-=> Quoting Reggie Arford to Alec Cameron <=-
 AC>On (02 Jul 97) Reggie Arford wrote to Gregory Procter...
 AC> But, some of your comments to him were aimed at my message
 AC> so I will add to the discussion:
 AC> RA> steam locos do not have "a" rated horsepower as a Diesel does;
 AC> RA> they cannot. As any motor turns faster, its power increases (up
 AC> RA> to a point).    ^^^
 AC>Quite wrong! Most electric motors [both AC and DC] reduce in power
 AC>output as the speed increases.
 RA> Well, yes, but at zero speed power is (by definition) zero; at
 RA> some small speed, power is more than zero. As I say, "up to a point".
 RA> For an electric motor, at low speeds, the controlling parameter is
 RA> the current that can be applied.
Torque or pulling power is dependent on Amps (after deleting all the
other, lesser factors)
Horse power is torque multiplied by RPM (times a constant)
At starting/stall the electric motor produces maximum torque but zero
horsepower. The torque will steadily drop as revs increase, while
horsepower will increase to the designed maximum at say, 75% maximum
revs, and then steadily decrease.
Steam locos have a similar torque and horsepower curve but typically
maximum horse power is at about 33% of maximum speed.
A Diesel motor has no torque at zero rpm. In fact it must reach about
half maximum speed before usable torque is produced, hence the need for
an electric or hydraulic transmission.
 RA> Err, no. On a steam locomotive, all axles are typically fully
 RA> sprung and equalized. The equalizing system adjusts the spring
 RA> tensions so that all axles receive their share of the burden.
 RA> Note that lead and trailing truck axles are typicaly included,
 RA> but at a lesser rated burden.
On English steam locos, there is generally little in the way of
equalization provided. The loading of each axle is achieved by
adjusting the spring hangers, shackles or whatever adjustment was provided.
An advantage of this system is that the unbalanced connecting rod forces
are not transfered to the other axles. With the more even English trackwork,
the advantages of equalization were not so great.
Generally the locos exported from Britain followed British practice, so
Australia, New Zealand, South Africa etc. ended up with non-equalised
locos at times.
Greg.P.
  
... Catch the Blue Wave!
--- FMail 1.02
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