I did have such a prop oscillation, very audible. Looked like the prop tips were flexing. Happened around 4400-4800 RPM
That was the two-blade Performance prop from Clark Lydic.
Whenever he did to it handled it. I think he narrowed the tips a bit.

Finn

Russell Duffy wrote:

Greetings,

 

Below are the notes from today's adventure.    As you'll read, there are certainly some vibration issues. 

 

A question for Richard- Have you run your single rotor with a realistic sized prop, or just with the drive itself?  Have you added any flywheel weight? 

 

Rusty

 

 

Spent quite a bit of time running the engine today, and tying some various tests.  The good news is that the fluids all stay inside the engine where they belong, so no more leaks.  The bad news is that there are certainly some vibration issues.

 

Running the engine without the prop does not show any significant vibration, except for the expected roughness at low rpms, below about 1800 or so. 

 

Running the engine with the 3 blade Warp Drive prop, gives a few different vibrations.  The best bet for “idle” is about 2200 rpm right now.  Reducing rpm below that point hits a pretty severe “rattle” at about 2000 rpm. This is the same as the rattle I got with the redrive on the 13B, but it was around 1100 rpm on that engine.  Reducing below that will get out of the severe rattle, but into the expected single rotor roughness.  It’s possible to idle around 900 rpm, but you wouldn’t want to. 

 

If you start at 2200 rpm, and slowly increase the throttle, all is well until about 2500 rpm, then a high frequency vibration starts.  The vibration increases in frequency, and amplitude as the rpm increases, right up to 3100 rpm.  At 3100, as you increase throttle, initially nothing happens, but then the engine will suddenly jump to 3300-3400 rpm, and be smooth.  It’s just like someone flipped a switch to get rid of the vibration.  This vibration is pretty severe, and you can see things like the air filter shaking until they’re just a blur. 

 

The 3^rd problem is an odd “beat frequency” sort of vibration that happens at all rpms.  If you stand directly in line with the prop arc, you can see the prop tips oscillating forward and back about every second or so.  I only watched this at idle, but other observers said that it gets much worse at higher rpms, and I can certainly feel it.  I don’t really have a clue what this is, unless it’s some sort of interaction between the 2.85 drive, and the ratio of eshaft to rotor rpm.  3 blade prop???  Gotta think about this some.