#### Re: Arcane question of the week

Dave Nelson

Who better to ask than the members of this list?  You guys are all great.

The problem I was working on appears to be solved… the omission of a safe maximum unbalanced center of gravity – how far can the car be tipped to away from the direction of the curve (flat track) by centrifugal force and not be in any danger.  Apparently no value for that translated into not safe at any speed and I had neglected to provide one.  Plug in 6 inches and a reasonable center of gravity and the problem goes away. Any super elevation in quite a bit of extra safety.

But it is still an interesting question… gets you thinking of how the weight difference between a flat car and boxcar of reasonably similar construction translates into a different center of gravity… I would not think that much given the sides and roof panels for a boxcar are so thin.  In turn, this leads on to the question of why do empty covered hoppers have such a high center of gravity?  Those sides must be much more substantial than I thought.

Last… I quite enjoyed reading about the test procedure in San Diego.  It isn’t readily apparent to most model railroaders but long trains are really different.

Dave Nelson

From: STMFC@... [mailto:STMFC@...]
Sent: Saturday, March 19, 2016 1:38 PM
To: STMFC@...
Subject: RE: [STMFC] Arcane question of the week

Dave,

That could be the arcane question of the month, if not the year….

It's not clear to me whether you're talking about tipping to the inside of a curve in a stringline derailment, or overturning outside in an excess-speed derailment. Since speed is mentioned, I think it may be the latter.  Empty-car CG should be low enough that overturning shouldn't occur at any plausible combination of train speed and curve, so if the model is predicting otherwise, something is wrong.  In practical terms, it's likely that an L/V derailment, either wheel-climb or rail rollover would occur sooner.

Jack Mullen

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