"Dan Horton" wrote in message
ups.com...
There is nothing that eliminates a long shaft from the design of a
PSRU. Nonbelievers might be advised to consider ship propulsion; long
shafts, low cylinder counts, propellers operating in uneven flow, often
via a gearbox. Sound familiar?

The important issue is torsional stiffness of the shaft, not
length. A long shaft can be torsionally stiff or soft, depending on
diameter and material. The engineering process will tailor torsional
stiffness of the shaft (along with a number of other factors) to adjust
natural frequency.

The information you need is found in engineering texts, not on RAH.
The subject can be complicated, but there are no unknowns. You will
find most of the torsional vibration classics listed in the
bibliography of Taylor's "Internal Combustion....". Some texts, like
Wilson's "Practical Solution.." (the ultimate reference) will be
difficult to locate. Try a large university library. The best readily
available text (sort of the ultimate primer on all matters vibrational)
is JP DenHartog's "Mechanical Vibrations". You can buy it for less
than $15 at Amazon. Here is a short list:

CF Taylor, "The Internal-Combustion Engine in Theory and Practice",
1966 (vol. 1), 1968 (vol. 2), MIT Press

W Ker Wilson, "Practical Solution of Torsional Vibration Problems", 3rd
Ed, 5 Vols., 1956, 0412091100, Chapman & Hall

JP Den Hartog, "Mechanical Vibrations", 1956, 070163898, McGraw-Hill

My compliments to Mr. Christley, whose comment (re frequency) was a
sole beacon of accuracy.


Dan Horton

You are very probably right--and it won't be the first time that I believed
that something was still a "black art" until I found out otherwise. For
years after I first became an electronic technician, I believed that about
grounding problems--and then I read a book titled "Sheilding and Grounding
Techniques in Instrumentation." Even 20 years ago, that book was long out
of print; but could still be obtained by special order from University
Microfilm. Almost miraculously, the problems went away!

After reading your post, I decided to look for the books you mentioned and
found that you were correct about the difficulty of locating W Ker Wilson's
book. That could indicate that it is the true source, as the dates
mentioned for earlier editions suggest, and therefore a custom reprint could
be worth every penny and more if a source is known.

The other two books seem to still be available, although I have no idea when
I might find time to read them...

Peter