GB1605011A - Aircraft display systems - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO AIRCRAFT DISPLAY SYSTEMS (71)I, SECRETARY OF STATE FOR DEFENCE, LONDON, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to systems for aiding the piloting of fast flying aircraft at low levels.

Modern developments in radar and missile technology have resulted in greatly increased effectiveness of air defence systems. Consequently it has become necessary for aircraft in combat to fly fast at low altitudes to reduce the time during which they present themselves as targets.

When flying an aircraft at low altitude a pilot has to assess the potential danger of objects in his flight path and manoeuvre his aircraft to avoid them. In doing this it is probable that he assesses the overall angular velocity situation caused by the apparent increase in size of objects as the aircraft approaches them. The angular velocities of distant objects are viewed directly and of near objects by peripheral vision. The pilot manoeuvres his aircraft so that the overall angular velocity picture he sees is one which experience has taught him is safe. The ability of a particular pilot to fly an aircraft low and fast is therefore conditioned by his skill and training. There have been no innovations in the history of aircraft development which increase the innate ability of pilots to fly aircraft low and fast when relying on their vision. Consequently as aircraft speeds have increased, and as their weights have increased, resulting in greater inertial resistance to control inputs, the safe height at which they can be flown visually has increased.

Terrain Following Radar (TFR) systems have been designed which, in combination with autopilots, enable aircraft to be flown fast and low. Such systems, however, are expensive in terms of weight, complexity, installation space and cost. They are also vulnerable to radar jamming procedures, provide advance warning of an aircraft's approach to radar monitoring equipment and are ineffective when an aircraft is manoeuvring in combat conditions.

The present invention provides a visual display for a pilot to assist him in maintaining safe high speed low level flight.

According to the present invention display means in an aircraft comprises a display screen, means for displaying a series of moving symbols on the screen whereby to superimpose the moving symbols on a pilot's view of the ground ahead of the aircraft, and control means for controlling the rate of movement of the symbols in dependence upon the measured speed of the aircraft, such that, in use of the display means, the movement of the symbols across the screen coincides with the way in which the pilot's view of the ground ahead of the aircraft would appear to move across the screen if the aircraft was flying at or near a desired height, irrespective of the actual height of the aircraft.

In accordance with the invention the moving symbols may be super-imposed on a television type picture on the display screen presenting to the pilot a view of the ground ahead of the aircraft, or the invention may use the principal of the head-up display which is conventionally used to assist pilots in tasks, such as approaching to land, requiring a combination of visual and instrument flight. Thus the display screen may comprise a semi-transparent reflector (which can be the aircraft windscreen) arranged in the pilot's forward line of view of the ground ahead of the aircraft and the means for displaying the symbols comprises projection means for projecting an image of the symbols onto the semi-transparent re flector to produce a head-up display.

Preferably the projection means is a cathode ray tube and the control means is a computer.

Preferably the symbols are controlled to expand symmetrically normal to the longitudinal axis of the aircraft at a rate which matches the apparent expansion of objects on the ground as the aircraft approaches them when flying at the desired eight.

In one form of the invention the symbols are a series of horizontal lines, each of which appears on the semi-transparent reflector at a position approximating to the horizon as viewed by the pilot, and moves down the reflector as seen by the pilot, symmetrically widening as its moves down until it disappears at or near the bottom of the reflector. The edges of the horizontal lines are defined by a pair of lines which diverge from the top towards the bottom of the reflector.

One embodiment of the invention will now be described, by way of example only, with reference to the diagrammatic drawings accompanying the Provisional Specification, of which: Figure I shows an elevation in section of an aircraft cockpit, Figure 2 shows an elevation of a low flying aircraft, and Figure 3 is a view through an aircraft windscreen.

An aircraft cockpit 1 (Figure 1) has a windscreen 2 in front of which is a semitransparent reflector 3. A cathode ray tube 4 projects a series of moving symbols, in the form of horizontal lines, as shown at 5a to Se in Figure 3, onto the screen reflector 3. A pilot 6 sees the lines 5 (as indicated by the dotted lines 7 in Figure 1) as he looks forward through the semi-transparent reflector 3 and windscreen 2 (as indicated by the chain-dotted line 8 in Figure 1).

Movement of the lines 5 is controlled by a computer 9 according to a programme based on a desired height to be flown, selected by a control knob 10 in the cockpit 1, and on the airspeed of the aircraft as measured by an airspeed sensor 11 receiving an input from a pilot static tube 12.

Control by the computer 9 is such that, as viewed by the pilot (Figure 3) lines 5 appear, adjacent the external horizon indicated at 13, on the reflector 3 as shown at 5a. Each line moves vertically down the reflector 3, expanding horizontally as it does so with its ends travelling along a pair of downwardly diverging lines 20, to the position shown at 5e, then fades from the display. At any one time there are several lines displayed. When the aircraft is flying at the desired height, as selected by control knob 10, the lines 5 appear to move with the ground below the aircraft, and objects on the ground remain stationary relative to the lines 5 and appear to increase in size at the same rate as the lines 5 expand horizontally.

The effect is illustrated in Figures 2 and 3 where an aircraft (15 in Figure 2) flying at the desired height over ground 14 is approaching a building 16, aiming to pass to the left of the building. As seen by the pilot (Figure 3) the building 16, having appeared over the horizon 13 is shown at 16a adjacent to line 15a which has just appeared on the reflector 3. As the aircraft 15 approaches the building 16 the line moves through the positions 1 b, c, d and e whilst the building appears to retain the same position (along the longitudinal axis of the aircraft 15) relative to the line, and also to increase in size at the same rate as the line increases in length. The effect is illustrated in Figure 3 where the view of the building as the aircraft approaches is shown at 16a, 16b, 16c, 16d and 16e. Any change in airspeed of the aircraft 15 is noted by the airspeed sensor 11 and passed to the computer 9 which alters the rate of movement of the lines 5 to maintain the effect illustrated in Figure 3.

Should the aircraft 15 fly above the desired height, the lines 5 will appear to move faster than the ground, whilst below the desired height the ground will appear to move faster than the lines 5.

It will be appreciated that in practice, with the embodiment described above, the actual height at which coincidence between movement of the lines 5, and the apparent movement of the ground will occur, will depend upon the ground speed of the aircraft 15, and may therefore differ slightly from the desired height. Thus, when the ground speed of the aircraft is higher than the airspeed, the aircraft will have to be flown slightly higher than the desired height to synchronise the speed of the lines 5 with the apparent speed of the ground, and vice versa. The effect is slight and is in any case beneficial, providing a safety factor in that as ground speed increases, allowing a pilot less time to react to changes in the ground ahead of him, the aircraft height and hence the margin of safety increases.

It will be appreciated that many variations of the embodiment described above with reference to Figures 1 to 3 are possible within the scope of the invention. For example, whilst the pilot 6 is described as having control of the desired height using a control knob 10 (an arrangement which permits allowance to be made for conditions such as visibility and type of terrain being overflown), the height might be preset.

Alternatively the computer may be programmed to vary the desired height according to the airspeed, so that, for example, the desired height is increased as the airspeed increases to allow for the reduced reaction time available to the pilot. In aircraft equipped with ground speed measuring devices, ground speed rather than airspeed can be fed into the computer 9. It is also possible to use symbols other than lines 5 - for example pairs of circles, triangles or the like appearing at positions corresponding to the ends of line 5a and moving downwards and outwards to positions corresponding to the ends of line 5e, possibly expanding in size as they do so.

It will be apparent that the display described above can be added as one mode of operation of a conventional head up display system. Whilst in general, use of the display with a full conventional head up display presentation would be liable to cause confusion, it might in some cases be useful to have certain conventional parameters, such as airspeed, displayed concurrently with a display according to the invention.

Whilst the invention as described with reference to Figures 1 to 3 is of use mainly for daylight flying, it can also be used in conjunction with night vision sensors. Such sensors provide a television type cathode ray tube picture of ground ahead of the aircraft. The picture can either be projected as a head up display or shown as a head down display. In either case superimposition of a display according to the invention will assist in low flying. When flying with a head down display a pilot will ignore the view through the aircraft windscreen, and his visual line of sight will effectively be through the display.

WHAT I CLAIM IS: 1. In an aircraft, display means comprising a display screen, means for displaying a series of moving symbols on the screen whereby to superimpose the moving symbols on a pilot's view of the ground ahead of the aircraft, and control means for controlling the rate of movement of the symbols in dependence upon the measured speed of the aircraft, such that, in use of the display means, the movement of the symbols across the screen coincides with the way in which the pilot's view of the ground ahead of the aircraft would appear to move across the screen if the aircraft was flying at or near a desired height, irrespective of the actual height of the aircraft.

2. In an aircraft, display means as claimed in claim 1 wherein the display screen comprises a semi-transparent reflector arranged in the pilot's forward line of view of the ground ahead of the aircraft, and the means for displaying said symbols comprises projection means for projecting an image of the symbols onto the semitransparent reflector to produce a head-up display.

3. In an aircraft, head-up display means as claimed in claim 2 wherein the projection means is a cathode ray tube and the control means is a computer.

4. In an aircraft, display means as claimed in any one of claims 1 to 3 wherein the symbols are controlled to expand symmetrically normal to the longitudinal axis of the aircraft at a rate which matches the apparent expansion of objects on the ground as the aircraft approaches them when flying at the desired height.

5. In an aircraft, display means as claimed in any one of claims 1 to 4 wherein the symbols are a series of horizontal lines, each of which appears on the semitransparent reflector at a position approximating to the horizon as viewed by the pilot and moves down the reflector as seen by the pilot symmetrically widening as it moves down until it disappears at or near the bottom of the reflector.

6. In an aircraft, display means as claimed in claim 5 wherein the edges of the horizontal lines are defined by a pair of lines which diverge from the top towards the bottom of the reflector.

7. In an aircraft, display means as claimed in any one of claims 1 to 6 wherein the desired height is preset.

8. In an aircraft, display means as claimed in any one of claims 1 to 6 wherein the desired height can be selected by the pilot.

9. In an aircraft, display means as claimed in any one of claims 1 to 6 wherein, in use of the display, the desired height is automatically varied by the control means in dependence upon the measured speed of the aircraft.

10. In an aircraft, display means as claimed in any one of claims 1 to 9 wherein the measured aircraft speed is transmitted to the control means from an airspeed sensor.

11. In an aircraft, display means as claimed in any one of claims 1 to 9 wherein the measured aircraft speed is transmitted to the control means from a groundspeed sensor.

12. In an aircraft, head-up display means substantially as herein described with reference to Figures 1 to 3 of the drawings filed with the provisional specification.

13. An aircraft including display means as claimed in any one of claims 1 to 12.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (13)

**WARNING** start of CLMS field may overlap end of DESC **. time available to the pilot. In aircraft equipped with ground speed measuring devices, ground speed rather than airspeed can be fed into the computer 9. It is also possible to use symbols other than lines 5 - for example pairs of circles, triangles or the like appearing at positions corresponding to the ends of line 5a and moving downwards and outwards to positions corresponding to the ends of line 5e, possibly expanding in size as they do so. It will be apparent that the display described above can be added as one mode of operation of a conventional head up display system. Whilst in general, use of the display with a full conventional head up display presentation would be liable to cause confusion, it might in some cases be useful to have certain conventional parameters, such as airspeed, displayed concurrently with a display according to the invention. Whilst the invention as described with reference to Figures 1 to 3 is of use mainly for daylight flying, it can also be used in conjunction with night vision sensors. Such sensors provide a television type cathode ray tube picture of ground ahead of the aircraft. The picture can either be projected as a head up display or shown as a head down display. In either case superimposition of a display according to the invention will assist in low flying. When flying with a head down display a pilot will ignore the view through the aircraft windscreen, and his visual line of sight will effectively be through the display. WHAT I CLAIM IS:

1. In an aircraft, display means comprising a display screen, means for displaying a series of moving symbols on the screen whereby to superimpose the moving symbols on a pilot's view of the ground ahead of the aircraft, and control means for controlling the rate of movement of the symbols in dependence upon the measured speed of the aircraft, such that, in use of the display means, the movement of the symbols across the screen coincides with the way in which the pilot's view of the ground ahead of the aircraft would appear to move across the screen if the aircraft was flying at or near a desired height, irrespective of the actual height of the aircraft.

2. In an aircraft, display means as claimed in claim 1 wherein the display screen comprises a semi-transparent reflector arranged in the pilot's forward line of view of the ground ahead of the aircraft, and the means for displaying said symbols comprises projection means for projecting an image of the symbols onto the semitransparent reflector to produce a head-up display.

3. In an aircraft, head-up display means as claimed in claim 2 wherein the projection means is a cathode ray tube and the control means is a computer.

4. In an aircraft, display means as claimed in any one of claims 1 to 3 wherein the symbols are controlled to expand symmetrically normal to the longitudinal axis of the aircraft at a rate which matches the apparent expansion of objects on the ground as the aircraft approaches them when flying at the desired height.

5. In an aircraft, display means as claimed in any one of claims 1 to 4 wherein the symbols are a series of horizontal lines, each of which appears on the semitransparent reflector at a position approximating to the horizon as viewed by the pilot and moves down the reflector as seen by the pilot symmetrically widening as it moves down until it disappears at or near the bottom of the reflector.

6. In an aircraft, display means as claimed in claim 5 wherein the edges of the horizontal lines are defined by a pair of lines which diverge from the top towards the bottom of the reflector.

7. In an aircraft, display means as claimed in any one of claims 1 to 6 wherein the desired height is preset.

8. In an aircraft, display means as claimed in any one of claims 1 to 6 wherein the desired height can be selected by the pilot.

9. In an aircraft, display means as claimed in any one of claims 1 to 6 wherein, in use of the display, the desired height is automatically varied by the control means in dependence upon the measured speed of the aircraft.

10. In an aircraft, display means as claimed in any one of claims 1 to 9 wherein the measured aircraft speed is transmitted to the control means from an airspeed sensor.

11. In an aircraft, display means as claimed in any one of claims 1 to 9 wherein the measured aircraft speed is transmitted to the control means from a groundspeed sensor.

12. In an aircraft, head-up display means substantially as herein described with reference to Figures 1 to 3 of the drawings filed with the provisional specification.

13. An aircraft including display means as claimed in any one of claims 1 to 12.