I took this video from within a United, Embraer 120 Brasilia plane with an iPhone 5s. Explain why the propeller seems to be moving slowly to the left? The engine of this plane is made by Pratt & Whitney Canada. I investigated and discovered that the propeller speed is about 1900-2200 rpm (rotations per minute), which means 31-36 rotations per second. The propeller has 4 blades and they are indistinguishable; that is a 1/4 rotation implies changing the 1st blade location with the 2nd, and the 2nd with the 3rd, etc. So, if you sample 124-144 times per second, you will see it as stationary (not moving). Any slower or faster, it will move in one or other direction. On the other hand the iPhone 5s can take video at a speed of 30 fps (frames per second). In the video there seems to be 8 or even 10 propellers. Since the camera is about 4 or 5 times slower than the propeller, we see it as moving and also as having more than 4 propellers.
Posted on: Mon, 03 Nov 2014 06:00:54 +0000
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