Internal Aerodynamic Design
Internal Aerodynamic Design is a key factor in achieving optimal engine performance. The aerodynamic efficiency of the cowl inlet and ducting are measured on how well dynamic air pressure, created by the aircraft’s velocity through the air, is captured at the cowl inlet and converted into static pressure around the engine’s plenum. This static pressure is generally expressed as a percentage of what is known as ram air recovery. For instance, 100% ram air recovery would indicate that 100% of the dynamic air pressure is captured by cowl inlet and 100% of that is converted to static pressure at the engine’s plenum. The higher the ram recovery percentage, the better the engine will perform.
At a given interstage turbine temperature (ITT), there is a finite amount of energy that can be produced by a turboprop engine. This energy is shared by the two power absorbing sections of the engine—the compressor section, which compresses air for combustion, and the power section, which turns the propeller. By increasing the ram air recovery to the engine’s plenum, less energy is used by the compressor section leaving more energy to drive the propeller.