Calculated Performance Predictions for the 5AT
5AT Performance Predictions defined in Wardale’s FDCs
The “Deltic” performance predictions for the 80 tonne 5AT locomotive are astonishing when compared to similar sized locomotives of the “steam era”. It is hard to believe that a locomotive no bigger than a Standard Class 5 would be able to produce performances far superior to any British Pacifics of the steam era. Yet such predictions are based both on detailed engineering calculations and on the actual performance of “The Red Devil“, the sole member of the SAR Class 26 4-8-4 locomotive, as modified by David Wardale in the 1980s using the theories and practices developed by Ing. L.D. Porta in Argentina.
The calculations on which the performance predictions for the 5AT are based are referred to as the “Fundamental Design Calculations” or FDCs and were undertaken by David Wardale during 2002-2004, of which Part 1 is presented on this website. These calculations are split up into five sections:
- FDC 1.1 – “Determination of the Target Power and Tractive Effort vs. Speed Characteristics”, in which the “target” indicated power, indicated Tractive Effort (TE), drawbar power and drawbar TE are established;
- FDC 1.2 – “Determination of Target Load vs. Speed vs. Gradient Curves”, in which the drawbar TE values are compared to train resistance estimates to derive the maximum gradients that can be climbed over a range of constant speeds when hauling a 400 tonne train;
- FDC 1.3 – “Preliminary Basic Calculations” in which the axle loads, driving wheel size, cylinder stroke, boiler pressure, superheat temperature, adhesion limits and tender size are defined, from which the cylinder diameter is determined, steam and fuel consumption rates, operating range, indicator diagram, and exhaust emissions are estimated, all based on the target maximum indicated and drawbar power outputs..
- FDC 1.4 – “Tractive Effort Diagram” in which wheel-rim tractive forces are determined for each 15o rotation of the driving wheels at speeds of 113 km/h and 125 km/h in order to verify that slippage will be controlled under all normal operating conditions.
- FDC 1.3.F – “Preliminary Basic Calculations (Final Version)” – As stated in Note 1 of this set of calculations: “These calculations are the original calculations [FDC 1.3.] with data from other FDCs substituted for the original figures where it is different.”
See also Wardale’s chart comparing the Power-Weight ratios between the 5AT and various other well locomotives and diesel/electric multiple units.