It will be appreciated that, since both the lift and propulsive force of the helicopter are supplied primarily through the large rotating blade system, it is advantageous to provide a main blade configuration which achieves a high lifting force at a given airspeed and which does not experience a high aerodynamic drag.

Rotorcraft, such as helicopters, are supported vertically by a plurality of driven blades which rotate about a vertical axis. The present invention relates to a blade for a helicopter, and more particularly, to the airfoil cross section thereof. This application is a reissue of 06/903,169, U.S. The family of airfoil cross sections as recited in claim 4, wherein the values of Y u /t max and Y l /t max are within 3% of the tabulated values. T max is the maximum transverse thickness achieved by the airfoil cross section.ДҐ. Y l is the transverse displacement of the airfoil lower surface from the chord line and Y u is the transverse displacement of the airfoil upper surface from the chord line A family of airfoil cross sections for a helicopter blade each having a leading edge and a trailing edge, an upper airfoil surface and a lower airfoil surface, each surface extending between the leading and trailing edges and characterized by the tabulation: _Д¬ is the chordal length of the airfoil cross section measured between the leading and trailing edges The rotorcraft blade as recited in claim 1, wherein the values of Y l/C and Y u/C are within 3% of the tabulated values.Д¤. The high lift-low drag airfoil section is defined within that portion of the blade extending spanwisely from the root end to at least 90% of the distance to the tip end.ДЈ. The rotorcraft blade as recited in claim 1, wherein Y l is the transverse displacement of the airfoil lower surface from the chord line.Дў. Y u is the transverse displacement of the airfoil upper surface from the chord line and X is the linear displacement along a chord line extending between the airfoil leading edge and the airfoil trailing edge Д¬ is the chordal length of the airfoil cross section measured between the leading and the trailing edges

A blade for a rotorcraft having a first root end mounted to a central hub, a second tip end, and a span extending between the root and tip ends, the blade further including a high lift, low drag airfoil cross section having a leading edge and a trailing edge, an upper airfoil surface and a lower airfoil surface, each surface extending between the leading and trailing edges and characterized by the tabulation: _

Helicopter airfoil