Thrust

  What is it, and how is it calculated?
       A moving aircraft requires a force to be acting upon it in order to Ramjet Thrustmaintain a constant velocity or to accelerate. In jet aircraft this force is called thrust. Categorized as a contact force, thrust is generated when a jet or rocket engine expels gas molecules at large velocities. The exhaust gas, which applies a force to the gas molecules outside the engine, generates a reaction force on the engine accelerating the aircraft. This phenomena is explained by the application of Newton's 2nd and 3rd laws, which state:

Force(net) = Mass x Acceleration and,
Every force occurs as one member of an action/reaction pair, in which each member acts on a different object with equal magnitudes but opposing directions, respectively.

      The equation modeling thrust for scramjets contains three parts calculating: gross thrust, ram drag, and a pressure correction respectively. Free stream conditions are denoted by "0" subscript, while exit conditions are denoted by an "e" subscript. Gross thrust is calculated by multiplying exit mass flow-rate by exit velocity. The ram drag is then subtracted, and the pressure correction added. The pressure correction is typically very minor compared to the other terms of the equation, however it is included to compensate for the differences in pressure between the exiting exhaust and surrounding airstream. Ultimately the net thrust is calculated and can then be used to determine the acceleration of the aircraft after additional drag forces are subtracted.



Image Source: http://www.grc.nasa.gov/WWW/k-12/airplane/ramth.html   

Introduction
 		Overview
 Scramjet Propulsion
 Drag & Other Factors
 Bibliography
Background Image By: Lynn Chambers
Retrieved From: http://science-edu.larc.nasa.gov/SCOOL/cirrus.html