old thread but curious. How can a simple thought get more confused
sure, power varies at speed and torque, but so many steam engine ratings are noted at…like the nkp 765 64100 lbs tractive effort. All you want is a simple comparison to the diesel horsepower. So lets get a general ballpark figure than a rocket scientist description.
Well if the original poster wanted a simple answer, he should not have based his question on comparing an apple to an orange. Both steam and diesel locomotives have tractive effort and horsepower.
There is no formula to convert tractive effort alone into horsepower because horsepower is a measure of force and speed, whereas tractive effort is only a measure of force.
So the answer to the original poster’s question is no.
Yes, Quentin, I have seen, and may still have around somewhere, a circular slide rule. I do still have my 10" K&E slide rule, which I used in college when I did not need four or five place logarithms for my calculations. Now, did you ever see a 20" slide rule? one of my college friends had one; its case, which could hung from his belt, resembled a short sword scabbard.
I’ve still got mine from college.
I assume you guys are talking about the K&E Log log duplex decitrig. ( I threw that in to puzzle the youngsters.) I do remember in college seeing a round one and a 20-inch one.
I forgot about the one we had in the math classroom. It was about three feet long, was made of three tongue-and-groove boards–and had only two scales on it. It was used to demonstrate to the students who had never seen a slide rule how it worked for multiplying and dividing (adding and subtracting logarithms). You might have been able to read it to five places.
I was in one of those high schools that offered advanced Math/Engineering courses through the University, and we had one of those big “Demonstrators” for those of us with the GPA to participate and to get up to speed with slide rules before we went off to the college courses.
The personal slide rule was a hard steel, yellow Pickett Slide rule. High precision and good for self-defense as well …
I have a round one… 2nd one I got because I lost the first one. The first one was outstanding, but the one I have now was not well made and 2 x 2 does not equal 4 on it!
My brother had a Picket sliderule that he wore in a fancy leather scabbard on his belt. He said he wore it there so no one would “pocket his Picket”.
The steel Picketts came with a fancy hard plastic “scabbard” with both a belt loop through its leather covering, and a loop and clip. I never used the “belt loop” feature, which mimicked a gun holster or a Samurai sword I suppose. Last used that old slide rule on a motive power study in 1974. That Pickett is still here in my desk.
And yes, there is an accepted formula that converts tractive effort to horsepower at given speeds and it is the same formula for both Diesel-electric and Steam.
Most of the original power curves for steam and diesel utilized slide rules to make those calculations.
HP=(Tractive Effort x Speed)/375
Contrary to some of the comments, that “tractive effort” is a “railfans” view, the Tractive Effort is what is measured by the dynamometer car, FROM WHICH HORSEPOWER IS CALCULATED.
Tractive Effort is always the primary measure. Horsepower is always the secondary, calculated, measure.
The new math?[:)]
Au contraire mon ami…it is a perfectly made ‘quantum’ physics version which takes into account uncertainty. I mean, can we ever really be certain that one of the 2’s is really a 2?
[8-|]
Gee! I always thought it was just MY uncertainty in using a slide rule in the first place! It must actually be an artifact of my proving the Heisenburg principle wrong… I know both “Where” I was AND “When” I lost the first one.
The above tractive effort formula is correct, as long as you use the proper TE at each speed increment. However, dynamometer cars measure drawbar pull, not TE. TE at speed is calculated using mean effective pressure in the cylinders, which is estimated from indicator diagrams
Can we ever really be sure there is “effective pressure” in the cylinders? [^o)]
[:o)]
well then all the Diesel power ratings we see is deceptive. We can’t look at the basic ratings and compare just for the general interest without doing some rocket scientist calculations. It almost makes me think this is done on purpose to make the Diesel “look good” vs the steam engine.Just about every steam description I have seen says “Tractive Effort” and any diesel description says “Horsepower”. Duh.
Really, somebody somewhere decided this is going to be -THE- way to describe Diesel power. Fooey. Somebody fix this.
Dinwitty, I think that some of the explanations you’re seeking can be found in the book The Steam Locomotive, by Ralph P. Johnson.
There is no conspiracy to make diesels seem better than steam. But it is hard to state one common rating or measure of performance that is the most meaningful. Generally, the early diesels had considerably less horsepower than the modern steamers that they replaced. But diesels had the ability to M.U., so the horsepower disparity could be compensated for. And since M.U. operation adds more drivers, the tractive effort of diesels could rival or exceed that of a steam locomotive of equivalent horsepower.
But the greatest fundamental advantage of diesel over steam is the fact that a diesel can develop full horsepower when starting from zero speed, and deliver that horsepower when accelerating from a stop, as well as when lugging at near stall speed. Whereas a steamer cannot develop its full horsepower until it reaches its maximum speed
An SD90MAC-H has a starting tractive effort of 200,000 lbf. A Big Boy had a continouos tractive effort of 135,500 lbf.(no higher at starting). the MAC would pull the Big boy backward.
Electric traction motors produce significantly higher low end torque than a steam piston acting on a wheel does…
Anyone who wants to make the diesel look good will quote its so-called “Tractive Effort”, which would make a single F7 look comparable to a smallish 4-8-4. That would indeed be deceptive-- so you shouldn’t complain about diesel makers quoting horsepower.
And in most cases, all of a diesel’s weight is on the drivers - there’s no possible tractive weight lost to non-contributing pony or pilot trucks, or trailing trucks and tenders - except for when those are equipped with boosters.
Not quite - the diesel developing full horsepower is subject to/ limited by: