Power

[♣polkovnik♠]

How much horsepower do trains have in the game?

[Randox]

Might need some better measurements.

Did a calculation based on this: steam loco (100 tonnes), pulling a 400 ton train (converted to metric). Based on a run yesterday I think I was able to accelerate about 3 km/h per second at 80 km/h near the steel mill. Converted all that too into the usual units, and long story short I got a little over 11,000 hp. More if train weights are metric tonnes, but I want sure so I went imperial.

To be clear, that number is absolutely insane. That said, regardless of whether I did the math right or made semi reasonable assumptions, the SH282 has ludicrously high power output and torque at speed. This might be a scale thing though. If it were more realistic, the map would need to be way bigger to get up to speed and have track left to enjoy it. So I'll run the numbers again at a much lower speed, before the loco feels like turbo kicked in. Same weight and acceleration at 15 km/h gives:
2,160 hp

That would be a far more reasonable number for a loco of that size and configuration (very small driving wheels).

For reference, I got 386,142 N as the result for (100 tonnes + 400 tons) x 3km/h/s. .278 to convert mph to m/s, and 1.34 to convert kW to hp. Power equals force multiplied by velocity (W=N*v)

I'll do a little test this morning though with the shunter and steamer and see what I can get.

[GHKtruc]

Looking at the wikipedia page for the Union Pacific Big Boy, it seems steam engines gain hp at speed. But 11 000 Hp seems a little off

[Metallos]

Originally posted by Randox:

Converted all that too into the usual units, and long story short I got a little over 11,000 hp. More if train weights are metric tonnes, but I want sure so I went imperial.

Metric is usual all over the world (except less than 5 countries)... And hp (1 hp = 735 W) is only in common speech due to historical reasons so power ratings are officially in W and as a sidenote in hp for some appliances like cars.

(Ok, steam locos are measured in hp but they are from times where hp was also common in Europe for vehicles)

[Randox]

On second thought, testing is actually problematic. Aside from trying to arrange an appropriate train, taking a refresh on the subject, measuring steam locototive power output is rather difficult, which is why it's a rarely quoted figure (and when it is quoted, heavily disputed).

I did some playing around with numbers for the Shunter. At maximum throttle, it usually tops out around 70km/h. It can go faster solo, but that's where trains usually top out, so I'm going to use a mass of 200,000 kg, and because I need a force, I'm going to use an acceleration of 0.5km/h/s, or 0.14 m/s^2, which is 27.8 kN. Plug that all into the power equation and convert to imperial and you get ~700hp.

Frankly, that seems high. To sanity check my numbers I looked up the only visually similar engine I am familiar with, which is a GE 45 ton switching engine[en.wikipedia.org], which has two 150 hp diesel engines. I can't say for certain without knowing what engine(s) the DE2 is might actually based on, but reading up on the GE 45, I would have to assume the engine was scaled up for game reasons, or I vastly overestimated the force. Cutting the force in half, which may not be unreasonable to do, drops the measued hp down to maybe 250-350, which would be reasonable I think. Not implausible anyway. Now we've quickly hit the point though where I can just change numbers until I get something I like. Accepting that the performance figures have likely been altered for gameplay reasons, something like 600-700 hp might not actually be far off in the game. For a real engine of a similar design though, that's way too high.

For the steam engine...steam engines are weird.

A steam engine can produce full torque at rest, which is very special. It also plays havoc with the power equation. Understand that power is not how hard a locomotive can push or pull. That is tractive effort (torque). Power is the rate at which work is done. Put another way, it's how hard the engine can pull multiplied by how fast it is going (among the many equations for power, Power = Torque x Angular Velocity).

As a steam locomotive speeds up, it looses tractive effort. When starting, the cutoff can be placed at maximum, and the pistons are being pushed directly by boiler pressure. Inefficient but very forceful. As speed picks up and the piston moves more quickly, you start to waste power forcing exhaust steam out of the piston. So you roll the cutoff back, which is efficient because now you are extracting more thermal energy from the steam, but the energy being put into each cylinder stroke is smaller, so there is less force. The increase in speed though more than makes up for this in the power calculations, to a point. The measured power of a steam engine at 2km/h starting a heavy train will literally be double the measured horsepower at 1km/h. When the train is starting off, there will be a moment where it is pulling with maybe a couple hundred kilo newtons of force and generating no power at all, because power is always zero until work is being done (speed has to be greater than zero).

At the end of the day, power ratings on steam locomotives are disproportionately affected by weight and speed.

Practical demonstration. Union Pacific Big Boy[en.wikipedia.org] and Union Pacific FEF-3 (Engine 844)[http//%5Bhttps]. The Big Boy is, well, the big boy. UP844 is a (very impressive) mixed traffic engine. The horsepower ratings are very close. We'll say 4,500 vs 6,000. The tractive effort is not even in the same ballpark however. The Big Boy has about 600 kN of grunt, vs 280 kN from UP844. Big Boy is more than twice as strong, but doesn't generate that much more power. Union Pacific's Challenger (a baby big boy, basically), is rated only 500 hp above UP844, but for 430 kN.

844 compares very well on power because 844 has 80 inch driving wheels and was intended to pull passenger trains at a continuous 90 mph, with a design speed of 120 mph. Big Boy has a design top speed of 80 mph, on 68 inch drivers (still a good size for a freight engine).

Anyway, that's enough math for me for one day.

[rgx107]

Based purely on speculation and my own experience, I think the diesel engines are weirdly modeled, and gain power at higher speed. I would expect the pulling force or wheel torque to halve when speed doubles, i.e. I have half the force at 40 km/h compared to 20 km/h, and at 80 km/h only one forth. The DE2 shunter though seems to wheel slip at speeds over 70 km/h, easily. To make it worse, I suspect this affects the fuel consumption too - assuming that the consumption is based on throttle position and time only, if you then get twice the power at 40 km/h or four times at 80 km/h, your fuel efficiency increases as well. I haven't driven the DE6 enough yet but suspect it's the same there.

[♣polkovnik♠]

DE6 this is a terrible power