AIRCRAFT FLIGHT INSTRUMENT DISPLAYS

BACKGROUND OF THE INVENTION

The present application is a continuation-in-part of USSN 08/412,874 filed March 29, 1995 entitled "Aircraft Flight Instrument Displays" by Simon J. Durnford.

1 , Field of the Invention The present invention relates to flight instrument displays, particularly such displays for light aircraft and helicopters, and is of particular value in such aircraft having single pilots and no auto-pilot.

2. Discussion of Prior Art It is well known that aircraft pilots operating without automatic controls require visual references to maintain controlled flight. Under certain conditions, which are commonly met during normal operations, such as in moisture or dust clouds or similar low visibility, the visual reference has to be provided by instruments. Conditions where instruments must be used are known as instrument flight conditions (IFC). Physical or cognitive misconceptions, particularly in instrument flight conditions, may lead a pilot to an incorrect understanding of his aircraft's orientation, a condition known as spatial disorientation (SD). Studies have shown that between 80-100% of aircrew, fixed wing and helicopter, have suffered SD to some degree. Studies have also shown that SD is a cause of many accidents, for example, it has been reported as a major factor in 32% of military helicopter accidents.

It is an important consideration that instrument displays should be easy to read and that readings from various instruments should be easily correlated to give the pilot a true picture of his aircraft's flight path. This is particularly important for conditions where an aircraft suddenly and unexpectedly enters poor visibility and the pilot has to make a rapid transition from visual to instrument flight conditions.

There is a need, therefore, for a simplified instrument display which provides an adequate source of information for standard instrument flight and which also provides an easy source of information for maintenance or re- establishment of a correct flight path on an occurrence of SD.

SUMMARY OF THE INVENTION

The present invention is an aircraft flight instrument display that includes a display panel having a combined speed and heading indicator. A preferred embodiment of the invention has a heading indicator in the form of a central symmetrical shape surrounded by a scaled matrix pattern, where the divergence of an aircraft, in which the display is installed, from a desired speed and heading is indicated by displacement of an aircraft symbol from the central shape.

The aircraft having a flight control system and an attitude sensing system and the instrument display having a display control system, the attitude sensing system and the display control system having an interconnection with control laws such that, when the aircraft is displaced from its desired speed and heading, adjustment of the flight controls so as to pitch and roll the aircraft in a manner tending to return the aircraft to the desired speed and heading causes the aircraft symbol to move towards the central symmetrical shape.

The control laws are such that, when the aircraft has deviated from the desired speed and heading, the position of the aircraft symbol within the central symmetrical shape indicates that the pilot has applied control inputs to change the aircraft pitch and roll angles at a rate appropriate for a safe return of the aircraft to the desired speed and heading. The control laws are also preferable such that, as the aircraft speed and heading approach the desired speed and heading, the aircraft symbol moves out of the central symmetrical shape until the pilot again adjusts the aircraft control inputs (thereby moving the symbol back to the central symmetrical shape) so that the angles of bank and pitch are adjusted to steady the aircraft onto the desired speed and heading with the aircraft symbol within the central symmetrical shape. The control laws may demand a gradual change in aircraft control inputs as the desired speed and heading are approached.

Edges of the pattern may have, adjacent thereto, parameter indicators indicating various flight parameters. The central symmetrical shape may be a square. The scaled matrix will normally be symmetrical, may be a square, and may consist of a pattern of auxiliary symmetrical shapes which may be one or more types of symmetrical shapes such as squares, rectangles, circles, ovals or the like. The parameter indicators will include indicators showing parameters other than those indicated by the square pattern and aircraft symbol, and might also include indicators confirming the parameters indicated by the square pattern and aircraft symbol.

A typical parameter indicator pattern might include, for example, a vertical speed indicator (VSI), an altimeter, an airspeed indicator (ASI). a heading indicator and/or a slip indicator. These might conveniently be positioned with the VSI and altimeter, one on either side of the square pattern, the ASI and slip indicator below the pattern and the heading indicator above the pattern. The VSI and altimeter might be in the form of digital readings of actual and desired aircraft performance in combination with displacement measures in tape form showing displacement of the relevant parameter from that desired.

The display control system will have provision for a mode change of desired flight parameters, any such change being reflected in the control law algorithms applied to the output of the aircraft attitude sensor. Changes in the desired speed and heading will result in the movement of the aircraft symbol out of the central symmetrical shape until appropriate control inputs are made. In a further embodiment, actual aircraft heading and desired airspeed are indicated in dedicated locations around the pattern. Additionally, a linear slip meter indicating whether a tiirn is balanced is also located below the pattern. In this embodiment, a mode of operation can be enabled such that straight and level flight can be prompted by the flight display. Alternatively, standard rate turns, climbs and/or descents and even instrument flight instructions can be prompted by the display.

The various indicators are preferably color coded. For example, the aircraft symbol, which is preferably a triangle, may be green to indicate that the aircraft is at the correct altitude, red to indicate that the aircraft is low. and blue to indicate that the aircraft is high.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings:

Figure 1 is a schematic representation of the interrelationship between an aircraft and a display in accordance with the present invention;

Figure 2 is a front view of an instrument display in accordance with the present invention; and

Figure 3 is a front view of an instrument display in accordance with a further embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As shown in Figure 1, an aircraft 100 has a flight control system for controlling the aircraft in flight, an aircraft attitude sensor system 102 connected to a flight instrument control system 104 by an interconnection 106. The interconnection 106 could be merely cabling connecting the two systems where the subsequently discussed control laws implemented by the interconnection 106 are actually incorporated into one or both of the systems themselves.

The flight instrument control system 104 controls an aircraft flight instrument display 108 which has a display panel 10 having a central square 1 1 surrounded by a symmetrical pattern 12, indicated by the broken line, of auxiliary squares 13 (only a portion of which are labeled 13). The display panel 10 could be a cathode ray tube, a liquid crystal display, a plasma display or other convention display device. An aircraft symbol 14, in the form of a triangle, is adapted to be displaced from the central square 11. Displacement of the aircraft symbol in the x-axis is related to both the error between desired and actual headings of an aircraft in which the display is installed and to the aircraft's roll angle. Displacement in the y-axis is related to both the error between desired and actual speeds of the aircraft and to the aircraft's pitch angle. The two factors relevant to each axis act in the opposite direction to each other such that the symbol's displacement will be nil when predetermined pitch and/or roll changes

(appropriate to return the aircraft safely to the desired speed and heading) are sensed by the aircraft attitude sensor system 102.

To the left of the pattern 12 is a vertical speed indicator (VSI) 15 having a digital reading 16 of the rate of descent or ascent in conjunction with a strip display 17 of that rate. To the right of the pattern 12 is an altimeter 18 having digital readings of the aircraft's actual altitude 19 and desired altitude 20, and a strip display 21 showing the error between desired and actual altitudes. Below the desired altitude reading 20 is an altimeter pressure setting indicator 28 and above the reading 20 is a glide path selection 29. Above the pattern 12 is a heading indicator 22 having a desired heading 23 and an actual direction indicator (DI) 24. Below the pattern 12 is a digital airspeed indicator (ASI) 25 showing actual airspeed.

Auxiliary squares 26. horizontally aligned with central square 1 1, contain a digital reading of the desired airspeed and auxiliary squares above and below these indicate deviations between the desired and actual airspeeds.

Various of the display panel indicators may be color coded. For example, the aircraft symbol 14 might be green when the aircraft is at its correct altitude, red when the aircraft is low and blue when it is high. Similarly, the strip display 5 17 might be different colors to indicate climbing or descending and the strip display 21 different colors to indicate whether the aircraft is high or low.

The attitude sensor system 102 provides an output indicative of the actual pitch and roll angles of the aircraft. The interconnection 106 to the flight instrument control system 104 is programmed according to appropriate control ιo laws and is connected to the display panel 10, causing the display to indicate the desired flight program and the deviations therefrom.

In the display pattern as shown in Figure 2, the desired flight program is a speed of 100 knots (see box 26) at a height of 2,000 ft (see box 20) on a heading of 360° (North as in box 23). As can be seen, the actual speed is 67 knots (box

15 25). the height 3,159 feet (box 19) and the heading 278° (box 24). The displacement of the aircraft symbol 14 from the central square 1 1 indicates displacement (on the vertical or y axis) from the correct speed and/or the pitch change needed to achieve the correct speed and displacement (on the horizontal or x axis) from the correct heading and/or the roll change needed to achieve the 0 correct heading. Displacement from the correct altitude and from level flight are indicated by the altimeter and VSI displays, respectively.

The attitude sensor system 102 determines the aircraft's roll and pitch angles. The control laws programmed into the interconnection are the pitch and roll angles (dependent at least in part upon the speed and heading errors, 5 respectively) necessary to bring the aircraft back to the correct heading and airspeed in a timely fashion (which may be different from the subsequently discussed preferred embodiment, depending upon aircraft type, size, etc.). If the pilot adjusts either roll and/or pitch of the aircraft 100 closer to the programmed necessary roll and pitch changes, the aircraft symbol 14 moves towards the central square 11.

When the correct roll and pitch angles are achieved (as a result of the pilot's inputs to the aircraft control system), the symbol 14 will lie within the square 1 1. Once the aircraft approaches its correct speed and heading, the symbol 14 previously centered, will start to move out of the square 1 1 (in the opposite direction) until the existing pitch and roll inputs have been neutralized so as to maintain the aircraft at its desired speed and on its desired heading.

Heading Control

The heading control laws are such that, in a preferred embodiment of the present invention applicable to a utility helicopter, the aircraft symbol moves sideways along the x axis 1 cm for every 20° of heading error (left if the heading error is to the left and right if the heading error is to the right) with a maximum sideways displacement of 1.5 cm (equivalent to a heading error of 30 °). However, the aircraft symbol is displaced in the opposite direction 1 cm for every 10° bank, where the bank is in a direction which will reduce the heading error, e.g. if, as disclosed in Figure 2, the aircraft is to the left of the desired heading, only an appropriate bank to the right will return the aircraft symbol to the central box (and the aircraft back to its proper heading in a timely fashion). There is no limit or cap on the aircraft displacement due to roll and thus, if a roll input is larger than required, the aircraft indicator would actually move to and past the central square 11. inducing the pilot to reduce the bank angle.

Assume that the aircraft is 30° to the left of its desired heading, then the aircraft symbol will be displaced 1.5 cm to the left of the central square along the x axis. Even the disoriented pilot, viewing the display, can input a roll in the direction from the aircraft symbol towards the central square 11, i.e., a roll to the right. Using the above, it will be seen that a 15° roll to the right will move the aircraft symbol 1.5 cm to the right or directly over the central square 1 1 (because the original location being 1.5 cm to the left due to the heading error has been offset by the 1.5 cm movement to the right due to the roll). At this point the pilot knows that the appropriate amount of roll has been provided even though he may have no ground visibility and may still be disoriented (and thereby prevented from effectively using his normal attitude sensor). While the aircraft is off heading, it has also rolled into a turn which will bring it back to the desired heading.

Assuming that the same 15 ° bank is maintained, as the heading error decreases (as the aircraft turns towards the desired heading) the aircraft symbol will gradually move to the right of the central square because, while the rightward 1.5 cm displacement due to the 15 ° bank stays constant, the leftward displacement due to heading error is gradually decreasing to 0 cm. Accordingly, the effect on the pilot whose inputs are to try to keep the aircraft symbol centered on the central square, is that, as the aircraft symbol begins to move to the right of the central square, the pilot begins to roll left (the direction from the symbol to the central square) which reduces the bank angle. Ultimately, the pilot rolls out level on the desired heading.

Speed Control The speed control laws are such that, again in our preferred embodiment of the present invention applicable to a utility helicopter, the aircraft symbol moves vertically along the y axis 1 cm for every 20 knots of speed error (downwards if the speed error is below the desired speed and upwards if the speed error is above the desired speed) with a maximum displacement due to speed error of 1.25 cm i.e., a maximum vertical displacement of 1.25 cm due to a speed error of 25 knots. However, the aircraft symbol is displaced along the y axis, in the direction of the central square 1 1, 1 cm for every 10° pitch change, where the pitch change is in a direction which will reduce the speed error. For example, as disclosed in Figure 2, the aircraft is below the desired speed, a 10° pitch down of the nose of the aircraft will aid in the acceleration of the aircraft back to its proper speed. There is no limit or cap on the aircraft symbol displacement due to pitch changes and thus, if a pitch change is larger than that required, the aircraft indicator could actually move up to and past the central square 11, inducing the pilot to reduce the amount of pitch change.

Assume that the aircraft is 30 knots below its desired speed, then the aircraft symbol will be displaced 1.25 cm (the maximum displacement due to speed error is 1.25 cm) below the central square along the y axis. Even the disoriented pilot, viewing the display, can input a pitch change in the direction from the aircraft symbol towards the central square 1 1 , i.e., pushing the aircraft control stick forward. Using the above, it will be seen that a 15° pitch change downwards will move the aircraft symbol 1.5 cm upward and past the central square 11 (because the original location being 1.25 cm below due to the speed error has been offset by the 1.5 cm upward movement due to the nose down pitch change). At this point the pilot knows that more than the appropriate amount of pitch change has been provided and a slight raising of the nose will serve to center the aircraft symbol on the central square 1 1. While the aircraft is off of its desired speed, it has pitched down so that it will begin to accelerate up to the desired speed. Just as with the heading correction, as the speed error decreases (as the aircraft speed increases towards the desired speed) the aircraft symbol will gradually move above the central square 1 1 because, while the upward 1.5 cm displacement due to the 10° downwards pitch change stays constant, the downward displacement due to speed error is gradually decreasing to 0 cm (as the speed increases to the desired speed). Accordingly, the effect on the pilot, whose inputs are to try to keep the aircraft symbol centered on the central square, is that, as the aircraft symbol begins to move above the central square, the pilot begins to pitch the aircraft nose up (the direction from the symbol to the central square) which reduces the original downward pitch. Ultimately, the pilot levels off at the desired speed.

In practice, of course, and depending on his skill and experience, a pilot, in recovering from disorientation, may concentrate first on establishing the correct roll angle and then on the correct pitch angle, or vice versa, or both simultaneously.

Instrument Flight

While a major benefit of the present invention is to aid a pilot in recovering from an unusual attitude and/or spatial disorientation, the system is very useful during instrument flight rules situations (without reference to outside the cockpit visual cues as when flying in a cloudbank). A further embodiment of the present system is shown in Figure 3 which in addition to the features shown in Figure 2, there are a number of additional refinements. In addition to the desired heading 23, there is an actual heading indicator 50. While the actual direction indicator 24 provides an easy reference to the aircraft direction, heading indicator 50 provides a precise indication of the actual heading. Additionally, the digital airspeed indicator 25 is an indication of actual airspeed with a further indicator 51 in which the desired airspeed is set. As with other information provided to and displayed on the panel, desired airspeed, heading and altitude can be input by conventional keypad or keyboard, voice command, prerecorded flight profile, or other conventional information input method.

A linear slip meter 52 provides an indication of the apparent gravity vector in the aircraft. For example, if the aircraft is banked with insufficient rudder or anti-torque input to provide a balanced turn, the solid rectangle 53 will move away from the center position and towards the side of the bank indicating that that side's rudder pedal must be moved forward to move the rectangle back to the desired center position. As the correct amount of rudder pedal control input is supplied by the pilot (to create a balanced or coordinated turn) the rectangle moves back to the center position.

For example, if the aircraft is in a side slip to the left (a left bank angle without rudder input) the rectangle will move to the left indicating to the pilot that a forward movement of the left rudder pedal is necessary. As the pilot provides the control input in the form of a depression of the left rudder pedal, the rectangle will begin to move back towards its centered position. When a balanced or coordinated turn is achieved, the rectangle will be at the center position. However, if in a left turn, too much left rudder pedal has been applied, the indicator will move to the right of the center position indicating some right rudder pedal needs to be applied in order to achieve a properly balanced turn.

At the upper right portion of Figure 3, a display mode indicator 54 indicates the mode of operation of the display and may be changed in a manner similar to the information input to the system. During instrument flight rules, an aircraft, without any visual reference to the ground or even the relative horizon, must be capable of flying straight and level flight, performing standard rate turns, climbing and descending at specific rates of climb or descent. The flight instrument display aids in maintaining these conditions and the pilot can select the mode of flight desired and the flight instrument display will support and guide the selected mode of flight.

Straight and level flight (SL) is indicated in Figure 3 and, as described previously, is maintained by the display which targets airspeed, heading and altitude deviations and indicates the control stick motion necessary to achieve the desired heading, airspeed and altitude. Standard rate turns (SRT) comprise a turn of 3° per second and would be indicated by LSRT for a left standard rate turn and RSRT for a right standard rate turn at position 54. When a standard rate turn mode is selected by the pilot, the heading to which the aircraft will be turned is inserted into the desired heading box 23. Utilizing the same information presentation as previously discussed with respect to regaining a desired heading in the SL mode, the triangle aircraft symbol 14 will be offset from its central position (to the left for a RSRT and to the right for a LSRT) to prompt the appropriate roll input. When the pilot has rolled the aircraft to the right for a RSRT and to the left for a LSRT, the triangle aircraft symbol 14 will move back to neutral alignment. If the pilot does not coordinate the turn properly, the slip meter will provide the suitable guidance symbology discussed above to correct the error.

Because the bank angle required for a 3° per second turn rate is dependent upon aircraft speed (e.g., 19° at 120 knots), the triangle will remain in the central box 1 1 as long as the angle of bank appropriate to the actual airspeed for a standard rate turn is maintained. When the aircraft heading is within 20° of the desired heading, the heading control of the display reverts to the symbology for straight and level flight (SL) so that a gradual roll out from the standard rate turn bank angle to straight and level flight is achieved. When the desired heading has been gained, the display automatically reverts to the SL mode. Quite obviously, if rates of turn other than a standard rate turn are desired, they can be incorporated into the display.

Additionally, climbs and descents are of importance to a pilot during instrument flight rules operation. When a climb or descent mode is initiated, the altitude to which the aircraft must be climbed or descended is inserted into the desired altitude box 20 and as a result, the altimeter strip display 21 will provide an indication that the aircraft is presently too low (in the case of a climb) or too high (in the case of a descent). The pilot will provide a control input to reduce the altitude error being indicated by strip display 21 by either climbing or descending.

However, if a pitch change is made to effect the climb or descent, without a power change, aircraft speed will begin decreasing (in the case of a climb) or increasing (in the case of a descent) and vertical movement of the aircraft symbol 14 will signal a necessary power adjustment on the part of the pilot to maintain the set airspeed. As soon as the desired altitude has been gained, the display automatically reverts to the SL mode.

In a similar manner, climbing or descending standard rate turns can be maintained by the combination of the two modes described above, i.e., setting a standard rate turn to a heading set in box 23 and then establishing a climb or descent to the desired altitude set in desired altitude box 20.

The system can also be operated in conjunction with an instrument landing system which feeds variable values of desired heading, altitude and vertical speed to the display such that an instrument landing profile can be easily commanded and followed. With respect to helicopters, the display may be reconfigured so that the aircraft triangle system represents a hovering helicopter with the central square becoming a datum hover position over the ground.

Vertical movement of the aircraft system 14 on the display would be controlled by integration of ground speed and pitch angle of the aircraft with horizontal movement of the aircraft system being controlled by integration of sideways drift and roll angle.

It is understood that while portions of the above system have been discussed as separate elements, in practice, many of these elements would ordinarily be combined in a modern aircraft. For example the aircraft attitude sensor system 102 and the flight instrument control system 104 would normally be combined with any necessary control laws, represented by interconnection

106, incorporated therein.

It will be realized, of course, that in view of the above, many variations of the above system are possible within the scope of the present invention and would be obvious to those of ordinary skill in the art. For example, the rates and or angles of pitch and roll correction may be different from those discussed. In the display, other shapes than squares may be substituted for the central and auxiliary squares 1 1, 12, respectively. Indeed, the auxiliary pattern may be free of any auxiliary shapes. Further, although the primary benefit of the present invention is with respect to controlling both heading and airspeed, it could be used advantageously to provide information on only a single parameter. Additionally, while heading and speed parameters are used in the above preferred embodiment, any other aircraft control parameter could be displayed and controlled by the present invention. The invention provides a flight instrument display which enables a pilot of an aircraft to concentrate on maintaining or regaining a desired flight path without the need to monitor and respond to his aircraft's attitude sensor when disoriented. Accordingly, the invention is limited only by the following claims