RU2005666C1 - Method of determination of availability and intensity of icing of flying vehicle - Google Patents

Abstract

FIELD: aeronautical engineering. SUBSTANCE: two sections of surface with thermosensitive elements are placed in identical conditions of blowing by air flow and entrapping cloud drops of water. Full evaporation of entrapped water is ensured on one section and intensive blowing of water by incoming flow of air is ensured on other (compensating) section due to heating of it to temperature exceeding freezing point of water by to 5 C. EFFECT: enhanced efficiency. 2 dwg

Description

 The invention relates to aircraft, in particular to methods for determining the presence of icing and icing intensity of aircraft.

 A known thermal method for determining the presence of icing, based on measuring the temperature difference of the heated wetted (when icing) front and non-wetted rear surfaces of the sensor at a negative outside temperature.

 The implementation of this method is carried out in such a way that the measuring sensor is located on the front heated surface, on which cloud drops fall, and the compensating sensor is on the rear or side heated surface of the sensor, on which cloud drops do not fall. In addition, the same amount of heat is usually supplied to the front and rear (side) surfaces, but at a level such that all the ingress of water evaporates on the front surface.

 Closest to the invention in technical essence is a method for determining the intensity and presence of icing of an aircraft, based on the use of the temperature difference between two heated thermosensitive elements located on a measuring body made in the form of a wing profile, one on the frontal and the other on the tail profile.

 The known method for determining the intensity and presence of icing has a significant drawback, since it predetermines a large threshold for the sensitivity of the icing detector and a relatively large error when the intensity of icing changes. This is due to the fact that the conditions for blowing the air flow of thermosensitive elements are always unequal, since one element is protected from water droplets, which causes a change in the conditions of its blowing compared to another sensitive element. This predetermines the presence of a sufficiently high temperature difference between the sensitive elements under all flight conditions, regardless of the presence or absence of icing.

When flying outside the cloud ("in dry" air), a certain temperature difference (± Δ t _c ) arises between the measuring and compensating sensitive elements, which is determined by the difference in convective heat removal from the front and rear (side) surfaces of the sensor. The closer the value of the heat transfer coefficients on the front and rear (side) surfaces, the smaller will be the modulus of Δ t _c at a constant and the same heating power of the surfaces.

When it gets into the cloud, cloudy drops of water fall on the front surface and cool it by removing heat for heating and evaporation of water. If the heating power is such that complete evaporation of the water being pressed is ensured, then an additional temperature difference (± Δ t _ow ) will arise between the sensing elements, which is functionally related to the amount of water falling on the front surface of the sensor, i.e., the icing intensity or water content .

When implementing the known method, an icing signal should be issued when, at a negative outside temperature, Δ t _vl will be above a certain threshold value, which is determined by the maximum value of Δ t _s , otherwise the signaling device will give false icing signals when flying in a "dry" in the air. When measuring the icing intensity, the output signal depends on the sum Δ t _c + Δt _ow .

Thus, the value of Δ t _c for measuring the intensity of icing (water content) mainly determines the measurement error, and for the signaling device icing - the sensitivity threshold.

The maximum value Δ t _s is determined at all possible modes and configurations of the flight of the aircraft in "dry" air. The modulus of Δ t _, the less, the better the compensation of the convective component with the help of a compensating sensitive element, i.e., the closer the heat transfer coefficients of the front (α _p ) and rear (α _s ) surfaces of the sensor.

The conditions so that α _{p is} equal to α _s and that water drops fall on the front surface and do not fall on the back surface, as follows from the known method, are contradictory, since when protecting the back (side) surface from water drops, the regime of its flow around the air is necessarily violated flow compared to the front surface, since the aircraft has a wide range of changes in flight modes.

 An object of the invention is to increase the reliability of determining the presence of icing and the accuracy of measuring the intensity of icing.

This is achieved by the fact that in a method based on the difference in heat removal from two heated sections of the surface of the measuring body, one of which contains drops of water and the other is obscured by their ingress, both sections of the surface with heat-sensitive elements are placed under the equivalent conditions of airflow blowing and trapping cloudy water drops. In this case, the heat transfer coefficients in both parts of the surface will be equal. Since in this case the same amount of water falls on both surfaces, intensive and complete evaporation is provided only on one surface due to the supply of a sufficient amount of heat (q _p ) to it. To the other surface, where the compensating sensing element, is supplied only an amount of heat (q _k) to heat it to a positive temperature, but close to the freezing point of water ⁰ ° C, for example up to (-2 ± 5) ° ^C. In in this case, the surface is not covered with ice, and the film of water is intensively blown away from it by the free stream due to the low rate of evaporation of water and insufficient amount of heat supplied to completely evaporate the trapped water.

The heat flux density that must be brought to the surface to compensate for the heat of evaporation of water is directly proportional to the difference in the elasticities of water vapor taken at the surface temperature (l _tn ) and at the temperature of the outside air (l _t∞ ).

. Для компенсирующего чувствительного элемента при температуре, равной 5^оС, величина l_tn составляет 873

. Следовательно, при температуре поверхности 120^оС воды испарится в 50 раз больше, чем при 5^оС.Since the measuring sensor has a temperature, e.g., ^about 120 C, at a temperature of l _tn is greater than 5 × 10 ⁴

. For compensating the sensor element at a temperature of 5 ^{° C,} the amount is 873 l _tn

. Therefore, at a surface temperature of 120 ^{° C} to evaporate water to 50 times greater than at 5 ° ^C.

The change in heat removal from the compensating element is mainly affected by a change in only the convective component. Knowing the amount of heat (q _k ) that is supplied to the compensating sensitive element, and its surface temperature t _pc , which is maintained at a constant level, it is easy to determine the heat transfer coefficient of both surfaces.

, где t_ад - температура торможения потока.α =

, where t _hell is the braking temperature of the flow.

 Using the value of α, you can calculate the amount of water that evaporates on the surface with a measuring sensor.

, где t_пи - температура поверхности с измерительным чувствительным элементом (известная величина);
L_и - теплота испарения (известная величина).As
q _p = α (t _pi -t _hell ) + mb L _p ,
the amount of evaporated (trapped) water
m _in =

where t _pi is the surface temperature with a measuring sensor (known value);
L _and - heat of evaporation (known value).

Thus, when implementing the proposed method for measuring the intensity of icing, it is possible to accurately enough accurately calculate the value of mb, which characterizes the intensity of icing. When implementing the proposed method for signaling about icing of an aircraft, you can use the appearance of a signal corresponding to the presence of mb, as the fact of the presence of the process of water entering the surface of the aircraft. In this case, the sensitivity threshold during the implementation of the proposed method will be significantly lower than when implementing the known method. A change in the sensitivity threshold and accuracy of measuring the icing intensity is not affected by a change in flight modes, a change in the angle of attack or glide of the aircraft and the installation location of the sensor, since both surfaces are in the same airflow conditions. A small threshold of sensitivity m _{in the pores} will be determined by the errors in measuring and maintaining a given level of t _pi and t _pc .

 In FIG. 1 shows a device of a specific implementation according to the invention; in FIG. 2 is a structural diagram of a method implementation.

The device contains surfaces 1 and 2, separated from each other and from parts 3 and 4 of the body of the water sensor by heat-insulating gaskets 5. Surfaces 1 and 2 have separate and in-line heaters 6 and 7. On the upper part of the body there is a sensor 8 for braking air temperature. The temperature sensors 9 and 10 of surfaces 1 and 2 are offset along the OY axis and have the same position relative to the OX axis. Regulators 11 and 12 of the heating power according to the information from the sensors 9 and 10 by changing the temperature of the heat output temperature is maintained at a constant level, e.g. _pc t is 2 ^{° C} and t _pi is 120 ^C. The calculator 13 receives information about the power _{to the} heating q and q _p and braking temperature. When mb greater _bpor m and t _hell below 0 ^{° C} to the indicator 14 to signal the presence and intensity of icing icing.

 To prevent the formation of ice on surfaces 3 and 4, they have a built-in heater powered by source 15. (57) Tenishev R. Kh., Stroganov B.A. et al. De-icing systems of aircraft, M.: Mashinostroenie, 1967, p. 219-221.

 USSR copyright certificate N 154064, cl. G 01 W 1/00, 1965.

Claims (1)

METHOD FOR DETERMINING THE AVAILABILITY AND INTENSITY OF Aircraft icing, based on using the difference in heat removal from two heated sections of the surface of the measuring body with heat-sensitive elements, at one of which cloudy water droplets are captured and completely evaporated, characterized in that the second section of the surface with thermosensitive elements are placed in conditions equivalent to the first section of blowing air flow and, accordingly, trapping drops in rows, and maintained at a temperature of its heating for 2 - 5 ^o C above the freezing point of water.

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