This is part of a discussion on dynamic forces as they apply to
locomotives and dining cars from the NP list.
I thought the SF and RS lists would be interested in the SDPs and the
CB&Q list in the U25Cs (or both)
Terry
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With the Geeps, I noticed it only at higher speeds, above
about 40 or so. Speed had a lot to do with things, too, and
that gets into what mechanical engineers would call "dynamic
stability" or "dynamic augmentation." We hear a lot about
that with regard to steam engines bouncing and pounding the
track, but not as often with diesels. And yet, two diesels
were notorious for this: Amtrak's old SDP-40Fs, in use
during the 1970s, and NP's U-25Cs and U-28Cs, built in the
mid-60s.
For some reason, those U-boats were tolerable (barely) up to
about 55. Somewhere between 55 and 60, they became
"springless." It was like they had no springs. They rode
hard. To me, it felt like they were hitting or pounding the
track. And woe unto the green hogger who tried to take a
U-boat into a siding (no. 11 turnout, I believe, normally
good for about 22 mph) at anything over about ten miles per
hour. It would really get his attention. The U-boats also
seemed to lose all their power at about 60 or so. One
Staples engineer used to say something like, "They go from
2500 to 25 horsepower at 60 miles per hour."
And Amtrak's SDP-40Fs were so bad at high speed that they
made the Us look good. In fact, if memory serves, there was
even a speed limit slapped on the -40Fs account their very
rough riding qualities at speeds above 65 or so. The U's
rough ride was consistently rough; it was not irregular. But
those SDP-40Fs were erratically rough. They'd be smooth for
a few seconds, and then suddenly--WHAM--they'd throw you out
of your seat for no apparent reason. They were sort of mean,
the worst engines I ever rode on at high speed. Enginemen
that I rode with much preferred the older F-units for riding
qualities.
I talked with the experimenters at the DOT test track down
in Pueblo, Colorado, about those SDP-40Fs back in 1978. (I
was attending the Air Force Academy in Colorado Springs at
the time, and went to the test track as part of an
engineering course I was taking.) They knew all about the
SDP-40Fs at Pueblo, but for some reason just could not find
the exact cause of the phenomenon. And another strange
thing: One of them, either the 577 or the 579 (I forget
which) was the odd one in the bunch. It was noticeably nicer
than the others. Something different about it, I guess.
Engineer Ben Layton (Dilworth) would be delighted to get it
on a trip, for then he could expect to arrive Jamestown
without having his teeth knocked out.
Enough ramblin'. I think you are right to point out the
importance of perspective, though. It was a major factor in
many ways.
Best wishes,
Bill Kuebler
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