Finding the Equation

For Down Thrust

Basic Concept of a Helicopter Rotor:

The rotor of the helicopter creates the shape of a circle; the air being pushed down by the rotor creates a cylindrical shape.

 

The height of this cylinder is equal to the vertical velocity of the helicopter.

 


For reference purposes we always take the time as 1 second.

 

Key:                                                      Volume = Reference Area * ν                                         

π = (Constant Used in Circles)                             = πr2ν

r = Radius of Rotors                              Mass = Volume * ρ

ρ = Density                                                    = πr2νρ

ν = Velocity                                           Force * Time = Momentum = Mass * v

                                                                                        = πr2ν2ρ

                                                Force = πr2ν2ρ         

           

This is an ideal equation for down thrust, in practice we multiply the equation by the Coefficient of Life. The Coefficient of Lift can only be calculated for by experiments in wind tunnels.