Diaphragm construction for air cushion device

Claim 1

IN A GROUND PROXIMITY AIR BEARING, A RIGID PLATFORM, A COMPOSITE MATERIAL FLEXIBLE DIAPHRAGM EXTENDING BENEATH SAID PLATFORM, SAID DIAPHRAGM COMPRISING A LAYER OF FLEXIBLE POROUS MATERIAL CONNECTED AT ITS CENTER TO THE CENTRAL LOWER SURFACE OF SAID PLATFORM, A NON-POROUS ANNULAR LAYER OF MATERIAL OVERLYING A POROUS MATERIAL AND EXTENDING RADIALLY INWARDLY A PREDETERMINED DISTANCE FROM THE OUTER PERIPHERY OF THE LATTER, MEANS SECURING THE OUTER PERIPHERY OF BOTH LAYERS OF MATERIAL IN SEALED RELATION WITH THE OUTER PERIPHERY OF SAID PLATFORM, AND MEANS DIRECTING SUPERATMOSPHERIC AIR THROUGH SAID PLATFORM INTO THE SPACE BETWEEN SAID DIAPHRAGM AND THE GROUND, SAID POROUS MATERIAL ENABLING SUPERATMOSPHERIC AIR IN THE LAST MENTIONED SPACE TO PASS FREELY IN THE SPACE BETWEEN SAID PLATFORM AND SAID DIAPHRAGM AND URGE THE LATTER DOWNWARDLY INTO A BULGED CONFIGURATION FORMING A GENERALLY FRUSTO-CONICAL PLENUM CHAMBER BENEATH SAID PLATFORM WITH THE INNER PERIPHERY OF SAID NON-POROUS LAYER EXTENDING RADIALLY INWARDLY BEYOND AN IMAGINARY CIRCLE DEFINED BY THE LOWERMOST EXTREMITY OF THE POROUS MATERIAL WHEN THE LATTER IS IN SAID BULGED CONFIGURATION.