HOWEVER, it gives me the willies to consider a solid-crank IO-320 driving a CS-prop which had 7 inches chopped off the blades.

Jack,

 

That is the Hartzell design. It's a 84xx-14 --- 84 inch prop less 14 inches.  It is just that they don't need all the excess metal when they carve it.

 

<<<a) The IO-320 crankshaft does not have the torsional-absorbing counterweights which the higher-powered 360's have, and in certitfied form, most likely has a yellow band on the tach defining an RPM range best avoided due to harmful interwactions between the engine excitation and one or more natural frequencies of the prop blades;>>>>>

 

There are no restrictions on the "carved prop".  Note, however, that I use a Harmonic Damper (or dampener, if you wish).  Plus, my most recent engine reincarnation has a heavier crank/flange.  I find the smoothest operation above 2600 rpm, acceptable in the 2300-2550 rpm, and ugly in the below 2200 rpm range.  Those poor pistons.....

 

<<<c)  The lopping of your blades changed one or more of the blade natural frequencies (most likely causing them to increase), but the magnitude of the change is unknown without a survey. The resulting change could easily cause a serious interaction between a blade frequency and the second-order excitataion of your 4-cylinder engine, which could be stressing your blades to a level they cannot sustain;>>>

 

Yep.  My concern too.  Hartzell speaks through lawyers, so.... so far, nothing useful from them.  The prop shop wasn't too concerned, but I am after 150 hours of high speed operation with that nick on one blade about 4 inches from the end.

 

<<<d) Metal props on direct-drive piston engines pose a daunting set of vibration problems, the solutions to which are non-trivial, but which include blade profiles, mass distributions, root thicknesses, and a host of other factors, in order to avoid the harmful interactions described above.  Consider the fact that a prop which is safe on a particular certified IO-360 (8.7 compression, counterweighted engine) becomes UNSAFE after the STC'd installation of 10:1 compression pistons (more on that and other prop facts at >>>>

 

Thanks, I'll go look.

 

<<<) If you're determined to keep on flying this prop, you might consider having Hartzell do a vibration survey on your engine/prop/airframe combination. It's not cheap, but it sure beats the prospect of trying to land after the loss of a couple of inches off one blade tip (probably followed soon thereafter by the entire engine).>>>

 

Good Idea.  But I think I will contact the prop shop to see if we can make an arrangement about Hartzell carved blades.