I was breaking in new rings on a paramotor and getting very bored. Just for fun, I decided to do a little test to determine how the air flows into and out of the prop.
The test mount is a fence which blocks the airflow from the right side of the prop, but the left side where I was testing had free air ahead of it. I don't know if that affected the test or to what degree.
The 48" in prop is turning 2000 RPM. The tuft is a bundle of strands of nylon masons line tapped to a wooden dowel handle. For reference, the alternating colored strips on the handle are 1" wide and the tuft strands are 2-1/2" long.
I started the testing from in front of the prop and worked my way around to the rear.
Tuft held 4" in front of the prop and 6" inward from the tip.
Even though the tuft is well in front of the prop, the air is not flowing rearward and straight through the prop like I would have expected but more inward toward the hub.
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Here the tuft is about 2" in front of the very tip of the prop.
I was expecting some outward or rearward airflow but the tuft was only being drawn exactly straight inward.
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Here the tuft is neither ahead of or behind the prop but exactly in line with the tips.
The tuft is being drawn in and forward by the direction of airflow.
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The tuft is behind the prop and about 1/2" outside the tip line.
The airflow is moving very smoothly forward. Interresting.
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Just far enough behind to clear the prop, and about 1" inside the tip line.
The air is flowing smoothly forward through the prop.
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The tuft is behind and about 2" inside of the tip line and just clearing the prop.
The air is still flowing forward through the prop but beginning the become turbulent.
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Behind and about 2-1/2" in from the tip line and just clearing the prop.
At this point the air is confused and the tuft is just flailing around in no definite direction.
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Held 4-1/2" in from the tip line and about 2" behind the prop.
Finally, the flow is to the rear, but very turbulant. The camera didn't capture it but the tuft is flailing in a circle.
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5" in from the tip line and about 2" behind the prop.
The flow is mostly rearward but very turbulant with the tuft flailing in a wide conical shape.
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About 7-1/2" in from the tip line and 2" behind the prop.
This is how far in from the tips the tuft had to be moved in order to encounter smooth airflow going to the rear.
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Abour 7" behind the center of the prop hub.
The air here is completely confused, and not energetic in any direction.
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