RU2187821C1 - Device for measuring velocity head on helicopter main rotor blade - Google Patents

Abstract

FIELD: information and measurement systems of flying vehicles at subsonic speeds. SUBSTANCE: pressure differential sensor is connected with first pair of vent holes located at distance of (3-6)% of blade section chord from its leading edge on lower and upper sides in section of helicopter rotor blade where velocity head is measured. Second pressure differential sensor is connected with second pair of vent holes located at distance of (8-12)% of chord from leading edge in the same section of lower and upper sides of blade. Sensors are connected via amplifiers to input of adder shaping output signal proportional to velocity head and independent of angle of attack of blade. EFFECT: enhanced accuracy of measurement. 2 dwg

Description

 The invention relates to measuring equipment and can be used in information-measuring systems of aircraft at subsonic flight speeds, in particular in information-measuring systems of helicopters.

 There is a traditional method of measuring the pressure head (D. Braslavsky. Instruments and sensors of aircraft. M., Mashinostroenie, 1970, p. 392) - [1], in which the value of the pressure head is defined as the difference between the total and static pressures measured in the incident on an aircraft air flow using an air pressure receiver (LDPE).

 The main disadvantage of this method of measurement is that the presence of the angle of attack (the angle between the axis of the LDPE and the vector of the incoming flow) significantly affects the accuracy of measuring the magnitude of the pressure head (Bodner V.A. Aviation devices. M., Mechanical Engineering, 1969, p. 467) - [2]. Therefore, the implementation of this method for measuring the velocity head in a certain section of the rotor blade of a helicopter is undesirable, since the LDPE mounted in this case would work at variable and significant angles of attack created by the cyclic pitch of the blade, its swing movements, and due to the presence of a strong bevel of the flow variable per revolution of HB, which would ultimately lead to significant errors in determining the true velocity head in a given section of the blade.

 The prior art device for measuring the pressure head of an air stream running onto an aerodynamic profile in the form of a wing, comprising a pressure difference sensor connected to holes on the lower and upper sides of the wing in the same section, amplifiers and adder (US Patent 5257536 , November 2, 1993, 6 pp.) - [3]. The specified device is the closest to the claimed invention in terms of essential features and is adopted as a prototype.

 The disadvantage of the selected prototype is the lack of accuracy in measuring the velocity head during operation of the device in the field of variable flow bevels, since the velocity head measured by it depends on the angle of attack of the aerodynamic profile.

 The invention solves the problem of increasing the accuracy of measuring pressure head.

 This object is achieved in that the device for measuring the pressure head on the rotor rotor blades of the helicopter, containing a differential pressure sensor connected to a pair of drainage holes located on the lower and upper sides of the blade in that section in which the pressure head is measured, amplifiers and an adder, contains a second differential pressure sensor connected to a second pair of drainage holes located on the lower and upper sides of the blade in its same section, while the first pair of drainage holes is located the wife is at a distance of 3-6%, and the second pair of drainage holes is located at a distance of 8-12% of the chord of the sectional profile of the blade from its leading edge, depending on the type of profile, the outputs of the differential pressure sensors through the respective amplifiers are connected to the inputs of the adder forming the output signal, proportional to the value of the velocity head and independent of the angle of attack of the blade.

 Here is the rationale for the algorithm implemented by the proposed device and to improve the accuracy of the measurement system.

перепада давления

определяемого как разность полных давлений P₁ и P₂ в двух любых точках профиля, имеет место некоторая функциональная зависимость

где q - величина скоростного напора набегающего на профиль воздушного потока. Конкретный вид зависимости (1) определяется формой профиля и выбранными положениями на нем точек съема перепада давления. Исследования, выполненные на основе расчетных и экспериментальных данных распределения давления по профилю (Ушаков Б.Л. и др. Материалы по распределению давления на профиле и использование их при выборе профиля крыла скоростного самолета. Труды ЦАГИ, вып. 487, 1940, 180 с.) - [4], показали, что для авиационных профилей в случае определения перепада давления как разность давлений на нижней и верхней сторонах профиля в точках, отстоящих от передней кромки на одинаковом расстоянии в широком диапазоне положения этих точек по хорде профиля, зависимость (1) линейна.For flow velocities of the aerodynamic profile at which the compressibility effect between the coefficient of normal profile force C _N and the coefficient

differential pressure

defined as the difference between the total pressures P ₁ and P ₂ at any two points of the profile, there is a certain functional dependence

where q is the magnitude of the pressure head running on the air flow profile. The specific type of dependence (1) is determined by the shape of the profile and the selected positions on it of the points of removal of the differential pressure. Studies performed on the basis of calculated and experimental data on the pressure distribution over the profile (B. Ushakov and others. Materials on the pressure distribution on the profile and their use in choosing the wing profile of a high-speed aircraft. TsAGI proceedings, issue 487, 1940, 180 pp. ) - [4], showed that for aviation profiles in the case of determining the pressure drop as the pressure difference on the lower and upper sides of the profile at points that are at the same distance from the leading edge at a wide distance in the position of these points along the profile chord, the dependence (1) linear.

где

перепады давлений, замеряемых между точками первой и второй пар соответственно (фиг.1), a₁, a₂, b₁, b₂, - коэффициенты, определяемые теоретическим или экспериментальным путем. Исключая далее коэффициент нормальной силы С_N из уравнений (2) и (3), получим

где

Таким образом, располагая информацией о величине перепадов давлений

замеренных между определенным образом выбранными точками профиля, по линейной зависимости (4) можно вычислить величину скоростного напора q. Коэффициенты зависимости (4) могут быть определены теоретическим или экспериментальным путем.Therefore, for two pairs of points selected on the profile in a certain way, we can write the relation

Where

the pressure drops measured between the points of the first and second pairs, respectively (Fig. 1), a ₁ , a ₂ , b ₁ , b ₂ , are the coefficients determined theoretically or experimentally. Further excluding the coefficient of normal force С _N from equations (2) and (3), we obtain

Where

Thus, having information on the magnitude of pressure drops

measured between selected profile points in a certain way, the linear pressure (q) can be used to calculate the value of the velocity head q. The coefficients of dependence (4) can be determined theoretically or experimentally.

но величина вычисленного по формуле (4) значения скоростного напора q остается неизменной. Данный факт экспериментально подтвержден при апробации предлагаемого устройства для измерения скоростного напора в заданном сечении лопасти несущего винта вертолета при проведении испытаний на вертолетном стенде.It should be emphasized that the exclusion from the system of equations (2) and (3) of the coefficient of normal force С _N means the exclusion from the algorithm (4) of the functioning of the measuring system of the influence of the angle of attack of the profile. So, if a profile is flowed around with a velocity head q, then with varying angles of attack of the profile, the values of pressure drops

but the value of the velocity head q calculated by formula (4) remains unchanged. This fact was experimentally confirmed by testing the proposed device for measuring the pressure head in a given section of the rotor blade of a helicopter during testing on a helicopter stand.

следует руководствоваться двумя основными критериями. Во-первых, для выбранных зависимость (1) должна быть линейной, то есть иметь вид (2) или (3). Во-вторых, этот выбор следует сделать таким, чтобы погрешность измерения величины скоростного напора q была минимальной, а для этого следует минимизировать модули коэффициентов K₁ и К₂ зависимости (4), поскольку абсолютная погрешность измерения q согласно (4) равна

где

инструментальные погрешности датчиков перепада давлений

Исследования, выполненные для используемого в вeртолeтостроении профиля NACA-23012, показали, что оба критерия будут выполнены, если перепад давления

определять как разность давлений на нижней и верхней сторонах профиля в точках, отстоящих от носика профиля на расстоянии 5% хорды, а перепад давления

- в точках, отстоящих от носика профиля на расстоянии 10% хорды (Живетин В. Б. Аэромеханические измерения. Методы и устройства. Монография. Часть 1. КГТУ им. А.Н. Туполева. 1996 г., стр. 70) - [5]. В частности, коэффициенты линейных зависимостей (2) и (3) в этом случае для профиля NACA-23012 получаются равными
a₁=3,4517, b₁=-0,2378
a₂=2,4363, b₂=0,1259 (7)
а коэффициенты вычислительного алгоритма (4) равны
K₁=2,4028, K₂=3,4043 (8)
Для пояснения сущности предлагаемого устройства для измерения скоростного напора на лопасти несущего винта вертолета на фиг.2 представлена его блок-схема, где:
1, 2 - датчики перепада давления, замеряющие разности полных давлений в точках профиля сечения лопасти первой и второй пар соответственно;
3, 4 - усилители с коэффициентами усиления K₁ и К₂ соответственно;
5 - сумматор, вырабатывающий сигнал, пропорциональный величине измеряемого скоростного напора.When selecting pressure drop points

should be guided by two main criteria. First, for the selected dependence (1) must be linear, that is, have the form (2) or (3). Secondly, this choice should be made so that the error in measuring the pressure head q is minimal, and for this, the moduli of the coefficients K ₁ and K _{2 of} dependence (4) should be minimized, since the absolute measurement error q according to (4) is

Where

instrumental errors of differential pressure sensors

Studies performed for the NACA-23012 profile used in helicopter engineering showed that both criteria will be met if the pressure drop

determine as the pressure difference on the lower and upper sides of the profile at points spaced from the nose of the profile at a distance of 5% of the chord, and the pressure drop

- at points spaced from the nose of the profile at a distance of 10% of the chord (Zhivetin B. B. Aeromechanical measurements. Methods and devices. Monograph. Part 1. KSTU named after AN Tupolev. 1996, p. 70) - [ 5]. In particular, the coefficients of linear dependencies (2) and (3) in this case for the NACA-23012 profile are equal
a ₁ = 3.4517, b ₁ = -0.2378
a ₂ = 2.4363, b ₂ = 0.1259 (7)
and the coefficients of the computational algorithm (4) are equal
K ₁ = 2.4028, K ₂ = 3.4043 (8)
To clarify the essence of the proposed device for measuring the speed pressure on the rotor blades of a helicopter, figure 2 presents its block diagram, where:
1, 2 - differential pressure sensors, measuring the difference in total pressure at the profile points of the cross section of the blades of the first and second pairs, respectively;
3, 4 - amplifiers with amplification factors K ₁ and K _2, respectively;
5 - adder generating a signal proportional to the value of the measured velocity head.

The differential pressure sensor 1 is connected to the first pair of drainage holes located at a distance of (3-6)% of the chord of the section of the blade from its front edge, respectively, on the lower and upper sides in that section of the rotor blade of the helicopter, in which the speed head of the proposed device is measured, and the differential pressure sensor 2 is connected to a second pair of drainage holes located at a distance of (8-12)% chord from the leading edge in the same section also on the lower and upper sides of the blade, respectively. The indicated differential pressure sensors 1 and 2, measuring differential pressures at predetermined points, are connected respectively to the inputs of amplifiers 3 and 4 having amplification factors K ₁ and K ₂ , the outputs of which are connected to the first and second inputs of the adder 5.

 The device operates as follows. The signals from the differential pressure sensors 1 and 2 after appropriate scaling using amplifiers 3 and 4 enter the adder 5, the output of which forms a signal proportional to the velocity head and independent of the angle of attack of the blade.

 Induction sensors of the DMI type can be used as differential pressure sensors, and amplifiers and an adder can be made according to well-known schemes (VI Malinovsky, Handbook of Digital Computing. 1974, 472 p.) - [6].

 The use of the claimed device in comparison with the prototype provides high accuracy of measuring the pressure head, including when working in the field of variable bevels, since the influence of the angle of attack of the aerodynamic profile is excluded from the algorithm of the functioning of the claimed device.

Claims (1)

 A device for measuring the pressure head on the rotor blades of a helicopter, comprising a differential pressure sensor connected to a pair of drainage holes located on the lower and upper sides of the blade, in which it measures the pressure head, amplifiers and an adder, characterized in that a second sensor is introduced differential pressure connected to a second pair of drain rotor holes in the helicopter rotor blade located on the lower and upper sides of the rotor blade, the first pair of drain holes being located lies at a distance of (3-6)%, and the second pair of drainage holes is located at a distance of (8-12)% of the chord of the sectional profile of the blade from its leading edge, depending on the type of profile, the outputs of the differential pressure sensors through the corresponding amplifiers are connected to the inputs of the adder, generating an output signal proportional to the magnitude of the pressure head and independent of the angle of attack of the blade.

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