GB611140A - Improvements in or relating to safe-air-speed indicators for aircraft - Google Patents

Abstract

611,140. Aircraft safe-speed indicators. BEAMONT, W., and K.D.G. INSTRUMENTS, Ltd. April 23, 1946, No. 12237. [Class 106 (ii)] An instrument for indicating safe speeds for aircraft comprises, in combination, a device showing indicated air-speeds and a device responsive to changes in static air-pressure, the movements of the transmission means for the latter corresponding approximately to the tangent curve to a given equation, and means for indicating the output movements of the transmission means on the same scale as that employed for the air-speed device or on a scale having corresponding graduations in line with those of the air-speed device. It is shown that the safe indicated air-speed is a function of the static pressure at the altitude at which the aircraft is flying, and this can be obtained by converting the responses of a pressure gauge to satisfy the given equation. As shown, an evacuated capsule 10 responsive to static pressure operates on an attached stirrup 12 carrying a pivoted rock-shaft 13 which has secured thereto a spindle 14. The lower end of the spindle 14 abuts an adjusting-screw 15, and the upper end engages a straight edge 18 formed on one arm of a toothed sector 20 mating with a pinion 30 secured to a tubular spindle 29 carrying a pointer A. The sector 20 is pivoted at 21 between two plates 22 which are pivoted on a spindle 23, the lower plate 22 having rack teeth 25 engaging a pinion 26 on a shaft 27 which can be turned for adjustment purposes by the engagement of a screw-driver in the slot 28 in the end thereof. This adjustment may also be arranged to adjust a device for indicating Mach numbers. The screw 15 is used for zeroizing the pointer A. The response characteristic of the capsule 10 may be modified by arranging a set-screw 31 in the stirrup 12 to engage a spring blade 32, the stiffness of which is controlled by a number of adjusting screws 33 on a fixed carrier 34. The air-speed indicator comprises a second capsule 35, responsive to pressure according to the indicated air-speed, having a stirrup 36 for a rock-shaft 37 carrying an operating spindle 38. The upper end of this spindle engages a straight edge on an arm of a pivoted toothed sector 40 engaging a pinion 41 fixed to the spindle 23 which passes through the spindle 29 and carries a pointer B. The response characteristic of this second capsule is also capable of modification by a leaf spring 48 and screws 49, and the pointer B can be zeroized by a screw 51. The upper plate 22 carries a scale 45 of Mach numbers and the toothed hub 44 thereof is engaged by a toothed sector 46 secured to the shaft 27. Both pointers A, B traverse over an indicated air-speed scale (not shown) encircling the scale 45. The instrument is so adjusted that safe conditions prevail when the pointer B is reading a lower value than the pointer A.