Patent GB-694750-A (GB)
Title: Improvements in the automatic control of aircraft having pressurised cabins or the like
Inventor: LAMBERT DEREK JOSEPH
IPC: G05D1/06
Filed: 1951-01-17
Abstract: 694,750. Automatic control systems for aircraft. VICKERS-ARMSTRONGS, Ltd., and LAMBERT, D. J. Dec. 27, 1951 [Jan. 17, 1951], No. 1304/51. Class 38 (iv). Upon reduction of pressure in a pressurized aircraft cabin below a given value, e.g. due to a failure, pressure-sensitive means operate to control an automatic pilot so as to put the aircraft into a dive corresponding to a substantially constant " Mach " number not exceeding a critical value, and when the aircraft has descended to a critical altitude means become operative thereafter to maintain the aircraft at a substantially constant equivalent airspeed not exceeding a critical value, the aircraft being returned to level flight when an altitude is reached at which breathing of ambient air supports life and the pilot, when he recovers, can take over control. Dive or climb of the aircraft is controlled by a reversible A.C. motor PM, Fig. 3, supplied from a three-phase source 59, 60, 61, controlling a tilting platform carrying the pitch gyro of the automatic pilot. Within the cabin a pressure switch closes a contact LP on pressure failure. This results in energization of a relay DBA to operate dive-brakes or other drag-producing means (not shown), a relay TA to close the engine throttles (not shown) to a predetermined extent, and relays MR, COR to produce the actual dive by closing contacts MR5 to energize a potentiometer network MMP so that motor PM runs in the appropriate direction. Sliders 75 of potentiometer network MMP are controlled by a " Mach " meter so that rate of dive decreases with increase of " Mach " number, Fig. 4 (not shown). The " Mach " meter comprises a bellows responsive to equivalent airspeed and a bellows responsive to altitude, each controlling a slider 75. Besides controlling the potentiometer network each bellows is associated with a selector switch, Fig. 5 (not shown), and the arrangement is such that when the emergency dive occurs the " Mach " number increases up to a critical value at which both selector switches combine to energize a relay closing a contact VS1 energizing a relay SR to change over contacts SR1, SR2 and reverse motor PM. Contacts SR1, SR2 thereafter change over repeatedly to maintain the critical "Mach" number. When the critical altitude is reached the altitude-responsive bellows meets a stop so that only the selector switch associated with the airspeed bellows is effective to control relay SR and the critical airspeed is maintained. When a safe level is reached a pressure switch operates a contact NPS1 to energize relay SR and initiate a climb. However, as soon as the aircraft is level a mercury level switch opens a contact LS1 to prevent climb and closes a contact LS2 which is locked in by a magnet ML so that the aircraft is under the control of mercury level switch MJS. The aircraft thereafter continues in level flight under the control of mercury level switches until potentiometer network MMP is disconnected by the pilot opening switch CS so that contacts PCR1, PCR2, MR4 close and contact ECR4 opens to permit manual control of the elevators by operation of slider 62 of a potentiometer PCP.