Short explanation of the difference in calculating the tractive effort of compounding locomotives between 1924 ARA method laid out in Locomotive Encyclopedia and Locobase's guess about French and other methods.
The ARA method leans heavily on the difference in volumes between the high-pressure and low-pressure cylinders. The numerator of the formula takes the mean effective pressure of the boiler x the LP stroke x the LP cylinder diameter squared x a pressure lost factor of .85. The denominator divides the LP volume by the HP volume, adds one to that ratio, and multiplies it by the driver diameter. It's an attempt to balance the effort between the HP group and the LP group.
The French formula appears to balance the effort as follows: Calculate the tractive effort of the HP pair. To that add the HP tractive effort multiplied by a factor of somewhat less than 1 (.9, e.g.) to account for losses in the steam passages between high and low pressure cylinders.
Neither is entirely successful.
| Principal Dimensions by Steve Llanso of Middle Run Media | |
|---|---|
| Class | Compounding |
| Locobase ID | 2466 |
| Railroad | Compounding |
| Country | All |
| Whyte | |
| Number in Class | |
| Road Numbers | |
| Gauge | |
| Number Built | |
| Builder | |
| Year | 1998 |
| Valve Gear | |
| Locomotive Length and Weight | |
| Driver Wheelbase (ft / m) | |
| Engine Wheelbase (ft / m) | |
| Ratio of driving wheelbase to overall engine wheelbase | |
| Overall Wheelbase (engine & tender) (ft / m) | |
| Axle Loading (Maximum Weight per Axle) (lbs / kg) | |
| Weight on Drivers (lbs / kg) | |
| Engine Weight (lbs / kg) | |
| Tender Loaded Weight (lbs / kg) | |
| Total Engine and Tender Weight (lbs / kg) | |
| Tender Water Capacity (gals / ML) | |
| Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT) | |
| Minimum weight of rail (calculated) (lb/yd / kg/m) | |
| Geometry Relating to Tractive Effort | |
| Driver Diameter (in / mm) | |
| Boiler Pressure (psi / kPa) | |
| High Pressure Cylinders (dia x stroke) (in / mm) | |
| Low Pressure Cylinders (dia x stroke) (in / mm) | 26.5" x 27.6" / 673x701 |
| Tractive Effort (lbs / kg) | |
| Factor of Adhesion (Weight on Drivers/Tractive Effort) | |
| Heating Ability | |
| Tubes (number - dia) (in / mm) | |
| Flues (number - dia) (in / mm) | |
| Flue/Tube length (ft / m) | |
| Firebox Area (sq ft / m2) | |
| Grate Area (sq ft / m2) | |
| Evaporative Heating Surface (sq ft / m2) | |
| Superheating Surface (sq ft / m2) | |
| Combined Heating Surface (sq ft / m2) | |
| Evaporative Heating Surface/Cylinder Volume | |
| Computations Relating to Power Output (More Information) | |
| Robert LeMassena's Power Computation | |
| Same as above plus superheater percentage | |
| Same as above but substitute firebox area for grate area | |
| Power L1 | |
| Power MT | |