A jet engine derives its thrust by

• A. Cooling the combustor
• B. Drawing air into the compressor
• C. Impingement of the propelling gases on the outside air
• D. Reaction of the propelling gases

Answer: (C)

The thrust from a jet engine comes from moving air backward and exchanging momentum with the surrounding air. After combustion, the hot gases exit through the nozzle at high speed and collide with the ambient air, imparting momentum to that air and producing an equal and opposite reaction on the engine. This interaction—the impingement of the propelling gases on the outside air—creates the forward thrust. While drawing air into the compressor and cooling the combustor are essential parts of engine operation, they don’t by themselves generate thrust.