PERFORMANCE CONSIDERATIONS
Shape of Propeller Tips
Propeller tips can be rounded, swept or square. Various tips are often used to meet blade vibration resonance or special design conditions. Tip shape is also a function of aesthetics, noise requirements, flight performance, repairability and ground clearance.
Propeller Diameter
Propeller diameters are a function of engine and airframe limitations. Larger propeller diameters are preferred for low airspeed operation, while smaller diameters are best for high airspeeds. For example, the diameter of a fixed-pitch propeller is often large to favor low airspeed operation, while the blade size is small to favor higher airspeeds and faster turning at low airspeeds. The diameter and blade size of a constant-speed propeller is often larger (than a fixed-pitch), due to the variability of blade angles.
Engine Horsepower and RPM
For fixed-pitch props, at a fixed throttle setting, propeller and engine RPM increases or decreases with the airspeed. At a constant airspeed, fixed-pitch propeller and engine RPM change if power is increased or decreased. A constant-speed prop uses a governor to provide constant RPM at the selected throttle setting. The blade angle automatically increases or decreases as the RPM setting or engine power changes. With a fixed RPM and power setting, the blade angle automatically changes as airspeed increases or decreases.