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Static vs dynamic thrust in multirotor drones

By Keayvan Keramati · ~5 min read

Most propeller thrust figures you see — from manufacturers or bench tests — are static thrust: thrust at zero airspeed, on the bench. But your drone flies. As soon as it moves forward, each prop makes less thrust. Missing this is why builds that "should" have plenty of thrust run out of push at speed.

Why thrust falls with speed

A propeller works by accelerating air rearward. When the aircraft is already moving, the air arrives with some velocity, so the prop can add less to it — the effective "bite" shrinks. In the limit, when the aircraft reaches the prop's pitch speed (the no-slip advance speed), the blade stops adding momentum and thrust goes to zero.

A simple mental model

A useful first-order approximation is that thrust falls roughly linearly from its static value to zero at the pitch speed:

So if your cruise speed is, say, 75% of the pitch speed, you only have about 25% of the static thrust left to overcome drag and accelerate. Plan your margin accordingly.

What this means for design

• Pick pitch for your speed. The pitch speed must sit comfortably above your cruise speed — see how to size a propeller.
• Higher pitch = higher top speed, but usually lower static thrust (worse hover/climb). It's a trade.
• Don't size climb or acceleration off static thrust — use the thrust available at the speed where you actually need it.
• For a winged VTOL or tail-sitter, the same idea sets the thrust available during transition, where speed and angle both change.

Getting it right

The simple model above is enough to avoid the big mistakes. For a real design — especially with ducts, high disc loading, or a body in the slipstream — the thrust-vs-speed curve is best pinned down with propeller CFD or blade-element momentum theory validated against test data.