Method and a device for determining and displaying a flyaway distance for a rotorcraft while taking account of the height of waves

Abstract

A method and a device for determining and displaying a flyaway distance for a rotorcraft in the event of an engine of the rotorcraft failing, and while taking account of the height of waves being overflown by the rotorcraft. The method includes a first determination for determining a flyaway distance of the rotorcraft in the event of a failure of an engine and under current flying conditions, a second determination for determining a maximum altitude of the waves being overflown by the rotorcraft and displaying the flyaway distance and the maximum altitude on a display instrument of the rotorcraft indicating the relative height of the rotorcraft or else its altitude. A safety margin is preferably added to the maximum altitude of the waves, or else to the flyaway distance of the rotorcraft.

Claims

1. A method of determining and displaying a flyaway distance for a rotorcraft in the event of an engine of the rotorcraft failing, while taking account of variation in the height of waves over which the rotorcraft is flying, the rotorcraft having at least two engines, wherein the method comprises the following steps: a first determination for determining a flyaway distance of the rotorcraft in the event of an engine of the rotorcraft failing under current flying conditions of the rotorcraft, the flyaway distance being equal to a loss of altitude that is necessary to enable the rotorcraft to achieve a minimum speed following a failure of one of the engines of the rotorcraft; a second determination for determining a maximum position of the waves above which the rotorcraft is flying, the maximum position being an estimate of the vertical position of the highest wave among the waves; and displaying the flyaway distance and the maximum position on a display instrument of the rotorcraft.

2. The method according to claim 1, wherein the first determination for determining the flyaway distance of the rotorcraft comprises: a preliminary step of translating into software the charts that provide the flyaway distance of the rotorcraft depending on the flying conditions of the rotorcraft; substeps of determining the current flying conditions of the rotorcraft; and a final step of estimating the flyaway distance of the rotorcraft from the current flying conditions of the rotorcraft and from the charts.

3. The method according to claim 2, wherein the substeps of determining the current flying conditions of the rotorcraft comprise: a first measurement for measuring temperature outside the rotorcraft; a second measurement for measuring atmospheric pressure outside the rotorcraft; a third measurement for measuring the airspeed of the rotorcraft; and a third determination for determining the current weight of the rotorcraft.

4. The method according to claim 1, wherein the second determination for determining the maximum position of the waves above which the rotorcraft is flying, comprises: an initialization for initializing a maximum altitude of the waves above which the rotorcraft is flying; a fourth measurement for measuring a current relative height of the rotorcraft above the waves at a predefined position relative to the rotorcraft; a fifth measurement for measuring a first current altitude of the rotorcraft; a fifth determination for determining a second current altitude of the waves at the predefined position relative to the rotorcraft, the second current altitude being equal to the difference between the first current altitude of the rotorcraft and the current relative height a first comparison for comparing the maximum altitude and the second current altitude of the waves, and serving to define a new value for the maximum altitude.

5. The method according to claim 4, wherein during the first comparison, when the maximum altitude is less than the second current altitude of the waves, the maximum altitude takes the value of the second current altitude of the waves.

6. The method according to claim 4, wherein during the first comparison: when the maximum altitude is less than or equal to the second current altitude of the waves, the maximum altitude takes the value of the second current altitude; and so long as the maximum altitude is greater than the second current altitude of the waves, the maximum altitude varies following a predefined decreasing curve.

7. The method according to claim 6, wherein the predefined decreasing curve comprises a horizontal level during which the maximum altitude is constant over a predetermined duration prior to decreasing.

8. The method according to claim 6, wherein the predefined decreasing curve is a decreasing exponential curve.

9. The method according to claim 4, wherein the predefined position relative to the rotorcraft is situated vertically below the rotorcraft, the current relative height being measured vertically relative to the rotorcraft.

10. The method according to claim 4, wherein the predefined position relative to the rotorcraft is situated at a predefined distance from the rotorcraft, the current relative height being measured at the predefined distance from the rotorcraft in order to anticipate the waves over which the rotorcraft is about to fly.

11. The method according to claim 1, wherein while displaying the flyaway distance, a symbol representing the flyaway distance is displayed on the display instrument of the rotorcraft in such a manner that a base of the symbol is positioned at the maximum position of the waves.

12. The method according to claim 1, wherein while displaying the flyaway distance, a symbol representing the flyaway distance is displayed on the display instrument of the rotorcraft in such a manner that a base of the symbol is positioned at the maximum position of the waves plus a safety margin.

13. The method according to claim 1, wherein, when the display instrument displays a barometric altitude for the rotorcraft, the maximum position of the waves is the maximum altitude plus a scale correction value equal to the difference between the barometric altitude and the first current altitude of the rotorcraft.

14. The method according to claim 1, wherein, when the display instrument displays a relative height of the rotorcraft above the free water surface above which the rotorcraft is flying, the maximum position of the waves is a maximum vertical distance of a crest of the waves relative to a current position of the waves equal to the maximum altitude minus the second current altitude of the waves.

15. A device for determining and displaying a flyaway distance of a rotorcraft in the event of an engine of the rotorcraft failing and while taking account of variation in the height of waves over which the rotorcraft is flying, the rotorcraft having at least two engines, and the device comprising: devices for determining current flying conditions of the rotorcraft; a device for measuring a current relative height of the rotorcraft above the waves at a predefined position relative to the rotorcraft; at least one measuring device for measuring a first current altitude of the rotorcraft; at least one memory storing calculation instructions, charts providing the flyaway distance for the rotorcraft depending on the flying conditions of the rotorcraft, a maximum altitude, and where applicable the takeoff weight of the rotorcraft; at least one calculator suitable for executing the calculation instructions; and at least one display instrument for displaying a vertical position of the rotorcraft; wherein the device is configured to perform the method according to claim 1.

16. A method of determining and displaying a flyaway distance for a rotorcraft in the event of an engine of the rotorcraft failing, while taking account of variation in the height of waves over which the rotorcraft is flying, the rotorcraft having at least two engines, wherein the method comprises the following steps: determining the flyaway distance of the rotorcraft in the event of an engine of the rotorcraft failing under current flying conditions of the rotorcraft, the flyaway distance being equal to a loss of altitude that is necessary to enable the rotorcraft to achieve a minimum speed following a failure of one of the engines of the rotorcraft; determining a maximum position of the waves above which the rotorcraft is flying, the maximum position being an estimate of the vertical position of the highest wave among the waves; and displaying the flyaway distance and the maximum position of the waves on a display instrument of the rotorcraft.

17. The method according to claim 16, wherein determining the flyaway distance of the rotorcraft comprises: translating into software the charts that provide the flyaway distance of the rotorcraft depending on the flying conditions of the rotorcraft; determining the current flying conditions of the rotorcraft; and estimating the flyaway distance of the rotorcraft from the current flying conditions of the rotorcraft and from the charts.

18. The method according to claim 17, wherein determining the current flying conditions of the rotorcraft comprise: measuring the temperature outside the rotorcraft; measuring the atmospheric pressure outside the rotorcraft; measuring the airspeed of the rotorcraft; and determining the current weight of the rotorcraft; and determining the maximum position of the waves above which the rotorcraft is flying, comprises: initializing a maximum altitude of the waves above which the rotorcraft is flying; measuring a current relative height of the rotorcraft above the waves at a predefined position relative to the rotorcraft; measuring a first current altitude of the rotorcraft; determining a second current altitude of the waves at the predefined position relative to the rotorcraft, the second current altitude being equal to the difference between the first current altitude of the rotorcraft and the current relative height; and comparing the maximum altitude and the second current altitude of the waves, and serving to define a new value for the maximum altitude.

19. The method according to claim 18, wherein during the comparison, when the maximum altitude is less than the second current altitude of the waves, the maximum altitude takes the value of the second current altitude of the waves.

20. The method according to claim 4, wherein during the comparison: when the maximum altitude is less than or equal to the second current altitude of the waves, the maximum altitude takes the value of the second current altitude; and so long as the maximum altitude is greater than the second current altitude of the waves, the maximum altitude varies following a predefined decreasing curve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and its advantages appear in greater detail in the context of the following description of implementations given by way of illustration and with reference to the accompanying figures, in which:

(2) FIG. 1 shows a rotorcraft having a device for determining and displaying a flyaway distance for a rotorcraft while taking account of wave height;

(3) FIG. 2 is a block diagram of a method of determining and displaying a flyaway distance for a rotorcraft while taking account of wave height;

(4) FIGS. 3 and 4 are views of a display instrument displaying a vertical position of the rotorcraft; and

(5) FIGS. 5 and 6 show two examples of how the maximum altitude of waves can vary.

DETAILED DESCRIPTION OF THE INVENTION

(6) Elements present in more than one of the figures are given the same references in each of them.

(7) FIG. 1 shows a rotorcraft 10, also referred to as a “rotary wing aircraft” flying over a free water surface 5. The rotorcraft 10 comprises in particular a fuselage 11, a tail boom 12, a main rotor 13 providing it with lift and possibly also propulsion, and a tail rotor 14 positioned at the rear end of the tail boom 12. The rotorcraft 10 also has two engines that are not shown. The rotorcraft 10 is for use in particular in performing search and rescue missions at sea. During such operations, the rotorcraft 10 needs to act in complete safety while hovering or while flying at low speeds and at very low altitude in an environment that is often disturbed, and in particular with a free water surface that is rough, possibly associated with poor visibility.

(8) The rotorcraft 10 also has a device 50 for determining and displaying a flyaway distance H.sub.FlyA of a rotorcraft while taking account of the height of waves, together with an instrument panel 20 having a display instrument 21 for displaying a vertical position of the rotorcraft 10. The device 50 for determining and displaying a flyaway distance H.sub.FlyA of a rotorcraft includes devices 51-54 for determining current flying conditions of the rotorcraft 10, specifically a first sensor 51 for measuring temperature outside the rotorcraft 10, a second sensor 52 for measuring atmospheric pressure outside the rotorcraft 10, a wind gauge 53 for measuring airspeed relative to the rotorcraft 10, and a device 54 for determining a current weight of the rotorcraft 10.

(9) The device 50 for determining and displaying a flyaway distance H.sub.FlyA of a rotorcraft also includes a measuring device 55 for measuring a current relative height H.sub.Cur of the rotorcraft 10 above the ground or the free water surface over which the rotorcraft is flying, and at least one measuring device 56-57 for measuring a first current altitude Z.sub.Cur of the rotorcraft 10, a memory 58, and a calculator 59. The memory 58 serves in particular to store calculation instructions that the calculator 59 is suitable for executing.

(10) The device 50 for determining and displaying a flyaway distance H.sub.FlyA of a rotorcraft also makes use of the display instrument 21 of the rotorcraft 10. Furthermore, the devices 51-54 for determining current flying conditions of the rotorcraft 10, the measuring device 55 for measuring a current relative height H.sub.Cur above the ground or the free water surface, and each device 56-57 for measuring a first current altitude Z.sub.Cur of the rotorcraft 10 may be shared with other pieces of equipment of the rotorcraft 10.

(11) The device 55 for measuring a current relative height H.sub.Cur of the rotorcraft 10 above the waves may be a radioaltimeter performing this measurement substantially vertically under the rotorcraft 10. This device 55 for measuring a current relative height H.sub.Cur of the rotorcraft 10 may also be an ultrasound type device or a LIDAR type device enabling this measurement to be taken at a predefined distance from the rotorcraft, preferably in front of the rotorcraft, so as to act advantageously to anticipate the arrival of waves over which the rotorcraft 10 is about to fly.

(12) The device 56-57 for measuring the first current altitude Z.sub.Cur of the rotorcraft 10 may be a global navigation system (GNSS) receiver 56 supplying an absolute altitude relative to the mean free surface of the water constituting in particular seas and oceans, or indeed an altimeter 57 providing a barometric altitude measurement. The first current altitude Z.sub.Cur of the rotorcraft 10 may also be obtained by integrating a vertical speed of the rotorcraft 10.

(13) The memory 58 stores calculation instructions serving in particular to perform the method of determining and displaying a flyaway distance H.sub.FlyA of a rotorcraft while taking account of the height of waves, which method is summarized diagrammatically in FIG. 2.

(14) The method comprises three main steps:

(15) first determination 110 for determining a flyaway distance H.sub.FlyA of the rotorcraft 10 in the event of an engine of the rotorcraft 10 failing and in the current flying conditions of the rotorcraft 10;

(16) second determination 120 for determining a maximum position of waves over which the rotorcraft 10 is flying; and

(17) displaying 130 the flyaway distance H.sub.FlyA and the maximum position on the display instrument 21.

(18) The first determination 110 for determining the flyaway distance H.sub.FlyA of the rotorcraft 10 comprises a preliminary step 111 performed when installing the method of the invention in the rotorcraft 10, this preliminary step 111 consisting in translating into software the charts that provide the flyaway distance H.sub.FlyA of the rotorcraft 10 depending on the flying conditions of the rotorcraft 10. The memory 58 stores the charts providing the flyaway distance H.sub.FlyA of the rotorcraft 10 depending on the flying conditions of the rotorcraft 10.

(19) The flyaway distance H.sub.FlyA, as shown in FIG. 1, is the altitude that the rotorcraft 10 needs to lose following a failure of an engine of the rotorcraft 10 in order to reach a speed along a flight path 25 that is sufficient to enable the rotorcraft 10 to maintain a constant altitude or even to climb a little, while using only the power that is available from the engine that remains in operation.

(20) The first determination 110 for determining the flyaway distance H.sub.FlyA of the rotorcraft 10 also includes substeps 112-115 of determining current flying conditions of the rotorcraft 10:

(21) a first measurement 112 for measuring temperature outside the rotorcraft 10, taken by means of the first sensor 51;

(22) a second measurement 113 for measuring atmospheric pressure outside the rotorcraft 10, taken by means of the second sensor 52;

(23) a third measurement 114 for measuring the airspeed of the rotorcraft 10, as taken by means of the wind gauge 53; and

(24) a third determination 115 for determining a current weight of the rotorcraft 10, taken by means of the device 54 for determining the current weight of the rotorcraft 10.

(25) The third determination 115 for determining the current weight of the rotorcraft 10 may also be performed directly by the crew of the rotorcraft 10 by subtracting the weight of fuel that has already been consumed from the takeoff weight, possibly while also taking account of passengers and payloads that may be taken on board or unloaded. The memory 58 then stores the takeoff weight of the rotorcraft 10.

(26) The first determination 110 for determining the flyaway distance H.sub.FlyA of the rotorcraft 10 finally includes a final step 116 of estimating the flyaway distance H.sub.FlyA of the rotorcraft 10 as performed by the calculator 59, on the basis of the current flying conditions of the rotorcraft 10 and of the charts.

(27) Furthermore, the maximum position of the waves over which the rotorcraft is flying, as determined during the second determination 120, may be defined by a maximum wave altitude Z.sub.Max or indeed by a maximum vertical distance H.sub.Max of the wave crests relative to the current position of the waves. The maximum altitude Z.sub.Max of the waves is defined in absolute manner relative to a fixed reference frame REF and is used for a display instrument 21 that indicates in particular the barometric altitude of the rotorcraft 10. The maximum vertical distance H.sub.Max of the waves is used when the display instrument 21 is an instrument for giving the height of the rotorcraft above the ground or the free water surface over which it is flying.

(28) The reference frame REF and the maximum altitude Z.sub.Max of the waves and the maximum vertical distance H.sub.Max of the wave crests relative to the current position of the waves are shown in FIG. 1. The reference frame REF is generally constituted by the mean free surface of the water forming in particular seas and oceans.

(29) In addition, the maximum vertical distance H.sub.Max of the wave crests relative to the current position of the waves is determined by taking the difference between the maximum altitude Z.sub.Max and a second current altitude Z.sub.Wav of the waves. Specifically, whatever this maximum position of the waves, the second determination 120 for determining the maximum position of the waves above which the rotorcraft 10 is flying includes firstly an initialization 121 of a maximum altitude Z.sub.Max of the waves above which the rotorcraft 10 is flying. During this initialization 121, the maximum altitude Z.sub.Max is preferably defined as being equal to the second current altitude Z.sub.Wav of the waves.

(30) Thereafter, a fourth measurement 122 for measuring a current relative height H.sub.Cur of the rotorcraft 10 above the waves is taken at a position that is predefined relative to the rotorcraft 10 by the measuring device 55. The position that is predefined relative to the rotorcraft 10 may be substantially vertically below the rotorcraft 10, or it may be at a predefined distance from the rotorcraft 10, preferably ahead of the rotorcraft 10, as shown in FIG. 1.

(31) A fifth measurement 123 is taken for measuring the first current altitude Z.sub.Cur of the rotorcraft 10, preferably simultaneously with the fourth measurement 122, by means of the measuring device 56-57. This fifth measurement 123 may also be taken sequentially relative to the fourth measurement 122.

(32) After the fourth measurement 122 and the fifth measurement 123, a fifth determination 124 is performed by the calculator 59 for determining a second current altitude Z.sub.Wav of the waves at the predefined position relative to the rotorcraft 10, corresponding to the current position of the waves. This second current altitude Z.sub.Wav is equal to the difference between the first current altitude Z.sub.Cur and the current relative height H.sub.Cur of the rotorcraft 10, i.e.:
Z.sub.Wav=Z.sub.Cur−H.sub.Cur

(33) Finally, a first comparison 125 is performed by the calculator 59 between the maximum altitude Z.sub.Max and the second current altitude Z.sub.Wav in order to define a new value for the maximum altitude Z.sub.Max.

(34) During the first comparison 125, when the maximum altitude Z.sub.Max is less than the second current altitude Z.sub.Wav of the waves, the maximum altitude Z.sub.Max may take the value of the second current altitude Z.sub.Wav, whereas the maximum altitude Z.sub.Max remains unchanged when the maximum altitude Z.sub.Max is greater than or equal to the second current altitude Z.sub.Wav of the waves. As a result, the maximum altitude Z.sub.Max is defined as the maximum value reached by the second current altitude Z.sub.Wav of the waves throughout the emergency operation being performed by the rotorcraft 10.

(35) During the first comparison 125, the maximum altitude Z.sub.Max may also be defined so as to take account of possible variation in the amplitude of the waves, which might be a reduction in amplitude. For this purpose, when the maximum altitude Z.sub.Max is less than or equal to the second current altitude Z.sub.Wav of the waves, the maximum altitude Z.sub.Max takes the value of the second current altitude Z.sub.Wav and so long as the maximum altitude Z.sub.Max is greater than the second current altitude Z.sub.Wav, the maximum altitude Z.sub.Max varies following a predefined decreasing curve.

(36) Two examples of varying the maximum altitude Z.sub.Max of the waves using predefined decreasing curves are shown in FIGS. 5 and 6.

(37) In a first example shown in FIG. 5, the predefined decreasing curve begins with a horizontal level during which the maximum altitude Z.sub.Max is constant over a predetermined duration T.sub.1, typically of the order of one or two wave periods, prior to decreasing slowly and regularly with a slope that is constant depending on the difference between the maximum altitude Z.sub.Max and the second current altitude Z.sub.Wav of the waves.

(38) It is then observed, initially, that the maximum altitude Z.sub.Max follows the free water surface 5 of the second current altitude Z.sub.Wav as it increases, and then after the first crest of a wave, the maximum altitude Z.sub.Max is constant throughout the predetermined duration T.sub.1, with waves being of smaller amplitude during this determined duration T.sub.1. Thereafter, the maximum altitude Z.sub.Max decreases with a constant slope so long as the second current altitude Z.sub.Wav of the waves is less than the maximum altitude Z.sub.Max. As soon as the constant slope meets the free water surface 5, the maximum altitude Z.sub.Max follows the free water surface 5, with the maximum altitude Z.sub.Max being equal to the second current altitude Z.sub.Wav of the waves, which altitude is increasing. Once the second current altitude Z.sub.Wav starts decreasing again, the maximum altitude Z.sub.Max remains level and is constant until meeting a wave for which the second current altitude Z.sub.Wav is greater than or equal to the maximum altitude Z.sub.Max. Thereafter, the maximum altitude Z.sub.Max remains level and is constant during the predetermined duration T.sub.1, and then decreases with a constant slope so long as the second current altitude Z.sub.Wav of the waves remains less than the second maximum altitude Z.sub.Max of the waves.

(39) In a second example shown in FIG. 6, the predefined decreasing curve decreases following a decreasing exponential curve. As above, it can then be seen that the maximum altitude Z.sub.Max begins by following the free surface of the water 5 of increasing second current altitude Z.sub.Wav, and then after the first crest of a wave, the maximum altitude Z.sub.Max decreases following the predefined decreasing exponential curve so long as the second current altitude Z.sub.Wav of the waves remains less than the maximum altitude Z.sub.Max. As soon as this decreasing curve meets the free water surface 5, the maximum altitude Z.sub.Max follows the free water surface 5, with the maximum altitude Z.sub.Max being equal to the second current altitude Z.sub.Max of the waves, which altitude is increasing. As soon as the second current altitude Z.sub.Wav decreases once again, the maximum altitude Z.sub.Max decreases following the predefined decreasing curve until meeting a wave for which the second current altitude Z.sub.Wav is greater than or equal to the maximum altitude Z.sub.Max.

(40) Furthermore, when the maximum position of the waves is the maximum vertical distance H.sub.Max of the wave crests relative to the current position of the waves, the maximum vertical distance H.sub.Max is determined during a sixth determination 126 for determining the maximum vertical distance H.sub.Max included in the second determination 120 for determining the maximum position of the waves by subtracting the second current altitude Z.sub.Wav of the waves from the maximum altitude Z.sub.Max:
H.sub.Max=Z.sub.Max−Z.sub.Wav=Z.sub.Max−(Z.sub.Cur−H.sub.Cur)

(41) Consequently, the method of determining and displaying a flyaway distance H.sub.FlyA for a rotorcraft while taking account of the height of waves serves advantageously to determine firstly the flyaway distance H.sub.FlyA depending on the current flying conditions of the rotorcraft 10, and secondly to determine the maximum position of the waves over which the rotorcraft 10 is flying during an emergency operation, and which needs to be taken into account in the event of an engine failure in order to be able to reach safely the minimum speed that is required with only one engine operational.

(42) The first determination 110 for determining a flyaway distance H.sub.FlyA for the rotorcraft 10 and the second determination 120 for determining a maximum position of the waves above which the rotorcraft 10 is flying may be performed in sequential manner or else in simultaneous manner.

(43) Finally, the display 130 of the flyaway distance H.sub.FlyA and of the maximum position of the waves on the display instrument 21 serves to inform the crew of the rotorcraft 10 about this flyaway distance H.sub.FlyA while taking account of this maximum position of the waves. This flyaway distance H.sub.FlyA is displayed in the form of a strip type symbol 80 positioned at the maximum position of the waves.

(44) As a result, prior to beginning an emergency operation, since the display instrument 21 also displays a mark 70 representing the position of the rotorcraft 10, the crew of the rotorcraft 10 can see immediately, and without taking any action, whether a sufficient flyaway distance H.sub.FlyA is available in the event of an engine failure. In addition, this flyaway distance H.sub.FlyA is displayed and updated during the emergency operation, advantageously while taking account of variations in current flying conditions and variations in the height of the waves, thereby enabling the emergency operation to be performed in complete safety, even in the event of an engine failure occurring.

(45) The display instrument 21 may be a barometric altitude indicator of the rotorcraft 10, as shown in FIG. 3, with the maximum position of the waves being the maximum altitude Z.sub.Max of the waves, or else it may be an indicator of the relative height of the rotorcraft 10 above the ground or the free water surface over which the rotorcraft 10 is flying, as shown in FIG. 4, the maximum position of the waves being the maximum vertical distance H.sub.Max of the wave crests relative to the current position of the waves.

(46) When the display instrument 21 displays a barometric altitude of the rotorcraft 10, and when the first current altitude Z.sub.Cur of the rotorcraft 10 is not supplied by a barometric altimeter, a scale correction value equal to the difference between the barometric altitude Z.sub.Bar and the first current altitude Z.sub.Cur of the rotorcraft 10 is added to the maximum altitude Z.sub.Max in order to display 130 the symbol 80.

(47) Furthermore, in both situations, a safety margin H.sub.Mrgn may be added to the maximum position of the waves, i.e. the maximum altitude Z.sub.Max or else the maximum vertical distance H.sub.Max.

(48) Naturally, the present invention may be subjected to numerous variations as to its implementation. Although several implementations are described, it will readily be understood that it is not conceivable to identify exhaustively all possible implementations. It is naturally possible to envisage replacing any of the means described by equivalent means without going beyond the ambit of the present invention.