The thrust equation for a jet engine can be expressed as:
\[ T = \dot{m} \cdot (V_e - V_0) \]
where:
- \( T \) is the thrust,
- \( \dot{m} \) is the mass flow rate of air through the engine,
- \( V_e \) is the exhaust velocity (velocity of the jet),
- \( V_0 \) is the inlet velocity (aircraft speed).
To analyze how increasing the airspeed \( V_0 \) affects the terms in the thrust equation, let’s consider each scenario:
-
Mass Flow Rate (\( \dot{m} \)):
- Generally, as airspeed increases, the aircraft ingests more air, which tends to increase the mass flow rate. However, the actual change may depend on the engine design and operating conditions.
-
Jet Velocity (\( V_e \)):
- For an idealized pure jet engine, the jet velocity largely depends on the thrust produced and is relatively constant for a given engine setting (assuming similar operational conditions). Thus, we might expect \( V_e \) to remain approximately constant while increasing \( V_0 \).
-
Thrust (\( T \)):
- If the mass flow rate \( \dot{m} \) increases and the jet velocity \( V_e \) remains approximately constant, the thrust produced might also remain approximately constant, especially when considering the term \( (V_e - V_0) \). In this scenario, if \( V_0 \) increases, the difference \( (V_e - V_0) \) can decrease, which tends to lead to a drop in thrust if not compensated by the mass flow rate increasing.
Considering these points, the most accurate scenario is:
- The mass flow increases, the jet velocity stays approximately constant, and the thrust stays approximately constant.
Thus, we can conclude that as airspeed increases, mass flow typically increases (though not proportionally) while the jet velocity remains constant, which keeps thrust approximately constant.