How to Calculate Lift for Rotor Blades

helicopter image by Irina Kodentseva from

The study of lift force falls under fluid dynamics, in physics, and is primarily concerned with motion generated by airflow. When rotor blades turn in helicopters such that pressure of layered air below the blades is greater than pressure of the layered air above the blades, the rotorcraft will fly vertically.

The difference in air pressure is directly proportional to upward-acting vertical force, which causes aircraft to lift off the ground into hover. The modern lift equation offers a means to compute the magnitude and units of lift force on aircrafts. A standard unit for measuring lift is newton (N). Another unit is pascal meter squared (Pa.m2) because pressure equals force per unit surface area.

Obtain the proper information to make the calculation. Whether you use data from homework or from experiment, use the lift equation. The modern lift equation states that lift (L) is equal to the lift coefficient (Cl) times the density of the air (r) times half of the aircraft velocity (V) times the reference area (A). This means you will need to know "r," "Cl," "V," and "A."

Convert the quantities to correct units. The final units of lift force determine the units of parameters required to calculate lift. If you expect lift to be in newton (N), then "r" will be in kilogram per meter cubed, "Cl" in radians, "V" in meter per second and "A" in meter squared.

Calculate user defined values. If the question provides all the parameters you need to compute "L" directly, then perform the calculation otherwise you will need to calculate them. You can obtain the value of "r" at a specified altitude from the appendix of an aerodynamic textbook or use an "Atmospheric Properties Calculator" like "Cl" is approximately two times pi (3.14159) times the angle of attack expressed in radians, "V" equals altitude in meters divided by the corresponding travel time in seconds and "A" equals pi (3.14159) times blade radius (in meters) squared.

Perform the calculation. Multiply density of air by lift coefficient by half of the square of the velocity with the aid of your calculator to obtain the lift force.

Check your value and units to ensure that they are correct. If your final units is either kilogram-metre second squared (Kg.m/s2) or pascal meter squared (Pa.m2), that is fine because they are equivalent to "N."