Patent GB-766873-A (GB)
Title: Improvements in machmeters
IPC: G01P5/175
Filed: 1952-11-13
Abstract: 766,873. Electric indicating systems. GELIX, A. J. M. L. Nov. 13, 1952 [Dec. 14, 1951], No. 28632/52. Class 40 (1). [Also in Group XIX] . A machmeter for aircraft in flight comprises a first two-armed lever pivoted on a fixed frame in a given equilibrium position, having one arm loaded normally to its length at a fixed distance from the pivot by a thrust derived from opposed linked pressure capsules and proportional to the difference between the static and dynamic pressures of a Pitot head responsive to air-speed, and the other arm normally loaded at a variable distance from the pivot by the thrust of a roller carried at one end of a second two-armed lever parallel to the first, which is pivoted on a carriage traversible by a reversible servomotor along a lead screw parallel to the levers; the remaining arm of the second lever being normally loaded at a variable distance from its pivot and at a fixed distance from the pivot of the first lever by the thrust of a second roller linked to a pressure capsule responsive to ambient static pressure, and the servomotor being operated by deviations from equilibrium of the first lever to traverse the carriage in either direction with the two variable distances maintained equal, so that balance of the lever is restored and the rotational displacement of the motor shaft and thus the carriage deflection (which may be transmitted to remote indicators by known means) is proportional to the Mach number for prevailing flight conditions. In Fig. 2, a thrust derived from the differential pressure #p between the dynamic and static pressures of a Pitot head operating opposedly connected pressure capsules 101, 102 is applied by roller 3 to doubleended lever 1 fixedly pivoted at 2 and is opposed by a thrust applied by roller 8 carried by double-ended lever 6 pivoted at 7 to a carriage 11 traversible laterally on horizontal rails 12 by leadscrew 13 driven by reversible servomotor 15. The free end of lever 6 receives over roller 17 a thrust derived from connected pressure capsules 103, 104 of which the latter is exhausted while the former is supplied with the static ambient pressure Pz, and any unbalance of lever 1 closes or opens contacts 4, 5 normally in a state of hunting equilibrium) to operate motor 15 through relay means to traverse carriage 11, lever 6, and roller 8 until balance is restored. Construction is such that the distance from pivot 2 to the point of contact 9 of roller 8 is always equal to the distance from pivot 7 to the point of contact 18 of roller 17 and is denoted by x. If the distance from pivot 7 to point of contact 9 is b and the distance from pivot 2 to roller 3 is a, then at equilibrium; where M is the Mach number for the prevailing flight conditions and k is a constant, so that the Mach number may be indicated by the displacement of the servomotor measured by a pointer 106 rotated thereby over a scale 105. Further indicators are operable by the same motor, and static errors may be cancelled by moving the frame 90 carrying pressure capsules 101, 102 horizontally towards or away from the pivot 2. Fig. 3 shows a modification which is symmetrically balanced so that extraneous couples due to accelerations acting on the inertias of the several elements of the system are cancelled out. Two pairs of capsules 101a, 102a; 101b, 102b responsive to the differential pressure #p are mounted on a frame 136 whose level is adjustable by screws 138, and exert the resultant horizontal forces in opposite directions on the dependent arms 127a, 127b of the T-shaped levers pivoted at 2a and 2b; the inner ends of whose horizontal arms are loosely pivoted together by a pin and yoke at 128. A pair of pressure capsules 103, 104 responsive to the static pressure Pz are interconnected by a vertical member 121 to which a balance beam 123 is pivoted at 122, bearing through rollers 124a, 124b at its ends on levers 6a, 6b which are pivoted to yokes 11a, 11b and have rollers 125a, 125b at their free ends which contact the outer horizontal arms 126a, 126b of the T-members. The yokes 11a, 11b are arranged to be symmetrically displaced towards or away from each other by an inversely threaded lead screw driven as above by a servomotor, controlled by contacts 4, 5, operated by arm 126a, which restores equilibrium. Errors due to the action of vertical acceleration on capsules 103, 104 and their interconnecting member 121 are compensated by pivoted horizontal levers 129a, 129b whose outer ends carry weights 132a, 132b and whose inner ends are pivotally connected at 131 to member 121. Acceleration errors in the remainder of the system are compensated by its dynamic symmetry. The Mach number is a function of the displacement of the servomotor, which may be electrically, photo-electrically, or pneumatically controlled. The device is also applicable to determining the square root of the ratio of two input thrusts from unspecified sources (Fig. 1, not shown).