Month in the Patent Office

Apparatus for maintaining an aircraft at a particular altitude comprises an aneroid capsule 1 housed within a container 2 which has an opening 3 communicating with the atmosphere. The interior of the capsule is in communication with the atmosphere through conduits 4, 5, a solenoid operated valve 6 and a conduit 7 except when the aircraft is at said particular altitude, when a remote‐control signal operates the solenoid to close the valve. The conduit 4 has an extension 8 connected to an insulated air reservoir 9 which reduces adverse pressure changes in the capsule caused by variation in the temperature of the ambient air. The capsule is connected to an arm 10, pivoted at 11 to wipe on a potentiometer resistance 13, the current taken off being used to energize power means to operate the control surfaces of the aircraft. In operation the valve 6 remains open, thereby maintaining the capsule 1 in equilibrium, until the aircraft‐reaches the particular altitude. A signal is then transmitted to the solenoid of the valve which closes. Subsequently, any variation in altitude causes the capsule 1 to operate the potentiometer arm 10 to effect movement of the control surfaces of the aircraft in a direction to restore the aircraft to said particular altitude.