thrust calculationthe amount of thrust produced

Question

Thrust calculation:

The amount of thrust produced depends upon two things:-

The MASS of air which is moved rearwards in a given time, the ACCELERATION imparted to the air.It can be expressed as:-  

                                              Thrust = Mass x Acceleration

The MASS is defined as "the quantity of matter in a body".It is expressed as :-   W/g

Where:-

            W = the weight of the body (in lb's or newtons) and

            g = the gravitational constant (taken as 32 ft/sec/sec or 9.81 m/sec² )

 

The ACCELERATION imparted to the air is the difference between its inlet and outlet velocity.If we let: - 

          V₂ = the air velocity at exit (in ft/sec/sec or  9.81m/sec² )

          V₁ = the air velocity at inlet (in ft/sec/sec or 9.81m/sec² )

                       It may be expressed as V₂ - V₁

 

Taking these expressions for Mass and Acceleration, the thrust produced by an engine or propeller can be calculated from the following formula:-

 

                                       THRUST = W/g( V₂  - V₁ )

Example 1.

The airflow through a propeller is 256 lbs/sec, Inlet velocity  0 ft/sec, outlet velocity 700 ft/sec.Thrust developed will be:

Solution:-

                     THRUST =  W/g( V₂  - V₁ )

                     THRUST = 256/32 x (700 - 0)

                                    = 5600 lbs