163 is fed to a clipping circuit 164 (similar to clipping circuit 137) and over amplifier 165 to the video amplifier (FIGURE 12) of the display device 146. The basic units 161-165 of the flight path generator in the normal condition of flight, i.e., in the absence of deviation or error signals, establish a ribbon-like path which, as shown in FIGURE 7, extends from the bottom of the display screen in the direction of the horizon, and in the manner of a perspective showing, appears to converge at a point on the horizon.

The path may be adjusted to different shapes and to diiferent positions on the screen as shown in FIGURES 8-11. Thus, for example, in the use of equipment with the blind landing installations (ILS), the flight path may be positioned as shown in FIGURE 8 to show deviation of the plane to the left of the proper approach path, and as shown in FIGURE 9 to show deviation of the plane below the proper approach path. As shown in FIGURE 10 the path may be curved to show the proper path to be flown to reach the point of touchdown or some other desired destination.

The equipment for adjusting the shape of the flight path in such' manner may include ILS receiver equipment, such as illustrated unit 166B, which is operative to receive the signal output of the ILS transmitting equipment (not shown), and a data computer 166A which is controlled in its operation by such signals. The output signals are fed to the path control equipment 167 which is operative in turn to couple variable value signals to the variable delay pulse circuit 162 to control same to vary the timing of the pulse generated thereby during each horizontal trace of the display device. In this manner, the position of the successive path representing pulses as coupled to the display device effect a corresponding adjustment of the path position. It is apparent that a flight path of any desired shape maybe generated in this manner. Ostensibly, the system is also readily adapted for use with other types of sensor equipment, such as for example radar units which are operable to detect enemy targets. In such arrangement an associated data computer is operative to compute a preferred path of attack and retreat, and to feed such path into the path control unit 167. Other similar applications will be apparent to parties skilled in the art.

In certain of these applications it may be desirable to provide an indication to the pilot as to altitude of the aircraft relative, to a predetermined guide path. In the use of the system with ILS equipment, for example, the receiver equipment 167 is connected to feed indicator signals to the altitude above and below path equipmerit 168 which is operative to couple indicating signals to the clipping circuit 164 toprovide a flight path on the display which provides such information to the pilot. In

F the particular embodiment shown herein, the flight path shown on the display device in the event the pilot is on the desired approach path will comprise a ribbon path which extends across the ground texture to convergence at a point on the horizon (FIGURE 7), and as the craft rises to successively higher altitudes relative to the desired path, the flight path on the dispiay device becomes narrower and narrower. As the aircraft descends below the desired path, the flight path is immediately inverted, (FIGURE 9) and extend from the horizon to the direction of the upper margin of the display.

According to the invention, a center line is provided in the flight path so that the approach path is divided into two lanes in the manner of a highway, and traffic can be assigned to the different lanes in accordance with In the flight path display on known trafiic regulations. the device, the assigned lane will be aligned with the central set of symbols of the ground texture when the pilot is on course, and [will] may be displaced therefrom in the event of maneuvering of the craft from its proper position relative to the assigned lane.

In a' further "modification of the device, a speed oscillator 169 modulates the output of the clipping circuit 164 at a rate which results in the introduction of cross-grid lines at successively spaced increments along the flight path to showmotion to the aircraft over the path, and also to show the difference in speed of the craft relative to the path as related to the speed of the aircraft relative to the ground.

The device may also include a program speed oscillator 170 which is connected to couple a symbol indicating circuit to the clipping circuit 164 for effecting the reproduction of further speed symbols on the flight path. In one preferred embodiment, such signal comprises a series of'circle symbols spaced at successive increments along the center line of the flight path, the

. symbols being maintained motionless during the periods varying the pulse output of the speed oscillator 170 as described heretofore in the matter of the speed oscillator .144.

DESCRIPTION OF BASIC CUE GENERATOR CIRCUIT (a) Symbol Group Generation The electronic visual cue generator (FIGURE 12) for generating basic cues relative to azimuth, altitude, pitch and speed, as shown in FIGURES 14, '15, 16 and 17, is controlled in its operation by the pulse output of a television timing pulse generator 100, which may be of the type commercially available as a Hickock Model 650C universal video generator, and which provides a set of horizontal sync impulses at the rate of 15,750 pulses per second, and a set of vertical sync impulses at the rate of 60 pulses per second. Other types of timing pulse generators of a more simplified construction which may be used in such arrangement will be readily apparent to'parties skilled in the art.

The horizontal sync output of the timing pulse generator 100 is coupled over terminal 1001-1 to the input circuit for the flight path generator 160 (FIGURE 13);

' bodiment, the first group generator 1 provides a pulse for'each horizontal trace which determines the position of a portion of a symbol of the first path (FIGURE 5) of the three groups on the display device; the second group generator 2 provides a pulse output for each horizontal trace delayed in time relative to the output of the first group generator 1,'to thereby determine the position of a portion of :a symbol in the second path (FIGURE 5), and the third group generator 3 provides a pulse for each horizontal pulse delayed in time relative to the first time pulses to provide a portion of a symbol of the third path (FIGURE 6). Thus, the number of groups of symbols to be provided in the ground texture of the ultimate display is determined by the number of group generators which are included in the system, the number of generators illustrated in the present arrangement being limited to three for purposes of simplicity of disclosure. Although each group of symbols provided by each group generator 1, 2, 3 in the example of the present disclosure, are aligned in rows, it will be apparent from the teaching of the manner in which the flight path is adjusted to different shapes hereinafter that such principle may be utilized to adjust the shapes of the path of FIGURE 5, and thereby provide a random texture pattern in lieu of the rows of symbols shown herein.

Each of the group generators l, 2, 3 are similar in structure, and accordingly only group generator 1 has been shown in detail. With reference thereto, (FIG- URE 14) group generator 1 may comprise a pulse delay circuit 101 and a triangle generator 105. Pulse delay generator 101 may comprise a twin'triode tube 202, commercially available as a 12AU7, connected in a univibrator circuit, and may include anodes 203, 206, con- I trol grids 204, 207, cathodes 205,208. Anode 203 of the first section is coupled to a 300 volt B+ source over load resistor 209; control grid 204 is coupled to the input circuit over capacitor 210, and control grid 204 is additionally connected over negative clipper circuit comprised of diode 211 and resistor 212 to ground; and cathode 205 is connected over cathode resistor 213 to ground.

Anode 206 of the second section is coupled over load resistor 214 to 300 volt 3-]- supply; control grid 207 is coupled over capacitor 215 to the plate circuit of the first section of tube 292, and additionally over the voltage divider network comprised of resistor 216, 217, 218 and 219 and capacitor 219-to a resistance section on the azimuth positioner potentiometer 300 in theme symbol positioner 104 to ground. As each horizontal sync impulse output of timer is coupled to the pulse delay circuit 101, the circuit is operative in the manner of a conventional univibrator' circuit to generate the leading edge of a square Wave pulse (as shown in FIGURE 14). The square wave impulse thus generated is coupled to the triangle generator, the duration of the pulse being determined by the value of the signals (representative of azimuth, pitch and altitude) which are coupled thereto over conductor 220a (such control signals being described in more detail hereinafter).

Briefly as each horizontal sync pulse is coupled over capacitor 210 and rectifier 211, resistor 212 to the control grid 204 of the first section of tube 202, the first section of tube 202 is rendered conductive and the decreasing potential which appears in the anode circuit thereof is coupled over capacitor 215 to drive control grid 207 negative relative to cathode 208 and thereby decrease the conductivity of the second section of tube 202. Capacitor 215 charges during the period of the pulse, and as the incoming sync pulse is terminated to terminate the change of potential in the anode circuit of the first section capacitor 215 discharges over [resistor] resistors 216, 217 and 213 to ground. The negative potential which appears at the grid 207 maintains the second section nonconductive, and the negative potential which appears at the cathodes 205, 208 maintains the first section conductive subsequent to the discharge of capacitor 215 through resistors 216, 217 to cathode 208, and for a time period determined by the value of the control signals coupled to the timing circuit by cue symbol positioner 104. This is done by mixing the control signal with the discharge voltage at grid 207.

The decreasing potential which appears in the anode circuit of the first section of tube 202 is also coupled over-capacitor 221 to the triangle generator 105 to provide the leading edge of a negative square wave pulse as shown in FIGURE 14 adjacent the anode output circuit for the first section of tube 202.

As capacitor 215 discharges to complete the timing cycle (which is of a duration determined by the control signal output of cue. symbol positioner 104) cathodes 208 and 205 return to their normal positive biassed condition, and the first tube section is once more biassed to cutofi. The rising potential which now appears in the anode circuit of the first section constitutes the trailing edge of the negative square wave output pulse shown in FIGURE 14.

It is apparent therefore that as each sync pulse is coupled to the pulse delay circuit, a negative square wave output pulse having a duration determined by the altitude, pitch and azimuth of the aircraft is generated and coupled to the triangle generator 105.

Triangle generator 105, which is coupled over capacitor 221 to the output circuit of the pulse delay genera tor 101, comprises a twin triode tube 222 which may he of the type commercially available as a 12AU7 having anodes 224, 230, control grids 226, 232, and cathodes 228, 234. Anode 224 of the first section is coupled over resistor 236 to 300 volt B+ supply, control grid 226 is coupled over capacitor 221 to the output side of the pulse delay circuit 101, and also over negative clipping circuit comprised of diode 240, and grid resistor 242 to ground; and cathode 228 is coupled over cathode resistor 244 to ground. Anode 230 of the second section of tube 222 is coupled over load resistor 246 to 300 volt B+ supply, and over capacitor 248 to the input side of the integrating circuit 252 which includes resistor 254a-nd capacitor 258 (FIGURE 14); control grid 232 is coupled over capacitor 238 to anode 224 of the first section and also over resistor 250 to cathode 234, which is in turn coupled with cathode 228 over resistor 244 to ground.

As the negative square wave impulse generated by the pulse delay circuit 101 is coupled to the triangle generator circuit 105, the positive-going portion of the pulse is integrated by capacitor 221, rectifier 240, and resistor 242 to control the tube 222 which is connected as a univibrator to provide a square wave output pulse, it being apparent that as the incoming impulse changes in duration as the result of the control signal coupled to the pulse delay circuit 101 by the cue symbol positioner 104, the trailing edge of the negative square wave pulse output thereof will likewise change in time relative to the horizontal sync pulse, and a like change in the time of generation of the output pulse during a horizontal line trace by the triangle generator circuit 105 Will result.

The univibrator circuit including tube 222 in triangle generator 105 is operative in the manner of the univibrator circuit including tube 202 of the pulse delay circuit 101, the time duration of the output pulse however being fixed in the illustrated embodiment and the layed in time relative to each horizontal sync pulse of V the system, and by a value determined by the control signal output of cue symbol generator 104, and the amplitude thereof.

Integrating circuit 252 includes resistor 254 connected in series with capacitor 258 to ground, and resistor 256 connected with capacitor 258 and resistor 254 to provide a discharge path for capacitor 258. With the application of each square wave impulse to the integrating circuit 252, an output sampling signal comprising a triangular shaped impulse is coupled over a diode 260 and mixing circuit 136' to the input side of the clipping circuit 137 (FIGURE 16).

Each of the group generators 1, 2, 3 comprise a similar set of equipment, and are operative to provide a triangular impulse at the output side thereof for mixing in the clipping circuit 137. Since the signals coupled to the respective inputs of the pulse circuits 101-103 are of different values, the triangular waveform, pulse output of the group symbol generators are out of phase with one another by a corresponding time period, whereby a composite waveform of the shape indicated in FIGURE 14 is coupled to the clipping circuit 137 by the three [generator] generators during each horizontal line trace of the raster.

(1)) Integration of Sensed Information Into Cues The cue symbol positioner 104 couples signals over conductors 220a220c to each of the pulse delay circuits 101-103 of the group generators l3 to adjust the time period between the triangle pulses in the composite output pulse of the three generators to different values in accordance with changes in values of the pitch, azimuth and altitude as detected by the pitch sensor equipment 109, azimuth sensor equipment 111, and altitude sensor 113. As will be shown hereinafter, variation in the time or distance between the successive peaks in the composite wave efiects a corresponding adjustment in the distance between the rows or groups of symbols which appear on the display screen.

More specifically, the cue symbol positioner 104 (FIG. 15) comprises a vertical sawtooth generator stage 274 and a phase inverter stage 275 and an azimuth positioner stage 276. i The vertical sawtooth generator stage 274 may comprise a twin section tube 277 commercially available as a 6U8 in which .the first section comprises an anode 278, a control grid 279, cathode 280, and the second section includes antanode 281, suppressor grid 282, screen grid 283, control grid 284, and cathode 285. Anode 278 of the first section is connected to 300 volt B+ supply, control grid 279 is connected over capacitor 286 to the vertical sync output of the timing pulse generator 100, and also over resistor 287 to ground. Cathode 280 is coupled to the plate 281 of the second section of tube 277 and also to the phase inverter stage 275 and capacitor 291 to ground. Suppressor grid 282 is connected'internally to the cathode 285, and screen grid 283 is connected over voltage divider circuit 283', 290, control grid 284 is connected over adjustable resistor 28% to ground, and also over adjustable arm 3151) to the resistance segment 28% of' pot 239, the junctions 316b, 317b on pct 28% being connected to ground and 50 v. respectively; and cathode 285 is connected over resistor 288 to ground. Resistor 289 having an adjustable arm thereon for coupling the signals representative of the pitch of the aircraft (as determined by the position of the arm 315b on resistor 28%) to the control grid 284' in the second section of tube 277.

Pitch sensor 273 may comp-rise conventional sensor equipment coupled to the vertical attitude gyro of the aircraft, and connected in the manner setforth in the above identified copending. application, which controls a conventional servo system 272 over section 28% of the four section potentiometer-239 to adjust the potential which is coupled to the control grid 284 of second section of tube 277 which is connected as a vertical sawtooth generator. The-indications of changes in pitch attitude of the aircraft as derived by the pitch sensor equipment 273 are also represented by changes in the value of the potential which is coupled over potentiometer section 28921 to the speed oscillator equipment 144; over potentiometer 289c to the clipping circuit 137; and over potentiometer section 289d to the horizon line generator circuit 138. More specifically, signals representing changes in pitch are coupled to the system by adjusting the four wiper arms 315a-315d respectively to different positions, the servo unit 272 and vertical gyro sensor 273 controlling the wiper arms in such operation as the pitch of the aircraft is varied. The first section 289a of pitch potentiometer 289 is coupled over two terminals 316a, 317a respectively to ground, and is coupled over wiper arm 315a and conductor 380' to the speed oscillator 144-as more fully described hereinafter. Each of the arms 315a-315d are in the illustrated position with the aircraft in a normal level flight condition. With variations in the pitch attitude the wiper arm 315a is adjusted in the indicated directions to correspondingly adjust the value of resistance in the oscillator circuit 144, and thereby the relative speed of movement of the ground cue symbols across the display as the pitch of the aircraft is varied.

As the aircraft is maneuvered into adive attitude of increasing value, the value of the resistance connected in the speed oscillator circuit 144 by potentiometer arm 315a and section 289a is correspondingly decreased to decrease the rate of movement of the symbols across the display. As the aircraft is placed in a vertical dive, the wiper arm 315a will have been moved to the terminal 317a, and zero resistance will be connected in the speed oscillator circuit 144, whereby the ground cue symbols are maintained stationary on the display device. Other relative conditions of operation will be apparent therefrom.

The second section 28% of pitch potentiometer 289 is coupled over terminal 316b to ground and over terminal 317b to the negative terminal of the 50 volt potential source. Wiper arm 315b for the second section 28% is connected to the vertical sawtooth generator stage 274. With variations in the pitch attitude of the aircraft from level flight, the wiper arm 315b is adjusted in the alternative directions indicated in FIGURE 15 to correspondingly adjust the value of the potential signal coupled to the verticalsawtooth generator stage 274. Thus a more negative signal is coupled to stage 274 as the plane is placed in the dive condition, and a less negative signal is coupled to stage 274 as the plane is placed in a climbing condition. As shown in more detail hereinafter, as the plane is placed into a diving condition, the resultant increase in the value of the negative-potential signal coupled to stage 274 will correspondingly reduce the amplitude of the vertical sawtooth output'signal of stage 274,'and thereby the degree of skewing of the cue symbol paths in the ground texture of the display.

The third section 289c of pitch potentiometer 289 is coupled over terminals 316c to the positive terminal of the 50 volt potential source and over terminal 31-70 to the negative terminal of the 50 volt potential source. Wiper arm 315c is coupled over conductor 353' to the clipping circuit 137. In the level flight condition of the aircraft, potentiometer arm 315c is in the illustrated position, whereby substantial zero voltage signal is coupled to the clipping circuit. With variations in the pitch attitude of the aircraft, wiper arm 315:: is adjusted in the directions indicated in FIGURE 15 to correspondingly 275 is related to the pitch of the aircraft.

into a condition of increasing climb attitude, wiper arm- 315c will be adjusted to provide a signal of an increasingly positive value to the clipping circuit, and the ground portion of the pattern on the display screen will become smaller and smaller. As the true vertical climb position is reached, the wiper arm 315c will be on terminal 316c and only the sky portion will be shown on the display. As a true vertical dive condition is reached wiper arm 315c will be on terminal 317c and only the ground pattern will be shown on the display.

The fourth section 289d of pitch potentiometer 289 is coupled over terminals 316d and resistance 317a to the positive terminal of the potential source; and over terminal 317d, resistance 317f to the negative terminal of the potential source. In normal level flight, wiper arm 315d associated with the fourth section of pitch potentiometer 289 is in the illustrated position, and a signal of substantially zero value is coupled over conductor 317' to the horizon line generator circuit 138 to control the horizon line generator to provide a horizon line to appear at the approximate midpoint of the raster trace. With variations of the pitch attitude of the aircraft, the wiper arm 315d is adjusted in the alternative directions indicated in FIGURE 15 to correspondingly adjust the value of the potential signal which is coupled to the horizon line generator circuit 138 and thereby the position of the horizon line on the display. Ostensibly'with maneuvering of the aircraft to a dive position, wiper arm 315d is adjusted in the direction of terminal 317d to couple a signal of increasing negative value over conductor 317 to the horizon generator circuit to adjust the point of occurrence of the horizon line at a position closer to the upper margin of the display as more fully described hereinafter.

It is apparent from the foregoing description that signals indicative of the change of the pitch attitude of the aircraft are coupled by the pitch sensor equipment 273, 272, and potentiometer 289 to the system to effect a corresponding adjustment of (a) the relative speed'of movement of the ground symbol cues; (b) the skew of the paths of ground symbol cues; (c) the initial point'of occurrence of the first ground symbol cue of each path; and (d) the relative position of the horizon line.

The specific manner in which the changes in pitch attitude efi'ect these different adjustments is set forth in more detail in the further discussion of the several stages of the system.

Briefly, as the vertical sync output pulses which trigger each frame scan are also coupled over capacitor 286 to the vertical sawtooth generator stage 274, and specifically to the control grid 279 of the first section of tube 277 at the rate of 60 pulses per second, the positive-going portion of each pulse renders the first section of the tube 277 conductive and capacitor 291 is charged positively overthe circuit extending from 300 volt positive source over the conducting first section of tube 277 and capacitor 291 to ground. As the trailing edge of the incoming vertical sync pulse is coupled to the vertical sawtooth generator 274, control grid 279 is driven negative relative to cathode 280 and capacitor 291 discharges over the circuit including the second section of tube 277, resistor 288 to ground, the rate of discharge being determined by the value of the resistance connected in such circuit and the pitch control voltage on grid 284.

In that the position of the adjustable arm 315b resistance 28% is determined by the pitch attitude of the aircraft, the rate of discharge of capacitor 291, and therefore the amplitude of the vertical sawtooth wave which is coupled to the input circuit of the phase inverter stage In the present

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