Air cushion vehicles having attitude-correcting skirts

Claim 1

A VEHICLE FOR TRAVELLING OVER A SURFACE AND WHICH IN OPERATION IS SUPPORTED ABOVE THAT SURFACE, AT LEAST IN PART, BY A CUSHION OF PRESSURISED GAS FORMED AND CONTAINED IN A SPACE BENEATH THE VEHICLE, COMPRISING A MOVABLE STRUCTURE ATTACHED TO THE MAIN BODY OF THE VEHICLE AND EXTENDING DOWNWARDLY AWAY FROM THE BOTTOM SURFACE OF SAID MAIN BODY, SAID STRUCTURE COMPRISING AN UPPER STAGE AND A LOWER STAGE FLEXIBLY ATTACHED TO THE LOWER PART OF THE UPPER STAGE, MEANS FOR MOVING THE STRUCTURE VERTICALLY, AS A WHOLE OR LOCALLY, RELATIVE TO THE VEHICLE SO AS TO VARY THE POSITION OF THE LOWER PART OF THE STRUCTURE RELATIVE TO THE SURFACE, SAID MEANS INCLUDING MEANS FOR MOVING VERTICALLY AT LEAST THE LOWER PART OF THE UPPER STAGE, MEANS FOR DETECTING A VARIATION IN ATTITUDE OF THE VEHICLE FROM A DESIRED ATTITUDE RELATIVE TO THE MEAN SURFACE, AND CONTROL MEANS OPERATIVE TO CONTROL THE MOVEMENT OF THE STRUCTURE IN ACCORDANCE WITH THE VARATION SO DETECTED TO MOVE THE STRUCTURE DOWNWARDLY AT A LOCALITY AT WHICH THE CLEARANCE BETWEEN THE MAIN BODY OF THE VEHICLE AND THE SURFACE IS DECREASED TO PRODUCE VERTICAL FORCES ON THE VEHICLE IN OPPOSITION TO SUCH VARIATION IN ATTITUDE.