Which system provides best compressor efficiency while preserving stall margin?

• A. Compressor Variable Geometry (CVG).
• B. Fan Variable Geometry (FVG).
• C. Variable Exhaust Nozzle (VEN).
• D. Anti-Icing System.

Answer: (A)

Adjusting the compressor’s geometry on the fly lets the engine stay near its best efficiency point across different speeds and throttle settings while keeping enough margin to avoid surge. By changing parts of the compressor flow path (inlet area or stator vane angles) as operating conditions change, the engine can maintain optimal flow coefficient and pressure rise without pushing the compressor into unstable loading. This directly improves efficiency at the point the engine operates and preserves stall margin, so you don’t sacrifice stability for a bit of extra efficiency.

The other options don’t target the compressor’s operating point the same way. A variable geometry on the fan isn’t the primary lever for the compressor’s efficiency and stall margin. A variable exhaust nozzle changes the afterburner/exhaust flow, not the compressor’s internal flow, and the anti-icing system isn’t related to compressor performance or surge margin.