Air-breathing Engine Net Thrust formula
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| \( F _n \;=\; \dot m_f \cdot v_e - \dot m_a \cdot v_a + \left( p_e - p_a \right) \cdot A_e \) | ||
| Symbol | English | Metric |
| \( F_n \) = Net Thrust Force | \(lbf\) | \(N\) |
| \( \dot m_f \) = Mass Flow Rate of the Exaust | \(lbm \;/\; sec\) | \(kg \;/\; s\) |
| \( v_e \) = Exaust Velocity | \(ft \;/\; sec\) | \(m \;/\; s\) |
| \( \dot m_a \) = Mass Flow Rate of the Incoming Air | \(lbm \;/\; sec\) | \(kg \;/\; s\) |
| \( v_a \) = Incoming Air Velocity | \(ft \;/\; sec\) | \(m \;/\; s\) |
| \( p_e \) = Exaust Pressure | \(lbf \;/\; in^2\) | \(Pa\) |
| \( p_a \) = Ambient Pressure | \(lbf \;/\; in^2\) | \(Pa\) |
| \( A_e \) = Exit Area of the Nozzle | \(in^2\) | \(mm^2\) |
Air-breathing engine net thrust is the effective propulsive force generated by an air-breathing engine, such as a turbojet, turbofan, or ramjet, after accounting for all forces acting on the engine during operation. It represents the difference between the gross thrust produced by the engine, resulting from the acceleration of exhaust gases expelled at high velocity from the engine’s nozzle and the drag forces, primarily the inlet drag (or ram drag) caused by the momentum of the incoming air. Net thrust is calculated as the mass flow rate of the exhaust multiplied by the difference between the exhaust velocity and the incoming air velocity, adjusted for pressure differences at the nozzle exit. This metric is critical in evaluating an engine’s performance, as it determines the actual force available to propel an aircraft forward, influencing its speed, efficiency, and overall capability. Factors such as airspeed, altitude, engine design, and operating conditions like throttle setting or afterburner use significantly affect net thrust, making it a key parameter in aerospace engineering for optimizing aircraft performance.