Controllable pitch propeller having low pitch stop

Claim 1

IN A CONTROL SYSTEM FOR THE BLADES OF AN ADJUSTABLE PITCH PROPELLER HAVING A DRIVE ENGINE AND A ROTARY HUB STRUCTURE INCLUDING ADJUSTABLE SUPPORTING MEANS FOR SAID BLADES, A HYDRAULIC MOTOR WITHIN SAID HUB STRUCTURE INCLUDING A CYLINDER AND PISTON, MEANS CONNECTING SAID PISTON WITH SAID SUPPORTING MEANS TO INCREASE AND DECREASE THE PITCH OF SAID BLADES IN RESPONSE TO MOVEMENT OF SAID PISTON INWARDLY AND OUTWARDLY OF SAID CYLINDER RESPECTIVELY, MEANS DEFINING THE MINIMUM PITCH LIMIT POSITION FOR SAID OUTWARD MOVEMENT OF SAID PISTON, CONTROL SPRING MEANS ARRANGED TO BIAS SAID PISTON INWARDLY OF SAID CYLINDER, MEANS FOR SUPPLYING HYDRAULIC PRESSURE FLUID TO SAID CYLINDER TO MOVE SAID PISTON AGAINST SAID CONTROL SPRING MEANS, AND SELECTIVELY OPERABLE VALVE MEANS FOR RELIEVING SAID PRESSURE FLUID SUPPLY, THE COMBINATION OF A STOP MECHANISM FOR SELECTIVELY BLOCKING INCREASE IN THE PITCH OF SAID BALDES BEYOND A PREDETERMINED LOW PITCH, COMPRISING LATCHING MEANS SUPPORTED ON SAID HUB STRUCTURE FOR MOVEMENT RELATIVE THERETO BETWEEN A RELEASE POSITION OFFERING NO RESISTANCE TO THE MOVEMENT OF SAID PISTON AND A LATCHING POSITION BLOCKING SAID PISTON FROM MOVEMENT INWARDLY OF SAID CYLINDER BEYOND AN INTERMEDIATE POSITION CORRESPONDING TO SAID PREDETERMINED LOW BLADE PITCH, AND DIFFERENTIAL PRESSURE MEANS RESPONSIVE TO THE PRESSURE WITHIN SAID CYLINDER AND CALIBRATED TO EFFECT MOVEMENT OF SAID LATCHING MEANS TO SAID RELEASE POSITION WHEN THE PRESSURE WITHIN SAID CYLINDER IS ABOVE A PREDETERMINED VALUE WHICH IS GREATER BY A PREDETERMINED AMOUNT THAN THE PRESSURE EQUIVALENT OF SAID CONTROL SPRING MEANS TO EFFECT MOVEMENT OF SAID LATCHING MEANS TO SAID LATCHING POSITION WHEN THE PRESSURE WITHIN SAID CYLINDER IS BETWEEN SAID PREDETERMINED VALUE AND SAID PRESSURE EQUIVALENT OF SAID CONTROL SPRING MEANS.