April 7, 1959
`
`M. B. COTTON
`
`.
`
`2,880,617
`
`GYROSCOPIC APPARATUS
`
`Filed Jan. 26, 1956
`
`.
`
`5 Sheets-Sheet 1
`
`
` Lpnnn—
`
`INVENTOR
`MicHAEL BEN COTTON
`
`Hobostheasedoen
`
`HP Inc. - Exhibit 1031- Page 1
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`HP Inc. - Exhibit 1031 - Page 1
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`

`

`April 7, 1959
`
`Filed Jan. 26, 1956
`
`M. B. COTTON
`GYROSCOPIC APPARATUS
`
`2,880,617
`
`‘5 Sheets-Sheet 2
`
`RECTION
` INVENTOR.
`
`MicHaeL: Ben Cotton
`
`HobosLpasecchton
`
`HP Inc. - Exhibit 1031 - Page 2 -
`
`HP Inc. - Exhibit 1031 - Page 2
`
`

`

`filed Jan. 26, 1956
`
`-
`
`:
`
`OF FLIGHT
`
`April 7, 1959 ~
`
`M. B.COTTON
`GYROSCOPIC APPARATUS
`
`2,880,617
`
`5 Sheets-Sheet 3 DIRECTION
`
`INVENTOR
`_
`MicHAcL Ben Cotton
`
`HobePheerporn
`
`HP Inc. - Exhibit 1031 - Page 3
`
`HP Inc. - Exhibit 1031 - Page 3
`
`

`

`April. 7, 1959
`
`M. B. COTTON
`GYROSCOPIC APPARATUS
`
`2,880.617 _
`
`5 Sheets-Sheet 4
`
`Filed Jan. 26, 1956
`
`A,os—1KS}YAY
`
`73
`
`INVENTOR
`MicHaceL Ben “Cotton
`
` WabettProebomn
`
`HP Inc. - Exhibit 1031 - Page 4
`
`HP Inc. - Exhibit 1031 - Page 4
`
`
`

`

`5 Sheets—-Sheet 5
`
`April 7, 1959
`
`M. B. COTTON
`
`2,880,617
`
`GYROSCOPIC APPARATUS
`
`Filed Jan. 26, 1956
`
`Z
`
`re
`
`oOo
`
`2a
`
`.bexS0
`257M
`—|ui<xo=>
`MehHerre
`
`** ATTORNE
`
`HP Inc. - Exhibit 1031 - Page.5
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`HP Inc. - Exhibit 1031 - Page 5
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`

`

` United States Patent Office
`
`2,880,617
`Patented Apr.7, 1959
`
`i
`
`2,880,617
`GYROSCOPIC APPARATUS
`
`28 Claims.
`
`(Cl. 74—5.47)
`
`Michael Ben Cotton, East Molesey, England, assignor
`to The Sperry Gyroscope Company Limited, Brent-
`ford, England, a company of Great Britain
`‘
`Application January 26, 1956, Serial No. 561,626
`‘Claimspriority, application Great Britain
`January 28, 1955
`
`2
`It has long been appreciated that a tilt detector ar-
`ranged to measuretilt of the platform about a roll axis
`will be affected by centrifugal force during a turn, and,
`in the absence of special preventive measures, the tilt de-
`tector will produce an erroneousroll étror signal which
`will result
`in an erroneous angular positioning of the
`platform about the roll axis. The preventive measures
`‘proposed or put into practice have included interrupting
`the path of the signal from the tilt detector to a roll
`‘correction motor so as to render the roll correction motor
`inoperative during a ‘turn, and arranging that both a rofl
`correction motor and a pitch correction motor be oper-
`ated during a turn in response to signals from a pitch
`detector. These preventive measures may be brought
`into effect by conditions prevailing during a turn, or by
`This invention relates to systems and apparatus for
`the operation of means for initiating a turn or bank.
`aeroplanes, which systems and apparatus includetilt de-
`However,
`it has been discovered that not only a roll
`tectors and are arranged tostabilise a platform carried in
`detector, but a pitch detector may produce signals erro-
`the aeroplane, or the aeroplane itself, against erroneous
`neously ‘indicating tilt of the platform as a result of
`tilting movements. The platform referred to may be,
`centrifugal force occurring during a turn. This can be
`for example, an aeroplane, a gyroscopically stabilised
`explained in the following manner. With a standard set
`element of a gyroscopic instrument or system such as the
`- of conditions;
`load, speed, air density and so on, an
`rotor case of a gyro horizon, a follow-up element in such
`aeroplane when flying straight and level moves through
`an instrument or system, or a platform which is main-
`the air in a mean direction which can be precisely de-
`tained at an angular relation to the aeroplane corre-
`fined with reference to the aeroplane. This direction
`sponding to-the desired angular relation between the
`will be referred to hereinafter as that of the fore-and-aft
`aeroplane and at least one external reference direction
`During a turn, however, in other-
`’ axis of the aeroplane.
`(such as the vertical) and from which is derived signals
`wise similar conditions,
`‘the instantaneous direction of
`for operating, or correcting the operation of control sur-
`motion of the aeroplane, that is to say, the direction of
`faces to turn the aircraft to maintain the angular rela-
`30
`the tangent to.
`its path through the air, departs appre-
`tion between the platform and the external reference
`_ Ciably from the direction of the fore and aft axis. This
`diréction substantially constant. The invention also re-
`’
`is because thelift of the wings has to be increased soas
`lates to tilt detectors suitable for use in such systems
`to balance the resultant of the weight of the aeroplane and
`and apparatus.
`,
`:
`‘
`the centrifugal force occurring in the turn. The’ in-
`A tilt detector, or an accelerometer, such as a mercury
`creased lift necessitates an increased angle of attack,
`switch or a pendulum constrained to move’in one plane,
`hence, the fore-and-aft axis becomes “nosed-in” towards
`has what may be called an axis of response. The de-
`the centre of the turn, and if the turn is made without
`tector responds to components of gravitational and ac-
`change in height, the fore-and-aft axis is also somewhat
`celeration forces which lie along this axis, but not to
`elevated at the forward end in relation to the horizontal:
`components perpendicular to the axis.
`In the case of a
`Owing to this “nosing-in” of the fore-and-aft axis, a
`mercury switch tilt detector the axis of response gen-
`component of centrifugal force occurring in the turn must
`erally lies along the longitudinal axis of
`the switch,
`“be directed along the fore-and-aft axis of the aeroplane,
`while in the case of a pendulum constrained to move in
`and a component of slightly less magnitude will be di-
`one plane, the axis of response lies along the tangent to
`rected along the projection of the fore-and-aft axis on to
`the path ofits centre of gravity.
`the horizontal plane.
`A_ pitch responsive tilt detector
`More generally, a tilt detector usually consists essen<
`having its axis of response aligned with either of these
`tially of a two-part device, comprising a “fixed” part
`components of centrifugal force may operate so erro-
`which is mounted on the object or platform whosetilt
`neously during a turn as to give rise to serious errors in
`is to be measured, and a movable part which moves in
`the operation of a stabilising system.
`relation to the fixed part in response to the action of
`The systems and apparatus to which the invention re-
`gravitational and acceleration forces, the fixed part hav-
`lates more particularly includeatilt detector (referred
`ing pick-off means (such as electrical contacts) which
`to hereinafter as a pitch detector) which responds to
`provides a signal commensurate with or in response to
`deviations from the horizontal of the fore-and-aft axis
`components of relative motion of the fixed and movable
`of an aeroplane, or of a normally horizontal axis which
`parts which are directed along an axis of the fixed part,
`is on.a relatively movable platform in an aeroplane and
`but which provides no signal commensurate with or in
`which is arranged to lie approximately in a vertical plane
`response to components ofrelative motion,if any, which
`. parallel
`to the vertical plane through the fore-and-aft
`are directed perpendicularly to the said axis of the fixed
`axis.
`‘The response of.the pitch detector provides a con-
`part. This axis will be hereinafter referred to as the axis
`trol quantity which is used to control servo means (such
`of response.
`as a pitch-erecting torque motor, a servo motor, or aero-
`A complex tilt detector may be constituted by a pair of
`plane control surfaces) to reduce the said deviation from
`proportional responsetilt detectors having their axes of
`the horizontal. Such systems and apparatus will be re-
`response mutually directed at right angles and a resolver,
`ferred to hereinafter as systems and apparatus “of the
`the resolver comprising a pair of primary windings hav-
`kind specified.”
`ing their axes mutually directed at right angles and re-
`Systems of the kind specified thus include systems in’
`spectively arranged to be supplied with energising signals
`which a relatively movable platform or the equivalent
`by the tilt detectors, and a secondary winding having an
`(such as a vertical gyroscope casing, a follow-up plat-
`axis rotatable in a plane parallel to the plane through the
`form associated with a vertical gyroscope, or a platform
`Such a complex tilt de-’
`axes of the primary windings.
`stabilised by rate-responsive gyroscopes)
`is maintained
`tector, considered as a whole, is to be regarded as hav-
`substantially horizontal in an aeroplane by servo motors
`ing an axis of response which is dependent on the angu-
`responsive to the indications of pitch and roll detectors;.”
`lar position of the secondary winding axis in relation
`. associated with the platform. Further, they include auto-
`to the axes of the primary windings.
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`3
`matic control systems in which a platform is supported
`in an aeroplane in a desired angular relationship there-
`with, and in which the movement or setting of the
`aeroplane controls is automatically influenced by the in-
`dications of pitch and roll detectors carried on the plat-
`form.
`invention, a
`According to one aspect of the present
`stabilising system or apparatus of the kind specified is
`arranged during a turn to respond appropriately to
`signals from a pitch detector but has provision for elimi-
`nating or reducing an error in the operation of the
`Servo means attributable to the effect on the pitch de-
`tector of a component of centrifugal force directed along
`the fore-and-aft axis of the aeroplane during the said
`turn.
`-
`According to a second aspectof the invention, a pitch
`detector suitable for a stabilising system or apparatus
`of the kind specified has an axis of response which is
`automatically varied in response to centrifugal force oc-
`curring during a turn.
`In the stabilising system or apparatus, the control quan-
`tity which is used to control
`the servo means during a
`turn may be provided by a pitch detector having its
`axis of response directed during the turn at an angle
`to the projection of the fore-and-aft axis of the aero-
`plane on to the horizontal plane.
`In one embodiment
`including a platform or the equivalent which is kept
`substantially horizontal, a pair of pitch detectors 1s
`mounted on the platform with their axes of response
`relatively skewed in azimuth, means being included for
`rendering one or other of the pitch detectors ineffective
`during turns in a manner whereby errors in the opera-
`tion of the servo means due to a component of cen-
`trifugal force directed along the fore-and-aft axis during
`the turn tend to be reduced.
`In another embodiment
`a vertical
`gyroscope
`having
`appreciable pendulous
`moment has a single pitch detector mounted on the
`gyroscope casing, or on a member which moves in pitch
`correspondingly with the gyroscope casing, so as to lie
`at an angle to the vertical plane through the fore-and-aft
`axis, whereby, for turns to one side,
`the error due to
`the mutually augmenting effects of pendulous momentof
`the gyroscope and a component of centrifugal force di-
`rected along the fore-and-aft axis is reduced from an
`excessive value to an acceptable value.
`The stabilising system or apparatus, in another form
`may include a single pitch detector the axis of response
`of which is automatically varied in direction during a
`turn, preferably so that the axis of response lies perpen-
`dicularly to the resultant of centrifugal and gravitational
`force impressed on the pitch detector at
`least during
`a certain typical
`turning condition. Thus in apparatus
`including a platform or the equivalent on which the
`pitch detector is mounted and whichthe apparatus con-
`trols to maintain substantially level,
`the platform may
`be. arranged to be turned automatically in azimuth in
`relation to the vertical plane through the fore-and-aft
`axis during a turn.
`In another arrangement, the pitch
`detector is arranged to be automatically turned in azimuth
`in relation to the platform. Again,
`the pitch detector,
`instead of being rotatable in azimuth in relation to the
`platform may be arranged to be tilted down at the front
`end in relation to the platform. The function of a
`single pitch detector rotatable in azimuth may be. per-
`formed by a resolver and a pair oftilt detectors of the
`graded or proportional signal type mutually directed at
`an angle and supplying signals to the resolver,
`the ar-
`Yangement being such that the resolver, during a turn,
`derives from the signals. of the tilt detectors a signal
`equivalent to the signal which would be produced by. one
`simple pitch detector having its axis of response auto-
`matically varied in direction in an appropriate manner
`during the turn.
`Theinvention is not limited to arrangements for turn-.
`ingthe axis of response, of the pitch detector. Thus. a.
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`stabilising system or apparatus may include a graded
`or proportional signal type pitch detector along whose
`axis of response a componentof centrifugal force is di-
`rected during a turn and means operative during the
`turn for compensating the erroneous component of the
`pitch detector signal due to the action of centrifugal
`force on the pitch detector. The compensating means
`may operate to modify a signal from the pitch detector
`before that signal is applied to an erection or servo motor.
`Where the platform is the casing of a vertical gyroscope,
`the compensating means may operate to apply a com-
`pensating torque to the gyroscope during the turn.
`In those embodiments of the invention in which the
`axis of response of the pitch detector is rotatable in
`relation to a platform maintained substantially level, the
`axis of response may in most instances, be automatically
`rotated through an angle of fixed value for each direc-
`tion of turn, or may be automatically rotated through
`an angle computed to suit
`the actual
`turn made.
`In
`many cases the provision for eliminating or reducing
`pitch error due to centrifugal force in a turn may either
`be arranged to become effective in response to means
`for initiating the turn or the bank, or may be arranged
`to become effective in response to conditions prevailing
`during a turn, such as centrifugal force, change in the
`angle of attack, or bank of the aircraft.
`Stabilising systems and apparatus of the kind specified
`-sometimes include an accelerometer arranged to cut out,
`during excessive fore-and-aft acceleration of the aero-
`plane, a control action normally effected in response to
`a signal from the pitch detector. Where a system or
`apparatus according to the invention includes such an
`accelerometer, a component of centrifugal force directed
`along the fore-and-aft axis during turns may be of suffi-
`cient magnitude to bring the accelerometer into. opera-
`tion.
`In such a case, means must be provided to pre-
`vent the cutting out of the control action in any proper-
`ly executed turn.
`Such means may take the form of
`provision for rotating the accelerometer to maintain its
`axis of response substantially perpendicular to the re-
`sultant of gravitational and centrifugal forces occurring
`during a turn, or of means for rendering the response
`of the accelerometer ineffective to cut out
`the control
`action during turns.
`A. system or apparatus according to the invention
`which includes a vertical gyroscope having appreciable
`pendulous moment and a pitch detector giving a gradu-
`ated or proportional response, may be modified by hay-
`ing the pitch detector so directed during turns that it
`produces. a signal which evokes from the pitch-erection
`torque motor a torque opposite and substantially equal
`to the torque impressed on the gyroscope about
`the
`roll axis by reason of the said pendulous moment.
`The system or apparatus is preferably arranged. not
`only to. eliminate or reduce errors due to the effect of
`centrifugal force. on a pitch detector, but to. reduce or
`eliminate errors due to the effect of centrifugal force on,
`a roll detector. To this end, the signal fromthe roll
`detector
`is preferably rendered ineffective to operate.
`the. servo or torque motor providing correction about
`the roll axis. The roll-correction servo or torque motor
`may thus be rendered inoperative during turns, or it
`may. be arranged. to operate in response to signals from
`the pitch detector.
`The invention has athird aspect according to which
`a. stabilising system or apparatus including a stabilised.
`platform mounted to rotate. about. a “pitch” axis with.
`respect
`to a gimbal frame which rotates relatively to
`the aeroplane about a “roll” axis extending generally in
`the direction of the fore-and-aft axis has provision for
`varying the relative angular direction of the “roll” axis
`in relation to the fore-and-aft axis in response to a
`change in, or a condition accompanied by a change. in,
`the angle of attack. in a manner tending to maintain,
`the roll axis more nearly in alignment with the relative.
`
`HP Inc. - Exhibit 1031 - Page 7
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`HP Inc. - Exhibit 1031 - Page 7
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`axis ofthe aeroplane at an angle equal to the angle be-
`responsive to the angle of
`Preferably means.
`wind.
`tween the relative wind direction and the fore-and-aft
`attack, or to conditions which determine the angle of
`axis multiplied by the cosine of the angle of bank, the
`‘attack,
`is adapted: to maintain the “roll” axis substan-
`angles concerned being those pertaining at the typical
`tially aligned with the projection of the relative wind
`turning condition. The pitch detector selected by the
`direction on to the plane of symmetry of the aeroplane.
`switch 13 to remain operative has its axis nosed outward-
`Dueto the platform remaining level when the aeroplane
`ly in relation to the centre of the turn.
`is banked over in the turn, the platform and the pitch
`In one case it was found, with a single pitch detector
`detector mounted upon it is turned outwardly with re-
`directed straight forward, that for turns to the right the
`spect to the aeroplane by the angle between the fore-
`erroneous signal caused by the response of the pitch
`and-aft axis and the roll axis, multiplied by the cosine
`detector to centrifugal force practically compensated for
`of the angle of bank. Whenthe roll axis is parallel with
`the effect of pendulous moment, while. for turns to the
`the relative wind direction, the pitch detector is turned
`left, the two errors, augmenting one another, reached a
`in azimuth by the precise amount necessary to avoid
`prohibitive total. Fig. 1 shows the pitch detectors angu-
`centrifugal force error in the pitch detector.
`larly positioned to suit such a case, pitch detector 4a,
`In order that the invention may be clearly understood
`operative during turnsto the right, being directed parallel
`and readily carried into practice, a number of embodi-
`to the vertical plane through the fore-and-aft axis, while
`ments will now be specifically described by way of ex-
`pitch detector 4b, operative during turns to the left is
`ample, with reference to the accompanying drawings.
`directed at about twice the angle first specified to the
`In the drawings;
`vertical plane through the fore-and-aft axis,
`Fig.
`1 shows a vertical gyroscope provided with a
`Fig. 2 is a circuit diagram showing one manner in
`pair of pitch detectors relatively skewed in azimuth,
`which the pitch detectors 4a, 4b, and the centrifugal-
`Fig. 2 is a circuit diagram for the embodiment of
`force-responsive switch 13 are electrically connected.
`Fig. 1,
`The switch 13 contains a centre electrode 13a, connected
`shows. a vertical gyroscope provided with a
`3.
`Fig.
`to one pole of the supply, and two end electrodes 13c,
`single pitch detector skewed in azimuth,
`13d respectively connected to centre electrodes of the
`Fig. 4 shows a vertical gyroscope provided with a
`pitch detectors 4b and 4a, The end electrodes 13c, 13d
`roll axis which is variable in direction to vary the di-
`extend nearly to the centre of the switch, so that, when
`rection of the pitch detector,
`a mercury drop 13e is in the centre of the switch, the
`Figs. 5, 6 and 7 show ways in which the axis of re-
`two end electrodes and hence the centre electrodes of
`sponse of a pitch detector may be turned in azimuth
`both pitch detectors are connected to the supply, while
`with respect to a stabilised platform,
`when the mercury drop departs from its central position,
`Fig. 8 shows the manner in which a compensating
`only one of end electrodes .13c, 13d is connected by the
`downward tilt may be applied to a pitch detector,
`drop to the.centre electrode 13a and to the supply. Thus
`Fig.. 9 shows a modification of the arrangement of
`the centre electrode of one or otherof the pitch detectors
`Fig. 5 in which the single pitch detector is replaced by
`4a and 4b is disconnected from the supply during turns
`two tilt detectors and a resolver,
`according to the end of the switch 13 towards which
`Fig. 10 shows a vertical gyroscope in which provision
`the mercury drop 13e is deflected by centrifugal force.
`is made for applying a torque about theroll axis to com-
`The embodiment of the invention shown in Fig. 3 is
`pensate for the effect on the pitch detector of a com-
`concerned with a vertical gyroscope 1 having appreciable
`ponentof centrifugal force during turns,
`pendulous moment which is a source of errors of about
`Fig. 11 shows a modification of Fig. 10 in which the
`the same magnitude as the errors which would be due
`compensating torque is variable with the angle of bank,
`to components of centrifugal force acting along the axis
`Fig. 12 shows a E-type pick-off version of a pitch
`of response of a pitch detector maintained parallel with
`detector modified in accordance with the present inven-
`the vertical plane through the fore-and-aft axis of the
`tion, and
`aeroplane. These errors are additive for turns in one
`type of pitch detector
`Fig. 13 shows a liquid-level
`direction and subtractive for turns in the other direction.
`modified in accordance with the present invention.
`Thus if the gyroscope rotor rotates in a clockwise sense
`Referring now to Fig. 1, a vertical gyroscope 1 has
`when viewed from above, a turn to the right, owing to
`a roll detector 2 which supplies a controlling signal to
`the pendulous tendency causing it to swing out on the
`roll erection torque motor3, and a pair of mercury switch
`turn, tends to pitch the rotor axis rearwardly at the top.
`pitch detectors 4a and 4b which control a pitch erection
`A componentof centrifugal force acting rearwardly dur--
`torque motor 5. The pitch detectors and roll detector
`ing a turn on a pitch detecting switch parallel with the
`are mounted not on the gyroscope casing buton a fol-
`vertical plane through the fore-and-aft axis results in
`low-up platform 8 which is maintained level with the
`the pitch erecting torque motor applying a torque such
`gyroscope casing by roll and pitch servo motors 9 and
`as to precess the gyroscope axis forwardly at
`the top.
`10. Servo motors 9 and 10 are respectively responsive
`Thus the errors approximately cancel for turns to: the
`to signals from roll and pitch pick-offs 11 and 12.
`right.
`In a turn to the left, however,
`the pendulous
`Pitch erection torque motor 5 receives signals from
`tendency of the gyroscope casing and the erroneous action
`both pitch detectors 4a and 4b during straight flight by
`of the pitch detecting mercury switch both result in the
`way of a centrifugal-force-responsive mercury switch
`top of the gyroscope being precessed forwardly, so that
`13. During turns, when the centrifugal force exceeds
`the errors augment each other for turns to the left, and
`a predetermined value, the switch 13 appropriately cuts
`may reach a prohibitive value.
`-
`out one or other of the pitch detectors according to the
`Tn accordance with the invention, a single pitch detector
`direction of the turn.
`4 is set skewed in azimuth so that it operates less errone-
`A pitch-roll switch 14 responsive to the angle between
`ously for turns to one side, the right in the present in-
`the outer gimbal ring and the aeroplane is arranged in
`stance, and more erroneously for turns to the other side.
`a known manner to control the roll torque motor ap-
`For example,
`it can be angularly set so as to operate
`propriately from the operative pitch detector instead of
`correctly, that
`is to say, to lie along the direction of
`from the roll detector when the bank exceeds a pre-
`relative wind, during a given, typical, left turning con-
`determined magnitude.
`dition. Then the precession error of the gyroscope. will
`The axes of the two pitch detectors may be so di-
`be due to pendulous moment alone for turns to the left.
`rected as to be aligned with the relative wind over the
`For turns to the right, the pitch detector error will be
`aeroplane during a particular typical
`turning condition
`roughly doubled, and the total-error will be approximately
`for turns to either side. Each should then be directed
`equal to the original pitch detector error..In this manner.
`in relation to the vertical plane through the fore-and-att.
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`a
`the errors may be substantially equalised for turns to
`either side, and prevented from reaching a prohibitive
`value.
`In order ‘to prevent the roll-erection torque motor 3
`Tesponding to erroneous signals from the roll detector
`due to the lateral component of ‘centrifugal force ‘during
`turns, known means (not shown)is provided for render-
`ing the roll erection circuit
`inoperative during turns.
`For example, the roll detector switch 2 may be arranged
`to cut itself out under excessive gravitational or accelera-
`‘tion forces directed along its-axis of response.
`In the embodiment shown in Fig. 4, a vertical gyro-
`scope 1 has a mercury switch roll detector 2 which ‘sup-
`plies a controlling signal to roll erection torque motor 3
`‘and a mercury switch pitch detector 4 which supplies a
`controlling signal to pitch erection torque motor 5. The
`pitch erection motor 5 operates about an axis 17 which
`is maintained in alignment with the air path of the craft,
`except in conditions of sideslip, whatever the angle of
`attack. To this end, the gimbal ring 15 of the gyroscope
`is supported from an auxiliary gimbal ring 16 and rotates
`in relation thereto about a generally forwardly directed
`axis 17. The gimbal ring 16 is pivoted about a pitch axis
`18, and the axis 17, when there is no sideslip, is main-
`tained along the direction of relative wind by means of
`a pair of synchros 19 and 20 respectively mounted on
`the axis 18 and connected to wind vane 21. As in the
`previous embodiment, the roll detector 2 is arranged to
`cut out in an excessive apparent roll condition such as
`occurs ina turn.
`The pitch detector 4 has its axis of response lying in,
`or parallel to a plane which passes through the axis 17,
`and which is maintained substantially vertical. Hence,
`during a properly executed turn,
`that
`is to say, when
`there is no sideslip or change in height, the axis of re-
`sponse of the pitch detector when correctly positioned
`lies parallel to the direction of relative wind projected on
`to the horizontal plane. Accordingly there is no com-
`ponent of centrifugal force directed along the axis of
`response of the pitch detector, so that there is no errone-
`ous response of pitch detector 4 to centrifugal force dur-
`ing the turn.
`The embodiment of Fig. 4 may be modified in various
`ways. For example, instead of the wind vane 21, other
`means Tesponsive to the airflow may be employed to
`determine the direction of relative wind. Again,
`the
`direction of relative wind may be determined by a com-
`puter which is responsive, for example, to air speed and
`to acceleration along the yaw axis of the aeroplane.
`Further, to provide an approximate correction, means
`responsive to a condition prevailing during a turn, or
`to the operation of means for initiating a turn or bank
`may be arranged to tilt the axis 17 through a fixed angle
`corresponding to the change in direction of relative wind
`in a particular typical turning condition.
`In yet another
`modification,
`the axis 17 is permanently directed at an
`angle to the fore-and-aft axis.
`In the latter modification,
`the pitch detector is directed precisely parallel with the
`vertical plane through the fore-and-aft axis when the
`aeroplane is not banked, while when bank is applied, the
`gyroscope casing with the pitch detectors thereon is auto-
`matically turned outwardly in azimuth. However,
`the
`correction will be precise only at one rate of turn for
`any given speed,
`Fig. 5 showsa vertical gyroscope arrangement general-
`ly similar to that of Fig. 1. One difference is that a single
`pitch detector 4 is employed and is mounted on a cradle
`28 which is pivoted to turn in azimuth with respect
`to
`the follow-up platform 8, Centrifugal-force-responsive
`mercury switch 13 controls electro magnet 29 to swing
`the cradle to one side or the other against adjustable
`screws 30, 31. Adjustable spring means 31a maintains
`the axis of response of Pitch detector 4 parallel with
`the vertical plane through the fore-and-aft axis when
`the electro-magnet 29 is de-energised, and the adjustable
`
`30
`
`35
`
`40
`
`The correction given by the arrangementof Fig. 6 will
`be precise only at one rate of turn for any given speed.
`The relative proportions of the parts may readily ‘be
`calculated from the angle of bank and the direction of
`relative wind when the particular turning conditions in
`which precise correction is required have been decided
`upon.
`"Various modifications of the embodiment of Fig. 6
`are possible. Thus,
`instead of the pendulum swinging
`freely during the turn, it may urge the cradle 32 against
`a preferably adjustable stop, or the action of the pendu-
`lum may be opposed by spring means tending to centre
`the cradle 32.
`‘The application of the invention is not, of course, con-
`fined to systems employing pitch detectors of the liquid-
`level type. Fig. 7 shows the arrangement of Fig. 6 with
`the liquid level pitch detector replaced by a pitch detector
`comprising an E-type pick-off and an armature hung as
`a pendulum above the pick-off. Such a pitch detector
`is shown, for example,
`in the embodimentillustrated in
`Fig. 2 of the specification of British Patent No. 715,313.
`That specification, incidentally is concerned with an auto-
`matic control system in which a platform is supported in
`an aeroplane in an angular attitude with respect to the
`aeroplane corresponding to the desired attitude of ‘the
`aeroplane with respect to an external frame of reference.
`The movement or setting of the aeroplane controls is
`automatically influenced by the indications of pitch and
`roll detectors carried by the platform.
`It will be appreci-
`ated that the invention is no less applicable to such a
`system or apparatus than to systems and apparatus
`centred around a vertical gyroscope which provides a
`constant vertical reference.
`Fig. 8 shows a pitch detector arrangement which could
`be substituted for that of Fig. 5. A cradle 36 is pivotally
`mounted on the platform 8 to rock in a vertical plane
`about an axis 49. The cradle supports pitch detector 4
`and may also, if desired, support an accelerometer cut
`out, which is not shown. The cradle 36 has only two
`positions, since it is arranged to be rocked down at the
`front by electro magnet 37 for turns to either side. A
`spring 41 normally maintains the cradle in engagement
`with an adjusting screw 30a, which is set to give a level
`attitude for the pitch detector. The setting of adjusting
`screw 31a determines the angle through which the cradle
`and pitch detector are tilted when electro magnet 37 is
`energised. This angle should be such as to bring the
`axis of response of the pitch detector perpendicular to
`the resultant of gravitational and acceleration forces
`during a particular, typical turning condition.
`
`2;880,81'7
`
`S
`screws 30, 31 are set so that the axis of response of pitch
`detector 4 lies ‘in the vertical plane through the relative
`wind during particular typical
`turning conditions ‘for
`turns to either ‘side.
`Signals from pitch detector 4 to pitch erection torque
`motor ‘5 go by way of an accelerometer cut-out 4¢ which
`cuts out the torque motor 5, ina known manner, under
`excessive fore-and-aft acceleration. Accelerometer cut:
`out 4c is also mounted on the cradle 28 so as not to be
`erroneously operated by a:component of centrifugal force
`during turns.
`,
`Fig. 6 shows one manner in which the embodiment of
`Fig. 5 may be modified. The pitch detector 4 is mounted
`on a cradle 32 which is rotatable in azimuth in relation
`to the platform 8 about an axis 33. A pendulum 35
`pivotally hung at a level above the pitch detector hasits
`arm embraced by a fork 34 on the end of cradle 32.
`The direction of flight of the aeroplane in which the
`stabilising system including the pitch detector of Fig.
`-6
`is fitted should be downward and to the