In my previous post, I mentally wrongly combined two separate items of correspondence between EMD and Clyde, one referring to the Queensland GEs and one outlining the "Model G" locomotive.
I attach below the "Model G" letter, which outlines the design considerations for an export road switcher. One imagines the correspondence on the GP7 might have been similar.
GENERAL MOTORS CORPORATION
LA GRANGE ILLINOIS
June 28, 1951
TO ALL ASSOCIATES -
Nydqvist & Holm Aktiebolag
The Clyde Engineering Co. Pty. Ltd.
Re: Standard Narrow Gauge Locomotive
We are giving very considerable study to a design of a standard narrow gauge diesel electric locomotive. Our studies are directed primarily to the following:-
A. A roadswitcher type of dimensions such that the construction can be standardised for a wide variety of clearance diagrams with minimum structural modifications limited if possible, to the cab.
B. Space to provide alternatively for our 8 or l2 cylinder engine, but with a preference for the 12 cylinder rated at 1000 HP, bearing in mind that this size is more competitive in price (7% increase in weight, 7% increase in cost, up to 50% increase in horsepower) and that derated to this output the engine can use practically any grade of fuel or lube oil.
c. Mechanically driven auxiliaries reduce weight and cost and facilitate local manufacture of maximum locomotive parts.
D. Four traction motors, type D19, which will provide a maximum locomotive speed of 50 miles an hour and a continuous rating of 24,000 pounds.
E. A Total locomotive weight approximating 150,000 pounds
The principle remaining relates to the number of axles and on this we would welcome your comments.
A. We are satisfied that 4 driven axles are sufficient.
B. To provide maximum performance, best adhesion, low center plate, minimum weight transference, short wheel base, better ride, we much prefer a 2 axle truck. Although the axle load will be 37,500 pounds, we can, we think, prepare technical data, perhaps tests, to establish that this is no worse than a steam locomotive with an axle load of 25,000 pounds. (Cooper rating E25). We realise that it would be difficult to convince Civil Engineers that this load is acceptable.
C. The alternative of providing a truck of the normal three axle type with two driven axles is objectionable in that it increases the truck wheel base, the locomotive length and the cost.
D. The primary purpose of this letter is to invite your reactions to a suggestion which the writer made to Mr. Dilworth.
Mr. Dilworth is not presently attracted as he feels that the suggestion is outside the normal range of Electro-Motive previous experience.
On several previous designs by competitors, they have used what is basically a 2 motor, 2 axle truck, and have interposed central third axle of small wheel diameter, to reduce the axle load on the driven axles. It is possible that in our design such an axle could be accommodated without increasing the wheel base beyond say 9', and without substantial increase in the -locomotive weight.
It has been suggested such an axle would normally be attached to the frame by a leaf spring, and that it would not have any brake rigging, and would be designed so that, within fixed and standardised dimensions in the spring plate sizes, the number of plates could be readily varied to the weight carried on the center axle.
It is believed that there is some commercial advantage in this suggestion in that it would allay the fears of Civil Engineers. We think it is probable that over the course of time it would be regarded as a dispensable part of the truck and would, in fact, be removed when maintenance standards had risen and when the Civil Engineer's confidence had satisfied him that it safe to use the two axle truck without the center axle.
Since a recent design of this sort for the Ethiopian Railways originated from Europe, we would welcome the comments of our European associates.
We would appreciate it if an early reply could be sent, as this design is actively under study at the present time.
Very truly yours,