GB2547635A

GB2547635A - Sensor method

Info

Publication number: GB2547635A
Application number: GB1602687.4A
Authority: GB
Inventors: A Penny William
Original assignee: Penny and Giles Aerospace Ltd
Current assignee: Penny and Giles Aerospace Ltd
Priority date: 2016-02-16
Filing date: 2016-02-16
Publication date: 2017-08-30
Also published as: GB201602687D0

Abstract

A method and system, for detecting precipitation elements 18 (solid particles, ice crystals, liquid droplets) in the air whilst an aircraft is flying, comprising a sensor 10 having a measurement surface 14 on which the particles/droplets impact and a means to record the impact to provide a signal. Additionally a gas turbine engine is provided. The gas turbine engine comprises the sensor, a recorder, a store 22 and a comparator 20. The recorder records the impacts and provides a recorded signal. The store comprises reference signals, one of which corresponds to hazardous conditions. The comparator compares recorded signals with reference signals and alerts a control system to operate the engine in a safe mode if the comparator determines that the recorded signal matches the signal corresponding to a known hazardous condition. The sensor may comprise a piezoelectric sensor 12 responsive to impacting particles on the measurement surface.

Description

SENSOR METHOD

Field of the Invention

The present invention relates to a method for detecting and identifying ice particles, solid particles and liquid droplets when they are present in the air in which an aircraft is flying.

Background

Many aircraft are equipped with sensors and systems which can detect and alert the crew of the presence of hazardous environmental conditions, including icing.

Over the years, a wide variety of ice detection systems have been developed mainly based on the effects of ice accretion on cold surfaces. However, these systems are not able to detect the presence of glaciated icing conditions, as ice crystals bounce off the cold surfaces of the aircraft. Neither can they discriminate super-cooled liquid droplets (SLD’s), nor provide accurate characterisation of encountered icing conditions, nor detect the presence of solid particles such as volcanic matter.

The presence of solid particles, ice crystals or SLDs can create hazardous conditions for flying. If the airplane is equipped to fly in hazardous environmental conditions the sensor, which is the subject of the present invention, can be used to alert those responsible for safety of the aircraft to take appropriate action or to activate the ice protection system, or the system can automatically activate based on a signal from the sensor.

Ingestion of ice crystals into a gas turbine engine during flight may result in accretion on components of the engine and shedding into the core of the engine. This could cause damage to engine components and may cause compressor surge and/or flame out in the combustor of the gas turbine engine. This engine malfunction creates risks to flight safety and is a well-known problem in the industry. If the risk of ingestion is high, and is known, it is possible to make adjustments to the engine settings to minimise the possibility of engine malfunction. These adjustments may reduce engine efficiency so would only be made when needed.

With optical or radar sensing methods particle sizes are too small for detection. Supercooled water droplets cannot be detected by optical or radar methods. US 8869537 claims to identify particles by measuring acoustically the impact on a surface of the engine or aircraft. Given the background noise in this environment such an approach must be limited in terms of accurate identification of the particles. Furthermore, this method will not identify super-cooled water droplets. It is also possible that icing of the impacted surfaces could alter the characteristic of the acoustic signals.

Summary

The purpose of this invention is to provide a method and associated sensor with an accurate and reliable means of identifying and measuring the solid particles, including ice crystals, or liquid droplets in the air in which the aircraft is flying. This information can then be used to alert the flight crew so corrective action can be taken, or to provide a control system signal for automatic corrective action. The device and the method described is for the purpose of informing those responsible for operating an aircraft that solid particles or liquid droplets are present in the air in which it is currently flying.

According to a first aspect of the present invention there is provided a method for detecting precipitation elements that comprise solid particles, including ice crystals, and/or liquid droplets in an environment in which an aircraft is flying, comprising: providing a sensor having a measurement surface; exposing the measurement surface to the environment such that solid particles and liquid droplets impact the measurement surface and thereby generate a force; and recording the impact forces over time to provide a recorded signal.

The method may entail quantifying and recording the impact forces with respect to time during the process of accelerating a solid particle or liquid droplet from a quasi-static state to the known velocity of the aircraft.

Alternatively, the method may entail quantifying and recording the impact forces with respect to time during the process of decelerating a solid particle or liquid droplet from the downward air velocity created by rotor downdraft to the known vertical velocity of the aircraft.

By accessing environmental data from other aircraft sensors, such as outside air temperature, it can be determined whether the liquid droplets are super-cooled liquid droplets (SLDs), which are known to be hazardous to flight safety.

By sensing the impact forces with respect to time the recorded signal can be compared to stored data to identify the presence and type of solid particles (e.g. ice crystals) or liquid droplets (e.g. water droplets that may be super-cooled). In addition, the use of a measurement surface in the sensor provides a more accurate means of identification and avoids the problems referred to above of relying on detection by acoustic means of impacts on surfaces of the aircraft.

As noted above, a turbine engine is often operated under particular conditions to avoid damage caused by solid particles and liquid droplets. Such conditions may not provide optimum performance so it is important to know when such conditions are really required and when they can be avoided. If not required, the aircraft can be operated more efficiently.

Embodiments may additionally comprise comparing the recorded signal to one or more reference signals and determining if there is a match. A library of reference signals can be collated corresponding to various hazardous conditions which may be encountered. In embodiments the recorded signal matches a hazardous reference signal and an alert is triggered.

In embodiments the alert notifies a pilot. Additionally, or alternatively the alert sends a signal to a control system to adjust the operation of the aircraft (e.g. the gas turbine engine) such that it operates in a safe mode.

The measurement surface may be a measurement diaphragm, e.g. a sheet of corrosion resistant metal or alloy. Corrosion resistant metals and alloys can include phosphor bronze, beryllium copper or stainless steels.

The measurement surface may be circular.

The sensor may be a piezoelectric sensor or a sensor employing other means responsive to impacting precipitation elements. A piezoelectric sensor uses the piezoelectric effect to measure changes in pressure, acceleration, temperature, strain, or force by converting them to an electrical charge. The piezoelectric sensor may comprise piezoelectric ceramics. The piezoelectric sensor may comprise single crystal materials.

In embodiments the diaphragm is a sheet of corrosion resistant alloy bonded to a piezoelectric sensor material. the impact signal may be generated by a piezoelectric sensor with a measurement diaphragm.

For fixed wing aircraft, when solid particles or liquid droplets impact the diaphragm they are accelerated from their quasi static state to the aircraft velocity and this impact creates a force/time characteristic which can be detected by the sensor. Particles of different mass or elasticity will provide different force/time characteristics and liquid droplets will be recognised by a distinctive splash phenomenon.

The measurement surface may lie in a plane substantially perpendicular to the direction of the aircraft.

For rotary wing aircraft (helicopters), solid particles and/or liquid droplets present in the air will be accelerated downwards in the downdraft created by the rotor blades. The diaphragm may be placed under the rotor blades in a position perpendicular to the downdraft air flow. When the solid particles or liquid droplets impact the diaphragm they are decelerated causing an impact signal to be generated. Particles of different mass or elasticity will provide different force/time characteristics and liquid droplets will be recognised by a distinctive splash phenomenon.

The measurement surface may lie in a plane substantially perpendicular to the direction of the downdraft airflow.

According to a second aspect of the present invention there is provided a gas turbine engine and an apparatus for operating the gas turbine engine, comprising: a sensor having a measurement surface to detect impacts of precipitation elements that comprise solid particles and liquid droplets on the measurement surface; a recorder to record the impacts and provide a recorded signal; a store of reference signals, at least one of the reference signals relating to hazardous environmental conditions; a comparator to compare the recorded signals with the one or more reference signals, the comparator arranged to send an alert to a control system for the gas turbine engine to adjust the operation of the gas turbine engine such that it operates in a safe mode of operation if the comparator determines that the recorded signal matches a reference signal corresponding to hazardous environmental conditions.

According to a third aspect of the present invention there is provided a sensor system for detecting precipitation elements that comprise solid particles, including ice crystals, and/or liquid droplets in an environment in which an aircraft is flying, the system comprising: a measurement surface arranged to be positioned on the aircraft so as to be exposed to the environment such that solid particles and liquid droplets impact the measurement surface and thereby generate a force; and means for recording the impact forces over time to provide a recorded signal.

The means for recording the impact forces may comprise a piezoelectric sensor or a sensor employing other means responsive to impacting particles.

In embodiments the measurement surface comprises a measurement diaphragm in communication with a sealed piezoelectric sensor. The piezoelectric sensor may be sealed from the environment by the diaphragm

The measurement diaphragm may comprise a sheet of corrosion resistant metal or alloy. Corrosion resistant metals and alloys can include phosphor bronze, beryllium copper or stainless steels.

In embodiments the diaphragm is a sheet of corrosion resistant alloy bonded to a piezoelectric sensor material.

The measurement diaphragm may be circular.

The system may comprise a plurality of sensors. In one such embodiment the sensor system comprises a sensor array.

The system may comprise a housing.

The comments above in relation to the method apply equally to the apparatus.

Brief Description of the Drawings

Figure 1 is a schematic representation of a sensor.

Figure 2 is a typical Force/Time characteristic from sensor.

Figures 3a and 3b illustrate mounting arrangements for the sensor of Figure 1.

Figure 4 is a schematic arrangement of a sensor system incorporating the sensor of Figure 1.

Detailed Description

Referring to figure 1 there is shown a schematic diagram of a sensor 10 in use in the vicinity of a moving aircraft. The direction of movement of the aircraft is indicated by an arrow. The sensor 10 comprises a housing 11 that contains a piezoelectric element 12 having a sensor diaphragm 14. The diaphragm lies in a plane perpendicular to the direction in which the aircraft is moving and hence perpendicular to the air flow. A bracket 16 attaches the housing 11 to the aircraft (not shown) at a suitable location such that the housing 11 and diaphragm 14 are situated away from any surfaces that could affect the air flow relative to the sensor 10.

In areas known to be hazardous to flight, particles 18 (e.g. ice crystals or solid particles or liquid droplets, shown as dots in the diagram) are suspended in the air. The particles or droplets are said to be quasi static until they make contact with the measurement diaphragm. When solid particles or liquid droplets impact the diaphragm 14 they are accelerated from their quasi static state to the aircraft velocity and this impact creates a force/time characteristic which can be detected and recoded in real time by the sensor and sensor electronics. The information is recorded and stored electronically.

Referring to figure 2 there is shown a typical schematic diagram of a force, F (N) against time, t (pS) graph for a given solid particle. For a constant air speed, at t = 0, the force is constant and close to zero. As the particle impacts the sensor diaphragm the force increases sharply to a peak value (shown as approximately 375 N in this diagram) and then recedes back to the near-zero constant value.

The force diagram will be different for various particles or droplets, depending on the size, mass and elasticity of the particle and the velocity of the aircraft. The measured parameters that will vary could be the amplitude, the aspect ratio of the curve and the rate of change of force against time. A liquid droplet will provide a characteristic splash signal which will be very different in time and amplitude to a solid particle.

Referring to Figure 3a, for fixed wing aircraft the sensor 10 is mounted on a body part of the aircraft such that the sensor’s measurement surface (or diaphragm) 14 lies in a plane substantially perpendicular to the direction of the aircraft. When solid particles or liquid droplets impact the diaphragm they are accelerated from their quasi static state to the aircraft velocity and this impact creates a force/time characteristic which can be detected by the sensor.

Referring to Figure 3b, for rotary wing aircraft (helicopters) the sensor 10 is mounted on a body part of the aircraft such that the sensor’s measurement surface (or diaphragm) 14 lies in a plane substantially perpendicular to the direction of the downdraft airflow. Solid particles and/or liquid droplets present in the air will be accelerated downwards in the downdraft created by the rotor blades. The diaphragm is placed under the rotor blades in a position perpendicular to the downdraft air flow. When the solid particles or liquid droplets impact the diaphragm they are decelerated causing an impact signal to be generated.

Particles of different mass or elasticity will provide different force/time characteristics and liquid droplets will be recognised by a distinctive splash phenomenon.

Referring to Figure 4, there is shown a schematic block diagram of a sensor system, including the sensor 10 as described above. Signals from the sensor 10 are provided to a processor 20. The processor 20 also receives data signals from other aircraft sensors. The processor 20 is also connected to a memory 22 for storing data. The data may comprise characteristics of different impact force/time characteristics for different types of precipitation elements such as solid ice particles, or SLDs. The processor 20 is configured to interpret the data received from the sensor 10 by comparing this with the data characteristics stored in the memory so as to determine the type of precipitation element impacting the sensor. The processor 20 also provides an output in the form of data for informing those responsible for safety of the aircraft (e.g. the pilot) to take appropriate action.

Claims

CLAIMS:

1. A method for detecting precipitation elements that comprise solid particles, including ice crystals and/or liquid droplets in the air in which an aircraft is flying, comprising: providing a sensor having a measurement surface; exposing the measurement surface to the environment such that solid particles and liquid droplets impact the measurement surface and thereby generate a force; and recording the impact forces over time to provide a recorded signal.

2. The method of claim 1, additionally comprising comparing the recorded signal to one or more reference signals and determining if there is a match.

3. The method of claim 2, wherein the recorded signal matches a reference signal which relates to known hazardous conditions and an alert is triggered.

4. The method of claim 3, wherein the alert notifies a pilot and/or sends a signal to a control system to adjust the operation of the aircraft.

5. The method of any one of the preceding claims, wherein the measurement surface lies in a plane substantially normal to the direction of travel of the aircraft.

6. The method of any of claims 1 to 4, wherein the measurement surface lies in a plane substantially normal to the direction of downdraft of airflow from rotor blades.

7. The method of claim 6 comprising quantifying and recording the impact forces with respect to time during the process of decelerating a solid particle or liquid droplet from the downward air velocity created by rotor downdraft to the known vertical velocity of the aircraft.

8. The method of any one of the preceding claims, further comprising accessing environmental data from other aircraft sensors to determine whether the liquid droplets are super-cooled liquid droplets (SLDs).

9. The method of claim 8 wherein the environmental data includes an outside air temperature.

10. A gas turbine engine and an apparatus for operating the gas turbine engine comprising a sensor having a measurement surface to detect impacts of precipitation elements that comprise solid particles and liquid droplets on the measurement surface; a recorder to record the impacts and provide a recorded signal; a store of reference signals, at least one of the reference signals corresponding to known hazardous conditions; a comparator to compare the recorded signals with the reference signals, the comparator arranged to send an alert to a control system to adjust the operation of the gas turbine engine such that it operates in a safe mode of operation if the comparator determines that the recorded signal matches a reference signal corresponding to known hazardous conditions.

11. A sensor system for detecting precipitation elements that comprise solid particles, including ice crystals, and liquid droplets in an environment in which an aircraft is flying, comprising: a measurement surface arranged to be positioned on the aircraft so as to be exposed to the environment such that solid particles and liquid droplets impact the measurement surface and thereby generate a force; and means for recording the impact forces over time to provide a recorded signal.

12. The sensor system of claim 11 wherein the means for recording the impact forces comprises a sensor employing means responsive to impacting particles.

13. The sensor system of claim 12 wherein the measurement surface comprises a measurement diaphragm.

14. The sensor system of claim 13 wherein the sensor comprises a piezoelectric sensor responsive to impacting particles on the measurement diaphragm.

15. The sensor system of claim 14 wherein the piezoelectric sensor is sealed from the environment by the diaphragm.

16. The sensor system of any one of claims 13 to 15 wherein the measurement diaphragm comprises a sheet of corrosion resistant metal or alloy.

17. The sensor system of claim 16 wherein the corrosion resistant metal or alloy includes one or more of phosphor bronze, beryllium copper or stainless steels.

18. The sensor system of claim 16 or claim 17 wherein the diaphragm is a sheet of corrosion resistant alloy bonded to a piezoelectric sensor material.

19. The sensor system of any one of claims 14 to 18 wherein the measurement diaphragm is circular.

20. The sensor system of any one of claims 11 to 19 comprising a plurality of sensors.

21. The sensor system of claim 20 comprising a sensor array.

22. The sensor system of any one of claims 11 to 21 comprising a housing.

23. A sensor system substantially as hereinbefore described with reference to the accompanying drawings.