The International Steam Pages

Researching a Track-Friendly Modern Steam Locomotive

Harry Valentine, Transportation Researcher,  writes:

In selecting locomotives, most railway companies seek suspension designs that extend the life expectancy of rail wheels and curved sections of rail. Rail wear on curves is caused mainly by the interaction between wheel flanges with the inner sides of curved rails. One method of reducing the flange/rail interaction, has been to use steerable railway axles on axle trucks (bogies) that keep wheel flanges tangent to the curvature of the rail. Traditional Stephensonian-types of steam locomotives with rigid driving wheelbases can be modified so as to reduce wear on wheel flanges as well as on curved sections of rail.

The 2-2-2 wheel arrangement could be adapted for modern railway operation, by keeping all wheel flanges tangent to the rail curvature, thus minimizing both flange and rail wear. The bolster-mounted non-powered outer axles would each be connect to the locomotive centre line via a pivot located near to and on either side of the central driving axle. The steerable outer axles would be mechanically cross-linked, a feature that would counteract the locomotive's yawing tendencies. The 2-2-2 could be expanded into a 2-6-2 wheel arrangement, where outer non-powered axles the centre driving axle would be flanged, while the outer non-flanged driving axles would have widened steel tyres. On a curve, the flanged axles axle would align with the curve radius, greatly reducing flange/rail wear. 

The 2-6-2 could be expanded into a 2-10-2 concept, where the 2-non-powered outer axles would be Krauss-Helmholtz bogies that would pull the non-flanged outer drive-axles (#2 and #6) sideways on curves. The 2-10-2 layout using a Stephensonian cylinder and side-rod drive system could be a heavy-haul, low-speed concept with flanged wheels located only on the 2-cross-linked non-powered outer axles and on the central driving axle. In operations where extra weight needed to be carried, extra non-powered axles could be added at either end. If the locomotives were essentially uni-directional, two non-powered trailing axles could be closely spaced and mounted on the same suspension sub-assembly, with one axle flanged and the other non-flanged. 

A 2-axle (4-wheel) non-powered leading bogie/truck could be adapted to steer its axles so as to keep them aligned with the centre of rail curvature. The bogie/truck would be bolster-mounted to give it a degree of controlled lateral freedom, while it would also be connected via a mechanical linkage to the trailing non-powered axles. This linkage would counter yawing tendencies, restricting the non-powered axle sets to moving laterally only in the same direction as would happen in a curve. If the locomotive were to be developed for bi-directional operation, the 2-axle (4-wheel) steerable bogies/trucks interconnected by a linkage, would be located on either side of the rigid driving wheelbase. While an odd number (3 or 5) of driving axles on the rigid wheelbase would assure minimal rail wear from the central flanged driving axle, an even number of driving axles (eg; 4-8-4) may also be used, but only the two inner driving axles would be flanged on a 4-axle driving set.

The concept using a 3-axle rigid driving wheelbase would lend itself to a variety of drive-train and steam engine concepts. It could be developed for higher-speed freight operation pulling intermodal trains, or operate excursion passenger/tourist trains. The traditional side-rod driving system could be modified to be gentler on the rails, while retaining its simplicity, efficiency and reliability. Side-rods are a rotating mass that can be dynamically balanced. Two side-rods can be closely spaced inside the same casing, their cranks set 90-degrees out of phase and the entire system dynamically balanced to drive a rigid 3-axle wheelbase. The casing would be located outside of the wheels and drive the axles through flexible quill-drives that could allow vertical wheel movements while also reducing unsprung mass. 

Two large crank-counterbalanced 90-degree Vee-2 steam piston engines would be mounted next to the non-flanged driving axles, on the opposite side of the locomotive, transmitting power to the axles through flexible quill-drives. Low unsprung weight would be maintained on the axles, eliminating the "hammer-blow" effect that could otherwise damage the rail joints. Henschel built a steam locomotive that used 4 x 90-degree Vee-2 steam engines, driving the axles through flexible couplings. More recently, Ted Pritchard (, a steam power developer from Australia, proposed to use highly efficient modern uniflow (inlet valves, exhaust ports) 90-degree Vee-2 steam engines to drive railway axles using a variation of this same layout.

Higher horsepower and torque can be provided from piston steam engines on this locomotive concept, if needed. Research precedents from the Honda Motor Company as well as from Ducati have shown that fully counterbalanced narrow-angle Vee-2 engines are possible. Three narrow-angle Vee-2 steam engines may drive all three driving axles from the same side. The side-rod case would ensure higher starting tractive effort by reducing wheelspin on any single axle. The short length of the Vee-2 engine may be maintained while increasing total engine volume, by "twinning" each cylinder. Parallel cylinders would be connected to common sliding crossheads driving common connecting rods, in turn driving the single-throw counterweighted crankshaft. The volume and power of the short 90-degree W-4 engine would be double that of the Vee-2 engine. A narrow-angle, counterbalanced split-pin crank W-4 engine layout would also be possible.

The drive arrangement involving an enclosed side-rod case on one side and counterbalanced steam piston engines on the opposite side of the locomotive, with both connected to the axles through flexible quill-drives, would provide several advantages:

1) It would eliminate hammer-blow effects on the rails due to low unsprung mass.
2) It would provide high starting traction due to the linked drive system.
3) It would greatly reduce rail and wheel flange wear on curved rail sections.
4) It is a gearless drive system, reducing maintenance requirements and costs.
5) The drive system will use roller bearings, raising mechanical efficiency.
6) The roller bearing drive train will offer long life and require low maintenance.
7) The side-mounted steam engines offer easy access for easy maintenance, easy inspection, easy removal and easy engine replacement.
8) The side-mounted side-rod drive case offers long service life, easy access, easy removal and easy replacement.
9) The Vee-2 steam engines could be complimented with a rotary steam engine to allow for higher power availability at higher rail speeds.
10) It is an efficient mechanical system that reduces the cost, the complexity and the efficiency losses incurred when using an electrical power transmission. 

An alternate method of increasing horsepower at higher rail speeds, would be to use a rotary steam engine in the system. This would require that the side-rod drive case would link 4-shafts on a 3-axle drive system. The rotary steam engine would be located outside the rigid driving wheelbase, perhaps ahead of the first drive-axle. Among the various rotary engine choices, there is the quasiturbine engine from Quasiturbine Group of Montreal, Quebec, the Rand Cam engine from the Western Railway Group of Boise, Idaho, and the "Mighty (Mi-Ti) Engine" from California. Despite not being a true rotary engine, this latter concept is very compact and has high power output potential.

All three rotary engines can deliver high power outputs at high speed (900-RPM) and may all need to drive through a planetary reduction gearbox placed between the rotary steam engine and the side-rod drive case. At speeds below 25-miles/hour, the Vee-2 steam engines would provide all the tractive effort. The Mighty Engine and the quasiturbine engine could be blended-in at speeds above 20-miles/hour, at which speed the Vee-2 engines could be reset to their lowest possible inlet-valve cut-off ratios (as low as 15%). The Rand Cam engine would be best blended in at speeds above 30-miles/hour. 

Both the Rand Cam and the Quasiturbine engines offer the potential of high levels of engine efficiency, due to their "uniflow" operational characteristic. The Mighty Engine is a concept still under development. All three engines have the potential to excel at high speed freight operation (above 50-miles/hour), as well as in passenger train operation up to 100-miles/hour. Unlike a steam turbine that has to operate at over 80% of its maximum design speed to deliver a high level of thermal efficiency, the Quasiturbine, Rand Cam and Mighty Engine can operate efficiently at 25% of maximum design speed. The quasiturbine offers a high level of zero-RPM starting torque when 2-such units are set at 45-degrees out of phase to each other. To date, these three engines have been dynamometer tested using pressurized air and can all be adapted to steam operation.

Rob Dickinson