How does engine thrust vary with ambient temperature?

• A. Increase in temperature gives greater thrust because of low friction in compressors.
• B. Low temperature gives greater mass flow and therefore greater thrust.
• C. Low temperatures give low thrust.
• D. Thrust is independent of temperature.

Answer: (B)

Ambient temperature directly affects air density, and thrust is strongly tied to how much air mass the engine can push through per second and how that mass is accelerated to the exhaust velocity. Cooler air is denser, so for the same engine speed and intake area more air mass enters per second. That increase in mass flow means more momentum being imparted to the exhaust, resulting in greater thrust. Warmer air, being less dense, reduces mass flow and thus reduces thrust. So cooler ambient temperatures lead to higher thrust because of increased mass flow, while higher temperatures reduce thrust. The idea that thrust is independent of temperature or that it increases with temperature due to lower friction doesn’t align with how air density drives mass flow in the engine.