Transition Curves

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ChuckHackett-844
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Location: Tampa, Florida

Transition Curves

Post by ChuckHackett-844 »

Does anyone have a formula for 7.x gauge transition curves?

I have always done it "by eye" but can't in this case.

I have looked at "full size" formulas but didn't know if these would scale (we usually aren't running as fast, scale-wise) or if they were overly-complicated.
Regards,

Chuck Hackett, UP Northern 844, Mich-Cal Shay #2
Owner, MiniRail Solutions, LLC, RR Signal Systems (http://www.MiniRailSolutions.com)
"By the work, One knows the workman"
R Paul Carey
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Joined: Sun Sep 06, 2009 7:28 am
Location: Reedville, VA

Re: Transition Curves

Post by R Paul Carey »

As you have done in the past. I have located and maintained "transition curves", also known as "spirals" for smooth entry and exit from curves, all located by eye. I don't have a formula for this purpose. My trackage is 7-1/4" gauge, with a mix of Culp and other rail in scale between 85# and 115#. My spirals are variable in length between the tangent point (zero cross-level) and the point where the full body of the curve begins.

The maximum scale speed here is 45 mph on the main track. Ballast is pea gravel, track is raised and tamped by hand. In construction the body of the curve is formed first, upon the compacted subgrade.

My procedure starts with a designated elevation for a particular curve itself, usually between 1/4" and 1/2", measured by a clinometer I have built for this purpose. My primary reason for maintaining elevation is for safety of operation: to detect and correct REVERSE elevation before it appears. Passenger carrying cars are flat cars with individual bench seats affixed through the stake pockets on the flat cars. There are NO high center of gravity/mass "captain's chairs" in use here. No spirals are necessary for curves in yards or other areas that are limited to scale speeds at or below 20 mph.

Variation in ambient temperature and exposure to sun will produce a tendency of aluminum rail to buckle (in heat) or stringline (in cold). The spirals are a very useful area to adjust the track, lining to the outside in summer, or to the inside in winter, as your circumstances require. In this environment, I can think of no reliable formula that can produce year-round track stability any better than your trained eye.

If useful to you, I can send a photo of the clinometer I use to measure the degree and uniformity of cross-level.
Glenn Brooks
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Location: Woodinville, Washington

Re: Transition Curves.

Post by Glenn Brooks »

I would be interested in seeing your inclinometer. Post here on the thread if you can.

Also, can you give us an some idea of length of your spirals in relation to curvature, or overall length of the particular curve?

Thanks
Glenn
Moderator - Grand Scale Forum

Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....
R Paul Carey
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Joined: Sun Sep 06, 2009 7:28 am
Location: Reedville, VA

Re: Transition Curves

Post by R Paul Carey »

Here's the Track Clinometer, built upon a Mountain Car truck and using a common surveyor's plumb bob. Because of the minimal rolling resistance of this truck, the Clinometer also excels in locating minor variations in grade, as well.

From the "Zero Cross-level" mark at the center, the two marks to the right and left indicate increasing elevation of 1/4" and 1/2", respectively. The maximum designated elevation on this railroad is 1/2", equivalent to 4" in full scale.

Spirals are essential to avoid a "jerk" moment entering and leaving curves at speed. The length of any particular spiral is dictated by the degree of curvature and characteristics of the available space. The spirals here are between 2 and 4 feet in length, plus or minus.

The Clinometer photograph dates from 2015 when performing pre-season tie replacement, raising, and surfacing.

Also attached is a photo of a low center of gravity car, for the passengers. We don't use "captain's chairs" here.

This railroad, the "Sunnybank, Putnam, and Pacific", has been built through an old-growth forest, via a loop that returns to the origin point. In the trailing video, you will approach and pass the Clinometer's photo location at 2:51 minutes.

The following video (4:14 minutes) was taken in 2009 before construction of a turning loop and turntable at the origin. As a result, alternate trips in that period were operated with the engine (in this case, DL&W camelback 988), as on this trip, in reverse!

Rather than describe the feel of the curve geometry, you can better experience it virtually. The maximum speed (in scale) on this line is 45 MPH.

Enjoy! www.youtube.com/watch?v=WTiWVs_T1Fg
Attachments
Track Clinometer.JPG
For the Passengers.JPG
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Erskine Tramway
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Re: Transition Curves

Post by Erskine Tramway »

While maybe not as sensitive as Paul's version, here is my track surfacing car.
DSC_0037.JPG
Besides a level, it holds my stadia rod for raising track. There are a pair of 'hooks' that clamp the car down to the rail for lifting and levelling with the trailer jacks. Fortuitously, the stock-size pads on the jacks fit nicely between my ties. Here's a view of testing, before it was painted. I use my wife's old spading fork for ballast tamping, the prongs are spaced just right.
5-12-13 leveling.jpg
Mike
Former Locomotive Engineer and Designer, Sandley Light Railway Equipment Works, Inc. and Riverside & Great Northern Railway 1962-77
BN RR Locomotive Engineer 1977-2014, Retired
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