Method and a device for determining the wind speed to be taken into account in order to optimize the takeoff weight of an aircraft

Abstract

A method of determining the speed of the wind to be taken into account for determining a maximum authorized takeoff weight of an aircraft. A measured speed TAS.sub.mes of the local wind is calculated from at least one current speed TAS.sub.inst of the local wind and an observed speed TAS.sub.obs of the local wind on the basis of weather observations and on the basis of a heading value. The measured speed TAS.sub.mes is compared with the observed speed TAS.sub.obs in order to determine a calculated speed TAS.sub.perfo of the local wind while also making use of at least one instability criterion of the local wind as supplied by the weather observations and weather forecasts. The calculated speed TAS.sub.perfo is then for taking into account in order to optimize the maximize authorized takeoff weight of the aircraft.

Claims

1. A method of determining the speed of the wind that is to be taken into account when determining the maximum authorized takeoff weight of an aircraft, the aircraft waiting to take off, and including at least: anemometer means; receiver means for receiving observation information and weather forecast information; consolidation means; and display means; the method comprising the following steps: determining a heading value in a terrestrial reference frame; measuring at least one current speed value TAS.sub.inst of the local wind in a predefined direction, the predefined direction being a direction corresponding to the heading value; receiving weather observation information and weather forecast information for the area in which the aircraft is situated or for a nearby area; calculating a measured speed TAS.sub.mes of the local wind in the predefined direction from at least one current speed value TAS.sub.inst of the speed of the local wind; calculating an observed speed TAS.sub.obs of the local wind in the predefined direction from the weather observation information and the heading value; comparing the measured value TAS.sub.mes and the observed speed TAS.sub.obs of the local wind; determining a calculated speed TAS.sub.perfo of the local wind for taking into account when determining the authorized maximum takeoff weight of the aircraft in the predefined direction; and displaying the calculated speed TAS.sub.perfo of the local wind on display means.

2. A method according to claim 1, wherein the measured speed TAS.sub.mes of the local wind is equal to the current speed value TAS.sub.inst.

3. A method according to claim 1, wherein at least two current speed values TAS.sub.inst are measured over a predetermined duration, and a mean measured speed TAS.sub.moy of the local wind in the predefined direction is measured from the current speed values TAS.sub.inst measured over the predetermined duration, the mean measured speed TAS.sub.moy being equal to the mean of the current speed values TAS.sub.inst, the measured speed TAS.sub.mes of the local wind being equal to the mean measured speed TAS.sub.moy.

4. A method according to claim 3, wherein the predetermined duration is equal to 2 min.

5. A method according to claim 1, wherein the heading value is determined by a pilot of the aircraft, the instantaneous heading of the aircraft also being determined when the heading value is different from the instantaneous heading of the aircraft in order to calculate a bearing of the predefined direction relative to a longitudinally extending direction of the aircraft extending between the front and the rear of the aircraft.

6. A method according to claim 1, wherein the aircraft has means for determining the heading of the aircraft, the heading value is equal to the instantaneous heading of the aircraft as determined by the means for determining the heading of the aircraft, the predefined direction then being a longitudinally extending direction of the aircraft extending from the front to the rear of the aircraft.

7. A method according to claim 1, wherein the weather observation information is decoded and a mean observed speed of the local wind and an observed direction of the local wind together with a first instability criterion for the local wind are extracted from the observation information, and then the observed speed TAS.sub.obs of the local wind in the predefined direction is calculated from the mean observed speed, from the mean observed direction of the local wind, and from the heading value.

8. A method according to claim 7, wherein the weather forecast information is decoded and a second criterion for instability of the local wind is extracted from the forecast information.

9. A method according to claim 8, wherein when the measured speed TAS.sub.mes and the observed speed TAS.sub.obs are positive, a speed of the local wind in the predefined direction is considered to be positive when the local wind constitutes at least in part a head wind relative to the aircraft; and if the first instability criterion and/or the second instability criterion for the local wind indicate(s) instability of the local wind, the calculated speed TAS.sub.perfo of the local wind is equal to the observed speed divided by two, TAS.sub.obs/2; if the measured speed TAS.sub.mes is greater than or equal to the observed speed TAS.sub.obs and if the first instability criterion and the second instability criterion for the local wind do not indicate any instability of the local wind, the calculated speed TAS.sub.perfo is equal to the observed speed TAS.sub.obs; if the measured speed TAS.sub.mes lies strictly between the observed speed TAS.sub.obs and the observed speed divided by two, TAS.sub.obs/2, and if the first instability criterion and the second instability criterion for the local wind do not indicate any instability of the local wind, the calculated speed TAS.sub.perfo is equal to the measured speed TAS.sub.mes; if the measured speed TAS.sub.mes is less than or equal to the observed speed divided by two, TAS.sub.obs/2, and if the first instability criterion and the second instability criterion for the local wind do not indicate any instability of the local wind, the calculated speed TAS.sub.perfo is equal to the observed speed divided by two, TAS.sub.obs/2; if no measured speed TAS.sub.mes is provided and if the first instability criterion and the second instability criterion for the local wind do not indicate any instability of the local wind, the calculated speed TAS.sub.perfo is equal to the observed speed divided by two, TAS.sub.obs/2; and if no observed speed TAS.sub.obs is available and if the first instability criterion and the second instability criterion for the local wind do not indicate any instability of the local wind, the calculated speed TAS.sub.perfo is equal to the measured speed TAS.sub.mes divided by two.

10. A method according to claim 1, wherein when the measured speed TAS.sub.mes and/or the observed speed TAS.sub.obs are negative, a speed of the local wind in the predefined direction being considered as being negative when the local wind constitutes at least in part a tail wind relative to the aircraft, the calculated speed TAS.sub.perfo is equal to the minimum value from among the measured speed TAS.sub.mes and the observed speed TAS.sub.obs.

11. A method according to claim 1, wherein the aircraft includes locating means, and location information and time information supplied by the locating means is used to determine the observation information and the forecast information that is to be used.

12. A method according to claim 1, wherein a pilot of the aircraft supplies location information for the aircraft and time information in order to determine the observation information and the forecast information for use.

13. A method according to claim 1, wherein the observation information and the forecast information come from reports containing digital data corresponding to the position of the aircraft and to the current time.

14. A method according to claim 1, wherein the observation information comes from a METAR report and the forecast information comes from a TAF report.

15. A method according to claim 1, wherein the aircraft is a rotary wing aircraft having at least a main rotor and possibly a tail rotor, and each current speed value TAS.sub.inst is corrected in order to take account of the disturbances caused by the main rotor and/or by the tail rotor on each current speed value TAS.sub.inst.

16. A method according to claim 1, wherein each current speed value TAS.sub.inst is measured in the immediate surroundings of the aircraft.

17. A method according to claim 1, wherein each current speed value TAS.sub.inst is corrected with a predetermined error margin.

18. A method according to claim 17, wherein the predetermined error margin is equal to 2 kt.

19. A method according to claim 1, wherein the aircraft has a plurality of anemometer means and each current speed value TAS.sub.inst is consolidated by redundancy, by monitoring, or by testing for consistency.

20. A method according to claim 1, wherein each current speed value TAS.sub.inst has a non-indicated predefined error probability.

21. A method according to claim 1, wherein the maximized authorized takeoff weight of the aircraft is calculated as a function of the calculated speed TAS.sub.perfo for the local wind, and is displayed on the display means.

22. A device for determining the speed of the wind that is to be taken into account when determining the maximum authorized takeoff weight of an aircraft, the device comprising at least: anemometer means; receiver means for receiving observation information and weather forecast information; consolidation means including at least one computer and at least storage means; and display means; wherein each anemometer means measures at least one current speed value TAS.sub.inst of the local wind, each receiver means for receiving weather observation and weather forecast information serves to receive weather observation information and weather forecast information for the area in which the aircraft is situated or for a nearby area, each consolidation means calculates a measured speed TAS.sub.mes of the local wind from at least one current speed value TAS.sub.inst, calculates an observed speed TAS.sub.obs of the local wind from the weather observation information and a heading value, compares the measured speed TAS.sub.mes with the observed speed TAS.sub.obs of the local wind, and then determines a calculated speed TAS.sub.perfo of the local wind to be taken into account for determining the maximized authorized takeoff weight of the aircraft, the device performing the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention and its advantages appear in greater detail from 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 an aircraft fitted with a device of the invention; and

(3) FIGS. 2 and 3 are two block diagrams showing two implementations of the method of the invention.

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

DETAILED DESCRIPTION OF THE INVENTION

(5) In FIG. 1, there can be seen an aircraft 10 that has a main rotor 11 located above a fuselage and an anti-torque tail rotor 12 that is positioned at the rear end of a tail boom.

(6) A local reference frame (X, Y, Z) is associated with the aircraft 10, and more particularly with its center of gravity. The longitudinally extending direction of the aircraft 10 corresponds to the axis X and extends from the front of the aircraft 10 towards the rear of the aircraft 10. A vertically extending direction of the aircraft 10 corresponds to the axis Z and extends upwards perpendicularly to the longitudinal direction X. Finally, a transversely extending direction of the aircraft 10 corresponds to the axis Y and extends from right to left perpendicularly to the longitudinal direction X and the direction in elevation Z.

(7) The longitudinal direction X is the roll axis of the aircraft 10, the transverse direction Y is its pitching axis, and the direction in elevation Z is its yaw axis.

(8) The aircraft 10 also has a device 1 for determining the wind speed to be taken into account for determining the maximum authorized takeoff weight of the aircraft 10.

(9) The device 1 comprises anemometer means 21 positioned above a mast 13 of the main rotor 11. The anemometer means 21 may for example be an optical anemometer such as a LIDAR anemometer using a laser beam. It serves to measure the magnitude and the direction of the air speed of the aircraft 10 in a local reference frame, e.g. the reference frame (X, Y, Z), and to do so in accurate and of integrity. The anemometer means 21 serve in particular to determine the longitudinal speed and the transverse speed of the local wind at the aircraft 10, while the aircraft 10 is stationary.

(10) The device 1 is also provided with first receiver means 22 for receiving weather observation information and second receiver means 23 for receiving weather forecast information. Each receiver means 22, 23 can receive weather observation or weather forecast information in digital form, e.g. coming from the aerodrome where the aircraft 10 is situated while waiting to take off. The observation information may for example be taken from a METAR report and the forecast information may be taken from a TAF report.

(11) The device 1 also has means 13 for determining the heading of the aircraft 10, such as AHRS device and locating means 14 such as a GNSS receiver for determining the instantaneous position, attitude, and heading of the aircraft 10 in a terrestrial reference frame (X.sub.t, Y.sub.t, Z.sub.t), and also a current time.

(12) The device 1 also has consolidation means 30 comprising a computer 31 and storage means 32.

(13) The storage means 32 can store information received by the receiver means 22, 23 and by the locating means 14, together with measurements taken by the anemometer means 21 and by the heading determination means 13 of the aircraft 10. The storage means 32 may also store instructions that are executed by the computer 31 making use, amongst other things, of the stored information and measurements.

(14) Finally, the device 1 includes display means 25 such as a display screen for displaying information for the pilot and/or some other member of the crew of the aircraft 10.

(15) FIGS. 2 and 3 show two implementations of a method of determining the wind speed that is to be taken into account when determining the maximum authorized takeoff weight of an aircraft 10. This method makes it possible to determine the greatest possible wind speed for taking into account when determining the maximum authorized takeoff weight, depending on real weather conditions, but without degrading safety requirements, and it also makes it possible to determine the corresponding maximized authorized takeoff weight.

(16) The device 1 can perform two implementations of the method of determining the wind speed for taking into account when determining the maximum authorized takeoff weight of an aircraft 10.

(17) Thus, in a first step 110, at least a value for the heading is determined in the terrestrial reference frame (X.sub.t, Y.sub.t, Z.sub.t).

(18) This value for the heading may be obtained by the heading determination means 13 and it then corresponds to the instantaneous heading of the aircraft 10.

(19) This value for the heading may also be defined manually by a pilot or indeed some other crew member of the aircraft. This value for the heading may then be equal to the instantaneous heading of the aircraft 10, or it may be different therefrom, e.g. corresponding to the takeoff heading that the aircraft 10 is going to adopt very quickly after taking off.

(20) This value for the heading makes it possible to define a predefined direction that is characterized in the terrestrial reference frame (X.sub.t, Y.sub.t, Z.sub.t).

(21) When the value for the heading is equal to the instantaneous heading of the aircraft 10, the predefined direction coincides with the longitudinally extending direction of the aircraft 10.

(22) In contrast, when the value for the heading is different from the instantaneous heading of the aircraft 10, the predefined direction is at an angle relative to the longitudinally extending direction of the aircraft 10, this angle corresponding to the relative bearing of the predefined direction. The instantaneous heading of the aircraft must then also be known in order to be able to calculate the bearing of the predefined direction relative to the longitudinally extending direction of the aircraft.

(23) During a second step 120, at least one current speed value TAS.sub.inst is measured for the speed of the local wind by means of the anemometer means 21, this local wind being characterized by a longitudinal component and by a transverse component.

(24) During a third step 130, the weather observation information and the weather forecast information for the area where the aircraft 10 is situated or for a nearby area is received by the receiver means 22, 23.

(25) Thereafter, during a fourth step 140, the weather observation information is decoded in order to extract a mean observed speed for the local wind and the mean observed direction of the local wind together with a first instability criterion for the local observed wind. During this fourth step 140, the weather forecast information is also decoded in order to extract a second instability criterion for the forecast local wind.

(26) Thereafter, during a fifth step 210, a measured speed TAS.sub.mes of the local wind in the predefined direction is calculated from at least a current speed value TAS.sub.inst of the local wind by using the consolidation means 30.

(27) During a sixth step 220, an observed speed TAS.sub.obs of the local wind in the predefined direction is calculated from the weather observation information and from the value for the heading by the consolidation means 30. For this purpose, the observed speed TAS.sub.obs of the local wind in the predefined direction is calculated from the mean observed speed and the mean observed direction of the local wind, and also from the value for the heading.

(28) During a seventh step 310, the measured speed TAS.sub.mes is compared with the observed speed TAS.sub.obs of the local wind by the consolidation means 30.

(29) During an eighth step 320, a calculated speed TAS.sub.perfo for the local wind in the predefined direction is determined by the consolidation means 30 for taking into account when determining the maximum authorized takeoff weight of the aircraft 10.

(30) Finally, during a ninth step 330, the calculated speed TAS.sub.perfo of the local wind is displayed on the display means 25.

(31) The first implementation of the method as shown in FIG. 2 is constituted by these steps being chained in sequence.

(32) Nevertheless, it is also possible to perform some of the steps in simultaneous manner. For example, in the second implementation of the method shown in FIG. 3, the first, second, and third steps 110, 120, and 130 can be performed simultaneously. Likewise, the fourth and fifth steps 210 and 220 can be performed simultaneously.

(33) Furthermore, this second implementation of the method also includes intermediate steps.

(34) Thus, after the second step 120, a first intermediate step 121 and a second intermediate step 122 take place. During the first intermediate step 121, each current speed value TAS.sub.inst as measured during the second step 120 is corrected by subtracting a determined error margin therefrom. During the second intermediate step 122, a mean measured speed TAS.sub.moy of the local wind in the predefined direction is calculated as the mean of the current speed values TAS.sub.inst as measured during the second step 120 over a predetermined duration.

(35) Thereafter, during the fifth step 210 of this second implementation of the method, the measured speed TAS.sub.mes of the local wind is calculated as being equal to the mean measured speed TAS.sub.moy of the local wind over the predetermined duration.

(36) In contrast, during the fifth step 210 of the first implementation of the method, the measured speed TAS.sub.mes of the local wind is calculated as being equal to the current speed value TAS.sub.inst. This measured speed TAS.sub.mes of the local wind then corresponds to the instantaneous measured speed of the local wind.

(37) During the seventh step 310, the measured speed TAS.sub.mes is compared with the observed speed TAS.sub.obs of the local wind, while distinguishing three main situations in which the measured speed TAS.sub.mes and the observed speed TAS.sub.obs are positive, the measured speed TAS.sub.mes being compared with the observed speed TAS.sub.obs and the observed speed divided by two, TAS.sub.obs/2.

(38) Nevertheless, these three circumstances are applicable only when the observed local wind is stable and the forecast local wind is also stable, i.e. providing the first and second instability criteria indicate no instability in the observed local wind and no risk of instability in the forecast local wind.

(39) As a result, during the eighth step 320, the calculated speed TAS.sub.perfo of the local wind is calculated using the following conditions relating to each of these three situations.

(40) Firstly, if the first instability criterion and/or second instability criterion indicate(s) instability in the observed local wind or a risk of instability in the forecast local wind, then the calculated speed TAS.sub.perfo of the local wind is equal to the observed speed divided by two, i.e. TAS.sub.obs/2.

(41) Thereafter, if the measured speed TAS.sub.mes is greater than or equal to the observed speed TAS.sub.obs, the calculated speed TAS.sub.perfo is equal to the observed speed TAS.sub.obs.

(42) Furthermore, if the measured speed TAS.sub.mes lies strictly between the observed speed TAS.sub.obs and the observed speed divided by two, TAS.sub.obs/2, then the calculated speed TAS.sub.perfo is equal to the measured speed TAS.sub.mes.

(43) Finally, if the measured speed TAS.sub.mes is less than or equal to the observed speed divided by two, TAS.sub.obs/2, then the calculated speed TAS.sub.perfo is equal to the observed speed divided by two, TAS.sub.obs/2.

(44) In addition, if no measured speed TAS.sub.mes is provided, the calculated speed TAS.sub.perfo is equal to the observed speed divided by two, TAS.sub.obs/2.

(45) In contrast, when no observed speed TAS.sub.obs is available, the calculated speed TAS.sub.perfo is equal to the measured speed TAS.sub.mes divided by two.

(46) Finally, if no measured speed TAS.sub.mes is available and no observed speed TAS.sub.obs is available, then the calculated speed TAS.sub.perfo is equal to 0 kt.

(47) Furthermore, when the measured speed TAS.sub.mes and/or the observed speed TAS.sub.obs are negative, the calculated speed TAS.sub.perfo is equal to the minimum of the measured speed TAS.sub.mes and the observed speed TAS.sub.obs.

(48) Furthermore, this second implementation of the method includes a third intermediate step 325 that takes place after the eighth step 320. During this third intermediate step 325, the authorized maximum takeoff weight of the aircraft 10 is calculated as a function of the calculated speed TAS.sub.perfo of the local wind, e.g. using charts as supplied by the manufacturer of the aircraft 10.

(49) Finally, during the ninth step 330, the calculated speed TAS.sub.perfo of the local wind and possibly also the maximum authorized takeoff weight of the aircraft 10 is/are displayed on the display means 25. Other information that might be of interest to the pilot may also be displayed, such as the mean measured speed and the mean direction of the local wind together with the mean speed and the mean direction of the observed local wind and any variations therein.

(50) These two implementations of the method of determining the longitudinal speed of the wind to be taken into account when determining the maximum authorized takeoff weight of an aircraft 10 thus make it possible to consolidate local wind measurements from an onboard anemometer that is accurate and of integrity with weather observations and forecasts, so that if weather conditions are stable and favorable, it is possible to optimize the takeoff capacity of the aircraft.

(51) Furthermore, when the value for the heading is different from the instantaneous heading of the aircraft 10 prior to takeoff and defines a takeoff heading value, it is advantageous to calculate the maximum authorized takeoff weight of the aircraft 10 with the wind speed to which the aircraft is subjected when using that takeoff heading value. The method of the invention must then be applied by using as the value for the heading the value of the takeoff heading that corresponds to the heading that the aircraft 10 will quickly take on while taking off. This takeoff heading value needs to be defined manually by the pilot.

(52) 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.