GB663287A - Apparatus for measuring the mach number - Google Patents

Abstract

663,287. Measuring Mach numbers. WULFSON, W. Feb. 22, 1949 [Feb. 25, 1948], No. 4849/49. Class 97 (ii). The Mach number of a solid moving rela.- tively to a fluid medium is measured by determining the ratio of the drag coefficients for two aero-dynamically different bodies carried by the solid. One such surface P is blunt in the forward direction and the other Q is sharp-pointed and they may be so selected that the drag ratio P/Q is a linear function of the Mach number M. In the preferred embodiment, the bodies P, Q are each attached to an arm a, only one of which is shown, which are both pivoted to a bracket f mounted in a casing n. The bracket f carries a moving element b which is capable of longitudinal movement in bearings d, e against a spring c by an amount proportional to the sum S of the actual drags on the bodies P, Q. Each arm a is integral with a lever m pivotally connected to a cross-bar g supported by the end of a leaf-spring b, the other end of which is fixed to the bracket f and the cross-bar g is therefore capable of movement transversely of the member b by an amount proportional to the difference S of the drags on the two bodies P, Q. A beam is pivoted at C to the bracket f and intermediate its length has a pin and slot connection with the cross-beam g. Its outer end D partakes of both the longitudinal motion of the element b and of the transverse motion of the cross-bar g and therefore moves through an angle α whose tangent is proportional to the ratio D/S. The Mach number M is determined from the ratio P/Q which is equal to 1+K tan α/1-K tan α where K is a constant. The angular movement of the end D of the beam i may be amplified and utilized to provide an indication of the Mach number by means of a pointer E. Alternatively this angular movement may be transmitted to a distance or utilized to operate a recording mechanism. If desired, the sum and difference factors Sand D may be separately indicated or recorded, and in combination with a thermometer they may be utilized to determine the actual speed of the body.