How many times does the first propeller spin?

How many times does the first propeller spin?

• A. 1
• B. 1 1/4
• C. 2
• D. 1 1/2

Answer: (D)

Gears and belts change rotation speed according to size ratios, so the overall speed of the first propeller comes from multiplying the speed ratios of each stage. In this setup, the connections add up to a 3-to-2 ratio, meaning for every 2 turns of the input, the first propeller makes 3 turns. That’s a speed-up of 1.5 times, which is why the first propeller spins 1 1/2 times. You can check by following the motion from the input through each belt/gear stage—the intermediate speeds combine to give the final 3/2 result.

Gears and belts change rotation speed according to size ratios, so the overall speed of the first propeller comes from multiplying the speed ratios of each stage. In this setup, the connections add up to a 3-to-2 ratio, meaning for every 2 turns of the input, the first propeller makes 3 turns. That’s a speed-up of 1.5 times, which is why the first propeller spins 1 1/2 times. You can check by following the motion from the input through each belt/gear stage—the intermediate speeds combine to give the final 3/2 result.