'Ram Ratio' in a gas turbine engine is defined as the ratio of:

• A. Total pressure to static pressure at the air intake
• B. Total temperature to static temperature
• C. Dynamic pressure to static pressure
• D. Total pressure to total temperature

Answer: (A)

The concept being tested is what happens to the air as it is slowed to rest at the engine inlet and how that changes pressure. When air is brought to zero velocity at the intake, its pressure becomes the stagnation (or total) pressure. The ram ratio is this stagnation pressure divided by the free-stream static pressure at the air intake. In other words, it measures how much the air is “rammed” into the engine due to forward motion, and it depends on the flight Mach number.

Why this is the best description: P0 represents the stagnation pressure after decelerating the air to rest, and P is the ambient static pressure. Their ratio directly captures the ram effect at the inlet, which is exactly what the term ram ratio refers to. The other options mix in temperatures or dynamic pressure, which describe different concepts and are not what the ram ratio uses.