RC Propellers: Size, Direction and Selection

What do 10×4.7 and 5×4.3×3 mean?

Common markings give diameter followed by pitch, usually in inches. One inch equals 25.4 mm. A 10×4.7 propeller has a 10-inch diameter and 4.7-inch geometric pitch. Pitch describes blade geometry, not the aircraft’s actual travel per revolution.

Multirotor labels often include blade count: 5×4.3×3 usually means 5-inch diameter, 4.3-inch pitch and three blades. Brands may also use four-digit labels or product codes. Check the manufacturer’s convention when abbreviations are unclear.

• APC: Propeller Size and Naming (PDF)

Diameter, pitch and blade count all affect load

With similar motors and voltage, increasing diameter or pitch usually increases load and current. More blades also change load. Larger propellers or more blades are not automatically more efficient or better for your aircraft.

Begin with the motor manufacturer’s battery and propeller combination, then adjust based on the complete aircraft. After moving to a higher cell count, the original propeller may no longer be suitable. Even if the ESC has enough current capacity, the motor may overload first.

• Great Planes: Motors, Propellers and Current (PDF)

Electric, slow-fly and multirotor propellers

Propellers for different applications may differ in material, blade shape, hub design and RPM limits. In APC naming, E denotes electric, SF slow-fly, MR multirotor and F folding propellers. These letters are not universal across brands.

A slow-fly propeller is not suitable for a high-RPM system merely because it fits. Electric-only propellers must not be used on combustion engines. Folding propellers also need compatible blade grips, hubs and spinners, with clearance in both extended and folded positions.

• APC: Product Types and Applications
• APC: Propeller RPM Limits

Check blade orientation as well as rotation

Motor rotation, propeller direction and thrust direction must agree. A pusher installation cannot be solved simply by flipping any ordinary propeller. Printed lettering is not a universal orientation rule; use the manufacturer’s diagrams to identify leading edges and blade orientation.

On multirotors, check each flight-controller motor position, rotation direction and matching propeller. Verify motor direction without propellers, then disconnect power before installation. Incorrect positions or orientation can cause abnormal thrust or a flip on takeoff.

• APC: Fixed-Pitch Propeller Orientation

Checks before and after installation

1. Disconnect the flight battery. Inspect blades and hub for cracks, chips, deformation or significant wear. Replace damaged propellers.
2. Check shaft bore, adapter rings, propeller mount and fasteners. The propeller must seat correctly without wobble. Never force it onto an incompatible shaft.
3. Follow the manufacturer’s balancing and fastening instructions. Check clearance from the aircraft, ground and neighboring propellers.
4. Powered checks with propellers installed require an open area, a securely restrained model and a clear propeller disc and surrounding area. Keep people out of the plane of rotation.
5. Stop and disconnect power immediately if vibration, unusual noise or insufficient power occurs. Check installation, direction and component matching.

• APC: Propeller Safety

Inspect after a crash before deciding to reuse

Impacts can damage the propeller, adapter, motor shaft and frame together. Do not glue broken propellers or replace a propeller while ignoring a bent shaft or loose motor mount. When damage cannot be confidently assessed, replacement is usually preferable to taking the risk.

During normal use, watch fasteners, vibration and material aging. Changing to another brand or blade shape at the same nominal size still requires checking power-system load and temperature rise again.