Patent GB-389911-A (GB)
Title: Improvements in and relating to indicating instrument for use in aircraft
IPC: B64D43/00
Filed: 1931-11-23
Abstract: 389,911. Instruments for use on aircraft. UPSON, R. H., 1407, Lincoln Avenue, Ann Arbor, Michigan, U.S.A. Nov. 23, 1931, No. 32391. Convention date, Nov. 22, 1930. [Class 97 (ii).] An attitude-indicating instrument for aircraft comprises means, e.g. a body of liquid, movable in response to the difference in air pressure at an orifice placed at or near the leading edge of an airfoil and an orifice placed where the flow lines are substantially parallel to the adjacent surface of the airfoil. To counteract centrifugal force each side of the movable means may be connected to an orifice on the airfoil at the remote side of the aircraft's longitudinal axis. In the form shown in Fig. 6, the movable means comprises liquid in a U-tube with arms 47, 48, connected respectively to suction orifices 37, 37<1>, Fig. 1, by ducts 36. A third tube 49 connected at its lower end to the portion 50 of the U-tube joining the arms 47, 48 is connected at its upper end by a conduit 52 to an orifice 53. The latter is arranged, preferably outside the zone of influence of the wash from the propeller 54, at the leading edge of the wing so that the pressure induced in the tube 52 increases as the aircraft increases its speed or decreases its angle of attack. The orifice 53 may be positioned so that as the angle of attack approaches the angle of stall, the pressure induced in the tube 52 is transformed into a suction causing the liquid in the tubes 47, 48, 49, which normally stands higher in the tubes 47, 48 than the tube 49 because of the suction induced by the orifices 37, to adopt the same level in the three tubes. Alternatively the arrangement may be such that an equality of level of the liquid in the three tubes indicates optimum gliding conditions. Preferably two orifices 53 are provided, one on either side of the propeller wash, and are connected to the tube 49 through a pressure averaging or controlling casing 56. The disposition of liquid in the outer tubes 47, 48 indicates the lateral position of the air craft whilst the level in the central tube 49 in conjunction with that in the outer tubes gives an indication of the longitudinal attitude relative to the air stream. The instrument may be employed as an air speed meter and for this purpose the scale 63 is provided and the tubes 47, 48, 49 are formed with varying diameters or with shaped filler plugs 65, 66, to modify the rate of rise of the liquid in the tubes. To seal the tubes 47, 48, 49 on inversion of the aircraft the plugs 65, 66 may be provided at the top with valves or floating balls may be provided. The instrument frame 64 is mounted on the main frame 85 for vertical adjustment by means of the rack and pinion 86, 87 and is provided with a bank indicator comprising a sector-shaped casing 68 supporting by means of a cylindrical bearing 69, 70 a pendulous vane 71 provided with an upstanding pointer 73. The orifices 37, 53 may be arranged in stream-lined protuberances on the aircraft structure or may be arranged in auxiliary members or located at the throats of Venturi tubes. In a modified construction, shown in Fig. 22, two cylinders 112 connected at their lower ends to the tube 52 are provided with spring-urged pistons 115. The upper ends of the cylinders are connected by pipes 36 to the orifices 37 and the movement of the pistons is caused to adjust the position of a cross link 131. The latter is caused by the effect of side slip of the aircraft on the orifices 37 to indicate lateral tilting and also during straight flight indicates air speed against the scale 135.