Calculating Scale MPH... the only formula you'll ever need....

Model Railroader General Discussion (Model Railroader)
1

OK guys, here it is…

If you want your train to be traveling a certain scale miles per hour…

Q=(17.6M)/(SC)

Q=inches traveled in real time, M=desired mph, S=the scale (87 for HO, 48 for O, etc), C=the setting of your fast clock.

So to lets say…

M=30mph(scale) desired

S=87 for HO

C=4 because your fast clocks are running at four times normal speed

You get Q=(17.630)/(874)=1.52 inches/per real second

How fast is the train going? Simple…

M=(QSC)/17.6

(letter mean the same as above)

So a HO train traveling 6 inches per real second on a railroad that uses 4x fast clocks is…

M=(6874)/17.6

M=118.636 scale miles per hour (too darn fast unless your modeling a TGV or something like that)

For you metric folks:

Substitute the 17.6 in the above formulas with 27.778 to convert centimeters per real second to scale kilometers/hour.

Yes, this is the kind of stuff I think about.

2

Hit a F + Number Key and hear voice sprout speed number by single digits.

Speed Equals One One

or 11 scale mph.

Done. Easy peasy.

3

Back to the drawing board.

SCALE speed doesn’t change just because you choose to use a fast clock. All the fast clock does is make our midget main lines seem longer and shorten a day’s worth of operations into something a crew can handle between lunch and dinner.

For you HO-scalers, here’s a real down-and-dirty:

In 1:1 scale, 60MPH is 88FPS. Therefore, 60 scale MPH is 1FPS, well within standards for speedometer error. One inch per second = 5 HO scale miles per hour.

My own computations are metric, to a scale used only by those who model Japanese prototype. I won’t bother you with the details.

Chuck (modeling Central Japan in September, 1964 - 5:1 scale time, 2.5m SKM)

4

Speed is a function of time. By altering ‘railroad’ time, you need to include it in the formula to equate it to real time… don’t make me get all Einstein on your arse. [swg]

[zzz]

5

Thanks. Thank the Lord I got Pre algebra last year, lol.

6

I have another perspective to this question: What if you use “Smiles”? This was the term for shortened scale miles to give the impression of a longer mainline. I use these on my layout, where the mileposts are about 500 scale feet apart. That way, I can run mile long trains that fit in my sidings - using about 10 cars! If I used real scale miles, my mainline would be around a mile…

Would you scale the MPH to “smiles” or scale MPH?

7

That my friend is a whole 'nother can of worms.

Basically, if your ‘smiles’ are all the same, then you could include it in the calculations.

BUT if your ‘smiles’ are different in different places, then if you really cared that much, you’d need to think about it this way…

Let’s say your layout has three towns: Apple, Orange, and Lemon.

The distence in real feet between Apple and Orange is 15 feet.

The distence n real feet between Orange and Lemon is again 15 feet.

BUT! The ‘make believe’ distance between Apple and Orange is 15 miles, the distence between Orange and Lemon is 20 miles…

Now you would need different calcualtions for each area… fock me.

8

You don’t have to, “Get all Einstein,” on this long-time technocrat. You just have to realize that the scale time ratio and the scale distance ratio are supposed to be the same - and thereby cancel out (since your distance/time in full scale computation becomes R x distance over R x time, where R equals the scale time, scale distance ratio.)

Using Frank Ellison’s 12:1 scale time ratio, your formula would have a model loco running at 5 scale miles per hour. Even if your intellect was telling you, ‘It’s doing 60!’ your unmodified eyeballs will be saying, ‘I can jog faster than that!’

Wazzamatter? Too simple and straightforward for you?

Ever hear of the KISS principle? Try it, you’ll like it.

Chuck (modeling Central Japan in September, 1964 - and running at scale speed)

9

And, actually, it was Einstein who said, “Make everything as simple as possible, but not simpler.” I think he knew something about mathematics.

Tom

10

Whatever… I’ll just take my caculator and go gome. [D)]

11

a 1:1 scale vehicle going 1 mile per hour moves 1.467 feet per second. this is a standard. so 30 miles per hour is 44 feet per second, 60 miles per hour is 88 feet per second and so on.

a 1:87 scale vehicle is moving 1.467 scale feet per second at 1 mile per hour. 50 miles per hour will be 73.3 ho scale feet per second.