Locomotive Engineering Question:

[redskinsdb21]

Hello guys, I have a Locomotive Tractive Effort question I cant seem to figure out, it goes like this:

What is the net tractive effot (kg) of a 300 KW locomotive operating at 80 % efficiency and a velocity of 20 km/h if the total tractive resistance is 3500 kg?

I have tried using the Horsepower equation:

HP = (TE) (V) / 2690 ( E)......rearranging:

TE = 2690*E*HP / V....not really even geting clost to correct answer. any suggestions?

Thanks

[Terkhen]

Welcome to the forums.

The wiki mentions this: http://wiki.openttd.org/Tractive_Effort. I'm quite bad with formulae, so I don't know if they are correct or not.

[Erik1984]

Physics homework?

[redskinsdb21]

Actually, I am studying for the P.E. exam and locomotives are one of the many topics that must be reviewed....I have ran across the question and cant seem to figure it out based on equations already reviewed.

[michael blunck]

[...] What is the net tractive effot (kg) of a 300 KW locomotive operating at 80 % efficiency [...]

What means "operating at 80 % efficiency"?

regards
Michael

[redskinsdb21]

It means the Loco is operating at 80 % efficiency...power wise I am pretty sure

[michael blunck]

It means the Loco is operating at 80 % efficiency...power wise I am pretty sure

Well, it´s all in my old post (which that Wiki entry references):

To move one ton on level track (e.g., µ = 0.35) you´ll need a force of 35 Newton.

I.e., that´s your "total tractive resistance" of "3500 kg" ~ 34.335 kN. (Mind you that "kg" is wrong in this context, because it´s a unit for weight, but we are calculating a force, hence using either "Newton" (N) or "kilo pond" (kp). Amazingly, "kg" would be equal to" kp" here. )

Now, given that "80% efficiency" of 300 kW means that the locomotive yields a power of 240 kW, we get (with P = power, F = force, v = speed):

P = F * v -> F = P / v -> 240 kW / 20 km/h -> 240 kW / 5.55 m -> 43.2 kN

That´s the effort available by the engine (gross effort). The "net tractive effort" is the gross effort minus the total tractive resistance:

43.2 kN - 34.335 kN = 8.865 kN, or 904 kp.

HTH
Michael

[redskinsdb21]

Your answer is correct Michael...thanks a lot.