Hello Folks,
I asking for responses from any who have converted from a 2-blade to 3 blade
prop on their plane. I not interested in any performance claims but just
specifically the issue of cockpit vibration.
The prop mfg's and STC rep's are aware of this issue but express their
bewilderment to me. I've been looking for a common thread but haven't
found it yet. . There may be some engineer in a backroom somewhere who
knows the answer, but I haven't talked with him yet.
I don't have a better answer than anybody else.
I have been polling other owners groups and will later post what results I
can come up with.

It goes across the popular airframe models. Simply some are happy, others
are not. Even after a dynamic prop balance, some owners are not l not
happy with the different vibration, and different noise.
At the present, the conventional wisdom for those contemplating conversion,
is to not let go of the 2-blade until you are sure and make the deal to be
able to return the 3-blade for a refund if you choose.

It seems maybe that 6 Cyl Continentals which do not have a crankshaft 5th
order dampner or counterweight do not like 3 blades. i.e. Cessna 182 with
O-470-L or a Beech V35 with IO520-BA. Every Cessna produced with a
3-blade option, has an engine with a 4th,5th and 6th counterweight. Others
engines didn't, like the O-470L which has a 4th order and two 6th orders.

It could be that the models with scimitar blade design are the chief
culprit.
Some owners of Pipers and Mooneys with 4 cylinder Lycomings have asked me
about the vibration. All of them were scimitar blades.

Another factor is whether the conversion was done in conjunction with a
fresh engine overhaul versus midtime. Some speculate that at midtime, the
crank counterweights may have already worn in, taken a set, to the old prop
vibration.

I'd appreciate those who wish to participate if you let me know what
airframe and engine you have and what prop you went to, scimitar blade or
not. And whether the conversion was done fresh or at midtime and whether
you were happy or not with the cockpit vibration and noise.
Also useful would be a short note on how you percieved the vibration.

You can email me directly if you wish.


Thank you very much

Kent Felkins
Tulsa Oklahoma