4 or 6 axels
Friarsp
heard a request for additional engines for a particular train. The reply was
that there were a number of 4 axle engines but no 6 axel engines available. The
first voice complained that 4 axle engines wouldn't work.
What difference does the number of axles of an additional units a consist make?
Thanks for your thoughts.
Deranged 1
the six axle units would give you two extra traction motors per unit, and probably
a lot more horsepower, which in turn would provide greater tractive effort and
engine braking where the 'steel meets the rail.'
However, I just work on them, I don't drive 'em.
Philip J. Kuhl
weight in on each axle. If you have two locomotives of the same weight, the
six axle unit will have less of that weight per axle. A light branch line
may have been built to standards that can't cope with a particularly heavy
amount of weight per axle and thus may require a six axle unit rather than a
four.
Phil
Deranged 1
Salinas/Watsonville area, who told me that he would love to have the larger 6
axle units, but they were just too heavy (at 200+ tons each) for the poor
condition of the rails in his jurisdiction.
Lstuder
pulling power, for the same Horsepower.
LArry (Lstuder @ aol.com)
Jim and Diane
axel locomotive. Consider that the if the engines have the same HP a
four axel unit must dissipate more heat (and HP) per traction motor than
a 6 axel unit. Placing a 4 axel unit in with some 6 axel units limits
all of the consist to the abilities of the four axel unit. This is a
serious consideration for a heavy train so as not to overheat and ruin
the traction motors. If it were light train it would not be nearly as
critical.
Now for the critics out there. I know that this is somewhat over
simplified but is more or less correct.
--
Jim
David A. McConnell
(2 more axles w/traction motors) The 4 axle units are usually somewhat
lighter duty and geared for more speed and less pulling power.
James Robinson
At low speeds, where the horsepower per axle is important, the four axle
locomotives have a power matching feature that reduces the total
horsepower output of the locomotive.
In the case of a four axle GP-40, as an example, they are reduced to a
total of about 2,000 horsepower at 12 mph. They therefore produce 500
hp per axle, which is the same output of a the six axle SD-40. The
locomotives can be combined in a locomotive consist without reducing the
capabilities of the six axle locomotives, and without worrying about
overheating the four axle locomotive's traction motors. Each locomotive
contributes to the pulling power on the train in proportion to the
number of axles.
At speeds above about 25 mph, the GP-40 will produce the full 3,000 hp,
since power matching will no longer be effective. The two types of
locomotives, SD-40 and GP-40, will be for all intents the same, as they
both produce the same amount of horsepower.
Thomas White
James Robinson wrote in message <36AF05...@ERIE.NET>...
~~
~~
>At low speeds, where the horsepower per axle is important, the four axle
>locomotives have a power matching feature that reduces the total
>horsepower output of the locomotive.
>
>In the case of a four axle GP-40, as an example, they are reduced to a
>total of about 2,000 horsepower at 12 mph. They therefore produce 500
>hp per axle, which is the same output of a the six axle SD-40. The
>locomotives can be combined in a locomotive consist without reducing the
>capabilities of the six axle locomotives, and without worrying about
>overheating the four axle locomotive's traction motors. Each locomotive
>contributes to the pulling power on the train in proportion to the
>number of axles.
~~
~~
Correct except in 2 details:
In DC motor locomotives the Minimum Continuous Speed, the minimum speed at
which full power may be continuously applied without overheating the motors,
is higher for the 4 axle locomotive. In the example, the GP40 will have a
MCS around 12 mph and the SD40 around 9 mph. Below MCS, the locomotive may
be operated at full power for a limited amount of time: 15, 30, 45, or 60
minutes at specified amounts of current. When 4 axle and 6 axle locomotives
are mixed, the pulling power is limited by the locomotive having the highest
MCS: higher speed less pulling power. The 9 mph 6 axle units are limited in
the the power that can be applied by the need to operate at 12 mph to keep
from overheating the 4 axle locomotive.
4 axle locomotives typically have less weight per powered axle than do 6
axle locomotives: a GP40 at about 125 tons has 31.25 tons per powered axle
and an SD40 at about 196 tons has about 32.6 tons per powered axle. The 4
axle locomotive will slip more easily than the 6 axle units, limiting the
power that the 6 axle units can use because the throttle must be reduced to
the point at which the 4 axle locomotive stops slipping [aside from wheel
slip control that takes care of the power reduction in the individual
locomotive without requiring the power applied to other units in the consist
to be adjusted]. This situation can sometimes be mitigated by placing the 4
axle unit at the rear of the consist of 6 axle locomotives and allowing the
locomotives ahead of it to handle the snow, ice, moisture, etc. on the rail,
leaving somewhat better adhesion conditions behind them.
The BN Guy
curves and switches better than a six axle.
Friarsp wrote in message <19990125175109...@ng146.aol.com>...
Old And Tired
wrote:
>I'm going out on a limb here: four axle loco's can operate on tighter
>curves and switches better than a six axle.
Most roads have done a mod to the truck to allow for greater lateral
movement on the center axle set for track curvature, but they will
develop a high tractive effort.. which can be a problem switching on
light rail.
James Robinson
> Correct except in 2 details:
>
> In DC motor locomotives the Minimum Continuous Speed, the minimum speed at
> which full power may be continuously applied without overheating the motors,
> is higher for the 4 axle locomotive. In the example, the GP40 will have a
> MCS around 12 mph and the SD40 around 9 mph.
The minimum continuous speed of GP and SD-40s is established by the
rating on the traction motors. Specifically it is based on the motor
type, the gearing, and the horsepower applied to the motor. While not
explicitly stated in the example I gave, each of these factors was the
same and therefore the continuous speed of both locomotives (GP-40 and
SD-40) would be the same. With 62:15 gearing and D-77 motors the
continuous speed the would be about 11 mph, and the tonnage ratings for
each locomotive would be additive in a combined consist. No reduction
would be required for matching the locomotives with a different number
of axles.
A continuous speed of 12 mph is possible with the GP-40, since a number
of railroads purchased them with 61:16 or even 60:17 gearing, which
would increase the minimum continuous speed. A continuous speed of 9
mph for an SD-40 is a bit low for the most common 62:15 gearing matched
to D-77 motors. The only way to get this low a continuous speed would
be to use a very odd gearing, or to have replaced the original motors
with a newer type with a higher capacity. The same lowering of the
continuous speed would occur if the motors were replaced under the four
axle unit with a similar type.
> Below MCS, the locomotive may
> be operated at full power for a limited amount of time: 15, 30, 45, or 60
> minutes at specified amounts of current. When 4 axle and 6 axle locomotives
> are mixed, the pulling power is limited by the locomotive having the highest
> MCS: higher speed less pulling power. The 9 mph 6 axle units are limited in
> the the power that can be applied by the need to operate at 12 mph to keep
> from overheating the 4 axle locomotive.
The above is correct where there is a difference in continuous speed,
but is not an inherent design difference between 4 and 6 axle
locomotives. (Assuming four axle units with power matching.) It is
because the types and gearing of the motors under the locomotives are
different, which yield the different continuous speeds. As noted, if
identical motors with identical gearing were applied to both
locomotives, then the continuous speeds would be identical as well.
> 4 axle locomotives typically have less weight per powered axle than do 6
> axle locomotives: a GP40 at about 125 tons has 31.25 tons per powered axle
> and an SD40 at about 196 tons has about 32.6 tons per powered axle.
125 tons is a bit low for the typical GP-40 with full fuel. In most
cases they were in the range of 132 to 136 tons. This gives a weight per
axle of 33 tons to 33.9 tons. SD-40s weighed as little as 185 tons, and
were as heavy as 205 tons. In most cases, they weighed about 195 tons
for a per axle weight of 32.5 tons. Thus the 4 axle GP-40s were
typically (there are exceptions) slightly heavier per axle than six axle
locomotives. Overall, the slight differences in the weight per axle
would not make a significant difference when the locomotives were
combined in a consist.
> The 4 axle locomotive will slip more easily than the 6 axle units, limiting
> the power that the 6 axle units can use because the throttle must be reduced to
> the point at which the 4 axle locomotive stops slipping [aside from wheel
> slip control that takes care of the power reduction in the individual
> locomotive without requiring the power applied to other units in the consist
> to be adjusted]. This situation can sometimes be mitigated by placing the 4
> axle unit at the rear of the consist of 6 axle locomotives and allowing the
> locomotives ahead of it to handle the snow, ice, moisture, etc. on the rail,
> leaving somewhat better adhesion conditions behind them.
As the speed increases above 12 mph, the power matching on the four axle
locomotives will increase the horsepower of the four axle locomotive
toward its full rating. As such, the horsepower per axle of the four
axle locomotives will increase to 50% above that of the six axle units
with the same horsepower rating. This will result in a tendency for the
four axle locomotive to slip more at these higher speeds when
encountering poor rail conditions. As suggested, having the four axle
units trailing will sometimes help the situation.
BN-Train...@usa.net
"The BN Guy" <theb...@swbell.net> wrote:
> I'm going out on a limb here: four axle loco's can operate on tighter
> curves and switches better than a six axle.
Yeah, I think that's generally the case, too. The exception might be the
radial truck SD70MACs. Those things are so sweet. Assuming the track can
withstand the additional weight, I imagine they can handle any curve a GP
can.
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