REFLECTOR: mt RPM Restriction

[michalk]

HYTEC45 at aol.com wrote:
> After constant problems with my mt leaking grease and breaking down 
> blade bearings due to blade vibration on my non-counterweighted IO-360, 
> and after arguing that I never operate in the restricted range 
> (2250-2550), mt has come up with what they think is the problem.
>  
> More good news.
>  
> The problem is that I am using electronic ignition.   Apparently mt's 
> vibration analysis is only good for magneto equipped engines.  Since I 
> am using one mag, and one EI, all bets are off, and they cannot 
> provide a range.  If we throw in high compression pistons, we really 
> have a problem.  Apparently the blades can't handle it.  So now I 
> must lay down more cash for the "new" blades that "should" work.
>  
> TEC

Interesting.  We had a discussion maybe a year ago about harmonics.  I 
came away with the feeling that all one could do is to move the 
sympathetic vibrations to a different range.  If one damped the 
vibrations, the energy has to go somewhere, and it's in heat, or damage 
to something.  If it's done with some sort of elastic system, the energy 
is returned to the system.

Seems/sounds similar to the problem with IVO.

I have this picture in my mind of a hub with springs that are partially 
compressed when the engine is at full horsepower.  The springs would 
never completely uncompress, smoothing the torque pulses to the blades. 
  Of course at lower RPM's somewhere along the power range those springs 
will be in tension and compression when the prop is unloaded.