Damper construction

Claim 1

AN AERODYNAMICALLY OPERATED PIVOTED DAMPER BLADE HAVING A LEADING EDGE AND A TRAILING EDGE FOR USE IN A DAMPER STRUCTURE WHICH IS INTEDED FOR DISPOSITION IN THE AIR FLOW PATH OF A BLOWER DEVICE EFFECTIVE TO CLOSE THE PATH WHEN THE BLOWER IS INOPERATIVE AND EFFECTIVE TO OPEN UNDER AIR PRESSURE WHEN THE BLOWER BECOMES OPERATIVE, SAID DAMPER BLADE HAVINGA PIVOTAL AXIS AND COMPRISING IN COMBINATION, (A) AN AIRFOIL SECTION HAVINGA DEFINABLE LEADING EDGE AND A TRAILING EDGE, SAID AIRFOIL SECTION BEING CONVEX UP AND CONCAVE DOWN TO FORM A PLENUM UNDER THE AIR FOIL AND BEING SPACED DOWNWIND FROM THE PIVOTAL AXIS OF THE BLAD WHEN THE BLADE IS OPERAIVELY DISPOSED IN THE AIRSTREAM, AND (B) AIRSTREAM GUIDING MEANS EXTENDING FROM SAID PIVOTAL AXIS TO SAID AIRFOIL SECTION AND FIXEDLY POSITIONING THE AIRFOIL SECTION FOR REVOLVING MOVEMENT ABOUT SAID PIVOTAL AXIS, SAID AIRSTREAM GUIDING MEANS BEING SHAPED TO DIVIDE THE AIRSTREAM TO CAUSE SEPARATE PORTIONS OF THE LATTER TO FLOW RESPECTIVELY ABOVE AND BELOW SAID GUIDING MEANS AND BEING EFFECTIVE TO DIRECT THE AIRSTREAM TOWARD THE LEADING EDGE OF SAID AIRFOIL SECTION AT A NON-ZERO ANGLE OF ATTAC K LES THAN THE STALL ANGLE OF THE AIRFOIL SECTION WHEN THE DAMPER BLADE HAS ROTATED TO A POSITION WHICH IS AT LEAST HALF OPEN IN THE AIRSTREAM, THE MAXIMOUM DEPTH OF SAID PLENUM UNDER SAID AIRFOIL OCCURING AT A POINT CLOSER TO THE TRAILING EDGE OF SAID BLADE THAN TO THE LEADING EDGE OF SAID BLADE.