Who would win in tug of war Big Boy vs. EMD DDA40X?

You can find a good bit of info on the question here....as stated in the article, the power curves of steam vs. diesel are totally opposite, with diesels having a big advantage at starting a heavy train and at low speeds.

http://de.answers.yahoo.com/question/in ... 703AAuFPLK

Re the comment about the drawbars being the biggest losers... I think the Milwaukee actually did stage a "tug of war" between one of their then-new electric locomotives and an articulated steamer... except that, in deference to the drawbars, it was actually a head-to-head shoving match (which the electric won handily).
So, small change of visuals, but the fantasy match-up can go ahead.

I put my money on the DD40A: electric traction motors have smooth torque, so my guess is that the piston-powered drivers of the Big Boy would slip first.

(When the SD70MAC was introduced, and EMD man with a sense of history remarked that EMD now, finally, had a single-engined unit which could out-pull a (Norfolk & Western) Y6b.)

timz wrote:But a DDA40X doesn't have a huge advantage over a 4-8+8-4. It may not have any.

First question: are we talking about an actual DDA40X, which had 59:18 gearing?

Unless we modify it, the diesel's control system won't allow an instant buildup of tractive effort. If it takes, say, 10 seconds to build up full TE, the 4-8+8-4 might well outpull the diesel for the first few seconds. So we need to know what a diesel's TE is at minus-3 miles/hour-- will it be able to stop its backward motion?

By the way-- in a tug of war, the 4-8+8-4's tender will be an equal burden to each engine. Think of it this way: what if the tender weighed a million tons? Would that improve the diesel's chances of winning the tug of war?

The DD40AX has 8 electric traction motors turning it's driving wheels and all axles are powered. The Big Boy has 4 steam pistons turning it's drivers. An electric motor produces more low end torque than a steam cylinder. Again, it is not a matter of which machine has higher maximum Horsepower but which has the higher starting tractive effort..
Advantage Centennial

Allen Hazen wrote:Re the comment about the drawbars being the biggest losers... I think the Milwaukee actually did stage a "tug of war" between one of their then-new electric locomotives and an articulated steamer... except that, in deference to the drawbars, it was actually a head-to-head shoving match (which the electric won handily).
So, small change of visuals, but the fantasy match-up can go ahead.

I put my money on the DD40A: electric traction motors have smooth torque, so my guess is that the piston-powered drivers of the Big Boy would slip first.

(When the SD70MAC was introduced, and EMD man with a sense of history remarked that EMD now, finally, had a single-engined unit which could out-pull a (Norfolk & Western) Y6b.)

When the Milwaukee Road did their "push of war" the steamer at first pushed the electric easily. Once the engineer of the electric started to throttle up his unit the steamer eventually stopped and was then shoved backwards by the electric.

Stuart

Find a bunch of really heavy duty steel cable and a huge pulley with some giant anchor, bring these to Kenefick Park in Omaha NE and we'll find out.

"I'll go light the firebox in the Big Boy, you watch out for cops"

Here are the specs I've been able to find for both models:

Big Boy
Horsepower: 6300 (approx)
Weight on drivers: 540,000 lb
Starting tractive effort: 135,000 lb

DDA40X
Horsepower: 6600
Weight on drivers: 545,000 lb
Starting tractive effort: 134,000 to 136,000 lb

These numbers are remarkably similar, and at first glance would suggest a dead heat.

However, there are some crucial differences between steam and diesel-electric power that some people have already pointed out. Above the wheelslip threshold, a diesel-electric is a constant-horsepower machine. A steam locomotive generates a flatter tractive effort curve until steam pressure drops at higher speeds, and it is only at higher speeds that it can develop full horsepower. At low speeds, the tractive effort of the DDA40X would be limited only by the adhesion of the wheels, since electric motors can smoothly produce immense torque from a standstill. In contrast, the Big Boy would also be limited by steam pressure, meaning that it could not develop anywhere near full horsepower at lower speeds. Its power delivery would also not be as smooth. The advantage here goes to the DDA40X.

Of course, with modern AC motors and wheelslip controls, an SD70ACe or ES44AC would out-pull both of these units. Even the SD70M-2 can produce an additional 30,000 lb of starting tractive effort.