Definition
The speed at which a point on a rotating propeller blade moves around the hub, expressed in distance per unit of time. Because the blade is spinning, points farther from the hub travel a greater distance per revolution and therefore have a higher rotational velocity than points closer to the hub, even though the whole blade turns at the same RPM.
Plain English
How fast a point on the spinning propeller blade is moving in a circle. The tip of the blade moves faster than the part near the center, because it has farther to go in one turn.
Context Anchor
Seen in propeller theory when comparing the blade’s spinning motion with the airplane’s forward motion through the air.
Derivation
Rotational comes from the Latin rotare, meaning 'to turn.' Velocity comes from the Latin velocitas, meaning 'speed.' Together: the speed of turning. In propeller theory, it specifically means the speed of a point traveling around the hub.
Why Pilots Care
It changes the direction and magnitude of relative wind striking each blade section, directly affecting thrust, efficiency, and the risk of the blade tips approaching the speed of sound.
Analogy
On a spinning fan, the outer tip of a blade travels much farther in each turn than a spot near the center. Both make one turn in the same time, but the tip has a higher rotational velocity.
Intuition Check
Do not read rotational velocity as the airplane’s forward speed. Here it means the circular speed of the propeller blade as it spins around the hub.
Example Sentence 1
The propeller tip has a much higher rotational velocity than the blade root, which is why the blade is twisted from root to tip.
Example Sentence 2
A fixed-pitch propeller is designed so that the combination of forward speed and rotational velocity produces the best angle of attack for cruise RPM.