Linn W. Moedinger Wrote:
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> Three comments on wheel slip. I have heard from
> old heads over the years that you get the best
> traction with a "quarter slip". This is when the
> wheel breaks loose but does not spin. I have
> noticed this phenomenon on many occasions in
> starting, where with careful attention to the
> throttle, you can regulate the steam to maintain a
> partial slip and it seems to work better than
> stopping the slip completely and attempting to go.
> My only guess why this seems to work is that
> possibly enough heat is generated at that tiny
> intersection between the wheel and the rail, and
> the wheel metal heats enough to increase the
> friction slightly. Total guess on my part.
>
> I agree with Earl regarding some engineers being
> clueless. Was on a mainline trip with 972 one
> time. Ran out of sand moving at about 35 to 40
> mph. The engine broke free and the cab full of
> people all knew it - except for the engineer. The
> wheels accelerated to some unknown speed that was
> sufficient to bounce the locomotive violently
> enough to propel the oil cans vertically about 8
> inches. The engineer noticed the flying oil cans
> and then figured out we were slipping.
>
> That being said, I have plowed snow many times
> where we hit drifts higher than the Russell blade
> and maybe 50 -100 yards long. You need to hit at a
> pretty high speed and it feels like hitting a very
> large pillow that won't move. Shortly after impact
> all visual references outside the cab disappear in
> the snow cloud. I have found my only clue as to
> whether I am moving or not is to monitor the
> density of the snow cloud. Listening to the engine
> is of no use as I found out early in my career
> when the snow cloud settled and the engine was
> chugging merrily along without moving.
Same principle when drag racers spin their tires before the race. It makes them stick to the asphalt better. But steam locomotives have steel on steel contact, so maybe there is something going on.
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