Measurement system for measuring the velocity of an aircraft

The disclosure herein relates to a measurement system to measure characteristics of the velocity vector of an aircraft in relation to a surrounding air mass, the measurement system comprising—a frontal surface of the aircraft, two primary sensors, each being fixed to the frontal surface of the aircraft and able to deliver an output value relating to the deformation experienced by the sensor, and a processing unit able to receive the output values and able to calculate the angle of attack and/or the velocity of the aircraft on the basis of these output values.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of and priority to French patent application No. 14 54230 filed on May 13, 2014, the entire disclosure of which is incorporated by reference herein.

BACKGROUND

The present disclosure relates to a system for measuring characteristics of the velocity vector of an aircraft in relation to a surrounding air mass, such as the velocity, angle of attack, and angle of sideslip of the aircraft.

The disclosure herein also relates to an aircraft equipped with such a measurement system and also to a method for updating such a measurement system.

Currently, the characteristics of the velocity vector of an aircraft are measured with the aid of sensors placed in the flow of air surrounding the aircraft. Thus, the velocity of an aircraft is measured with the aid of pitot tubes, the angle of attack of an aircraft is measured by angle of attack probes, and the angle of sideslip of an aircraft, on some aircraft, is measured by sideslip probes.

In some conditions these sensors may give false indications. For example, when they are blocked or obstructed by water or frost.

It is therefore beneficial to have another means for measuring the characteristics of the velocity vector of the aircraft.

SUMMARY

An object of the present disclosure is to provide a system for measuring characteristics of the velocity vector of an aircraft that does not have the disadvantages of the prior art.

To this end, a measurement system to measure characteristics of the velocity vector of an aircraft in relation to a surrounding air mass is disclosed, the measurement system comprising:two primary sensors fixed to a frontal surface of the aircraft, each sensor being able and configured to deliver an output value relating the deformation experienced by the sensor, anda processing unit able to receive the output values and able to calculate the angle of attack and/or the velocity of the aircraft on the basis of these output values.

Such a system does not present the same risks of failure as the sensors of the prior art and gives indications of the velocity vector that make it possible to augment the information given by the other navigation systems.

The measurement system advantageously also comprises two complementary sensors, each complementary sensor being fixed to the frontal surface and able to deliver an output value relating to the deformation experienced by the sensor, and the processing unit is able to receive the output values of the two complementary sensors and to calculate an angle of sideslip of the aircraft on the basis of these output values.

The frontal surface is advantageously a radome arranged at the front of the aircraft.

One of the primary sensors is advantageously disposed at the top part of the radome, and the other primary sensor is disposed at the bottom part of the radome.

The two primary sensors are advantageously disposed on a plane of symmetry P of the radome.

The two complementary sensors are advantageously disposed symmetrically on either side of a plane of symmetry P of the radome.

For each sensor, the variation of the output value is advantageously proportional to the deformation experienced by the sensor.

The processing unit advantageously comprises:a receiver to receive a series of values of the angle of attack, the velocity, and possibly the angle of sideslip from other instruments of the aircraft,a comparer to compare each series of values thus received with the corresponding series of values calculated on the basis of the output values, andan updater to update the corresponding coefficients and/or constants for which the comparer has emitted a negative signal.

The disclosure herein also proposes an aircraft comprising a frontal surface and a measurement system according to one of the preceding variants.

The disclosure herein also proposes a method for updating a measurement system according to a preceding variant, the method comprising:a receiving step, during which the processing unit receives a series of values of the angle of attack, of the velocity, and possibly of the angle of sideslip from other instruments of the aircraft,a step of comparison, during which the processing unit compares the series of values thus received with the corresponding series of values calculated on the basis of the output values,for each pair of series of values thus compared, when the comparison is negative, an updating step, during which the processing unit updates the corresponding coefficients and/or constants.

DETAILED DESCRIPTION

In the following description the terms relating to a position are taken with reference toFIG. 1, in which an aircraft has a longitudinal axis x, a transverse axis along the axis y, and a vertical axis along the axis z.

FIG. 1shows the front part100of an aircraft in a surrounding air mass.

In the embodiment of the disclosure herein presented here, the front part100comprises:a cockpit102,a lower structure106fixed beneath the cockpit102,a chin fairing104fixed in front of the lower structure106, anda radome108fixed in front of the chin fairing104.

The radome108assumes there the form of a dome having an axis x with an apex S and a plane of symmetry P passing through S and parallel to the vertical axis z.

FIG. 2shows the front view of the radome108arranged at the front of the aircraft and constituting a frontal surface of the aircraft.

The front part100also has a measurement system150to measure characteristics of the velocity vector of the aircraft in relation to the surrounding air mass. These characteristics of the velocity vector may be the value of the velocity, the angle of attack and/or the angle of sideslip of the aircraft.

The measurement system150comprises:the radome108of the aircraft,two primary sensors152a-b, each being fixed to the radome108, and able to deliver an output value relating to the deformation experienced by the sensor, anda processing unit154able to receive the output values and able to calculate the angle of attack and/or the velocity of the aircraft on the basis of these output values.

Such a measurement system150therefore is not disturbed by the ambient conditions and can thus deliver reliable velocity information. The placement of the primary sensors152a-bon the radome108is particularly interesting because the radome108is a lightweight part, which is not structural and which deforms relatively easily under the action of the pressure.

The primary sensors152a-bare more particularly fixed inside the radome108and are thus presented in a transparent view inFIG. 2.

In the embodiment of the disclosure herein presented, the processing unit154is disposed on the lower structure106, but could also be disposed in the aircraft and could even be integrated in the pre-existing electronic systems.

The processing unit154is able to transmit the velocity and angle of attack information to a display housed in the cockpit102so as to provide this information to the pilot.

Here, information is transmitted between each primary sensor152a-band the processing unit154by wired connection.

Each primary sensor152a-bis a strain gauge of which the variation of the output value is proportional to the deformation experienced by the sensor.

In order to determine the angle of attack, one of the primary sensors152ais disposed at the top part of the radome108and the other primary sensor152bis disposed at the bottom part of the radome108, i.e. on either side of a plane P′ passing through the apex S and parallel to the transverse axis y.

For reasons of symmetry, the two primary sensors152aand152bare disposed over the plane of symmetry P of the radome108.

The angle of attack can be evaluated on the basis of a formula of the type:

where α is the angle of attack, Kαis the linear coefficient of the primary sensors152a-brelating to the angle of attack, A is a constant, and gaand gbare the values given by the primary sensors152a-b. The coefficient Kαand the constant A are determined by calculation, for example by performing simulations of the deformation of the radome108under the effect of the pressure of the air, or by way of experiment. As the case may be, the value thereof may be different depending on the value ranges of the different sensors, so as to take into account any non-linear effects of the deformation of the radome108.

The calibrated airspeed can be evaluated on the basis of a formula of the type:
Vc=ƒ(PT−PS)  Equation (2)

where Vcis the calibrated airspeed, ƒ is a function, PTis the total pressure, and PSis the static pressure.

The static pressure can be determined on the basis of suitable measurement instruments or on the basis of data such as GPS altitude.

The total pressure can be obtained by a formula of the type:
PT=K1(ga+gb)+BEquation (3)

where K1is a linear coefficient of the primary sensors152a-brelating to the pressure and B is a constant.

In accordance with an alternative, the output values of the primary sensors152a-bare representative of the difference (PT−PS), since the pressure within the radome108is substantially equal to PS.

The pressure difference can be obtained by a formula of the type:
PT−PS=K2(ga+gb)+CEquation (4)

where K2is a coefficient relating to the pressure difference, and C is a constant.

The coefficients K1, K2and the constants B, C are determined by calculation, for example by performing simulations of the deformation of the radome108under the effect of the pressure of the air, or by way of experiment. As the case may be, the value thereof may be different depending on the value ranges of the different sensors, so as to take into account any non-linear effects of the deformation of the radome108.

In order to measure the angle of sideslip of the aircraft, the measurement system150comprises two complementary sensors152c-d, which are preferably of the same type as the two primary sensors152a-band are connected to the processing unit154.

The two complementary sensors152c-dare disposed symmetrically on either side of the plane of symmetry P.

Each complementary sensor152c-dis also fixed to the radome108and is able to deliver an output value relating to the deformation experienced by the sensor, and the processing unit154is then able to receive the output values and to calculate the angle of sideslip of the aircraft on the basis of these output values.

The angle of sideslip can be evaluated on the basis of a formula of the type:

where β is the angle of sideslip, Kβis the linear coefficient of the complementary sensors152c-drelating to the sideslip angle, D is a constant, and gcand gdare the values given by the complementary sensors152c-d. The coefficient Kβand the constant D are determined by calculation, for example by performing simulations of the deformation of the radome108under the effect of the pressure of the air, or by way of experiment. As the case may be, the value thereof may be different depending on the value ranges of the different sensors, so as to take into account any non-linear effects of the deformation of the radome108.

The characteristics of the sensors152a-dand of the radome108may vary over the course of time and from one aircraft to another, and it is thus preferable to devise an updating method during which the values of the different coefficients Kα, K1, K2, Kβand the constants A, B, C, D are updated.

FIG. 3shows a flowchart of an updating method300.

In the case in which the measurement system150measures the angle of attack and the velocity of the aircraft, the updating method comprises:a receiving step302, during which the processing unit154receives a series of values of the angle of attack and of the velocity from other instruments of the aircraft, for example velocity values given by the pitot tubes and angle of attack values given by the angle of attack probes,a comparison step304, during which the processing unit154compares the series of values thus received with the corresponding series of values calculated on the basis of the output values,for each pair of series of values thus compared, when the comparison is negative, an updating step306, during which the processing unit154updates the corresponding coefficient Kα, K1, K2and/or constants A, B, C.

When the comparison is positive there is no update.

The comparison is negative when the difference, in absolute value, between a pair of compared values or between the averages of compared value series is greater than a predetermined threshold, and the comparison is positive when the difference, in absolute value, between the compared value pairs or between the averages of the compared value series is below this predetermined threshold.

The update comprises finding the coefficient Kα, K1, K2and/or the constants A, B, C for which the output values give the received values, it being sufficient for this purpose to perform a digital interpolation in order to calculate the angle of attack and the velocity on the basis of the output values.

In the case in which the measurement system150also measures the angle of sideslip of the aircraft,the receiving step302also comprises, for the processing unit154, receiving a series of values of the angle of sideslip from other instruments of the aircraft, these being values given by sideslip probes, for example,the comparison step304also comprises, for the processing unit154, comparing the series of values of the angle of sideslip thus received with the corresponding values calculated on the basis of the output values,for this pair of series of values thus compared, when the comparison is negative, the updating step306comprises, for the processing unit154, updating the corresponding coefficient Kβand/or constant D.

The processing unit154comprises, to this end:a receiver to receive a series of values of the angle of attack, of the velocity, and possibly of the angle of sideslip from other instruments of the aircraft,a comparer to compare each series of values thus received with the corresponding series of values calculated on the basis of the output values, andan updater to update the corresponding coefficient Ka, K1, K2, Kβand/or constants A, B, C, D for which the comparer has emitted a negative signal.

In order to prevent the updates from introducing errors in the coefficients Kα, K, Kβ, and the constants A, B, C, D, the updating method can be performed taking into account the values collected over a relatively long period, for example the data collected during a previous flight. The values taken into account are, in this case, preferably those that have been collected over periods during which the measurements taken by the other instruments of the aircraft are assured, for example when the flight conditions are such that there is not risk of freezing of the pitot tubes or other sensors.

In the embodiment of the disclosure herein described above, the sensors are fixed to the radome of the aircraft, which is particularly suitable for measuring characteristics of the velocity vector of the aircraft. In fact, the location of the radome at the end of the front point allows it to directly receive the pressure exerted by the flow of air, without interference. In addition, because the radome is not a structural part of the aircraft, it has a relatively low rigidity, enabling it to deform relatively easily under the action of the pressure of the air.

It is, however, also possible to implement the disclosure herein on another frontal surface of the aircraft, i.e. on another surface in frontal contact with the flow of air resulting from the displacement of the aircraft. This frontal surface may be another surface of the fuselage nose of the aircraft, or an edge of attack of a wing, or the tail unit of the aircraft.