Development of the First Gas-Turbine Mechanical-Drive Locomotive

REALIZING THE TACTICAL ADVANTAGES of simplicity and good cold-weather operation, the Transportation Corps of the U. S. Army initiated a study in 1950, of the application of gas turbines to railway motive power. This preliminary study resulted in the following conclusions:

1. There existed the need for an extensive and practical study of this type of power which promised to supersede conventional forms of engines in many applications.
2. Further, there existed the need for a study of mechanical-drive applications to gas-turbine locomotives since the gas turbine has inherent torque characteristics which are ideally suited to a mechanical transmission.
3. These needs could be satisfied and invaluable experience could be gained economically by building a lightweight experimental locomotive which would be suitable for both switching and light road service and which would be comprised of as many standard components as possible.
4. The study of this small locomotive would be a direct approach to larger applications.

This paper is a summary of the progress thus far attained in the execution of this project.

MECHANICAL CONSTRUCTION

In the interests of roadability in spite of the light weight, it was decided to use a standard 30-ton switching locomotive with a 2-4-2 wheel arrangement. This then indicated a power plant with a horsepower rating of from 180 to 360 hp, on the basis of 6 to 12 hp per ton. Design details based on these specifications resulted in the construction of the locomotive.

The chassis was built by the Davenport Besler Corporation, Davenport, Iowa. It is a 30-ton, standard-gage, 2-4-2 locomotive with the cab mounted on one end and a hood which encloses the power plant mounted on the other end. The main frames and bumpers are rolled-steel slabs and the frame assembly is welded to insure maximum rigidity and strength. The spring rigging consists of semi-elliptic and equalized springs supporting each journal box on the drivers and coil springs on the trucks.

Side-rod coupling is provided between drivers as only one axle is driven by the transmission. The journal boxes are of the Timken taper-roller-bearing type, designed to take all thrust and radial loads.

The locomotive is supplied with Westinghouse schedule 6SL straight and automatic air brakes, a hand brake for holding the locomotive when not in use, air sanders designed to sand the rails ahead of the locomotive for either direction of travel, AAR type E couplers with release rigging operable from either side of the locomotive, footboards at both ends of the locomotive, front and rear headlights individually controlled, an air horn, and an air-operated bell.

A 200-gal-capacity fuel tank is provided. While this is considered extremely small in view of the high rate of fuel consumption of a gas turbine (approximately 50 gph under full-load conditions for this application), it was found that it was impossible to provide a larger capacity without a major revision to the frame of the locomotive. Such a revision to an otherwise standard item would impose a high cost which did not seem justifiable in an experimental locomotive.

POWER PLANT

The power plant was built by Boeing Airplane Company, Seattle, Wash., and consists of two Boeing Model 502-2E gas turbines which operate in parallel through a combining gear. The complete power plant including accessories is mounted on a base which can be removed from the locomotive frame as a unit to facilitate maintenance and overhaul. The Boeing Model 502-2E gas turbine consists of two major sections, namely, a gas producer and a power-output section. The gas producer contains a centrifugal compressor coupled to a single-stage axial-flow turbine, two combustion chambers, and an accessory-drive section. The power-output section incorporates a second axial-flow turbine, reduction gears, and an output shaft, and is joined to the gas producer by a duct.

Mounted on the gas-producer section of each turbine is a 24-volt combination generator starter which serves the dual purpose of starting the turbine and charging the battery once the turbine is running.

Control of the turbine is accomplished by means of a governor which controls the speed of the gas-producer section. The governor setting is pneumatically actuated by the operator's throttle lever.

The fuel supply for each turbine is turned on or off by an electric solenoid valve controlled by a switch located at the operator’s position. Provision is incorporated into this circuit for automatic turbine shutdown in case of low lubricating-oil pressure or output-turbine overspeed.

The turbine as installed is designed to operate on diesel fuel. However, it is possible to run the turbine on other fuels such as jet-engine fuel, kerosene, gasoline, or light fuel oils, with minor adjustments to the turbine.

Power from the two turbines is combined to drive the transmission at reduced speed through a combining re-duction gear. The output of each turbine is coupled to the combining gear through an overrunning clutch which allows single-engine operation of the power package.

An air compressor for the brakes and control air is driven off the output of the combining gear. This compressor is an air-cooled, two-cylinder, two-stage type with approximately 40 cfm displacement.

Mounted behind the engines and above the transmission is the lubricating-oil-cooling assembly, which consists of four separate cylindrical radiators, one for the oil from each turbine, one for the combining gear lubricating oil, and one for the transmission lubricating oil.

TWIN-TURBINE CONCEPT

The decision to use two turbines instead of one was based upon indications that such a setup would result in the following advantages:

1. Better fuel economy at partial load. One characteristic of the gas turbine which is a disadvantage for vehicle application is that the fuel consumption at partial load is extremely high; e.g., at one-quarter load the fuel-consumption rate is about 60 per cent of the full-load rate in quantity of fuel per period of time. The use of two turbines partially obviates this disadvantage since at half load one engine can be shut down, thus using the running engine at its peak efficiency.
2. Either turbine can be used to carry the base load. Thus, if one turbine should break down, it would be possible not only to get the locomotive back to the shop but also to do a limited amount of work using the remaining turbine.
3. Permits derating the turbine to increase life. The Boeing Model 502-2E is normally rated at 175 hp at standard conditions. However, in this particular application each turbine has been derated to 150 hp by limiting the maximum speed of the gas-producer section. Further, the time required to accelerate the gas-producer section from idle to full speed has been increased from 4 to 6 sec by adjusting the acceleration limiter in the fuel control. It is anticipated that the life of the turbine will be increased appreciably by these adjustments since the speed of the gas producer and the temperatures encountered during acceleration have a marked effect on turbine life.
4. The increase in weight and space is negligible because of the low-weight and compactness characteristics of the gas turbine.

MECHANICAL DRIVE

The output of the combining gear is coupled to the input of a Model TG-602 “Torqmatic” transmission which is manufactured by the Allison Division of General Motors Corporation. This transmission consists primarily of a compound planetary-gear train, which is in constant mesh, and provides, through the action of hydraulically actuated clutches, gear ratios of 4.4:1, 2.33:1, and 1:1. Positioning of the ratio selector which controls the hydraulic actuation is done by a four-position pneumatic cylinder with manual selection by the operator.

The Torqmatic transmission is capable of making quick shifts under full loads at wide-open throttle without interrupting the power flow from the turbines to the drivers. As will be pointed out later, this characteristic proved to be a disadvantage for this application.

The driving wheels are powered by the Torqmatic transmission through an axle-hung transmission which not only provides right-angle drive to the drivers but also serves as a reversing transmission thus providing, in conjunction with the Torqmatic transmission, three speed ranges in either the forward or reverse direction. Shifting of this transmission is done by a two-position pneumatic cylinder with manual selection by the operator.

PRELIMINARY-PERFORMANCE ANALYSIS

An analytical study of the performance and operating characteristics of the twin-turbine power plant installed in the locomotive promised several desirable characteristics.

Among these are a top speed of 35.5 mph, a maximum tractive effort of approximately 15,000 Ib, and the ability to haul 18 loaded freight cars at 18 mph, or 5 loaded cars at 34 mph.

For the purposes of the analysis it was assumed that the two turbines would drive through the combining gear (gear ratio—-1.375:1), the Allison Model TG-602 Torqmatic transmission (gear ratios of 4.4:1, 2.33:1, and 1:1), and a driving axle having a gear ratio of 6.7:1. In the calculations allowance was made for a 20-hp auxiliary load (air compressor, etc.) and a transmission efficiency loss of 10 per cent.

A slip point of 15,000 Ib tractive effort was determined by using a coefficient of adhesion between the track and the driving wheels of 0.30, since the turning moment produced by the turbines is uniform. Use of this value assumes reasonably clean drivers and rails.

Owing to the experimental nature of this locomotive, the operator is confronted with an array of meters, levers, and switches. The proper manipulation of these controls is rather complicated as little attempt has been made to provide automatic controls.

SHAKEDOWN TESTING

On May 7, 1954, the locomotive was towed out of the shop and into the yards of the Davenport Besler Corporation for its initial running and shakedown testing prior to delivery. First one and then the other turbine was fired and after the necessary last-minute checks were completed, the locomotive was put in gear and moved for the first time under its own power.

In the two weeks that followed, the locomotive was run almost every day and accumulated approximately 5 hours of operating time on each turbine. As can be expected in an experimental item, innumerable “bugs” developed and had to be corrected. The locomotive ran smoothly and its tracking ability was excellent even on the very rough track encountered in the yard. The acceleration, even under load, is not only smooth but remarkably fast for a locomotive of this size.

SHIFTING SHOCK

During the course of the shakedown testing it became apparent that one “bug” was going to give trouble. When the Torqmatic transmission was shifted into gear from neutral the locomotive drive train was subjected to a severe shock. This shock was caused bythe combination of two factors, namely, (1) the quick engagement of the Torqmatic transmission, and (2) the kinetic energy of the revolving parts ahead of the transmission which include the combining gear, the air compressor, the output-turbine wheel, and related shafting. The shock was so severe that, with the brakes released, a transmission engagement would produce a wheel slippage of approximately 10 deg.

A reinvestigation of the problem showed that the end rate of transmission engagement was far too fast for this application.

It was obvious that some solution to the problem must be devised before the locomotive could run any further—otherwise extensive damage might result. A pneumatically actuated hand brake on the transmission input shaft was added as a temporary expedient. This slowed the shaft to a point where a smooth engagement could be made but it also required one more control the operator must remember to use. Studies are being conducted to determine if there is a way in which the transmission can be modified effectively to slow down the engagement, thus eliminating the need for this transmission-shaft brake.

COMBINING-GEAR FAILURE

Fifteen days after the locomotive was first started, the effects of the shifting shocks proved to be too much for the combining gear. The locomotive had just finished a series of simulated switching tests when it was decided to make an acceleration run of the locomotive alone, using both engines. This run was normal up to the point of the second-to-third gear upshift, at which time there was a loud breaking noise and both engines shut down due to overspeed. An on-the-spot investigation showed a jagged hole in the combining-gear housing.

Subsequent teardown of the combining gear revealed serious failure of all its components. The final drive-gear hub and spider were shattered and all gears showed considerable tooth damage. The bearings and the housing, except for the hole, were undamaged.

Analysis of the failure has shown that the loads imposed by the shifting shocks were greater than anticipated in the design and that the repeated shocks caused the failure.

To prevent the recurrence of the combining-gear failure the combining gear was redesigned to provide greater strength, and the Torqmatic transmission was modified to slow the clutch-engagement time.

These changes were to be followed by delivery of the locomotive to the Rock Island Arsenal, Rock Island, Ill., for a 3-month operating test.

ADAPTABILITY TO MILITARY USE

The development of the 30-ton gas-turbine locomotive has led the author to the following conclusions concerning the design of gas-turbine locomotives for military use:

1. The gas turbine offers distinct advantages over the diesel engine for military use, viz., reduction of field maintenance, simplicity, unit-replacement practicability, and good cold-weather operating characteristics.
2. The gas turbine lends itself readily to mechanical drive even though several outstanding design problems are involved.
3. The gas turbine has several unique characteristics which must be taken into account when a design is formulated, viz., high rate of fuel consumption (larger fuel tank), and simplicity and compactness (more room for other items).
4. The twin-turbine concept with proper control is an important answer to the problem of the relatively high rate of fuel consumption at partial loads.
5. The control system should be designed so that the operation of the locomotive from the operator's viewpoint is similar to a diesel-electric, in order to avoid special training.
6. The gas-turbine mechanical-drive combination will outperform a diesel-electric of the same engine-output rating.
7. The gas turbine as a form of railway motive power is here to stay!