FR2692036A1 - Aircraft attitude indicator. - Google Patents

Abstract

A housing (10) has a window (11) and is designed to be mounted in an instrument panel (12) inclined at a THETA angle to the roll axis (14) of the aircraft. A support member (15) is supported in the housing (10) to rotate about the longitudinal axis (16) of the instrument, this axis being normally perpendicular to the instrument panel (12). The support element (15) supports a gyroscope (17) with a single degree of freedom, which has a rotor (18) supported in an inner circle (19) to be movable in rotation around an axis (21) perpendicular to the longitudinal axis (16). An indicator element (22) having the shape of a drum or a sphere is supported by the support element (15) so as to be movable in rotation about an axis parallel to the axis (21) of the inner circle ( 19) and it carries a horizon indicator (23) which intercepts the longitudinal axis (16) when this axis is horizontal. An inverting transmission (24) interconnects the inner circle (19) and the indicator element (22). A model (25) is fixed to the instrument housing, adjacent to the surface of the indicator element (22), and spaced from the longitudinal axis (16) by a distance equal to the offset of the indicator horizon (23).

Description

Attitude indicators for aircraft, commonly known as

  of artificial horizons, are used in planes to indicate to the pilot the attitude of the plane relative to a reference, usually the horizon, although it is actually a horizontal plane It is a considerable importance that the instrument be precise since it gives the pilot the only reference he has when the real horizon is not visible Although it is usual to make instruments controlled by inertial navigation systems, it It is also usual practice to provide at least one electromechanical instrument as a backup instrument in anticipation of the case where the complex inertial navigation system is faulty for a

whatever reason.

  The usual type of electromechanical instrument uses a gyroscope whose rotor is rotated about a substantially vertical axis, in an inner gimbal circle which is supported to be rotatable in an outer gimbal circle around a transverse axis to the roll axis of the aircraft This latter circle is itself supported to be movable in rotation in a housing which contains the instrument, the axis of the outer circle usually being perpendicular to a window of the housing An indicator element, which is frequently in the form of part of a sphere is also mounted in the outer circle to be rotatable around an axis parallel to that of the inner circle The indicator element is connected to the inner circle of the gyroscope by an inverting mechanism, so the indicating element is rotating relative to the outer circle in the opposite direction to the inner circle The window of the housing carries a mock-up you

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  appearing the plane, placed in the center of the window, and the surface of the element carries marks which indicate the horizon and, possibly, also the deviations in pitch compared to the horizontal flight We already know several different physical arrangements for the inner circle and for the indicator element contained in the outer circle. An instrument of the general type described above is designed to be mounted in such a way that the axis of the outer circle is parallel to the roll axis of the aircraft However, aircraft are usually equipped with an instrument panel inclined to facilitate the visibility of the instruments This means that the conventional instrument is capable of being mounted with the axis of the outer circle inclined at a certain angle relative to the roll axis of the aircraft, an angle which can

reach up to 10 to 200.

  The use of the conventional instrument mounted in this way can lead to errors in the indication given by the instrument, which can reach serious proportions If, for example, an instrument of the type described is mounted in an inclined panel of 100 on the vertical, the axis of the outer circle is inclined by below the roll axis of the plane Usually, the instrument is adjusted by shifting the horizon indicator so that the instrument gives a correct indication when the airplane is in horizontal flight If the airplane rolls over 1800 while flying in horizontal flight, the outer circle moves by an angle of 200 in the vertical plane which contains the roll axis of the plane, since the axis of the circle

  exterior is now 10 above the roll axis of the aircraft.

  The instrument therefore shows an offset of 20 upwards from

  horizontal flight, even if the aircraft is still horizontal flight.

  An object of the invention is to provide an aircraft attitude indicator in which the pitch errors are

considerably reduced.

  According to the present invention, an aircraft attitude indicator intended to be mounted in an inclined instrument panel is produced, the indicator comprising a housing intended to be fixed to the panel and having a longitudinal axis arranged to be perpendicular to the plane. of the panel in use, a support element mounted in the housing to be movable in rotation around said longitudinal axis, an indicator element supported by the support element to be movable in rotation around an axis perpendicular to said longitudinal axis and having on its surface a specified horizon which cuts the longitudinal axis when this axis is horizontal, a gyroscope with a single degree of freedom, having an inner circle mounted on the support element with its axis of rotation parallel to that of the indicator element, a transmission reversing machine, which interconnects the inner circle of the gyroscope and the indicator element, and a model fixed to the instrument case nt, in a position adjacent to the surface of the indicator element and which is offset from said longitudinal axis by a distance substantially equal to the offset between the indicated horizon and this axis when the airplane is in a

predetermined attitude.

  When we say that the offset of the model is "substantially equal" to that of the indicated horizon, this covers small variations of position intended to cancel the parallax errors due to the fact that the line of sight of the observer of the instrument does not coincide with the longitudinal axis of the instrument It is assumed that, as is normal in these instruments, the model is placed very close

  of the surface of the indicator element.

  The predetermined attitude of the aircraft, taken for reference when positioning the model, may depend on the type

  and the mission of the aircraft on which the instrument is used.

  The invention will now be described with reference to the accompanying drawing, which shows a diagram of an attitude indicator of a

airplane according to the invention.

  We will now refer to Figure 1; this figure shows an instrument comprising a housing 10 having a transparent window 11 at one end A mounting flange 12 is provided for fixing the instrument to an instrument panel 13 The panel is shown in an inclined arrangement of an angle O on the vertical Line 14 in phantom represents the horizontal axis (or roll axis) of the aircraft Inside the housing 10, there is a support element 15 presented in the form of an outer circle which is supported for be mobile in rotation around an axis 16 by appropriate bearings (not

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  The axis 16 is in fact the longitudinal axis of the instrument and it is perpendicular to the window 11 In the outer circle 15, is mounted a gyroscope 17 with a single degree of freedom having a rotor 18 carried in a circle inside 19 The axis of rotation 20 of the rotor 18 is substantially vertical when it is in operation The axis of rotation of the rotor is perpendicular to the axis 21 of the inner circle, which is itself perpendicular to the axis 16 of the circle exterior An indicator element 22 is also pivotally mounted in the support element 15, so as to be able to rotate about an axis parallel to the axis 21 of the interior circle. This element is a cylindrical element or in the form of a part of a sphere, a part of the surface of which is visible through the window 11 The surface of the indicator element 22 is divided into two parts by a line 23 parallel to the axis of rotation and representing the horizon, the parts of the surface which are at- above and below this line being usually of different colors Line 23 is positioned to be on the longitudinal axis 16 when this axis is horizontal Usually, the surface also carries indications of the angle of dive and ascent, while the roll angle can be indicated by the movement of a needle fixed to the circle 11, relative to a graduated scale fixed to the housing 10, and which are both visible through the window 11 The indicating element is driven by the movement of the inner circle 19, by some form of reverse gear mechanism, such as a gear train, shown here in the form which includes two intermediate gears carried by

the support element 15.

  A model 25, which represents the plane, is fixed to the housing 10 of the instrument or to the window 11 so as to be visible

  on the surface of the indicator element 22.

  When the instrument is mounted in an instrument panel inclined as shown, the horizon indicator 23 is moved away from the longitudinal axis 16 of the instrument by a specified angle, equal to the angle O of inclination of the panel However, the gear ratio 5 n of the reverse gear, which is interposed between the gyroscope and the indicator element, is usually greater than unity, for example 1.5 In this way, the indicator element 22 will actually be rotated by an angle n Y If the model was placed on the axis of the instrument, the instrument would indicate a dive angle of E when the roll axis 14 of the plane is actually horizontal For this reason, according to the invention, the

  model is shifted upwards to cancel the dive angle indicated.

  Assuming that the instrument is seen by an observer along a line of sight parallel to the axis 16, the model 25 is offset relative to this axis by a value equal to the offset of the horizon indicator 23, by so that the plane appears in horizontal flight If the plane turns around the horizontal axis 14, there is a downward movement of the model 25, according to a law identical to that of the downward movement of the horizon indicator 23 , so as to maintain a flight indication

  horizontal at all angles of inclination.

  One of the problems that arises when calibrating an airplane attitude indicator is to determine a reference attitude for the airplane. It is possible that the roll axis of the airplane on the ground is horizontal. Au on the contrary, in flight, the situation is different in that the airplane tends to fly horizontally in a nose-up attitude. However, the nose-up angle is itself variable, depending on the speed of the airplane and according to its load, at the times in total weight and in position of its center of gravity Although these criteria do not vary much in the case of a civil aircraft, the situaiton may be different in a military aircraft which carries dropable ammunition It follows that, whatever 'it either, the reference position which will be decided will be a compromise However, whatever the reference attitude for which the model is fixed, the pitch attitude indicated of the aircraft will always be error free when the plane flies in an attitu of pitch, for all values of the roll angle If the pitch attitude changes, the maximum error shown at a roll angle of 1800 will be double the difference of the pitch angle from the reference This will be less than the maximum error, which could reach twice the tilt of the instrument panel, which would have occurred

in a standard instrument.

  As already indicated, the position that we decided to give to the model can take into account the fact that the instrument is not seen along a line of sight parallel to the axis of the instrument The resulting parallax error correction is easy to calculate

  when we know the average position of the eyes of the observer.

  In addition, if the model is at a significant distance from the surface of the indicator cylinder, parallax errors will be more pronounced, however, the construction of most

  attitude indicators is designed to reduce this effect.

  The reversing transmission which interconnects the inner circle of the gyroscope and the indicating element does not necessarily have to be a gear mechanism. Other forms of mechanisms suitable for this function are also known. Other modifications of known forms can be applied to other

aspects of the instrument.

Claims (1)

CLAIMS 1 Aircraft attitude indicator intended to be mounted in an inclined instrument panel, the indicator comprising a housing intended to be fixed to the panel and having a longitudinal axis arranged to be perpendicular to the plane of the panel in use, a support element mounted in the housing to be movable in rotation around said longitudinal axis, an indicator element supported by the support element to be movable in rotation around an axis perpendicular to said longitudinal axis and having on its surface an indicated horizon which cuts the longitudinal axis when this axis is horizontal, a gyroscope with a single degree of freedom, having an inner circle mounted on the support element with its axis of rotation parallel to that of the indicator element, an inverting transmission, which interconnects the circle interior of the gyroscope and the indicator element, and a model fixed to the instrument housing, in a pos ition adjacent to the surface of the indicator element and which is offset from said longitudinal axis by a distance substantially equal to the offset of the horizon indicated with respect to this axis when the aircraft is in a predetermined attitude. 2 indicator according to claim 1, characterized in that the housing comprises a window mounted perpendicular to said longitudinal axis. 3 Indicator according to claim 2, characterized in that the model is carried by the window. 4 Indicator according to any one of the claims   1 to 3, characterized in that the reversing transmission comprises a gear train.