Originally Posted by
EDML
Hi Chris,
from what I could find out the reduction gear for the R-2800 is 16:9. With a framerate of the camera of 25fps that would be 2666 engine RPM for the prop to look stopped: (25 RPs * 60 * 16) / 9.
That is pretty much in line with the 2700 RPM for the R-2800 at T/O power.
Hard to tell what that means for the perceived rotation of the prop.
Marcus
Hi Marcus,
You haven't stated your source for a 16:9 engine-to-prop reduction-ratio. Mine, from Janes for 1957/8, giving an engine : prop ratio of 8:3 (i.e., 16:6), would give a prop RPM only two-thirds of yours. Also, we don't know the frame-rate of the video camera used.
You'll agree that each of the three blades is not individually distinguishable. So, with a frame rate of 25 per second, a prop would appear stationary at 25 blades per second (500 prop-RPM), 50 blades per second (1000 prop-RPM), 75 blades per second (1500 prop-RPM) or even 100 blades per second (2000 prop-RPM).
So there's plenty of room for ambiguity, but we would certainly need the camera's frame-rate before postulating from the video. My assumption is that the engine RPMs would have been more or less equal (at about 2700 RPM) as the a/c was getting airborne at the beginning of the video. My GUESS is that the failing port engine was not much slower than the starb'd until the a/c passed over the perimeter fence. After that, it may have started to lose RPM (and therefore propellor thrust) by a significant amount. But I stand to be corrected.
Chris