How are helicopter blades designed?
A contemporary helicopter blade isn’t a single material but rather an engineered assembly of different components working together. The outer skin typically consists of carbon fiber or fiberglass reinforced polymer, providing the aerodynamic surface and primary structural strength. Most recently, blades made of modern composite materials, such as fiberglass, carbon fiber or Kevlar skin covering a foam or Nomex core, have brought multiple improvements to rotor-blade design. Composites do have a fatigue life; but unlike metal, composite materials have a failure mode that occurs very slowly.
How to design a rotor blade?
The design of rotor blades may be divided into two parts: (a) determination of the physical dimensions and (b) detail design involving airfoil characteristics, including moment coefficient, chordwise center of gravity, blade weight, external smoothness, blade twist, thickness ratio, and internal structure. The blade chord (width) is 32 inches, and the shape of the airfoil is asymmetrical (the upper and lower surfaces are of different shape). From root to tip, the blade has a 12 degree negative twist to provide for a greater control range throughout the entire flight envelope.
What is the shape of a helicopter blade?
The blades of a helicopter are long, narrow airfoils with a high aspect ratio, a shape that minimizes drag from tip vortices (see the wings of a glider for comparison). An airfoil that has the same shape on both sides of its center line. A symmetrical airfoil has a very small change in the location of its center of pressure as its angle of attack changes. For this reason, symmetrical airfoils are often used for helicopter rotors.
What is the rpm of a helicopter blade?
Generally, the RPM of helicopter rotors is 500 to 600 RPM. The blade pass frequency is the rotor speed (R) multiplied by the number of blades (n). Most helicopters thus have a main rotor blade pass frequency generally in the 10-25 Hz region.