a jet engine increases with its speed. If the speed is zero, then the propulsive power is zero. If a jet aircraft is at full throttle but attached to a static test stand, then the jet engine produces no propulsive power, however thrust is still produced. The combination piston engine–propeller also has a propulsive power with exactly the same formula, and it will also be zero at zero speed – but that is for the engine–propeller set. The engine alone will continue to produce its rated power at a constant rate, whether the aircraft is moving or not. Now, imagine the strong chain is broken, and the jet and the piston aircraft start to move. At low speeds: The piston engine will have constant 100% power, and the propeller's thrust will vary with speed The jet engine will have constant 100% thrust, and the engine's power will vary with speed Excess thrust If a powered aircraft is generating thrust T and experiencing drag D, the difference between the two, T − D, is termed the excess thrust. The instantaneous performance of the aircraft is mostly dependent on the excess thrust. Excess thrust is a vector and is determined as the vector difference between the thrust vector and the drag vector. Thrust axis The thrust axis for an airplane is the line of action of the total thrust at any instant. It depends on the location, number, and characteristics of the jet engines or propellers. It usually differs from the drag axis. If so, the distance between the thrust axis and the drag axis will cause a moment that must be resisted by a change in the aerodynamic force on the horizontal stabiliser. Notably, the Boeing 737 MAX, with larger, lower-slung engines than previous 737 models, had a greater distance between the thrust axis and the drag axis, causing the nose to rise up in some flight regimes, necessitating a pitch-control system, MCAS. Early versions of MCAS malfunctioned in flight with catastrophic consequences, leading to the deaths of over 300 people in 2018 and 2019. See also Aerodynamic force Astern propulsion Gas turbine engine thrust Gimballed thrust, most common in modern rockets Pound of thrust (same as pound (force)) Stream thrust averaging Thrust-to-weight ratio Thrust vectoring Thrust reversal Tractive effort References Aerodynamics Force Temporal rates