Patent GB-1101965-A (GB)
Title: Aircraft braking systems
Inventor: MORTIMER FRANK RADCLIFFE
IPC: B64C25/42
Filed: 1963-11-26
Abstract: 1,101,965. Aircraft braking system. DUNLOP RUBBER CO. Ltd. 16 Nov., 1964 [26 Nov., 1963], No. 46579/63. Heading F2F. An aircraft braking system comprises a pair of brakes associated respectively one with a port landing wheel and the other with a starboard landing wheel and a pair of electrical sensing units 4, 5; 6, 7 associated one with each landing wheel for sensing whether the wheel is rotating faster than a predetermined speed, each sensing unit being connected in an electrical circuit for preventing application of either brake until both wheels are rotating at a speed greater than the predetermined speed. The sensing units 4-7 each comprise a contact breaker 8-11 drivably associated with a landing wheel, an electrical relay 15-18 having contacts arranged in a circuit for operating a solenoid operated brake control valve 1 to apply the brakes, and an electrical circuit operated by the contact breaker and arranged to actuate the relay when the speed of the wheel is greater than the predetermined speed. Each sensing unit 4-7 comprises a flip-flop circuit 12 operated by impulses generated in the circuit by opening of the contacts of the contact breaker, an integrating circuit 13 being provided to accept a series of pulses from the flipflop circuit, the pulses having a constant amplitude and a frequency proportional to the speed of the associated wheel, an amplifier 14 being provided to operate the relay when the output from the integrating circuit rises above a predetermined level. The contacts of the relay in the sensing unit associated with a port landing wheel are connected in parallel with the contacts of the relay of the sensing unit associated with a starboard landing wheel to form a set of contacts in series with the solenoid operated brake control valve 1 such that the latter valve prevents the application of the brakes until the contacts associated with the port and starboard wheels are both broken. As shown in the Figure two pairs of electrical sensing units are associated respectively with two pairs of wheels each comprising a port and a starboard landing wheel, the sets of relay contacts of the pairs of sensing units being arranged in series with one another and with the solenoid operated brake control valve. A pair of weight switches 20, 21 may be provided one for each undercarriage and connected in series with a relay 19 having contacts in series with the solenoid operated brake control valve 1 such that when the aircraft nears the end of its landing run and the wheel speed drops to a level at which the sets of relay contacts associated with the contact breakers close again, the brakes may be prevented from being automatically released at this stage by the weight switches 20 and 21 associated with the undercarriages, which will have been operated, by the transfer of the aircraft weight to the undercarriages, to cause their associated relay contacts to open and break the crcuit to the solenoid operated brake control valve. The weight switches thus ensure that the brakes can still be applied at the end of the landing run. An interlocked switch 3 isolates the solenoid of the brake control valve until the undercarriage is lowered and a second switch 2 is provided which can be opened by the pilot to apply the brakes independently of the automatic control system. Instead of contact breakers which provide a series of impulses at a frequency which is proportional to the speed of rotation of the associated wheels other equivalent mechanisms may be used such as a variablereluctance transducer which will provide a current suitable to operate the flip-flop circuit.