Coupler offsets and angular mis-alignments on curves

Couplermis01

The picture above shows a model of a B&SR 26 foot boxcar (left) and a model of a B&SR 34 foot flatcar (right) on a piece of Precision Scale flex track curved to a 48″ radius on the centreline.

The table below lists the calculated coupler offset (radial displacement from the nominal centreline) and angular mis-alignment (angle between the coupler centreline and the track centreline at the coupler position) for a selection of Maine Two Foot rolling stock on curves of various radii. Note some pieces of information are missing. Modellers in scales other than 1:48th should note that the figures below have been calculated from scaled dimensions and geometry only. They do not include any allowance for wheel-set clearance within on the track gauge, and can therefore be scaled up or down for different modelling scales.  

The intention is to show how these parameters increase with decreasing radii.

Curve Coupler Coupler Coupler Coupler
radius Radial Radial Angle (F) Angle (R)
(ins) offset (F) offset (R)

(degrees)

(degrees)

Boxcar #47

30

0.138

7.05

Boxcar #73

30

0.161

8.82

Coach #17

30

0.367

12.32

Coach #18

30

0.313

11.40

Loco, #7 & #8

30

0.137

0.450

5.61

10.02

Boxcar #47

33

0.125

6.41

Boxcar #73

33

0.146

8.01

Coach #17

33

0.334

11.18

Coach #18

33

0.285

10.35

Boxcar #47

36

0.114

5.87

Boxcar #73

36

0.134

7.34

Coach #17

36

0.306

10.24

Coach #18

36

0.260

9.48

Loco, SR&RL #6

36

0.065

0.224

3.55

6.46

Loco, #7 & #8

36

0.114

0.375

4.67

8.35

Boxcar #47

42

0.098

5.03

Boxcar #73

42

0.115

6.29

Coach #17

42

0.263

8.76

Coach #18

42

0.224

8.12

Loco, SR&RL #6

42

0.056

0.193

3.04

5.54

Boxcar #47

48

0.086

4.4

Boxcar #73

48

0.100

5.5

Coach #17

48

0.229

7.66

Coach #18

48

0.195

7.1

Loco, SR&RL #6

48

0.049

0.168

2.66

4.84

Loco, #7 & #8

48

0.086

0.282

3.51

6.26

Boxcar #47

60

0.069

3.52

Boxcar #73

60

0.080

4.4

Coach #17

60

0.180

6.12

Coach #18

60

0.156

5.67

Loco, SR&RL #6

60

0.039

0.135

2.13

3.88

Loco, #7 & #8

60

0.069

0.226

2.8

5.01

Boxcar #47

120

0.034

1.76

Boxcar #73

120

0.040

2.2

Coach #17

120

0.092

3.06

Coach #18

120

0.078

2.83

Loco, SR&RL #6

120

0.019

0.067

1.07

1.94

Loco, #7 & #8

120

0.034

0.113

1.4

2.5

1/. Rolling stock refers to B&SR/B&HR examples unless otherwise noted.

2/. Boxcar #47 is a 26 foot long boxcar with 18ft 6in truck centres. This is the shortest example of normal revenue carrying freight car found on the B&SR/B&HR. Similar sized freight cars were common to all Maine Two Footers.

3/. Boxcar #73 is a 34 foot long boxcar with 27ft 6in truck centres. This is the longest example of revenue carrying freight car found on the B&SR/B&HR, and on any of the Maine Two Footers.

4/. Coach #17 is a 48 foot 9 inch long coach with 34ft 9in truck centres. This is the longest member of the passenger car fleet of the B&SR/B&HR, and is fairly representative of a number of B&SR/B&HR and SR&RL stock.

5/. Coach #18 is a 46 foot long coach with 32ft 6in truck centres. This is the shortest member of the passenger car fleet of the B&SR/B&HR.

6/. Loco #7 & #8 are Big 2-4-4T Forney type locomotives, prototypes weighed 32/35 tons and measured just over 33 feet long. These are the largest of the Two Foot Forneys and similar sized locomotives were found on the SR&RL system.

7/. SR&RL Loco #6 is a small 0-4-4T Forney type locomotive, the prototype weighed around 15/18 tons and measured 25 feet 6 inches long. This is a typical Maine Two Foot Forney, and similar sized examples were found on all lines.

Couplermis02

The picture above shows the front of SR&RL Locomotive #6 (left) and a B&SR 34 foot flatcar (right) on a piece of Precision Scale flex track curved to a 48″ radius on the centreline.

Couplermis03

The picture above shows the rear of SR&RL Locomotive #6 (left) and a B&SR 34 foot flatcar (right) on a piece of Precision Scale flex track curved to a 48″ radius on the centreline.

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2 thoughts on “Coupler offsets and angular mis-alignments on curves

  1. Pingback: Minimum radius, big Forneys and tight gauges, – some numbers! | The Maine On2 FAQ

  2. Pingback: Locomotive model minimum radius | The Maine On2 FAQ

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