SU38431A1 - Instrument for the experimental determination of aerodynamic coefficients of aerodynamic weights - Google Patents

Description

The commonly used instruments for determining aerodynamic coefficients (aerodynamic scales) necessitate a relatively long processing of test protocols in the computer bureau, and the expert himself also takes a relatively long time. In addition, scales are usually very complex, have inertia, and give average readings for a certain amount of time.

In the proposed aerodynamic balance, designed to eliminate these drawbacks, the elements that take up aerodynamic forces are capacitance capacitance, which are conventional variable capacitor capacitors. The force experienced by the model is perceived by the massdose connected to the primary AC circuit through a transformer connected to the secondary circuit including the other massdose and an ammeter-type measuring instrument. The second massdose takes into account the velocity head pressure (for example, through the Benturi nozzle).

The drawing shows a general diagram of the device.

(173)

An essential part of the instrument (scale) is the capacitive massdose 1, whose elastic dielectric directly absorbs the force. The degree of elasticity of the dielectric is determined by the magnitude of the measured effort. On both sides, in planes perpendicular to the direction of the force, the dielectric has two thin metal plates. Taken together, therefore, is a variable capacitor, the capacitance being proportional to the force. The balance must have at least two doses - for simultaneous measurement of the components of p and.

It is also possible to construct a massdose, composed. from a number of elementary massdos levied on each other.

Messdoz 1 is included in the AC circuit, as shown in the drawing, and, in addition to the mesdosa n current source, the circuit contains a 2 n transformer, two or more rheostats 3.

The secondary circuit of the transformer consists of a similar mass-dose 4, measuring the velocity head by; tubes 7 Pitot go Venturi and measuring device (ammeter) 5. The latter can be written.

To eliminate the effects of external influences, the entire electrical system is shielded.

The voltage of the primary circuit must be kept constant. Otherwise, it is monitored by a voltmeter 6 (also writing). The current in the primary circuit will be equal to:

R

/ -2 + (w1 -

jC

where t, e vi. L is constant, and C is the variable capacitance of the mass-dose 1. The current in the secondary circuit will be proportional to the current in the primary circuit, therefore, it depends on the force p received by the pressure cell 1. In addition, this force will also depend on the capacitance of massdose 4, measuring the velocity head, and thus for the indications of the measuring instrument (ammeter) 5 we obtain the following expression:

7 -

. R

lA.

,, + (, -)

Here is the proportionality factor for the transition from the primary circuit voltage to the secondary current strength, depending on the capacitance of mass-dose 1, and, consequently, on the value perceived by the last force p; r and L -states for the secondary circuit (ohmic resistance and self-induction); Cj is proportional to the velocity head q the capacity of a mass dose 4.

The rheostats 3 regulate the current intensity in the primary circuit, respectively, in terms of the values of the carrier surface S, for the midpoint of the aerodynamic coefficients, at half a head, etc.

The scale of rheostats is calibrated directly in these values. Thus, the coefficient fC turns out to be a function of these quantities, whereby the current measured by measuring instrument 5 is also a function of these quantities:

e / - - 9S hence,

1 / -N / 2.

Messodose 4 is calibrated directly in measured aerodynamic coefficients. Tape recorder drive; it's in motion by a clockwork; In studies of steady state conditions, it is more convenient to associate the tape feed mechanism with the mechanism of rearrangement of the angle of attack of the model, and thus obtain direct curves for changing the aerodynamic coefficients at the angle of attack of the model.

When using weights, in the primary circuit, by rheostats 3, 3, a current is established corresponding to constant multipliers in the formulas of aerodynamic coefficients, after which the force p, setting the appropriate capacity of the masses to dose 1, causes a current in the secondary circuit (in the presence of massdose 4), proportional to aerodynamic coefficients. The current acts on the measuring device 5, which can be calibrated directly, for example, for Su and Cx.

The subject matter of the invention.

1. Instrument for experimental determination of aerodynamic coefficients (aerodynamic balance), characterized by the use in the primary electric circuit of alternating current, capacitive capacitances in the form of capacitors, which change the capacitance under the influence of aerodynamic forces tested by the model, and in the secondary circuit, the analogous dosdose, taking into account the velocity head via a pitot tube or venturi nozzle.

2. Aerodynamic scales, characterized in paragraph 1, characterized in that, in order to obtain the readings of the measuring device 5, included in the secondary circuit, directly as defined abstract aerodynamic coefficients, a series of rheostats 3, 3 are included in the primary electrical circuit, taking into account the constant factors included in the formulas of abstract coefficients.

3. Aerodynamic scales, characterized in paragraphs. 1 and 2, characterized in that, for the purpose of automatic insertion of 3 readings of the measuring instrument, 5 corrections to the influence of constant additional forces caused by other elements of the test setup,

An appropriate tightening is applied to the corresponding process by informing her of an initial positive or negative force.

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