Self-Centering Prop?

[Dave Hederich]

I thought I'd get a good response to this in Power Systems, but there was little reaction. Maybe I should have posted it here in the first place.

I recently began using a prop saver for the first time, and was using a small nylon washer that just fit the gear shaft and indentation on the back of the hub to keep the prop centered as the gear shaft is much smaller than the shaft hole in the hub. It ran quite smoothly with no vibration to indicate imbalance. When switching props, I accidently left the washer out. When I first started to run the motor up, the prop was obviously off-center and vibrated badly. I immediately shut it down. Then, for the heck of it, I slowly ran it up to full throttle. At about half throttle, it started smoothing out and was vibration free at full throttle.

I shut it down and slowly ran it up again. This time it was much less rough at low throttle, and again smoothed out completely between half and full throttle. I'm using a pretty strong O-ring to hold the prop to the prop saver, so there's a lot of tension. I've never heard before of a prop self-centering on a prop saver when run up to speed. But that's exactly what appears to be happening here. One other person said they had experienced the same thing, but another person expressed doubt.

What's really going on here?

[Dave Hederich]

It must be magic. ;)

[AndyOne]

Dave,

There must be a force which pushes the blade which is further out back towards the centre, could it be the extra drag.

Andy.

[mc71]

Have you run it in the air ?

On the ground the prop might be pulling away from the prop-saver. Because the prop is off centre the tensions on either side of the O ring are different, it moves the prop into the centre so that the tensions are the same. Just a thought.

When in the air all this goes out the window.

Matt

[Dave Hederich]

I've been flying it for more than a week with the nylon centering washer removed, and it flies exactly as it did before. I can tell no difference at all. The tension on the O-ring is greater than the thrust created by the prop. So the prop remains in contact with the prop saver at all times, even when run up to full throttle while being held static. It really doesn't affect my flying enjoyment to know exactly why this is happening. But I'm still curious as to whether there is a known scientific principle at work here.