nrp wrote:
: That is an interesting site having a lot of the history of tuned
: absorbers.

Yes, I was most impressed with it. I can't find the article that I was
actually referring to anymore, though.. I especially liked the difficulties
with the 2:1 prop reduction drive!

: Obviously Piper was able to get by the need for RPM restrictions by
: stiffening the crankshaft slightly (i. e. the solid crank version) so
: that a damper wasn't needed on those 4 cyl installations. I'm
: surprised that small amount of increase in stiffness of the whole
: rotating structure could be enough, but at any rate, any field mixing
: errors in prop-engine-tachometer combinations could create a bad
: situation by not making original certification spec.

They probably added mass & stiffness to get the resonant frequency up
high enough that you'll never get there. Interestingly many medium-speed
marine diesels (that is, about 500 to 800 RPM redline) have prohibited
RPM ranges as well. Those engines surely have a very heavy crankshaft.

: Tuned absorbers are a hobby of mine. I designed the ones used to
: stabilize the John Hancock Tower in Boston and the CitiCorp Center in
: NYC against wind induced vibration. My dampers are bigger than
: yours..............!

Wow, I am truly impressed. One of the things that drove me into the
engineering field (I am an EE) was a set of pictures in my 9th grade
science book showing the tuned mass damper in the Hancock tower at rest
and in motion!
--
Aaron C.