RU2287795C1 - Device for measurement of aerodynamic force vector's components and of moment - Google Patents

Abstract

FIELD: measuring technique.

SUBSTANCE: device can be used for measurement of aerodynamic force vector's components and of moment acting on flying vehicles models inside aerodynamic tube flux. Device has multi-component tensometric balance which is mounted inside tested model onto two supports. Supports are made in form of tightened nose and tail parts and they have dynamometric members for making changes in supports' reactions. Balance is provided with two three-component dynamometric members, which are disposed along X axis. Reactions of supports are measured along Y and Z axes and reactive moments are measured around X axis. Balance is also provided with dynamometric member for measurement of longitudinal component of X vector of aerodynamic force. Dynamometric member has motionless rigid base and rigid movable platform. Base and platform are connected together by means of resilient hinges ad sensitive elements. Tested model is fastened to movable platform. Points of conjugation of sensitive elements with platform and with base belong to the same plane which has to be perpendicular plane of symmetry of dynamometric member. Precision of measurement is improved due to elimination of effect of bands' degree of tension and aerodynamic forces on results of measurement.

EFFECT: improved precision of measurement; reduced number of necessary tests.

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Description

The invention relates to the field of aeromechanical measurements, in particular to the measurement of the components of the aerodynamic force vectors and the moment acting on the model of aircraft in the flow of a wind tunnel.

Scope - experimental aerodynamics.

The dependences of the components of the aerodynamic force vectors and the moment on the flow velocity, the angular position of the model, and other test modes are the main aerodynamic characteristics of the aircraft.

Quantitative determination of aerodynamic characteristics is the goal of testing models of aircraft in wind tunnels.

A device is known for measuring the constituent vectors of aerodynamic force and moment — mechanical aerodynamic scales, consisting of a rigid frame (located outside the boundaries of the wind tunnel flow) and interconnected lever systems that hold it in equilibrium; the output links of linkages are connected to dynamometers (See Aviation Encyclopedia, Big Russian Encyclopedia Scientific Publishing House, Moscow, 1994, p. 82. - Aerodynamic characteristics).

The frame is a structure covering on all sides the flow of the wind tunnel, directed perpendicular to the plane of the frame.

The model is installed inside the frame using stretch marks, which are metal strips with a profiled cross section oriented along the flow. The components of the aerodynamic force and moment acting on the tested model and tapes are transmitted to the frame and measured using dynamometers.

The main disadvantage of the known solution is the low accuracy of measurements, especially of such an important characteristic of an aircraft as the drag coefficient of modern passenger aircraft, which has a value close to or even lower than the drag coefficient of the tapes.

Therefore, to obtain the result, it is necessary to subtract the resistance coefficient of the tapes from the measured characteristic.

The drag coefficient of the tapes is determined in the "empty" wind tunnel in the absence of a model in the same test modes as with the model, which leads to large material costs.

In addition, we are talking about the difference between two close physical quantities obtained in different experiments, which leads to a decrease in the measurement accuracy.

The closest is a device for measuring the components of the aerodynamic force and moment vectors - aerodynamic tensometric scales, consisting of an elastic body, dynamometric elements and strain gauges that convert deformations of sensitive elements into electrical signals. Torque elements are made together with the body and are oriented so that the deformation of the element caused by the corresponding component of the aerodynamic force or moment is maximum.

The scales are located inside the tested model and represent a console, on one end of which the model is rigidly fixed, and the free end is connected to a support, which is a rod holder, which goes to the mechanism for changing the model’s angular position (See Aviation Encyclopedia, Big Russian Encyclopedia Scientific Publishing House, Moscow, 1994, p.134 - Aerodynamic scales, p.224 - Aerodynamic measurements.Levitsky N.P., Postnov A.I. et al. Measurement of aerodynamic forces and moments using tensometric scales. Measuring technique and №11, 1979).

A distinctive feature of the known solution is the cantilever mounting of the model and the installation of the scales on one support, so that the internal forces arising in the model, holder and other structural elements do not act on the scales. The balance is solely under the influence of aerodynamic loads applied to the model.

The main disadvantage of the known solution is the presence of a holder in the bottom section of the model. Often, the holder diameter required by the strength conditions is greater than the diameter of the bottom cut. In this case, they resort to an artificial increase in the geometric dimensions of the tail of the model, deliberately distorting its geometry, which reduces the accuracy of determining the aerodynamic characteristics of the model.

Another source of error is the increase in pressure in the bottom region of the model due to the presence of a holder.

The task of the invention is to improve the accuracy of measurement.

The technical result is expressed in the ability to measure the components of the aerodynamic force and moment acting on the model, while remaining insensitive to the aerodynamic forces acting on the tapes supporting the model and the parasitic axial force acting between the tapes, thereby eliminating the influence on the measurement results of the degree of tension of the tapes and aerodynamic forces acting on them.

The technical result is achieved in that in a device for measuring the components of the vectors of aerodynamic force and moment, containing multicomponent tensometric scales, rigidly connected to the tested model, a support, tensometric scales are fixed on supports located inside the model and made in the form of stretched nose and tail ribbons, contain load cells for measuring supports reactions for which calculated magnitude of the normal force Y, lateral force Z, roll moment M _X, pitch moment M _Z, points Rys anija M _Y and load cell for measuring the longitudinal component of the X vector of aerodynamic force designed as a mobile platform to which is attached the tested model, coupled with the fixed base by means of elastic hinges and sensitive elements, points interfacing sensing elements X with the platform and the base are located on one plane, which is the perpendicular plane of symmetry of the dynamometric element.

For a more detailed explanation of the proposed device, we consider the scheme for installing the scales inside the model, their design and measurement equations that connect the components of the aerodynamic force and moment vectors with the output signals of the scales.

In FIG. 1 shows a diagram of the installation of scales inside the model with support on the bow and tail bands;

In FIG. 2 - schematic design of the device;

In FIG. 3 is a diagram of a device loading by a force Y and a moment M _Z ;

In FIG. 4 shows a plot of bending moments and cutting forces from the action of force Y;

In FIG. 5 - plot of bending moments and cutting forces from the action of the moment M _Z ;

In FIG. 6 is a summary diagram of bending moments and cutting forces from the simultaneous action of force Y and moment M _Z ;

In FIG. 7 shows a design of dynamometric elements measuring reactions in supports;

In FIG. 8 - the location of the strain gauges and the diagram of their connection to the measuring bridge.

Scales 1 through the axis of the bushings 2 and 3 are pivotally connected to the bow 4 and tail 5 tapes. The balance is equipped with two three-component dynamometric elements (DE) 6 and 7 for measuring the components Y, Z - force. M _Y , M _Z , M _X - moment and DE 8 for measuring the longitudinal component of X - force.

DE 8 consists of a rigid fixed base 9 and a rigid movable platform 10. The base and platform are interconnected, as a rule, by four packets of flat elastic joints 11. In the drawing, each packet consists of 4 joints. Two racks 12 are a sensitive element that converts component X of the force into an electrical signal. The tested model 13 is attached to the platform 10 using bolts 14. The origin of the rectangular coordinate system associated with the model with the axes X, Y, Z is located at the NK point (coordinate origin) lying on the X axis of the balance.

The NK point is located at a distance of l ₁ and l ₂ from the axes of the hinges 2 and 3 of the bow and tail ribbons, respectively.

The device operates as follows.

The three-component DE 6 measures two reaction forces R _1Y , R _1Z in the hinge 2, directed along the Y and Z axes, respectively, and the reactive moment M _1X around the X axis. Similarly, DE 7 measures the reaction forces R _2Y and R _2Z in the hinge 3 and reactive moment M _2X around the axis X.

Based on the measurement results of these quantities, five components of the aerodynamic force and moment vectors are determined in the coordinate system associated with the model:

Y = R _1Y + R _2Y ; Z = R _1Z + R _2Z ; M _Z = R _1Y l ₁ -R _2Y l ₂ ; M _Y = R _1Z l ₁ -R _2Z l ₂ ; M _X = M _1X + M _2X

The component along the X axis (longitudinal aerodynamic force) is measured, as noted earlier, DE 8.

The force X is applied to the movable platform 10 and through elastic joints 11 is transmitted to the sensing elements 12.

Deformations of the sensitive elements are measured using strain gauges glued to the sensitive elements and included in the strain gauge bridge.

In this scheme, in addition to the measured components of force and moment, the parasitic internal axial force directed along the X axis acts on the balance. The main source of parasitic axial force is the reaction R ₁ in the hinge 2 of the nasal tape. The latter is decomposed into two components: R _1x - acting along the X axis of the balance and R _1t - acting along the tape.

The axial stiffness coefficient of the balance is many times greater than the tape stiffness coefficient along the X axis. For this reason, the parasitic axial force R _{1x is} almost completely applied to the balance.

DE 6 and 7 have zero sensitivity in the direction of the X axis of the balance and do not respond to axial force.

In the known solution, the scales, as noted earlier, are mounted on one support, and parasitic axial force is absent.

When they are mounted on two supports, the balance will fully feel the parasitic axial force, since it physically coincides with the measured component X.

In the proposed solution, DE 8 is made in such a way that it senses only component X of the aerodynamic force and does not respond to parasitic axial force R _1x .

The latter is achieved by the fact that DE 8 is equipped with a rigid movable platform 10, to which the tested model 13 is attached.

The platform using flat elastic hinges 11 is connected to the base 9. Between the platform and the base are sensitive elements 12, the deformations of which are measured.

The points 0-0 of the interface of the sensitive elements with the platform and the base are located on the same plane, which is the perpendicular plane of symmetry of the dynamometer element 8.

Under the action of a parasitic axial force R _{1X, the} base 9 experiences insignificant deformations due to the large cross section. In this case, due to the symmetry of the structure, the points 0-0 continue to remain on the same line, and signal deformation of the sensitive elements does not occur.

The action of the measured component X causes the displacement of the point 0 located on the moving platform to the right. As a result, the line 0-0, and with it the sensitive elements take an S-shape, and signal deformations appear on the flat faces of the elements.

An important issue is the sensitivity of the balance to temperature, especially to temperature gradients.

Temperature gradients cause uneven temperature deformations of structural elements, and, as a result, temperature stresses.

In this case, the DE 8, to which the tested model is attached, is potentially the most vulnerable to the action of gradients.

When the temperature of the gas stream changes, the temperature of the model changes, and temperature stresses arise in the area between the model mounting bolts, which are transferred to the mobile platform in the form of forces.

Due to the symmetry of the DE 8 structure, deformation of the platform, as well as the action of parasitic axial force, does not cause signal deformations of sensitive elements.

Thus, the proposed design of DE 8 is insensitive to spurious axial force and thermal deformation of the model.

For a more complete explanation of the essence of the proposed solution, we consider below an example of a three-component device for measuring longitudinal X, normal Y, and components of the aerodynamic force vector and component M _Z (pitch moment).

Note that for the belt suspension of the model, such a device is the main one. If a rack mount option is used, all six component vectors of aerodynamic force and moment are measured.

In FIG. 2 shows a schematic design of a three-component device.

As can be seen from FIG. 2, in the middle part of the tensile weights there is an element L _X for measuring component X. At some distance from this element on its two sides there are two dynamometric elements of length L, designed to measure the normal Y component of the aerodynamic force vector and component M _Z of the moment vector (pitch moment ) It is easy to see that the tensile weights are a beam with pivotally fixed ends (Fig. 3). The cross section of the beam has a vertical axis of symmetry, the applied loads act in the vertical plane of symmetry, and the beam is bent in the same plane.

ив опоре

.We plot the bending moments and cutting forces under the action of the force Y, for which we define the reactions in the support

willow

.

The corresponding reactions are:

на плече l₁ равен изгибающему моменту от реакции

на плече l₂ в точке приложения силы Y. При нагружении балки моментом M_Z в опорах возникнут равные по величине и противоположные по направлению реакцииA plot of bending moments and cutting forces from the action of force Y is shown in FIG. 4. As follows from FIG. 4, the bending moment from the reaction

on the shoulder l ₁ is equal to the bending moment from the reaction

on the shoulder l ₂ at the point of application of force Y. When loading the beam with the moment M _Z in the supports, equal in magnitude and opposite in the direction of reaction

The plot of bending moments and cutting forces from the action of the moment M _{Z is} shown in Fig. 5.

The total plot of bending moments from the action of force Y and moment M _{Z is} shown in FIG. 6.

, равная разности реакций от действий силы Y и момента M_Z.As can be seen from FIG. 6, in support A, the total reaction

equal to the difference of reactions from the action of force Y and moment M _Z.

равна сумме реакций от действия силы Y и момента M_Z.In support B, the total reaction

equal to the sum of the reactions from the action of the force Y and the moment M _Z.

The sum of the reactions in the supports is equal to the effective force Y.

и

равна измеряемому моменту M_Z. Действительно:Difference in bending moments

and

equal to the measured moment M _Z. Really:

и

, служащие для определения Y и M_Z, измеряются динамометрическими элементами 1, 2 (фиг. 2), поперечные оси которых проходят через сечения I-I и II-II (фиг. 6). Как следует из эпюр фигуры 6, в сечении I-I действует перерезывающая сила

и изгибающий момент

, а в сечении II-II - сила

и изгибающий момент

.Reactions

and

used to determine Y and M _Z are measured by dynamometric elements 1, 2 (Fig. 2), the transverse axes of which pass through sections II and II-II (Fig. 6). As follows from the diagrams of figure 6, in section II there is a cutting force

and bending moment

, and in section II-II - force

and bending moment

.

Both load cells have the same construction, the cross section of which is shown in FIG. 7. The design consists of two horizontally arranged beams a and elongated along the vertical axis of the beam b. Actually beam b is a sensitive element. The action of the shearing force Q causes tangential stresses in the beam, which, with the help of strain gauges glued to the vertical edges of the beam, are converted into an electrical signal. Beams a serve to protect the sensitive element from the action of bending moments M _I and M _II . The angular stiffness of the beams a around the Z axis is much higher than the corresponding stiffness of the beam b, and bending moments are perceived mainly by beams a. On the contrary, the linear stiffness of the beams a along the Y axis is commensurate with the stiffness of the beam b, and the measured force Q in a given proportion is applied to the sensitive element b.

In FIG. Figure 8 shows the location of the strain gages on the vertical faces of the beam b and the diagram of the inclusion of strain gages in the measuring bridge.

In FIG. 8 shows the directions of maximum sensitivity of the strain gages R ₁ , R ₂ (R ₃ ), (R ₄ ). The brackets are located on the opposite side of the beam b.

The plus sign in the diagram indicates a positive, minus - a negative increment of the resistance of the strain gauges from the force Q acting in the positive direction:

U _P - supply voltage of the bridge,

_Δ U is the output signal of the bridge, proportional to the force Q.

и

производится калибровка весов. Для этого весы при помощи болтов 14 (фиг. 1) крепятся к жесткому основанию так, чтобы ось весов заняла строго горизонтальное положение.In order to obtain dimensional reaction values

and

Calibration is performed. To do this, the scales with bolts 14 (Fig. 1) are attached to a rigid base so that the axis of the balance is in a strictly horizontal position.

и

по измеренным значениям _ΔU.Then, through the hinges 2 and 3, the weights are loaded with weights with different weights Q. Based on the data obtained, the dependence _Δ U on Q is constructed and the slope coefficients are determined, which are used in the future to determine reactions

and

according to the measured values of _Δ U.

According to known reactions are calculated:

The expression for M _Z includes the distances l ₁ and l ₂ . The latter are defined as follows. The base distance l between the axes of the hinges 2 and 3 of FIG. 1, which is equal to l = l ₁ + l ₂ .

The distance l ₁ from the axis of the hinge 2 to the point NK - on the axis of the balance (Fig. 1) is set in advance. It is chosen so that the NC point coincides with the conditional center of mass of the model or is in close proximity to it. After the manufacture of the balance, the NK point is applied to the balance in the form of a core or risks.

In the future, the measurement of the moments acting on the model will be made relative to this point.

So, the use of multicomponent tensometric scales of the original design, rigidly connected to the tested model, which at certain points is attached to the scales, mounted on supports made in the form of tensioned nose and tail bands and located inside the model, allows to measure the components of aerodynamic force and moment acting on model, remaining insensitive to the aerodynamic forces acting on the supporting model of the tape, and to the parasitic axial force acting between the tapes, thereby The influence on the measurement results of the degree of tension of the tapes and the aerodynamic forces acting on them is examined, and, as a result, it makes it possible to increase the accuracy of measurements.

The use of intramodel weights will increase economic efficiency due to the absence of the need to determine the drag coefficients of the tapes in the "empty" pipe in the absence of a model on the same as with the model, test modes, as well as the accuracy of determining the aerodynamic characteristics of the model.

Claims (1)

A device for measuring the constituent vectors of aerodynamic force and moment, containing multicomponent tensometric scales rigidly connected to the tested model, a support, characterized in that the tensometric scales are mounted on supports located inside the model and made in the form of stretched bow and tail bands, contain dynamometric elements for measuring supports reactions for which computed values of lift Y, lateral force Z, roll moment M _X, pitch moment M _Z, yaw moment M _Y and dinamometriche an element for measuring the longitudinal component X of the aerodynamic force vector, made in the form of a movable platform, to which the tested model is attached, connected to a fixed base by means of elastic hinges and sensitive elements, the contact points of the sensitive elements X with the platform and the base are located on the same plane, which perpendicular to the plane of symmetry of the dynamometric element.

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