How to Choose a Propeller for an RC Plane: Diameter, Pitch and Blades
A propeller is described by two numbers, such as 10×6: the diameter (10 inches) and the pitch (6 inches, how far it would move forward in one turn). Larger diameter gives more thrust at low speed, which suits slow planes, 3D and climbing; more pitch gives more speed. The prop must match the motor’s kV and battery so current and temperature stay within limits. Start with the motor maker’s recommendation, then test with a watt meter and check temperatures after flights.
By Kyle HilsonUpdated: October 20264 min read
Diameter and pitch
| Change | Effect |
|---|---|
| Bigger diameter | More static thrust, more current, better for slow flight |
| Smaller diameter | Less current, higher rpm |
| Higher pitch | Higher top speed, more current, weaker at low speed |
| Lower pitch | Better acceleration and climb, lower top speed |
| More blades | More thrust in the same diameter, less efficient, scale look |
Matching motor and prop
Low-kV motors turn large props slowly; high-kV motors turn small props fast. Put a large prop on a high-kV motor and the current climbs until the motor, ESC or battery overheats. Motor makers usually list recommended props for each battery voltage, with expected current and thrust; this is the best starting point. Sizing the motor itself is covered in how to size an electric motor for an RC airplane.
Props by plane type
- Trainers and slow flyers: large diameter, low pitch (for example 10×4.5 type).
- Sport planes: balanced diameter and pitch (for example 10×6 or 11×7 type).
- Speed planes: smaller diameter, high pitch.
- 3D planes: large diameter for hover thrust.
- Gliders: large folding props for efficient climbs.
- Scale warbirds: 3- or 4-blade props for looks.
Examples show typical proportions; the right size depends on your motor and plane.
Testing a prop
- Fit the prop securely and balance it.
- Measure full-throttle current with a watt meter on the ground.
- Compare with the motor, ESC and battery ratings; stay below them with margin.
- Fly, then check temperatures: motor, ESC and battery should be warm, not hot.
- Adjust one size at a time based on results.
Materials
Nylon and glass-filled nylon props are cheap and flexible, good for trainers. Electric-specific props (thin, efficient) suit most electric planes. Carbon props are stiff, efficient and expensive, and dangerous if they break. Wooden props are common on glow and gas engines. Use props designed for your power type: electric props on high-rpm glow engines can fail.
Safety
- Never stand in line with a spinning prop.
- Replace nicked or cracked props.
- Balance every new prop.
- Remove the prop when programming ESCs.
- Tighten prop nuts and check them before each session.
Fitting a prop correctly is covered in how to install a propeller on an RC plane.
Props for glow and gas engines
Engine makers list prop ranges for each engine. Running the right size lets the engine reach its working rpm without overheating. Too large a prop overloads the engine and makes it run hot and rich; too small lets it over-rev. Use sturdy props designed for engines, balance them carefully and check them for cracks, since engine vibration is harsh on props.
Folding props
Motor gliders use folding props that fold back against the fuselage when the motor stops, reducing drag. They need an ESC with a brake so the prop stops spinning and folds cleanly.
FAQ
What does 10×6 mean on a prop?
10 inch diameter, 6 inch pitch.
Bigger prop or more pitch?
Diameter for thrust and slow flight; pitch for speed.
How do I know if my prop is too big?
High current and hot motor, ESC or battery.
Are 3-blade props better?
They give scale looks and thrust in a smaller diameter, with slightly less efficiency.
More on this topic: the complete RC Airplanes guide covers the basics behind this article.
About 20 years in RC. Mostly boats in the NAVIGA Mini Eco Expert class, with many self-made parts; also a King Motor Baja 5B, a home-built electric plane, home-built nitro planes he has flown, and an RC helicopter. More about SwellRC
