how to figure the grade

[gregc]

mobilman44

One point that is important.....and to me this applies to the incline going from my below level staging up/down to the main level.  The incline should be measured in rather long increments.  Said another way, the grade should be checked in its entirety to assure consistency - especially if any curved trackage is involved.

Said a third way.......... a two percent grade should be two percent for each fraction of that incline - and not 1 percent here and 3 percent there, etc.

both points sound contradictory

I would agree with the first -- the grade should be made over a distance equal to the train and that it doesn't matter if it's 1% in spots and 3% in others.

[mobilman44]

Sorry for the confusion....brain drain I guess.

If one is building grades on the layout itself, do whatever suits your purpose.  What I was addressing - and did not make myself clear - is the grade that I have going from the lower and semi hidden staging area up to the main level.  My calcs came out to a 2 percent grade during the design phase.  This would give me a big enough rise to allow sufficient clearance to get to the lower level staging, while still allowing my locos to pull up a decent sized train.

But anything more that 2 percent would substantially cut into what the locos could pull, so I had to make certain that every part of this winding incline was a 2 percent grade and no more in any section.  I should have clarified that beforehand.

 

[gregc]

mobilman44

But anything more that 2 percent would substantially cut into what the locos could pull, so I had to make certain that every part of this winding incline was a 2 percent grade and no more in any section.  I should have clarified that beforehand.

what I don't understand is why does "every part" of tha grade have to be 2%?

what can't some parts of the grade be 2.5% and others 1.5% as long as the total grade --  level difference over the length of the longest train -- is 2%?

If a longer train (e.g. 10 cars) can handle 2%, shouldn't a smaller length train (e.g. 7 cars) behind the same locomotive be able to handle a section with a higher grade (e.g. 2.5%)?

[BroadwayLion]

gregc

what I don't understand is why does "every part" of tha grade have to be 2%? what can't some parts of the grade be 2.5% and others 1.5% as long as the total grade -- level difference over the length of the longest train -- is 2%?

Any change in grade is another opportunity for an uncoupling or a derailment. Tracks must be smooth both horizontally and vertically. A smooth transition from 0% to 2% will pass through 0.2 0.4 0.6 etc etc on its way to 2%, and then back through them smoothly to 0%.

Any dips will derail or uncouple your equipment.

The rule of Thumb (I do not know *why* Thumb must make all of the rules...) is there must be a full car length before you can transition from a right curve to a left curve.

I would offer the same rule for vertical curves.

Keep it simple. Keep it smooth.

 

That said, the LION's railroad *does* look like a rollercoaster in some places.

So if it works, it is OK, but LION runs 50' subway cars. A big steamer, or some 85' passenger cars may have a different opinion of the LION'S track work.

 

ROAR

[gregc]

BroadwayLion

A smooth transition from 0% to 2% will pass through 0.2 0.4 0.6 etc etc on its way to 2%, and then back through them smoothly to 0%.

my point is that the grade can smoothly transition from 0% to 3% and back to 0% and still be no more than a 2% grade over the length of the longest train.

[mobilman44]

Greg C...........

My incline from main level to "hard to reach" lower level staging was painfully built so as it is entirely at a 2 percent incline.  Two (IMO) is the max grade I wish to use, and anything more will cut into what amount of cars I can bring up.  Anything less reduces ther vertical clearance from the main to the staging level below.   That is all pretty straight forward, and what I chose for my current and previous layouts.  

For your or anyone elses, you can choose "whatever".

[gregc]

mobilman44

My incline from main level to "hard to reach" lower level staging was painfully built so as it is entirely at a 2 percent incline.

What is important is that the change in height over any section of the incline for the longest train length never exceeds the desired grade.

And if you apply easements as Lion discusses, then it's not possible to not exceed a 2% grade over a short stretch (a few car lengths) if the total change in height is 2" per 100".

 

[floridaflyer]

dante

 

floridaflyer

Of course if there is a curve in the grade that has to be factored in as it will increase the %of grade.

 

 

 

 

It will increase the effect of the grade on the pulling power of the loco because of the added friction of the curve but it will not increase the actual % of grade: rise/run formula remains the same.

Dante

 Very true, left out the word effective in my post

[cuyama]

Since this is a needlessly resurrected thread that likely no one cares about, the point is probably moot, but there are things being posted that could be confusing for someone who actually wants useful information.

If a model grade increases from 2% to 3% in the middle for any appreciable length, 3% becomes the ruling grade. Trains don't "average" the grade.

The transition from level to the desired grade takes about one car length per degree of nominal grade, in my experience. So there's a short run of vertical transition or easement, then the grade itself, and then another vertical easement back to level.

It is certainly possible to ease the grade a bit through curves to keep the effective grade closer to the nominal grade, but again one needs a bit of a transition between the different gradients and we often don't have that kind of length in the model.

[carl425]

cuyama

If a model grade increases from 2% to 3% in the middle for any appreciable length, 3% becomes the ruling grade. Trains don't "average" the grade.

When you watch a train going into a grade (no BEMF) it starts to slow down.  As more of the train hits the grade, it slows down more.  Only when the entire train is on the grade is the slowest speed reached.  This IMO demonstrates the averaging effect that Greg was talking about.

[gregc]

the thread is still a search item.

cuyama

If a model grade increases from 2% to 3% in the middle for any appreciable length, 3% becomes the ruling grade. Trains don't "average" the grade.

I don't understand, assuming that only part of the train is on the 3% portion of the grade.

if a train is approaching a grade and half the train is on the flat and the front half is on the grade, the locomotive is not working as hard as if the entire train were on the 2% grade (neglecting the easements).

similarly, I assume that if half the train in on a 1% grade and  the other half on a 3% grade, assuming equal weight for each half of the train, I would think that the locomotive is only working just as hard as if the entire train were on a 2% grade.

and similarly, if a train were cresting a hill, and half the train was going up and the other half were going down, the locomotive would be working the same as if the entire train were on a flat grade.   Gravity is pulling each half of the train down, the front half forward and the rear half backwards.

I think the physics does average the grade

[cuyama]

gregc

I think the physics does average the grade

Depends on the length of the train and the length of the higher grade and the easements from one gradient to another. One can construct as many hypoheticals as the number of angels dancing on the head of a pin, but from a practical standpoint on real layouts where there are signficiant variations in the grade there will be difficult spots that affect the engine more than the "average" grade over a long run. (The same is true of the real thing)

In my humble opinion, it's better to plan and build with typical best practices in mind.

[gregc]

Of course there will be the "difficult spot" on the grade.  I agree that it depends on the length of the longest train.   I think this is being practical.   If your not sure, you can always design conservatively.

But I think the full scale railroads are sure and will work things out to a sufficient number of decimal places to know whether they need to have a few less cars rather than waste fuel on an extra engine.

i think it's confusing to say that a 2% grade can't exceed the grade at any point on the grade.  

[cuyama]

gregc

But I think the full scale railroads are sure and will work things out to a sufficient number of decimal places to know whether they need to have a few less cars rather than waste fuel on an extra engine. i think it's confusing to say that a 2% grade can't exceed the grade at any point on the grade.  

I am just as sure that it would be confusing to newcomers, that's why I interjected. On the real railroad (and thoughtfully designed model railroads), the concept is called the "ruling grade".

If a real life railroad division has 95 miles built on 1% grade and 5 miles built on 3% grade, the grade calculation that matters to performance is not the 2% raw mathematical average nor the 1.1% grade/mileage average. It's that 3% ruling grade.

It's like the guy who says "I have a 24" minimum radius -- except for one mainline curve that is 18"." Nope, that’s an 18" minimum radius mainline. It’s the worst point that dictates.

Since to me there’s no use in arguing contrived hypotheticals and I’ve been able to include some practical information for anyone who resurrects this thread in another ten years, I’ll bow out and you all may continue as you like.

[gregc]

cuyama

If a real life railroad division has 95 miles built on 1% grade and 5 miles built on 3% grade, the grade calculation that matters to performance is not the 2% raw mathematical average nor the 1.1% grade/mileage average. It's that 3% ruling grade.

well of course it's a 3% grade if the length of the train is less than 5 miles.   Aren't most trains maybe a 1 mile long (100 50' cars).

but other parts of this thread have suggested that the grade is the maximum measured over less that a foot by the inclinometer.

[carl425]

gregc

but other parts of this thread have suggested that the grade is the maximum measured over less that a foot by the inclinometer.

Nobody suggested that.  I posted that picture in response to a comment made about the "Grade Gauge" from Walthers.

I assemble 8-12' sections of subroadbed with the risers clamped to the joists.  I then go back and permanently attach the risers and use this level to set the grade between each pair of risers to be the same as the calculated grade for the whole section.

While I don't believe the sky will fall if the grade is not exactly the same for the entire 12' of the section, I do try to make it that way.

[richhotrain]

Well, as cuyama pointed out a few replies back, this is a needlessly resurrected thread from 9 years ago.  The original question, how do I figure the percent on a grade, was fully answered by our fellow forum member, Selector, in January, 2009.

Rich

[oltmannd]

BroadwayLion

The rule of Thumb (I do not know *why* Thumb must make all of the rules...)

Speaking of rules of thumb...

A model railroad grade really doesn't need to be stated in more than 1-1/2 significant digits.  e.g. 1%, 1.5%, 2%, etc.  

[carl425]

richhotrain

The original question, how do I figure the percent on a grade, was fully answered by our fellow forum member, Selector, in January, 2009.

So what's new?  Virtually every thread on this forum carries on long after the original question is answered.

[richhotrain]

carl425

 

 

richhotrain

The original question, how do I figure the percent on a grade, was fully answered by our fellow forum member, Selector, in January, 2009.

 

 

So what's new?  Virtually every thread on this forum carries on long after the original question is answered.

 

Yeah, true, but this old thread was dead and buried, and if you look at the reply that revived it, it is all of two words that seem intended to do nothing more than bring an old thread to the surface for no apparent reason.

Rich