| Propeller Pi and Other Math Adventures | |
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Joe was fascinated to hear that airplane propeller blade tips can exceed the speed
of sound and that is one reason why they can be so loud.
But how fast are the tips of the propeller blades really travelling? For that you need to know the circumference of the circle that the propeller blade tips travel around. But how on earth do you measure that? The propeller is just like a stick, so there is no "circle" you can measure. You need pi !! |
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Joe measures the propeller diameter on 32Golf
Check Switches OFF First!! |
| This is a good exercise in getting familiar with pi in a practical application, and also involves lots of unit conversions (since the speed of sound is commonly thought of in units of miles per hour). We start with a metric measuring tape for most observations. | |
| Aircraft | Propeller | |||
| Diameter | Circumference | RPM | Tip Speed | |
| Cessna 150 (50Mike) | 175 cm | 549.78 cm | 2,000 | 412.35 MPH |
| Cessna 150 (32Golf) | 189 cm | 593.761 cm | 2,000 | 445.32 MPH |
| C-130J (Hercules) | 13' 6" | 51.84 feet | 1,020.7 | 602 MPH |
| Rubber Band Glider | 12.5 cm | 39.27 cm | ~840 | 12.37 MPH |
Project Gutenberg etext listing of 1.25 million digits of pi in only one megabyte of download!
Celebrating International Pi Day!!!
Counting down to 3.14159, which we observed at 1:59pm on 3/14, by slicing into a blackberry pie.
(We first measured the circumerence and diameter of course).
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Contact: Fritz Funk (fritzf@alaska.net)