Method for controlling Anti-icing means in an aircraft as a function of the ice accretion rate, and corresponding system

Abstract

A method for controlling an anti-icing device protecting at least one outer surface of an aircraft, the device being provided with at least one anti-icing means (5, 6) and with a means (4) for measuring the ice accretion rate, comprising steps of determining at least one parameter for the activation of the at least one anti-icing means (5, 6) as a function of the ice accretion rate determined by the measurement means (4), in order to prevent the accretion of ice on the at least one outer surface to be protected or in order to reduce the thickness of ice accreted on the at least one outer surface to be protected.

Description

[0001] DESCRIPTION

[0002] TITLE: Method for controlling anti-icing means in an aircraft as a function of the ice accretion rate and corresponding system.

[0003] Technical field

[0004] The technical field of the invention is a device for controlling means for combating frost, and more particularly, such a control device coupled to a device for detecting frost conditions.

[0005] Previous techniques

[0006] An aircraft may be subject to icing phenomena when operating in certain atmospheric conditions, particularly at temperatures close to and below the freezing temperature of water and in a humid atmosphere. This latter condition is particularly met when the aircraft flies through certain types of cloud.

[0007] Frost formation can block moving surfaces of the aircraft such as leading edges, flaps and stabilizers, and reduce the performance of the aircraft's engines or even damage its components.

[0008] Ice formation can also lead to a loss of lift and an increase in drag, possibly critical for the aircraft.

[0009] To avoid such consequences, methods of combating frost have been developed. These include thermal elements placed on the surfaces to be protected. They can be used preventively, in other words in "anti-icing" mode, by maintaining the temperature of these surfaces above the melting point of water. They can be used curatively, in "defrosting" mode, by intermittently heating the surfaces concerned to allow the accumulated frost to detach. The thermal elements can be of the electric type, using the Joule effect, but are more frequently hot air circulation thermal elements, using hot air from the engines. This type of thermal element using hot air circulation is used only in "anti-icing" mode.This is effective against frost, but cannot be controlled precisely and specifically and is accompanied by significant heat loss and, consequently, excessive fuel consumption.

[0010] As for systems that use electrical elements, they can be used in both "anti-icing" and "de-icing" modes on the same aircraft.

[0011] Frost control means may also include mechanical means, for example in the form of inflatable tubes, placed on the surface to be protected and inflated periodically in order to mechanically break up the accumulated frost.

[0012] Furthermore, various ice detectors have been developed over the years. While most ice detectors emit a binary detection result (presence or absence of icing conditions), the most advanced detectors are capable of providing information on the intensity of the icing conditions encountered by measuring the ice accretion rate (IAR). Document US8704181B2, in the name of the applicant, discloses such a detector.

[0013] The means of preventing and combating ice are activated by the aircraft pilot as soon as the detector indicates an icing condition. These activations do not really take into account the rate of ice accretion, and indifferently apply the energy necessary for maximum protection.

[0014] Such operation is not optimized, especially in a context of energy saving and longevity of anti-icing means. Activation of thermal elements, in particular, is notably energy-intensive.

[0015] Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new aircraft types and those already in operation, requiring the implementation of technological solutions to make them compliant with current regulations. Civil aviation has been mobilizing for several years now to make a contribution to the fight against climate change.

[0016] Technological research efforts have already made it possible to significantly improve the environmental performance of aircraft. The Applicant takes into consideration the impact factors in all phases of design and development to obtain less energy-intensive, more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental consequences with the aim of improving the energy efficiency of aircraft.

[0017] Consequently, the Applicant is constantly working to reduce its negative climate impact by using methods and operating virtuous development and manufacturing processes and minimizing greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0018] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to ensure propulsion, and, as an essential complement to technological progress, aeronautical biofuels.

[0019] To this end, the invention is the result of technological research aimed at significantly improving aircraft performance through energy savings and, in this sense, contributes to reducing the environmental impact of aircraft.

[0020] There is therefore a need for a system for controlling anti-icing means capable of activating said systems as a function of the rate of frost accretion. Presentation of the invention

[0021] The subject of the invention is a method for controlling an anti-icing device protecting at least one external surface of an aircraft, the device being provided with at least one anti-icing means and a means for measuring the rate of ice accretion, comprising steps of determining at least one activation parameter of the at least one anti-icing means as a function of the rate of ice accretion determined by the measuring means in order to prevent the accretion of ice on the at least one external surface to be protected or in order to reduce the thickness of ice accreted on the at least one external surface to be protected.

[0022] The at least one frost control means comprising at least one heating element frost control means, the control method may comprise the following steps:

[0023] - determination of a power density as a function of the frost accretion rate, aircraft attitude, airflow velocity and total environmental temperature received from a flight computer, and a predetermined temperature setpoint, and

[0024] - controlling an actuator of the at least one heating element anti-icing means such that a power depending on the determined power density is transmitted to the heating element anti-icing means so as to prevent the formation of frost on the heating element anti-icing means.

[0025] The at least one frost control means comprising at least one frost control means with a heating element and / or at least one frost control means with a mechanical element, the control method may comprise the following steps:

[0026] - determination of a duration between two activations depending on the frost accretion rate, of a correlation factor between the frost accretion rate measured by measuring the frost accretion rate and the frost accretion rate at the level of the external surface to be protected and of the maximum tolerated frost thickness, - control of an actuator of an anti-icing means each time the duration determined between two activations has elapsed, so as to reduce the thickness of frost formed on the at least one external surface to be protected.

[0027] The correlation factor may depend on aircraft attitude, airflow velocity, static environmental temperature, propeller rotational speed, and aircraft true airspeed.

[0028] The airflow speed may be equal to the true speed of the aircraft when the ice control means is arranged on a wing leading edge or on a tailplane of an aircraft or depends on the true speed of the aircraft and the rotational speed of the propeller when the ice control means is arranged on an engine air intake, an engine blade or a rotary wing blade.

[0029] The invention also relates to a system for controlling an anti-icing device protecting at least one external surface of an aircraft, the device being provided with at least one anti-icing means and a means for measuring the rate of ice accretion, the control system comprising a control means connected at the input to a flight computer, said flight computer being connected to a set of measuring means, comprising in particular a means for measuring the rate of ice accretion, said flight computer being connected at the output to at least one of said anti-icing means, the control means being capable of executing the control method as described above.

[0030] An anti-icing means may be selected from a heating element anti-icing means and a mechanical element anti-icing means.

[0031] Brief description of the drawings

[0032] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example and made with reference to the appended drawings in which:

[0033] - figure [Fig 1] illustrates the main elements of a system for controlling defrosting means according to the invention,

[0034] - figure [Fig 2] illustrates the time between two activations of an anti-icing means,

[0035] - figure [Fig 3] illustrates the evolution of frost thickness as a function of time and the duration between two activations of an anti-icing means, and

[0036] - figure [Fig 4] illustrates the difference between the air flow at the level of the means of measuring the frost accretion rate and the flow at the level of the area to be protected.

[0037] Detailed description

[0038] A system for controlling de-icing means 1 according to the invention comprises a control means 2 connected at the input to a flight computer 3 and to a means 4 for measuring the rate of ice accretion, and at the output to at least one means of combating ice 5, 6.

[0039] The frost control means 5,6 comprise at least one of a heating element frost control means 5, and a mechanical element frost control means 6.

[0040] Figure [Fig 1] illustrates such a system for controlling the defrosting means.

[0041] In one operating mode, the control means 2 controls an anti-icing means 5 with a heating element in “anti-icing” mode. In other words, the aim is to prevent the formation of frost.

[0042] In this "anti-icing" control mode, a sufficient power density dP to be applied is determined, taking into account accretion rate information so as to optimize, i.e. adjust or reduce the electrical power to be used (consume) so as to produce sufficient heating to prevent the formation of ice on the external surface of the aircraft to be protected. This temperature to be reached, and therefore the power to be supplied, will depend on the type of anti-icing desired, i.e. trickling, the impacting drops remaining liquid, or evaporative, the drops being evaporated upon impact.

[0043] To achieve this, the control means 2 determines the power P to be supplied by the heating element anti-icing means 5, based on the data received from the flight computer 3 and the means 4 for measuring the ice accretion rate.

[0044] The power P is the product of the surface area S of the surface to be protected by the power density dP, given by applying the following equation:

[0045] [Math 1 ] P ~ Qconv "f Qevp + Qsens ~ Qk aero ~ Qkdrop

[0046] Or :

[0047] Qconv • l a heat exchanged by convection between the protected surface and the air flow in contact with this surface and the means 4 for measuring the frost accretion rate;

[0048] Qevp • heat due to the evaporation of water droplets in contact with the protected surface;

[0049] Qsens • the heat required to change the temperature of the water in contact with the protected surface;

[0050] Q ^-^ k aero heat due to aerody warming J namiq 1 of the flow on the protected surface;

[0051] Qkdrop • l aheat due to the kinetic energy of the drops in contact with the protected surface.

[0052] The paper Meier & Scholz. "A Handbook method for the estimation of power requirements for electrical de-icing systems." DLRK, Hamburg, 31. August - 02. September 2010 describes methods for evaluating the energy balance terms of the equation [Math 1]. As a first approximation, this power density dP is determined based on the following parameters:

[0053] [Math 2] dP = f (LWC œ , p loc , Alt, ATT, V e , Temp, T surf target ) With: dP: Power density in W / cm 2 ;

[0054] LWC œ Liquid Water Content or water concentration of the cloud encountered by the aircraft (g / m 3 ) ;

[0055] Pi oc: Capture coefficient of the area to be protected linked to its geometric shape, the size of drops present in the cloud encountered and the speed and attitude of the aircraft. Dimensionless between 0 and 1;

[0056] ATT: Aircraft attitude, Incidence or flight phase, influence the live capture area;

[0057] V e : Air flow speed

[0058] Temp: Total (TAT) or static (SAT) environmental temperature;

[0059] Tsurf target Surface temperature threshold to be reached to obtain the anti-icing effect depending on whether it will be trickling or evaporative.

[0060] It should be noted that the air flow velocity Ve can be defined depending on the location of the frost control means.

[0061] The airflow velocity Ve is equal to the true airspeed TAS (acronym for "True Air Speed") for the leading edges of the wings and the tailplanes.

[0062] The airflow velocity Ve is equal to a combination of the true aircraft airspeed TAS and the engine rotational speed ER (acronym for "Engine Rounds per minute") for engine air intakes, engine blades or the rotary wing of a helicopter.

[0063] In order to solve the energy balance equation, we need to know the LWC value œ cloud water concentration and the capture coefficient / ? Zoc . The other parameters are given by the avionics systems, except for the surface temperature threshold T S u r f target a constant value chosen at the time of design of the heating element frost control means 5. The IAR information[DS frost accretion rate can be obtained analytically via the following equation:

[0064] The detector's IAR is analytically given by the following equation:

[0065] [Math 3]

[0066] . . D _ TAS ■ LW C IDS ■ P IDS • r lDS

[0067] 1 AK IDS —

[0068] Pi

[0069] Or

[0070] TAS = True Air Speed ​​or true speed of the aircraft (m / s)

[0071] LWC = Liquid Water Content or water concentration near the detector (g / m 3 )

[0072] PIDS = capture coefficient on the reference surface of the frost detector

[0073] RIDS = Freezing Fraction (FF), which is a dimensionless coefficient, between 0 and 1, indicating the portion of water that will freeze on the surface of the detector. pi = density of the frost (g / m3 ), generally pi=917000 g / m 3

[0074] The coefficient P IDS of capture on the reference surface of the frost detector is a function of the geometry of the surface, the diameter of drops present in the frosting cloud and their trajectory (i.e. therefore a function of the speed and the drag force exerted on the drops). It is a dimensionless coefficient between 0 and 1 which indicates the impact surface of droplets where there may be frost accretion.

[0075] This coefficient P IDS can be evaluated with numerical simulations of water capture on the reference surface of the detector and the freezing fraction r) IDSthrough ice accretion simulations based on the resolution of Messinger's balance equations (Messinger, B. L. (1953). “Equilibrium Temperature of an Unheated Icing Surface as a Function of Air Speed”. Journal of the Aeronautical Sciences, 20(1), 29-42. doi: 10.2514 / 8.2520). The ice detector, following the guidelines given by ED 103revB (EUROCAE ED 103. “Minimum Operational Performance Standard for Inflight Icing Detection Systems”. Revision B, April 2022) and Appendix K of AC 20-73A (FAA “Advisory Circular 20-73A. Aircraft Ice Protection”) dated April 16, 2006, must be installed on the aircraft in a position that allows it to measure a IAR representative of the IAR œ of the infinite upstream flow, where

[0076] [Math 4]

[0077] When the IAR value IDS tends towards the IAR value œ , the value t] IDS tends towards 1, the value [f DStends to 1 as well and the LWC value tends to the LWC value œ .

[0078] As defined in ED 103revB, the ice detector must be capable of providing an IAR measurement with the following accuracy:

[0079] [Math 5]

[0080] IAR[ DS = IAR œ + 30% IAR œ

[0081] The information provided by the measuring means 4 of the frost accretion rate makes it possible to deduce the LWC value œ cloud water concentration to be used for the energy balance:

[0082] [Math 6]

[0083] IAR[DS ' Pi

[0084] LWC œ " -

[0085] TAS

[0086] The capture coefficient? ioc can be considered equal to 1 in order to be conservative.

[0087] This LWC value can thus be used by the formula [Math 2] to deduce the minimum power density to be applied to the surface to be protected.

[0088] A power density dP is thus continuously determined as has just been explained, as a function of the IAR measurement, which is transmitted as a control input to the actuators of the heating element anti-icing means 5, and this as long as the IAR value is not zero.

[0089] The "anti-icing" control mode remains, in principle, very energy-consuming.

[0090] Another control mode, called "de-icing" control mode, makes it possible to reduce this consumption if the accretion of a certain thickness of ice is tolerated. This thickness must be defined by the aircraft manufacturer. It is thus provided that the control means 2 controls a means 5,6 for combating ice in de-icing mode.

[0091] The "de-icing" control mode allows the deposition or accretion of frost, of a thickness compatible with flight safety. The frost thus accreted is removed periodically before its maximum permissible thickness is reached.

[0092] The “defrost” mode can in fact:

[0093] - use heating element anti-icing means 5, such as those used in the “anti-icing” control mode described above, but with cyclical, intense activation, and / or

[0094] - use mechanical anti-icing means 6, with cyclical activation in order to break the accreted ice.

[0095] The means 6 for combating frost with a mechanical element are in particular “inflatable sausage” type actuators.

[0096] In the present invention, it is proposed to optimize this cyclic activation by determining the time interval dT between two activations A as illustrated in figure [Fig 2].

[0097] Figure [Fig 2] illustrates the time interval dt between two activations A of an anti-icing means 5, 6 in “de-icing” mode. This time interval dt, also called duration dt between two activations, is defined by the following equation:

[0098] [Math 7] T: frost thickness (in m).

[0099] IAR t0C Frost accretion rate of the surface to be protected (in m / s).

[0100] It is noted that the frost thickness T must be between a minimum thickness required for effective defrosting and a maximum thickness tolerable for safety and guaranteeing optimal performance of the means of combating frost.

[0101] Knowledge of the rate of frost accretion makes it possible to trigger the heating element anti-icing means in a time window such that the thickness of the frost deposit is between this minimum threshold (the minimum thickness required for effective de-icing, in particular 2 mm) and this maximum threshold admissible for aircraft safety (the maximum tolerable thickness, in particular 5 mm). The rate of activations (e.g. de-icing) thus becomes dependent on the rate of frost accretion.

[0102] Figure [Fig 3] illustrates the evolution of the frost thickness e as a function of time, the minimum frost thickness e min , the maximum frost thickness e max, as well as the duration dt between two activations A of the means of combating frost. At each activation of the means of combating frost, the thickness of frost is reduced to a negligible value. The trend curves of frost accretion are also shown in figure [Fig 3]. Due to the progressive growth of frost, it is understood that the intercycle duration dt, that is to say the time interval between two activations, varies between a minimum value dt m in when the second activation takes place as soon as the frost thickness is equal to the minimum value e min and a maximum value dt m ax when the second activation takes place when the frost thickness reaches the maximum value e max. The duration dt between two activations of the anti-icing means must therefore be chosen between this minimum value dtmin and the maximum value dtmax. This adjustment of the duration dt results from a strategy which makes it possible to optimize the energy performance, without compromising the safety and aerodynamic performance of the aircraft. The equation [Math 7] above does not take into account the activation duration of the anti-icing means. This activation duration must be significantly lower than the duration dt of the intercycle, (a few seconds at most), so as to limit the number of actuators activated simultaneously on the entire aircraft and maintain the energy gain provided by the "de-icing" mode. It should be noted that the activation duration of the anti-icing means has no link with the IAR. In addition, this duration is very dependent on the technology of the anti-icing means.

[0103] Figure [Fig 4] illustrates the difference between position 8 of a means 4 for measuring the frost accretion rate and position 9 of a surface to be protected. The air flow common to the means 4 for measuring the frost accretion rate and to the surface to be protected is also illustrated and referenced 10.

[0104] As the means of measurement 4 of the IAR frost accretion rate IDS is installed in an area different from the surface to be protected, it is necessary to correlate the measurement of the IAR frost accretion rate IDS received from measuring device 4 with the value of the frost accretion rate IAR t0C at the level of the surface to be protected to be applied in the equation [Math 7]. This is what makes it possible to determine the most suitable intercycle duration dt, i.e. the time interval dt (or) between two activations A of the most suitable means of combating frost 5, 6. The following equation takes this correlation into account.

[0105] [Math 8] lARioc= C ' IARIDS

[0106] The correlation coefficient C is given by the following equation:

[0107] [Math 9]

[0108] C = f V e ,ATT, SAT~)

[0109] In order to determine the function f which allows to evaluate the coefficient C, the following process steps can be carried out: 1. Identify at least one of the most critical flight conditions for the aircraft,

[0110] 2. For each critical flight condition, carry out an aerodynamic simulation and water capture simulations of the aircraft with the installed means of measuring 4 of the ice accretion rate. By water capture simulation, we mean a two-phase simulation in an aerodynamic field into which a distribution of drops representing an icing cloud encountered by the aircraft is injected.

[0111] 3. For each flight condition analyzed and each capture simulation, evaluate the IAR frost accretion rate IDS measured by the frost accretion rate measuring means 4 and the frost accretion rate IAR t0C of the surface to be protected. For the evaluation of the accretion rate of the surface to be protected, one can use analytical formulas as described in the aforementioned Messinger publication (B. L. (1953). “Equilibrium Temperature of an Unheated Icing Surface as a Function of Air Speed”. Journal of the Aeronautical Sciences, 20(1), 29-42. doi: 10.2514 / 8.2520), or carry out frost accretion simulations with dedicated tools.

[0112] 4. Based on the results of these simulations, use a linear regression approach to determine a polynomial approximation of the coefficient C. The following equation accounts for such a linear regression:

[0113] The coefficients b0, b lt b2, b3, b4 found with the methodology described above are valid only for the aircraft analyzed and the surface to be protected taken into consideration.

[0114] Knowing the correlation factor C, we can determine the inter-cycle duration dt as a function of the value of the frost accretion rate IAR [DS received from the measuring means 4 of the frost accretion rate by applying the following equation:

[0115] [Math 11]

[0116] T dt = -

[0117] C ■ IAR IDS

[0118] As indicated previously, this intercycle duration dt, between two activations of the anti-icing means 5, 6, is between a minimum duration necessary for a minimum thickness of ice to be accumulated and a maximum duration corresponding to the maximum thickness of ice acceptable for the protected zone.

[0119] The minimum frost thickness corresponds to the minimum thickness necessary for the actuator to be within its range of effectiveness. In particular, when the means of combating frost is a mechanical process, it is common for its effectiveness to only be exerted beyond a minimum frost thickness.

[0120] The maximum ice thickness corresponds to the maximum thickness that can be treated by the ice control means, beyond which the ice control means is no longer effective. However, the maximum ice thickness generally corresponds to the maximum value that can be tolerated by the aircraft, for technical, safety or regulatory reasons.

[0121] In one embodiment, the control means 2 periodically controls a mechanical element frost control means 6, in a "defrosting" control mode, in order to break up the frost present on the protected surface. The control of such means can be used alone or in combination with the control of heating element frost control means 5. The pieces of broken frost are then carried away by the air flow.

[0122] To achieve this, the control means 2 determines an intercycle duration dt, between two activations, by applying the equation [Math 7] above, in a similar manner to the determination of the duration between two activations for a means 5 for combating frost with a heating element. The intercycle duration dt thus determined then depends on the characteristics specific to the means 6 for combating frost with a mechanical element, in particular the minimum and maximum thicknesses of frost with which the means 6 for combating frost with a mechanical element can operate. The duration dt thus determined, elapsing between two activations of the means 6 for combating frost with a mechanical element can thus be different from the duration dt determined, elapsing between two activations of a means 5 for combating frost with a heating element.Indeed, in relation to the determination of the intercycle duration dt between two activations of a means 5 for combating frost with a heating element, the size of the pieces of broken frost must be taken into account. In order to limit the size of the pieces of frost thus carried away by the action of the means 6 for combating frost with a mechanical element, it is appropriate to limit the intercycle duration dt as a function of the IAR, so that the thickness of the broken ice does not exceed the authorized limit.

Claims

CLAIMS 1. Method for controlling an anti-icing device protecting at least one external surface of an aircraft, the device being provided with at least one means (5, 6) for combating ice and a means (4) for measuring the rate of ice accretion, comprising steps of determining at least one activation parameter of the at least one means (5, 6) for combating ice as a function of the rate of ice accretion determined by the measuring means (4) in order to prevent the accretion of ice on the at least one external surface to be protected or in order to reduce the thickness of ice accreted on the at least one external surface to be protected.

2. Method for controlling an anti-icing device in an aircraft according to claim 1, the at least one anti-icing means comprising at least one anti-icing means (5) with a heating element, the control method comprising the following steps: - determination of a power density dP as a function of the frost accretion rate, the aircraft attitude, the airflow velocity and the total environmental temperature received from a flight computer, and a predetermined temperature setpoint, and - controlling an actuator of the at least one heating element anti-icing means (5) such that a power depending on the determined power density is transmitted to the heating element anti-icing means (5) so as to prevent the formation of frost on the heating element anti-icing means (5).

3. A method of controlling an anti-icing device in an aircraft according to claim 1 or 2, the at least one anti-icing means comprising at least one anti-icing means (5) with a heating element and / or at least one anti-icing means (6) with a heating element. mechanical element frost, the control method comprising the following steps: - Determination of a duration dt between two activations depending on the frost accretion rate, a correlation factor between the frost accretion rate measured by measurement (4) of the frost accretion rate and the frost accretion rate at the level of the external surface to be protected, and the maximum tolerated frost thickness, - control of an actuator of an anti-icing means each time the duration dt determined between two activations has elapsed, so as to reduce the thickness of frost formed on the at least one external surface to be protected.

4. A method of controlling an anti-icing device in an aircraft according to any one of claims 1 to 3, wherein the correlation factor depends on the attitude of the aircraft, the air flow speed, the static environmental temperature, the rotational speed of the propeller and the true speed of the aircraft.

5. A method of controlling an anti-icing device in an aircraft according to any one of claims 1 to 4, wherein the airflow speed is equal to the true speed of the aircraft when the anti-icing means is arranged on a wing leading edge or on a rear empennage of an aircraft or depends on the true speed of the aircraft and the rotational speed of the propeller when the anti-icing means is arranged on an engine air intake, an engine blade or a rotary wing blade.

6. Control system for an anti-icing device protecting at least one external surface of an aircraft, the device being provided with at least one means (5, 6) for combating ice and a means (4) for measuring the rate of ice accretion, the control system comprising a control means (2) connected as input to a flight computer (3), said flight computer (3) being connected to a set of measuring means, comprising in particular a means (4) for measuring the rate of ice accretion, said flight computer (3) being connected at the output to at least one of said means (5, 6) for combating ice, characterized in that the control means (2) is capable of executing the control method according to any one of claims 1 to 5.

7. Control system according to claim 6, wherein an anti-icing means (5,6) is selected from an anti-icing means (5) with a heating element and an anti-icing means (6) with a mechanical element.

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