Patent GB-770311-A (GB)
Title: Equipment for determining the position of the centre of gravity of an aircraft
IPC: G01G19/07
Filed: 1954-06-02
Abstract: 770,311. Electric indicating systems. CONTINENTAL SILVER CO., Inc. June 2, 1954 [June 18, 1953], No. 16343/54. Class 40 (1). [Also in Group XXXVI] Apparatus for determining the total weight and centre of gravity referred to a datum position for an aircraft having main wheels and an additional which comprises weighing scales which receive the wheels and vary respective measuring impedances proportionally to the wheel loadings; the impedances being switchably connectible in a current circuit to develop a voltage proportionate to the total weight, which is measured by an automatically self-balancing potentiometer operating a total weight indicator and setting a variable resistance in accordance with total weight; the impedances of the individual wheel weighing scales being switchably connectible in further current circuits to develop voltages proportionate to the individual wheel loadings, which are respectively measured by automatically self - balancing potentiometers operating weight indicators, and the potentiometer balancing system of the additional wheel weight circuit setting a variable impedance in accordance with the additional wheel loading, so that the total and additional wheel loading impedances are connectible in a bridge network, also comprising an impedance representing the distance between the main and additional wheels and an impedance variable by an automatically rebalancing system responsive to the bridge unbalance voltage to a value representing the position of the aircraft C. of G. referred to the main wheels, which is also displayed by an indicator driven by the rebalancing system. In Fig. 1, the unbalance voltages of strain gauge bridges 11 placed at the corners of a weighing scale A receiving an aircraft nose wheel and A.C. energized by secondaries 12 of transformer 13, are connected in series over double-pole double-throw switch 41 in the normal position shown in opposition to a voltage from the slider 31 of potentiometer 23 in balancing circuit 20 energized from secondary 25, combined with a voltage from the slider 32 of potentiometer 27 energized from secondary 29 and manually adjustable to balance out the voltage component due to the tare of the weighing scale. The resultant imbalance voltage is amplified and applied over normally closed switches 35 to drive servomotor 34 to readjust slider 31 to zeroize the unbalance voltage. Indicator 37 is driven to indicate the nose wheel loading, and slider 71 is driven to adjust resistance 65 to a value representing such loading. Similar arrangements (but omitting potentiometer 65) comprising balancing circuits 40, 60 and responsive to the loadings of the main wheels received by scales B and C are provided, and after rebalancing is completed switches 35 are opened manually or automatically to disable the rebalancing servosystems, and switches 41 are changed over to connect the strain gauge bridges of the three scales in series to develop a total weight voltage which is connected in opposition to a voltage from the slider 31 of potentiometer 23 in a balancing circuit 54 similar to 20 described above, combined with a voltage from a similar potentiometer 27 adjustable in accordance with the total scale tare. The resultant unbalance voltage is amplified and similarly applied to a servosystem which readjusts slider 31 to zeroize the unbalance voltage, drives total weight indicator 37, and adjusts resistance 78 to a value representing the total loading, after which the servo system is disabled as above. Resistances 65, 78 are connected in opposite arms of a bridge 68 completed by resistance 84 representing the distance between the main and nose wheels, and resistance 86 in series with variable resistance 87 driven by rebalancing servomotor 89 responsive to the amplified bridge unbalance, which also drives a pointer 95 over dial 88 calibrated to indicate the position of the aircraft C. of G. as a percentage of its mean aerodynamical chord (Fig. 2, not shown). Resistances 84, 86 are calibrated in values peculiar to a given aircraft type, and may be made interchangeable for different types as a single plug-in unit. In a modification (Fig. 3, not shown), wide range self-balancing networks are provided for measurement and display of the several wheel loadings and the total loading, while additional switchable self-balancing networks operative over the narrower range of loads encountered in practice are provided responsive to the additional wheel loading and the total loading, and are arranged to regulate the resistances representing these loadings which are included in the self-balancing bridge which determines the centre of gravity. The loadresponsive impedances may be hydraulically or mechanically linked to the several weighing scales, and may comprise variable inductances or capacitances, while the apparatus may be built into an aircraft. The system may be D.C. energized, and the several strain gauges responsive to each weighing scale may be parallel connected.