Re: 422 Class

[mauried@tpg.com.au (Maurie Daly)]

On Thu, 3 May 2001 10:36:25 +1200, "Michael McDonald"
<michael.and.colleen.mcdonald@xtra.co.nz> wrote:

>"Maurie Daly" <mauried@tpg.com.au> wrote in message
>news:3aed5604.51998370@can-news.tpg.com.au...
>> On Mon, 30 Apr 2001 20:13:24 +1000, "Paul Jones"
>> <dj_wiseguy2_nospam@yahoo.com> wrote:
>>
>> Tractive effort is not always related to locomotive horsepower.
>> A good example of this is to compare a loco like the NR class
>> (a 4000 HP loco ) with a continous tractive effort of 370 KN against
>> a SRA 82 class (a 3000 HP loco) with a continuous tractive effort of
>> 413 KN.
>>
>> Another factor which affects tractive effort is the final gear ratio
>> of the traction motors , the lower the ratio , the higher is the locos
>> top speed and the lower is its tractive effort.
>
>Weight is one of the main limiting factors of tractive effort.  I'm not sure
>of actual figures, but for steel wheel on steel rail, the tractive effort
>can never be more than a certain percentage of the weight on the driven axle
>(about 25% ? - also depends on anti-slip methods deployed and the condition
>of the rail).  The horespower of the loco determines the maximum speed that
>can be attained with maximum tractive effort.
>
>Out of interest, are any lococ / railcars etc designed with motors that are
>incapable of producing wheel slip (assuming good rail conditions - anything
>will slip on greasy rail!)?
>
>Cheers
>Michael
>
>

Yes , the above comments are spot on .
The axle load directly affects maximum adhesion.
27 - 30 % is the normal figure that can be achieved with steels wheels
on dry rails without any forms of wheel slip control.
DC locos with super series can achieve 33 - 35% and AC locos 38- 40%.

Its interesting to note that with the common limitation of 22 tonnes
axle load , there isnt a lot to be gained by going from 3000 HP to
4000 HP in terms of pulling ability.

To really get the full benefit of a 4000 HP loco needs 28 tonnes or
more .

I beleive that locos like the old SRA 49 class was unable to spin its
wheels on dry rails , due to the low capacity of the DC generator.
Its also likely that other low HP locos with 6 traction motors would
have trouble wheel slipping.

MD