Can someone explain track radius to me?

[The Old Man]

For example, I don't understand why a track is called 22" radius instead of in degrees.

[Atlantic Central]

Radius of a circle = distance from center of circle to edge = 1/2 of the diameter of the circle. In the case of model train track, measured to the center of the track.

Degrees of circle = measurement of sements = complete circle = 360 degrees, 1/2 circle = 180 degrees, 1/4 circle = 90 degrees

The two have nothing to do with each other.

Model train track is not measured using the civil engineering method of degrees of change in direction - it is measured in radius.

Typical section track that comes with sets is 18" or 22" radius - making 36" or 44" diameter circles respectively. Typically 12 pieces of 18" radius to a circle and 16 22" radius to a circle - making each 18"R piece 30 degrees of the circle and each 22" radius piece 22.5 degrees of the circle.

Most more advanced modelers use flex track and larger curves in the 30" - 40" radius range.

Large/long locomotives and cars cannot negotiate tight curves like 18 and 22 inch radius.

Scaled down from real life, even a 36" radius curve in HO is very tight compared to what real trains run on.

Sheldon

[The Old Man]

Succinct!  Thank you.

[SteamGene]

In addition, most people wouldn't understand a turn measured in degrees.  And then I'd complain about degrees instead of the far more logical mils.   
Gene

[grumpy]

Sheldon
The radius of the curves used  on the layout has more to do with available space than it has to do with the sophistication of the modeler.Some of us even use EZ track and don't even count the rivets.

[Atlantic Central]

grumpy,

I did use the adjective "most" and I will admit I was raised to be an over acheaver who does not "settle" for mediocrity. So I made enough money to build a big enough garage to have a large enough room above it to have an 800 square foot layout with 36" plus radius curves.

But looking at many others I know in this hobby, my layout, its size and its cost is rather modest. Its all a matter of perspective.

Keep this in mind, scaled down to HO, the minimum radius of an EMD F7 would be 34". Our curves tend to border on rediculous - I do what I can to build model trains, not toy trains.

Sheldon

[ebtnut]

Maybe getting overly technical, but the measurement of degrees of curvature is as follows:  It is the number of degrees formed by a 100 foot long chord touching at either end of a circle.  The formula for computing radius from degrees is:  5730 divided by degrees of curve = radius in feet.  Most main line steam locos were limited to about a 15 degree curve, at low speeds.  This equates to a radius of 382 feet.  In HO, this would be about 52" radius. 

[bevernie]

 ???but, I've still got the question:
                           How do you know if the piece of track you are holding in your hand is 22" radius, or 15"? Perhaps the section that you need filled requires a 12"!!
                                                                             THANX!!
                                                                                Ernie

[SteamGene]

If you don't have the package it came in, try comparing it to a known piece.  If you know you have an 18" and the unknown is not as curved, you have a 22", if more curved, it's a 15".  If you need a 12" curve in HO you need to fall back and regroup, or take up street cars.
Gene

[r.cprmier]

Gene;
Circular Mils is not always the better way to express angle.

In my trade, we use degrees.  For example, three-phase power is measured one phase as 120 degrees out of phase in relation to the other two; thus the three legs will geometrically equal 360 degrees, or one revolution.

Circular mils is used in determining the area of a conductor, such as 200MCM would be 200,000 circular mils.  this aspect is essential component in determining a conductors rated ampacity.

I had always thought that somewhere in turnout computation that degrees was a computing component. 

Something that puzzles me, that maybe you do know.  In the movie, "The Enemy Below", the graphic expression on the u-boat's sonar screen puzzled me.  Every scope I have ever seen, it was expressed as a circle, with the respective boat as the centre, and everything radiating outward from it.  How was that German equipment set up?

Rich

[SteamGene]

Rich,
I have not seen, or do not remember the movie.  Hollywood can mess up the military something fierce.   All my real use of mils was in laying and firing artillery, and for that the mil is very useful.   Using mils for electricity is beyond me. 
Gene

[Virginian]

The radar scope on the U-boat in "The Enemy Below" was an accurate rendition of a German (I forget exactly what they called it !) scope.  If I remember correctly, the early British radar units, circa Battle of Britain time frame,  had a similar display.  Basically, if you took a round scope screen and cut it from the center to the top (although some may have been from bottom to center) , and then 'unwrapped it' counterclockwise to where it then ran straight out to the right, you would have the linear scope display.  You could adjust the range setting and the blip showed intensity and direction if I remember right.  All the old sets took a whole lot more skill to read them than (most of) todays computer readouts.
It's all in what you get used to using.  I had an early Loran with no graphical display, but I got so used to looking at latitude and longitude numbers and course tracks that I could look at the numbers and my brain did the math and I knew exactly which way to go to get somewhere.  A couple of friends had the graphical display style units on their boats and they were totally lost with my stuff.
Thaks for the reminder.  "The Enemy Below" is one of my favorite flicks.  One of Mitchum's best efforts.  Up there with "Thunder Road" for entertainment value.
Oh Gene, once upon a time a Va. Nat'l Guard battery, newly converted from a Nike missle battery to artillery, dropped a WP round in a motor pool because of the military's liking for zero to 3200 mils twice, rather than zero to 6400 mils.  It was not my battery, because at the exact same time I was arguing about the basic geometry of the situation with two lieutenants.  I believed some people learned something about turning people loose with artillery, live rounds, and a bunch of instruction books that day.  Just lucky they were 'only' 105s instead of the 155s they went to two months later.

[Terry Toenges]

Oh yah.... Thunder was his engine and white lightin' was his load.

[ebtnut]

I haven't played with HO sectional track for a long time, now, but aren't most of them marked somewhere with their radius?  I know the old Atlas sectional track had it cast into the bottoms of the ties. 

[Johnson Bar Jeff]

I haven't played with HO sectional track for a long time, now, but aren't most of them marked somewhere with their radius?  I know the old Atlas sectional track had it cast into the bottoms of the ties. 

I haven't had occasion to buy any Atlas for quite a few years now. I can't seem to locate the radius designation on the bottom of the my sections of EZ-track.