Hold a drone propeller up to the light and it looks simple: a hub and two blades. But each blade is a carefully shaped little wing, and once you understand that, a lot of things about drones suddenly make sense.
A spinning wing
Cut a propeller blade in half and look at the edge. You'll see the same shape as an airplane wing: a thick, rounded front edge (the leading edge) and a thin back edge (the trailing edge). The blade is also tilted slightly. As it spins, it slices into the air with its leading edge and pushes the air down. Every action has an equal and opposite reaction, so when the propeller pushes air down, the air pushes the propeller (and the drone) up. That push is called thrust.
thick · round · higher
thin
The blade is tilted a little, so as it spins it pushes air down.
Push air down → the drone goes up. Every action has an equal and opposite reaction.
Pitch: a screw in the air
You can think of a propeller as a screw going into wood. Pitch is how far the propeller would move forward in one full turn if the air were solid. A low-pitch prop has gentle blade angles: smooth, easy to control and kind to the battery. A high-pitch prop takes a bigger bite of air each turn: more speed and punch, but it also pulls more current from the battery.
Why the blade is twisted
In one turn, the tip of the blade travels a much longer circle than the part near the hub. That means the tip moves much faster through the air. If the whole blade had the same angle, the tip would do almost all the work. So propellers are twisted: steep near the hub, almost flat at the tip. That way every part of the blade pushes air evenly. It also explains why even a small chip at the tip makes the whole drone shake: the tip is where the blade moves fastest.
Two directions
A spinning propeller doesn't only push air down. It also twists the drone the opposite way. One propeller on its own would make the drone spin like a top. That's why a quadcopter has two propellers spinning clockwise and two counter-clockwise, placed diagonally. Their twists cancel each other out and the drone stays pointed where you want. To turn (yaw), the flight controller speeds up one pair and slows down the other, and the drone turns the opposite way to the faster pair.
That's also why there are two kinds of propellers. On our B200 drone-soccer drones they are marked A3 and B3.
Which way the pairs spin is a choice. With props in, the front blades swing in towards the middle of the drone, the Betaflight default, and how our B200 flies. With props out, the front blades swing outwards. Many racers prefer props out: grass, dirt and anything the props touch, like the edge of a gate, gets pushed away from the camera instead of into it. Both work: the flight controller just has to know which one you use.
The leading edge leads
Here's the rule that matters every time you change a propeller: a propeller always spins towards its leading edge. From above, A and B props look almost identical. Look from the side and you'll see it: the leading edge is the higher, rounder edge of the blade. If a propeller is on the wrong motor or upside down, it pushes air the wrong way, and the drone will flip over on take-off or simply won't lift.
Two, three or four blades?
Add blades and a propeller of the same size grips more air. But each extra blade flies through the swirl left by the blade in front of it, so it does a little less work for the energy it costs.
- Two blades are the most efficient: the longest flights and a light, slightly loose feel. You'll find them on long-range drones, tiny whoops and our B200.
- Three blades grip harder and keep the drone locked in through turns and propwash. They're the standard for racing and freestyle.
- Four blades get the most thrust out of a small propeller and run smoothly, but they drink battery. They're common on cinewhoops and ducted frames.
Rule of thumb: if you can't make the propeller bigger, add blades. If you can, fewer, bigger blades are almost always more efficient.
Long range, whoops, our B200.
The racing and freestyle standard.
Cinewhoops and ducted frames.
Sizes and kinds
Propellers are named with numbers. A 5143×3 is 5.1 inches across, has a pitch of 4.3 inches, and has three blades. Sizes go from 31–40 mm props on tiny whoops, through 2–3 inch micros and cinewhoops, to 5 inch racing and freestyle props and 7 inch and bigger long-range props.
Small propellers are simply pressed onto a smooth motor shaft and held by friction, like on the B200. That's why a loose one has to be replaced. Bigger propellers are bolted on with a nut or screws. Soft polycarbonate props bend in a crash and survive; stiffer, glass-filled props feel more precise but snap more easily.
And then there are the so-called silent props. Toroidal propellers loop each blade back into the next, so there is no sharp tip where the loudest whine comes from. They sound softer and less piercing, but today they are heavier and less efficient than normal props. Nice for flying in a park; not (yet) for racing.
diameter
pitch
blades
A prop is a spinning wing. The leading edge leads.
Read
- NASA Glenn, Beginner's Guide to Aeronautics: Propeller thrust
www1.grc.nasa.gov - NASA: The Science Behind Quadcopters (student reader, PDF)
nasa.gov - Smithsonian: How do propellers give thrust?
howthingsfly.si.edu - GetFPV: Understanding motor and propeller rotation
getfpv.com - Oscar Liang: FPV propellers
oscarliang.com - Oscar Liang: Toroidal propellers: a quieter future for FPV drones?
oscarliang.com
Watch
Videos are picked from search. We’re still checking them.
- How Does an Airplane Propeller Work?
youtube.com - Understand Airplane Propellers
youtube.com - How do Quadcopters Fly?
youtube.com - How yaw works? Drone yaw control
youtube.com - Inverted Prop Rotation (Quad Theory)
youtube.com
For trainers: the 10-minute plan
| Time | Slide | Talking points |
|---|---|---|
| 0:00 | Title | Hold up a B200 prop. "What does this actually do?" Let a few people answer. |
| 1:00 | Fig. 1 | A prop blade is a small wing. Cut it in half and you see the same shape as an airplane wing: thick round front (leading edge), thin back (trailing edge). It's tilted a bit, so as it moves it pushes air down. Push air down → drone goes up (Newton's third law). |
| 3:00 | Fig. 2 | Pitch = how far the prop would move forward in one turn, like a screw going into wood. Low pitch: smooth and gentle. High pitch: more bite and speed, more current. |
| 4:30 | Fig. 3 | The tip travels a much bigger circle than the root, so it moves much faster. That's why the blade is twisted: steep at the hub, flat at the tip, so the whole blade pushes evenly. A chip at the tip → vibration. |
| 6:00 | Fig. 4 | Every prop also twists the drone the other way. Four props the same way = the drone spins like a top. So: two CW, two CCW, cancelling out. To yaw, speed up one pair. That's why we have A and B props. |
| 7:30 | Fig. 5 | A prop always spins towards its leading edge. Wrong way round = air goes the wrong way → the drone flips on take-off or won't lift. On our B200: A3 = clockwise, B3 = counter-clockwise; drone with the tail LED facing you. |
| 8:00 | Fig. 6 | More blades = more grip from the same size, but each blade flies in the swirl of the one before → less efficient. 2 blades: longest flights, looser feel (B200, long range, whoops). 3: locked-in, racing standard. 4: most thrust from a small prop, thirsty (cinewhoops). |
| 9:00 | Fig. 7 (quick) | How to read 5143×3. Sizes from 31 mm whoop props to 7" long range. Friction fit vs nut. Soft vs stiff. "Silent" toroidal props: softer sound, heavier, less efficient. |
| 9:40 | Takeaway | "A prop is a spinning wing. The leading edge leads." Check every time you change a prop. |
Demo: Hand out a few old props. Everyone holds one up, finds the leading edge (the higher, rounder edge) and shows with a finger which way it spins. Then pair them: put an A3 next to a B3 and compare. Optional: hold a sheet of paper under a spinning prop on a bench quad (props on, strapped down, adult only) and feel the air go down.