GB2300167A

GB2300167A - Aircraft instrument for indicating rate of change of pitch

Info

Publication number: GB2300167A
Application number: GB9607429A
Authority: GB
Inventors: James Frederick Moore; Brian William Rawnsley; Alison Frances Starr
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1995-04-28
Filing date: 1996-04-10
Publication date: 1996-10-30
Anticipated expiration: 2016-04-10
Also published as: FR2733597B1; FR2733597A1; GB9508659D0; CA2175030A1; DE19615258A1; GB2300167B; GB9607429D0

Description

1 Aircraft Instruments This invention relates to aircraft instruments.

2300167 The invention is more particularly concerned with instruments for warning a pilot of an aircraft when the pitch rate deviates from a desired value during the rotation phase of take-off.

During take-off roll, the pilot rotates the aircraft (that is, lifts the nose off the runway) when the aircraft's rotation speed, Vr, is reached. The climb attitude of an aircraft is typically 20' from the horizontal. Before the pilot can put the aircraft safely into this attitude, the aircraft must have lifted sufficiently to ensure that its tail does not strike the ground. Wing lift does not occur immediately that rotation takes place because of the time taken by air circulation to build up around the wing. The tail strike angle for a typical large wide-bodied airliner is about 10', or about 12' when the suspension of main wheel landing gear is extended as a result of the weight of the aircraft being taken off the landing gear during rotation. With an extended version of the aircraft, these angles would be reduced to about 7' and 8' respectively. Tail strike can occur on the ground if the nose is raised too quickly before the main landing gear has lifted off the ground. Tail strike can also occur in the air if the nose is raised too quickly before sufficient height has been reached. The pilot must, therefore, ensure that he does not rotate the aircraft with too high a pitch rate, to avoid tail strike. Although instruments have been proposed previously for providing information to the pilot during the flare-up phase of take-off, such as described in US3309923, no instrument has previously been able to provide information warning of possible tail strike during the very early phase of take-off.

The take-off procedure is particularly stressful for the pilot because the engines are operating at full power and the plane is fully loaded with fuel. The pilot must monitor many instruments as well as controlling the engines and aerodynamic surfaces of the aircraft.

2 It is an object of the present invention to provide an aircraft instrument that can be used to assist the pilot during the rotation phase of take-off.

According to the present invention there is provided an aircraft instrument including means for providing a signal indicative of the rate of change of pitch angle of the aircraft, means for determining when the rate of change of pitch angle departs from a safe value, and display means for providing a warning display to the pilot when the rate of change of pitch angle during the rotation phase of take-off departs from the safe value.

The instrument preferably includes means for receiving an input from a sensor responsive to lifting of the aircraft nose wheel at the start of rotation. The instrument is preferably arranged to provide a first warning display when the pitch rate is too high and a different warning display when the pitch rate is too low. The warning display may include a representation of a symbol that moves vertically when the pitch rate departs from a safe value and that remains stationary when the pitch rate is at a safe value. The instrument may include a processor, comparator means, a reference source of maximum rate of change of pitch angle and a reference source of minimum rate of change of pitch angle, the processor being arranged to receive signals from a pitch angle sensor and to derive a signal indicative of rate of change of pitch angle, the comparator means receiving outputs from the reference sources of minimum and maximum rate of change of pitch angle and the signal indicative of rate of change of pitch angle, and the comparator means providing an output to initiate said warning display when the signal indicative of rate of change of pitch angle exceeds the maximum rate of change of pitch angle or falls below the minimum rate of change of pitch angle. The instrument may be arranged to maintain the display off until the aircraft nose wheel lifts off the ground. The instrument may be arranged to turn off the display a predetermined time after the main landing gear has lifted off the ground or after the aircraft has reached a predetermined height above the ground. The instrument may be arranged to provide an audible warning when 3 the rate of change of pitch angle during the rotation phase of take-off departs from a safe value. The display of the instrument is preferably arranged for mounting in the peripheral field of view of the pilot. The instrument may also be arranged to provide a warning display during descent if pitch angle of the aircraft exceeds a safe value, and to provide lateral guidance information to the pilot.

A tail-strike warning instrument for an aircraft, in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic illustration of an aircraft showing the installation of the instrument and various sensors; Figure 2 is a schematic diagram of the instrument; Figures 3A to 3B show different display representations provided by the instrument; and Figures 4 to 7 show alternative formats of display representation.

4 With reference first to Figures 1 and 2, the instrument includes an electronics housing 1 connected to a display unit 2 by a cable 3. The display unit 2 is mounted in the glareshield of the aircraft flight deck so that it is in the peripheral field of view of the pilot., the housing 1 may be mounted anywhere in the aircraft or within the same unit as the display itself The instrument receives inputs from a nosegear squat switch 4 and from a main gear squat switch 5. These switches 4 and 5 provide outputs to indicate whether or not the nose gear or main gear are on the ground. The instrument also receives an output 0 from a pitch angle sensor 6. This sensor 6 may be contained within the electronics housing 1 or it could be a discrete sensor located externally. Alternatively, the pitch angle sensing function could be provided by an existing pitch angle sensor used for other purposes.

The electronics housing I includes a processor 40, which receives the output from the pitch angle sensor 6 and, from this, derives an output; indicative of the rate of change of pitch angle. AJternatively, pitch rate may be input directly from a pitch rate gyroscope sensor. The processor 40 preferably also performs an averaging function to reduce the effect of pilotinduced oscillations or other small perturbations in the pitch angle signal. The output from the processor 40 is connected to one input of each of two comparators 41 and 42. One comparator 41 has its other input connected to a reference source 43, which sets a maximum value of rate of change of pitch angle 6,,.. The other comparator 42 has its other input connected to a reference source 44, which sets a minimum value of rate of change of pitch angle;.i,,. The outputs from the two comparators 41 and 42 are connected to a display driver unit 50. The display driver unit 50 also receives the outputs from the nosegear squat switch 4 and from the main gear squat switch 5. The display driver unit 50 is connected to the display unit 2 by the cable 3 and provides the output from the electronics housing 1.

The display unit 2 is of rectangular shape and has a front surface or screen 20 occupied by a matrix array of liquid crystal display elements 21, or some other electrically-energizable display elements, such as LEDs.

When the aircraft starts its ground roll, both its nose and main gear areon the ground and the sensors 4 and 5 supply signals indicating this to the instrument 1. During this part of the take-off procedure, the instrument 1 holds the display unit 2 off so that the pilot is not distracted.

When the pilot pulls back on the stick to raise the nose of the aircraft and start the rotation phase of take-off, the nose gear starts to lift away from the ground and the nosegear squat switch 4 changes its output. This causes the instrument 1 to energize the display unit 2. While the pilot maintains the pitch rate of the aircraft within safe limits, the display driver 50 produces a display representation on the screen 20 of the kind shown in Figure 3B. This comprises a number of dark horizontal bars 22 (three bars are shown in Figure 3B) extending across the display and separated by bright gaps 23. This display representation remains stationary while the aircraft is maintained within safe pitch rate limits, that is, less than max and more than. The pilot will see the display as it is turned on, in his peripheral field of view, so that he is notified that the nose gear has lifted ofFthe runway. During rotation, the pilot receives guidance from the display in his peripheral field of vision while looking forward out of the cockpit windscreen, and without having to focus his eyes on the display.

When the main gear of the aircraft lifts off the runway, the sensor 5 changes its output. This causes the processor 40 to start a timer and, after a predetermined time has elapsed sufficient for the aircraft to have achieved a height at which tail strike is no danger (typically about 5 seconds) the instrument 1 turns offthe display 2, which is no longer needed. Alternatively, the instrument could be connected to receive an output from the aircraft's radar 6 altimeter 7, instead of from a main gear squat switch 5. In this case, the display unit 2 would be turned off when the aircraft has achieved a safe height at which there is no risk of tail strike.

If, however, the pilot were to pull back on the stick too quickly and cause an excessively high pitch rate, sufficient for there to be a danger of tail strike, the input to the comparator 41 would exceed the reference value. from the source 43. The comparator 41 would then change its output to the display driver unit 50 so that the driver unit displaces the bars 22 downwards, giving an appearance of a continuous stream of bars moving down. The rate of movement of the bars is proportional to the magnitude of the difference between the actual aircraft pitch rate and the maximum safe pitch rate. This warning movement on the display is readily apparent to the pilot in his peripheral field of view without him having to look directly at the display. The pilot can, therefore, immediately take correcting action without having to turn his head or alter his focus. The pilot will notice that his correcting action produces a slowing down of the moving bars until the aircraft comes below the upper safe pitch rate limit, when the display representation again becomes stationary.

If the pilot were over cautious and did not produce a sufficiently high pitch rate, there would be a risk that the aircraft would not produce sufficient lift quickly enough and might run out of runway. When the pitch rate is too low, the input the processor 40 supplies to the comparator 42 faUs below that from the reference source 43. This causes the comparator 42 to change its output, which, in turn, causes the display driver unit 50 to move the bars on the display representation upwardly at a rate proportional to the magnitude of the difference between the actual aircraft pitch rate and the minimum safe pitch rate This warns the pilot that he must increase the pitch rate.

The present invention enables the pilot to be warned when the pitch rate of the aircraft is outside safe limits, without him being presented with distracting information when it is not needed.

7 The instrument could also have an audible warning, which it triggers when the visual warning does not produces a corrective response by the pilot within a predetermined time.

The display representation could take various other forms such as, for example, shown in Figures 4 to 7. In Figure 4B, the safe pitch rate is represented by a continuous, horizontal line extending across the display midway up its height. When the pitch rate is too high, the central part of the line is displaced down, as shown in Figure 4A; when the pitch rate is too low, the central part of the line is displaced up, as shown in Figure 4C. In the display representation shown in Figure 5, the correct pitch rate produces a blank display, as shown in Figure 5B, whereas too fast a pitch rate produces a downwardly-pointing arrow, as shown in Figure 5A, and too slow a pitch rate produces the upwardly-directed arrow, as shown in Figure 5C. The display representation could be arranged to change colour, as shown in Figure 6. When the pitch rate is within a safe range, the display representation is a plain green screen, as shown in Figure 6B; when the pitch rate is too high, the display changes to a red colour and text, such as "FAST" appears on the display, as shown in Figure 6A; and when the pitch rate is too low, the display changes to an amber colour and texi, such as the word "SLOW" is displayed. The display format of Figure 6 could be combined with a moving representation so that the pilot's attention is drawn to the display more forcefully.

The instrument could also be used to provide a warning of tail strike during landing as a result of too large a pitch angle during descent. The risk of tail strike during landing depends only on pitch attitude, rather than pitch rate, so the processor does not compute the rate of change of pitch angle during this phase.

In the display shown in Figure 7, the upper part of the display screen 70 shows a display representation of the same kind as that in Figure 6. The lower part of the screen 71 is occupied by a lateral guidance display. The lateral guidance display indicates to the pilot if the 8 aircraft deviates from the runway centre line. The lateral guidance display is formed by inclined stripes, which remain stationary when the aircraft is correctly aligned with the runway. When the aircraft heading deviates to right or left of the centre line, the stripes move across the width of the display to the right or left accordingly and at a rate dependent on the magnitude of the deviation.

Because the tail strike warning instrument is only used during the rotation phase of take-off, or during take-off and landing, it is possible for the display to be used for other purposes at other times. For example, it could be used to display a warning of collision avoidance action to be taken when there is a risk of a mid-air collision, in the manner described in GB 2226924. Alternatively, it could be used to display air traffic command instructions, as described in GB 2250494.

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Claims

An aircraft instrument including means for providing a signal indicative of the rate of change of pitch angle of the aircraft, means for determining when the rate of change of pitch angle departs from a safe value, and display means for providing a warning display to the pilot when the rate of change of pitch angle during the rotation phase of take-off departs from the safe value.
An aircraft instrument according to Claim 1 including means for receiving an input from a sensor responsive to lifting of the aircraft nose wheel at the start of rotation.
An aircraft instrument according to Claim 1 or 2, wherein the instrument is arranged to provide a first warning display when the pitch rate is too high and a different warning display when the pitch rate is too low.
An aircraft instrument according to any one of the preceding claims, wherein the warning display includes a representation of a symbol that moves vertically when the pitch rate departs from a safe value and that remains stationary when the pitch rate is at a safe value.
An aircraft instrument according to any one of the preceding claims, including a processor, comparator means, a reference source of maximum rate of change of pitch angle and a reference source of minimum rate of change of pitch angle, wherein the processor is arranged to receive signals from a pitch angle sensor and to derive a signal indicative of rate of change of pitch angle, wherein said comparator means receives outputs from the reference sources of minimum and maximum rate of change of pitch angle and the signal indicative of rate of change of pitch angle, and wherein said comparator means provides an output to initiate said warning display when the signal indicative of rate of change of pitch angle exceeds the maximum rate of change of pitch angle or falls below the minimum rate of change of pitch angle.
6. An aircraft instrument according to any one of the preceding claims, wherein the instrument is arranged to maintain the display offuntil the aircraft nose wheel lifts off the ground.
An aircraft instrument according to any one of the preceding claims, wherein the instrument is arranged to turn off the display a predetermined time after the main landing gear has lifted off the ground.
8. An aircraft instrument according to any one of Claims 1 to 6, wherein the instrument is arranged to turn off the display after the aircraft has reached a predetermined height above the ground.
9. An aircraft instrument according to any one of the preceding claims, wherein the instrument is arranged to provide an audible warning when the rate of change of pitch angle during the rotation phase of take-off departs from a safe value.

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10. An aircraft instrument according to any one of the preceding claims, wherein the display is arranged for mounting in the peripheral field of view of the pilot.
11, An aircraft instrument according to any one of the preceding claims, wherein the instrument is also arranged to provide a warning display during descent if the pitch angle of the aircraft exceeds a safe value.
12. An aircraft instrument according to any one of the preceding claims, wherein the instrument is also arranged to provide lateral guidance information to the pilot.
13. An aircraft instrument substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.
14. An aircraft instrument substantially as hereinbefore described with reference to Figures 1 to 3, as modified by any one of Figures 4 to 7 of the accompanying drawings.

Any novel feature or combination of features as hereinbefore described.