Calculating Thrust from Rocket Engine Ejection Velocity

[recon223]

The burned gases of a rocket engine are ejected from the rocket nozzle at a speed of 17,000 ft/sec. If the weight of gas ejected is one pound per second, find the thrust developed by the rocket.


I don't really have an equation to use here but my guess is F = M\32.2 * Ejection Velocity


F in lbs. = [ 1 lb / 32.2] * 17,000 = 527 lbs of thrust


Anyone care to verify that this is correctly calculated or have any ideas on a different calcualtion?

 

[lewando]

Analysis of units does not support your approach. Also 32.2 ft/s² is the terrestrial acceleration due to gravity. The rocket could be anywhere-- interstellar space or the moon. Thrust is a function of the rocket, not gravity.

 

[RTW69]

Thrust=dm/dt*Vel

Your work looks correct to me. 1 lb_f=32.4 Lb_m*ft/Sec²
The units of thrust is lb_f

 

[lewando]

This part got me-- "the weight of gas ejected is one pound per second". I read this as a dm/dt of 1lb_f/s. If this is read as 1lb_m/s then things to fall into place.

 

[rezeew]

Your calculation is correct. The equation you used, F = M\32.2 * Ejection Velocity, is known as the thrust equation and is commonly used to calculate the thrust produced by a rocket engine. In this equation, F represents the thrust in pounds (lbs), M represents the mass flow rate of the ejected gases in pounds per second (lbs/s), and 32.2 is the acceleration due to gravity in feet per second squared (ft/s^2). The ejection velocity is represented by the term Ejection Velocity in feet per second (ft/s).

In this scenario, the mass flow rate (M) is given as 1 lb/s, and the ejection velocity is given as 17,000 ft/s. Plugging these values into the equation, we get:

F = (1 lb/s / 32.2) * 17,000 ft/s = 527 lbs of thrust

This means that the rocket engine is producing a thrust of 527 lbs, which is the force pushing the rocket forward. This calculation assumes that all of the ejected gases are moving in the same direction and that there is no loss of energy due to friction or other factors. In reality, the actual thrust may be slightly lower due to these factors, but this calculation gives a good estimate of the thrust produced by the rocket engine.