Turn radius HO scale to real

[storknest]

Hi,

I'm trying to figure out what the HO turn radius masure out to in real world scale. Such as what an 18" curve is ini real feet.

I believe 0.138" HO = 1' real

So what would be the math formula for this? I'm thinking I divide 18" by 0.138" to get the result, which is about 130.4. Is that correct? Thanks.

Eric

[NZRMac]

I went 18" X 87 for scale, then divided by 12 came to 130.5

Ken.

[cacole]

No real train except perhaps a Heisler or Shay could ever go around a radius that was equivalent to what we use on our model layouts. We would probably need a football field sized room to model accurate curves.

[dinwitty]

The scale world has compromised a lot to get the stuff to run the sharp curves.
many mass produced articulateds have both driver sets rotating to take the curves, the prototype never did.

[johncolley]

Not a football field is needed! A 10 degree railroad curve (572.9 feet actual radius) is kind of tight and might need a speed restriction, scales out to 88" radius in HO. At least one modular group uses that as their minimum radius, and they look great!. Some other modular groups s go down to as low as 48" mainline and 36" branchline. Others use 42". It all depends on what size rolling stock you plan to use. With modern era cars and locos and/or full size passenger cars (85 foot) you really need a large curve radius with easements or they just look like toys. Enjoy!

[Anonymous]

There is one place I know of in my area where the track has a minimum 335-ft. radius-- The return loop under Grand Central Terminal in New York City.

That's pretty darn sharp, but Amtrak and Metro North has had no problems negotiating it with their very long P32AC-DM Genesis locomotives or with 85-foot-long Amfleet coach or Budd EMU cars. Very impressive.

[tomikawaTT]

There is one 'open country' traction line that, if built in American HO, could be modeled on a kitchen table. The curves scale out at 13 3/4 inches!

It's standard gauge, sports 8% grades and, in the 1960's, had heavy-duty dynamic brake grids on the car roofs. It also has numerous tunnels, spectacular bridges and three switchbacks. On top of that, the country it traverses is absolutely spectacular.

Google "Hakone Tozan Railway." The odakyu.jp/english/ link is the most informative, but didn't work here when I tried to add it to this post.

Chuck

[Don Gibson]

The Tehachapi loop works out to 7 FOOT radius and we want to talk inches?

[ddechamp71]

Other option: use Z scale ([;)]): a 10° curve is only 80 cm / 32" radius.....That's what I'm doing with my in progress empire, in a place where I should be able to work on an honest HO layout....

Dominique

[Anonymous]

QUOTE: Originally posted by storknest

I'm trying to figure out what the HO turn radius masure out to in real world scale. Such as what an 18" curve is ini real feet..... which is about 130.4. Is that correct? Thanks.Eric

Sounds right Eric. There is a chart on the N.M.R.A. web site under RP-11. A 20" radius in HO scale is 146' for the prototype.
However, railroads generally don't measure curved track by radius, but rather in degrees.

[ericboone]

According to my Pere Marquette locomotive diagram book, various locomotives can handle the following minimum curves:

Diesel :
SW-1 100 ft
70 ton 75 ft
NW-2 100 ft
E-7 274 ft or 21 deg

Steam:
0-8-0 16, 19, or 20 deg
2-8-0 18 or 20 deg
0-6-0 25 deg
4-6-2 20 deg
2-8-2 16 or 19 deg
2-10-2 16 or 19 deg
2-8-4 20 deg

According to the previously linked NMRA document, 20 degrees equals a 231 ft radius or 32 inches in HO scale. The sharpest any steamer could handle was 25 degrees, which according to the NMRA document, is 193 ft or 26.5 inches in HO scale. The least flexible locomotives could handle only a 16 deg curve, which correlates to a 359 ft radius or 49.5 inches in HO scale.