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Rusty,
You may be getting something that was studied with dirt bike singles and narrow angle v-twins (Harleys). These engines worked well in getting traction on dirt tracks due to their firing order. If I recall it was called climb and retreat by the guys actually studying it. It would apply to a prop very well. Your prop has at the very least some flexibility in the blades. The power pulse hits and forces the blade forward violently, followed by a lull. Think of it like driving a long screw into wood. Every 1/2 turn you must re-position your grip. Any twist in the shaft of the screwdriver is released until you start turning again. The fore and aft movement might be caused by the large power pulse of the single rotor. This may be a totally natural event. OF course I've been wrong before, YMMV etc...
Bill Jepson
-----Original Message-----
From: Russell Duffy <rusty@radrotary.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Tue, 5 Jun 2007 6:10 am
Subject: [FlyRotary] Re: Single rotor video
How about a freewheel unit (slipper clutch) - should prevent alt least the reversal part after the power-stroke...
I know Rotax used those to get rid of resonant problems with their 912S, and if I get to the point where I have to custom fit some sort of coupler, I'll consider trying it.
Also, visual impact is one thing, that may have NOTHING to do with the actual blade behaviour.
Unless you take a strobe and watch, you might get some "funny show" - frame rate of the video, etc.
This is true, but there's no optical illusion I know of that can make the prop move fore and aft when viewed directly from the side (in the arc). What you see is also consistent between viewing with your eyes, and the camera, which is another indication that it's real. A really high speed camera would be better for this though.
Rusty
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