WO2006117347A1

WO2006117347A1 - Combined instrument for a helicopter, method of determining the speed of a helicopter and method of adjusting a combined instrument for a helicopter

Info

Publication number: WO2006117347A1
Application number: PCT/EP2006/061938
Authority: WO
Inventors: Jacques Mandle
Original assignee: Thales
Priority date: 2005-04-29
Filing date: 2006-04-28
Publication date: 2006-11-09
Also published as: FR2885222B1; FR2885222A1

Abstract

The invention relates to a combined instrument (10) for a helicopter (21), a method of determining the speed of a helicopter (21) and a method of adjusting a combined instrument (10) for a helicopter (21). Numerous helicopters are already equipped with one such instrument. The invention improves the speed indicated on a screen of the combined instrument (10) by combining a first speed which is determined from data received from means for tapping the pressure (27, 28) of the air surrounding the helicopter (21) and a second speed (Vs) which is determined from a datum received from a position sensor (30) belonging to means (24, 25, 26) for controlling a cylcic pitch of a rotor (22) of the helicopter (21) and a datum received from means for measuring the attitude of the helicopter (21).

Description

Combined helicopter instrument, method for determining the speed of a helicopter and method of tuning a combined instrument for a helicopter

The invention relates to a combined instrument for a helicopter, a method for determining the speed of a helicopter and a method for adjusting a combined instrument for a helicopter. Such an instrument is already present in many helicopters. This instrument comprises display means in the form of a color screen. This screen displays various information necessary for the operation of the helicopter such as altitude, attitude and speed of the helicopter from information from means for measuring the pressure of the air flow surrounding the helicopter and an inertial measurement unit. The pressure measuring means, and the inertial measurement unit also belong to the combined instrument. This instrument is advantageously used in relief of primary means of altitude measurement, attitude and speed present on board any aircraft. The instrument is then called a combined emergency instrument. Speed is one of the essential data for flying the helicopter. It is known to determine the speed V of an aircraft and in particular a helicopter from measurement of the air pressure surrounding the helicopter. More precisely, by measuring the total pressure Pt, for example using a pitot tube, and the static pressure Ps of the air, the speed V of the aircraft can be determined by the following equation:

V ² Pt -Ps = ρ- where p represents the density of the air.

At low speed this method of measurement gives unreliable results. On the one hand, the square of the speed is proportional to the pressure difference Pt - Ps. Consequently a small error on the pressure measurements leads to a big error on the speed. More precisely, by deriving the equation quoted above, we obtain:

d (Pt -Ps) = p.V.dV

d (Pt -Ps) or dv = -

PV This shows that a finite error d (Pt-Ps) on the pressure measurements leads to an infinite error dV on the determination of the speed when the velocity is zero, or a large error on the determination of the velocity when the velocity is low. For example, at 10 knots true speed, an error of 1 hpa on the pressure measurements results in an error of 30 knots on the determination of the speed. When the error is greater than the measurement, the result is unacceptable. On the other hand, the flow of air generated by the rotor becomes predominant at low speed for two reasons: firstly because of the speed of the air generated by the rotor itself, typically 20 knots, and secondly the direction of rotation. the flow of air is modified at the entrance of the Pitot tube, which also disturbs the measurement of total pressure Pt. In conclusion, the pressure sensors used to measure the total pressure Pt and the static pressure Ps are incapable to provide sufficiently accurate information to determine the speed V of a helicopter when it is flying at low speed.

There is another method for measuring the speed V usable at low speed on a helicopter. This method is described in French patent FR 2 567 270. It is based on the principle that the air speed is proportional to the difference between the cyclic pitch of the lift rotor of the helicopter and the attitude of the helicopter. . The speed obtained by this method is called synthetic speed and will be called Vs. This principle makes it possible to determine both the direction and the modulus of the air velocity vector. This method has only been used to date in flight test centers to develop new helicopters. This method was not used in normal helicopter use mainly because of its higher cost of implementation than the first method using pressure measurements.

The invention aims to overcome the disadvantages of the methods described above and to give the pilot information on the speed of his helicopter with good accuracy at low speeds, especially below 50 knots. The combined instrument already has on its screen an area for displaying the longitudinal speed of the helicopter. The invention consists in improving the accuracy of the speed displayed on the screen of the combined instrument and in particular in extending the validity of the speed displayed at very low speeds. typical of the flight of a helicopter. This has the advantage of not modifying the ergonomics of the dashboard on which the combined instrument is installed.

For this purpose, the subject of the invention is a combined instrument for a helicopter, comprising means for determining a first speed of the helicopter on the basis of information received from means for taking pressure of the air surrounding the helicopter, means for determining the attitude of the helicopter, means for displaying the speed and attitude of the helicopter, characterized in that it further comprises means for determining a second speed of the helicopter; helicopter from information received from a control position sensor of a cyclic pitch of a rotor of the helicopter and information received from the helicopter attitude measuring means . The invention also relates to a method for determining the speed of a helicopter, characterized in that it consists in using means for determining the attitude of the helicopter present in a combined instrument mounted on board of the helicopter and information received from a control position sensor of a cyclic pitch of a rotor of the helicopter and to display the speed on display means of the combined instrument.

Another object of the invention is a method of adjusting the combined instrument described above, a combined instrument determining a first speed Vc of the helicopter from information received from means for taking pressure of the air surrounding the helicopter and a second speed Vs of the helicopter from information received from a position sensor of control means of a cyclic pitch of a rotor of the helicopter and information received from the helicopter. means for measuring the attitude of the helicopter, the second speed Vs being determined by the following equation:

Vs = [k1.arcsin (γ1 / g) + k2] - [k3.BI + k4] where γ1 represents the acceleration measured along an axis of the helicopter, g represents the acceleration of gravity and where k1 to k4 are coefficients, characterized in that it consists of: Helicopter (21) on the ground, the combined indicator (10) is set, when on the swashplate (24), the cyclic pitch control is varied and the ratio k1 / k3 = 1 is adjusted so as to that the speed indication Vs remains constant; • helicopter (21) hovering, at an altitude high enough to avoid ground effects, in zero wind, k2 - k4 is set so that the speed indication Vs is zero; if the wind is not zero, the axis of the helicopter (21) is placed perpendicularly to the axis of the wind; finally, helicopter (21) flying at a certain speed, for example

50 nodes, we set k3 / k1 so that the value of the first speed Vc is identical to the value of the second speed Vs.

By implementing the invention from an existing combined instrument, the adaptation of the instrument is easy to achieve. Indeed, the existing instrument already includes pressure sensors, an inertial unit and a computer. To implement the invention, it is sufficient to provide a connection to the control means of a cyclic pitch of a rotor of the helicopter. The implementation of the invention is all the more interesting as we are currently observing a helicopter generalization of this type of combined instrument to replace discrete instruments such as a conventional gyroscopic horizon, an altimeter, an anemometer and an aneroid capsule variometer.

The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given by way of example, a description illustrated by the accompanying drawing in which: FIG. 1 represents a combined instrument intended to be mounted on a helicopter; Figure 2 schematically shows an example of implementation of the combined instrument mounted on board a helicopter.

FIG. 1 represents a combined instrument 10 comprising means for measuring the pressure of the air flow surrounding a helicopter in which the combined instrument 10 is installed, means for Inertial measurement, calculation means and visualization means 1 1. The calculation means determine and display on the display means 1 1 the altitude, the attitude and the speed of the helicopter based on information from the means for measuring the pressure, and means for inertial measurement. The altitude of the helicopter is displayed on a straight portion 12 of a screen 13 of the display means 11. The attitude of the helicopter is displayed in the form of a mobile horizon 14 with respect to a silhouette 15 of the helicopter on a central portion 16 of the screen 13. The speed of the helicopter relative to the relative wind is displayed on a left portion 17 of the screen 13. Advantageously the screen 13 is a liquid crystal screen.

Advantageously, the inertial measurement means, included in the combined instrument 10, provide the computation means with two pieces of information representative of the acceleration of the helicopter each in one direction, the two directions forming a substantially frontal plane of the helicopter. The inertial measurement means may comprise at least two accelerometers measuring the acceleration of the helicopter along two axes of the substantially horizontal plane of the helicopter. The two accelerometers then provide the first and the second information. The means for measuring the pressure, the calculation means and the two accelerometers are for example located inside a body 18 of the combined instrument, body 18 located at the rear of the screen 13.

FIG. 2 shows a helicopter 21 comprising a lift rotor 22 and means 23 for controlling a cyclic pitch of the rotor 22. The control means 23 generally comprise a swashplate 24 whose orientation is determined by rods 25 and 26. For example, the link 25 controls the longitudinal orientation of the swashplate 24 and rod 26 controls the transverse orientation of the swashplate 24.

The helicopter 21 also comprises means 27 for taking a total pressure Pt, comprising for example a pitot tube, and means 28 for taking static pressure Ps. The pressure taking means 27 and 28 are connected by pipes to the means for measuring the pressure of the combined instrument 10 which processes the pressure information to determine a first speed Vc of the helicopter 21. The pitot tube is substantially oriented along a longitudinal axis of the helicopter 21 to determine the value of the speed along this axis. The longitudinal axis of the helicopter 21 is included in the plane of FIG. 2. It would of course be possible to place a second Pitot tube along a transverse axis of the helicopter 21, which axis is perpendicular to the plane of FIG. to measure the speed Vc along the transverse axis. However this measure is of little interest because the helicopter speed in a transverse axis is always low.

The combined instrument 10 gives the pilot of the helicopter 21 information concerning the speed, the altitude and the attitude of the helicopter 21. The combined instrument 10 comprises a calculator making it possible to determine the first speed Vc using the following equation:

Vc ² Pt-Ps = P- where p represents the density of the air at ground level.

According to the invention, the device comprises a position sensor of the cyclic control of the pitch of the rotor 21. The position sensor 30 can measure the absolute position or the relative position of the cyclic control. In the case of a relative position measurement the sensor may be a displacement sensor. The sensor 30 measures, for example, the position of one of the rods 25 or 26. Advantageously, the device comprises two position sensors of the cyclic control of the pitch of the rotor 21. In the case of two sensors, one makes it possible to determine the longitudinal cyclic pitch and the other makes it possible to determine the transverse cyclic pitch. It will be seen later that each of these two sensors makes it possible to determine the speed of the helicopter at low speeds, either longitudinally or transversely.

The sensor (or sensors) 30 is connected to the combined instrument 10 which comprises means for determining a second speed Vs from information received from the sensor 30 and information received from the measuring means of a sensor. helicopter attitude 21. For example, the second speed Vs can be determined using the following equation:

Vs = k (θ1 -B1) equation in which θ1 represents the accelerometric attitude along an axis, for example longitudinal, B 1 represents the cyclic pitch along the same axis and in which k is a constant function of the helicopter 21 and which can be determined experimentally. From the foregoing, it is easy to deduce that with the aid of two sensors, one for the longitudinal cyclic pitch and the other for the transverse cyclic pitch, as well as two accelerometers, one measuring the longitudinal attitude and the other the transverse attitude, it is possible to determine the speed Vs along a longitudinal axis and the speed Vs along a transverse axis of the helicopter 21. By combining these two speeds it is possible to determine the modulus and the direction of the speed vector Vs of the helicopter 1. The above equation can be adapted to the use of accelerometers usually intended to determine the attitude of the helicopter 21:

Vs = [k1.arcsin (γ1 / g) + k2] - [k3.BI + k4] where γ1 represents the acceleration measured along a longitudinal axis, g represents the acceleration of gravity and where k1 to k4 are coefficients adjusted empirically. This equation, giving the first speed Vs along a longitudinal axis, is of course adaptable to determine the first speed Vs along the transverse axis of the helicopter 21. To adjust the coefficients k1 to k4, it is possible to proceed as follows:

Helicopter 21 on the ground, the means for measuring a plane of the helicopter 21, in particular the combined indicator 10, when it comprises the accelerometer or accelerometers, on the swashplate 24, the command is varied. cyclic pitch and set the ratio k1 / k3 = 1 so that the speed indication Vs remains constant;

• helicopter 21 hovering, at an altitude high enough to avoid ground effects, in zero wind, we set k2 - k4 so that the speed indication Vs is zero; if the wind is not zero, we place the axis of the helicopter 21 according to which the acceleration is measured, here the longitudinal axis, perpendicular to the axis of the wind;

Finally, helicopter 21 flying at a certain speed Vc non-zero, for example 50 knots, speed Vc measured using pressure sensors 27 and 28, setting k3 / k1 so that the speed indication Vs indicates this same speed.

The means for determining the second speed Vs are formed by the computer of the combined instrument 10, a computer already used for calculating the attitude and calculating the first speed Vc. The invention is of particular interest when using components already present in the combined instrument 10 namely the computer and the accelerometers.

Advantageously, the (or) sensor 30 comprises a linear potentiometer supplied by the combined instrument 10. The potentiometer comprises a slider operated by the rod 25 or 26 with which it cooperates.

The combined instrument 10 further comprises means for determining a third speed Va from a weighting of the first speed Vc and the second speed Vs. Advantageously, the means for determining the third speed Va also use the calculator of the combined instrument 10 already used for calculating the attitude and calculating the speeds Vc and Vs.

Advantageously, the weighting is not done on all the speeds that the helicopter 21 can reach. More precisely, the third speed Va is equal to the second speed Vs when the second speed Vs is lower than a first speed value V1. The third speed Va is equal to the first speed Vc when the first speed Vc is greater than a second speed value V2. It is only between the two values V1 and V2 that the weighting is effective. For example, between

V1 and V2, we have:

Va = α.Vs + (1 - α) .Vc where α represents a weighting coefficient varying between 0 and 1. To avoid jumps in the value of Va, we will give α a value equal to 1 when Vs = V1 and a zero value when Vc = V2. From V1 to V2 and we will evolve α continuously between 1 and 0. We can for example give V1 a value of 30 nodes and V2 a value of 50 nodes. It is recalled that a node is equal to 0.51 m / s.

Claims

Combined instrument (10) for helicopter (21), comprising means for determining a first speed (Vc) of the helicopter (21) from information received from pressure taking means (27, 28) air surrounding the helicopter (21), means for determining the attitude of the helicopter (21), means for visualizing (11) the speed and attitude of the helicopter (21) , characterized in that it further comprises means for determining a second speed (Vs) of the helicopter (21) from information (B1) received from a position sensor (30) of means control (24, 25, 26) of a cyclic pitch of a rotor (22) of the helicopter (21) and information (γ1) received from the means for measuring the attitude of the helicopter ( 21).

2. Combined instrument (10) according to claim 1, characterized in that the means for determining the first speed (Vc) comprise means (7) for measuring a total pressure (Pt) of an air flow. surrounding the helicopter (1) and means (8) for measuring a static pressure (Ps) of the air flow.

3. Combined instrument (10) according to one of the preceding claims, characterized in that the means for determining the attitude of the helicopter (21) comprise inertial measurement means providing means for calculating the instrument combined (10) two information representative of the acceleration of the helicopter (21) each in one direction, the two directions forming a substantially horizontal plane of the helicopter (21) and that the inertial measurement means are included in the combined instrument (10).

4. Combined instrument (10) according to one of the preceding claims, characterized in that it comprises means for determining a third speed (Va) of the helicopter (1) from a weighting of the first (Vc) and the second speed (Vs).

5. Combined instrument (10) according to claim 4, characterized in that the third speed (Va) is equal to the second speed (Vs) when the second speed (Vs) is lower than a first speed value (V1), in that the third speed (Va) is equal to the first speed (Vc) when the first speed is greater than a second value (V2) in that the weighting is effective between the first value (V1) and the second value (V2) of speed.

Combined instrument (10) according to claim 5, characterized in that between the first speed value (V1) and the second speed value (V2) the weighting is defined as follows: Va = αVs + (1 - α) Vc where Va is the third speed, Vc is the first speed, Vs is the second speed and where α is a weighting coefficient varying between 0 and 1.

Combined instrument according to one of the preceding claims, characterized in that it comprises pressure measuring means, an inertial measurement unit and display means displaying the altitude, the attitude and the speed of the helicopter. from information from the means for measuring the flow pressure of the inertial measurement unit.

8. Device comprising a combined instrument (10) according to one of the preceding claims, the position sensor (30) and the control means (24, 25, 26) of a cyclic pitch of a rotor (22), characterized in that the control means (24, 25, 26) of a cyclic pitch of the rotor (22) comprise a swash plate (24) whose orientation is determined by links (25, 26), and in that the sensor (30) comprises a linear potentiometer supplied by the combined instrument (10), the potentiometer comprising a slider operated by the rod (25 or 26) with which it cooperates.

9. Device according to claim 8, characterized in that it comprises two sensors (30) of the position of the control of the cyclic pitch of the rotor (2) one for a longitudinal cyclic pitch and the other for a transverse cyclic pitch .

10. Method for determining the speed (Vs) of a helicopter (21), characterized in that it consists in using means for determining the attitude of the helicopter (21) present in a combined instrument (10) mounted on board the helicopter (21) and information (B1) received from a position sensor (30) of control means (24, 25, 26) of a cyclic pitch of a rotor ( 22) of the helicopter (21) and display the speed on display means (1 1) of the combined instrument (10).

1. Process according to claim 10, characterized in that it consists of:

Determining a first speed (Vc) of the helicopter (21) from information received from the pressure taking means (27, 28) of the air surrounding the helicopter (21),

Determining a second speed (Vs) of the helicopter (21) from the information received from a position sensor (30) of control means (24, 25, 26) of a cyclic pitch of a rotor (22) of the helicopter (21) and information received from the means for measuring the attitude of the helicopter (21).

12. Method according to claim 1 1, characterized in that it consists in combining the first speed (Vc) and the second speed (Vs) so as to determine a weighted speed (Va) along a longitudinal axis of the helicopter ( 21) and displaying the weighted speed (Va) on the display means (1 1) of the combined instrument (10).

13. A method of adjusting a combined instrument (10) according to one of claims 1 to 7, combined instrument (10) determining a first speed Vc of the helicopter (21) from information received means of setting of pressure (27, 28) of the air surrounding the helicopter (21) and a second speed Vs of the helicopter (21) from information Bl received from a position sensor (30) of control means (24, 25, 26) of a cyclic pitch of a rotor (22) of the helicopter (21) and an information item (γ1) received from the means for measuring the attitude of the helicopter (21), the second speed Vs being determined by the following equation: Vs = [k1.arcsin (γ1 / g) + k2] - [k3.BI + k4] where γ1 represents the acceleration measured along an axis of the helicopter, g represents the acceleration of gravity and where k1 to k4 are coefficients, characterized in that it consists of:

Helicopter (21) on the ground, the combined indicator (10) is placed on the swash plate (24), the cyclic pitch control is varied and the ratio k1 / k3 = 1 is adjusted so that the speed indication Vs remains constant;

• helicopter (21) hovering, at an altitude high enough to avoid ground effects, in zero wind, k2 - k4 is set so that the speed indication Vs is zero; if the wind is not zero, the axis of the helicopter (21) is placed perpendicularly to the axis of the wind;

Finally, helicopter (21) flying at a certain non-zero speed, for example 50 knots, we set k3 / k1 so that the value of the first speed Vc is identical to the value of the second speed

Vs.