The purpose of variable inlet guide vanes is to prevent compressor blade stall at what engine operating condition?

• A. Increase Fuel Flow
• B. Prevent Compressor Blade Stall At Low RPM
• C. Increase Exhaust Velocity
• D. Reduce Oil Consumption

Answer: (B)

Variable inlet guide vanes adjust the direction of the air entering the compressor to keep the airflow well-aligned with the rotor across different engine speeds. At low RPM, the compressor tends to stall because there isn’t enough mass flow to support the demanded pressure rise, and a poorly directed flow can separate or surge. By changing the inlet vane angles, the air is steered to enter the compressor at the optimal angle, improving stability and preventing blade stall during idle and throttle changes.

This function doesn’t involve increasing fuel flow, changing exhaust velocity, or reducing oil consumption, so those options don’t fit the purpose.