Going a bit further, the reason the torque of an electric motor drops off with speed is due to back-emf, basically a current induced by the rotation of the motor that “pushes” against the current that’s making the motor spin, which reduces the amount of current that’s actually spinning the motor, thus reducing its torque output. As to why this happens, remember that a motor and a generator are basically the same thing; the only difference is the direction the power flows. (This is also why dynamic/regenerative braking works)
Doesn't a similar effect apply to a steam engine? The faster the piston moves, the faster the steam has to go into the cylinder and out of it. Since the holes are fixed size, if the piston is moving faster, there should be higher back pressure from the exhaust and some resistance for the steam to go into the cylinder, reducing the force applied to the wheels. I do not know how relevant it is at the normal speeds though.
It's been a long time since my electrical engineering classes, but I think the back EMF explanation only applies to asynchronous machines. A synchronous machine such as an induction motor spins at the speed dictated by the frequency and number of poles. Torque is determined by current flow. Ultimate speed is capped by switching frequency capabilities of the electrical system, assuming the rotor doesn't fly apart. And ultimate power by how much current the windings can take before melting.
I've been turning something over in my mind related to this. The difference in TE for DC vs AC diesels and the rectification AC to DC then inversion back to AC.
Working for the Union Pacific, I've had this discussion with several employees about Tractive effort vs. Horse Power. Another thing to mention for modern locomotives. This is one of the reasons behind Slug Sets, having a pair SD40s switching yards. One Unit is a the "Mother" or controlling unit where the other has been completely stripped of it's generator and power assembles, leaving only the block. They fill the Fuel Tank with Concrete and add steel plates to bring the weight up. Then the Controlling unit it Hard wired to the Slave, or Daughter unit. We still have a single Unit that still only puts out 4000 HP but it now drives 12 Traction motors greatly increasing it tractive effort!
It’s really quite simple. Horse power is great but once you have enough more doesn’t matter. If you come up short is less of an issue because it just slows things down. Torque/tractive effort on the other hand… more is always better and when you don’t have enough everything stops. The two concepts are really two sides of the same coin.
That was the concept behind the baldwin centipedes, but unfortunately they were mechanical nightmares that never really had a chance to prove the concept.
@@Taskarnin Actually it is almost vice versa. You need enough torque/tractive effort to move a thing and more doesn't matter. But more power gets you more speed and allows more work to be done.
@@trex2621 quite the opposite… Torque is required for acceleration more torque the faster you can accelerate. Again torque and power are related mathematically. In fact you can’t even measure power directly (you measure torque and RPM…)
Someone described diesels being the best at starting with a heavy train while steam being the best as continuing with a heavy train and I think you just confirmed that.
Solution, steam loco with traction motors on the axles too. And a steam turbine and alternator. Can start out with electric power and switch to mechanical once underway 👌 maybe if its boiler is powerful enough, both methods at the same time, thinks of fletcher class destoryer boiler slapped on a big boy loco chassis 😂 with a steam turbine driving a dash9s genset and traction motors haha
@@jj3449 that would be cool, would probably need to modify the way the steam hits the turbine blades though i think, maybe with a rotatable vane like the chrysler turbine car has
My grandfather was an engineman on the D&H for 54 years, running both steam and diesels. When little, I asked him which was more powerful. His simple answer was "Diesels can start more, but steamers can pull more".
Im so fascinated on the amount of information you have in your blood.. Truly an Engineer.. not "just" a "train driver". Super interesting! Whenever I'm programming my own railroad game, I wanna ask you everything ^^
impossible to "drive" a train... since an engineer has no control of train direction (unless in a local or yard type job he helps a foreman/conductor), its controlled by other people. He controls (and now with GE, TO controls) forward and reverse motion.
He doesn't mention it but this Railroad Napkin math also explains why Super Heated Steam Engines were Light years better than their NonSuper Heated counter parts. This is why there's so much Argument on the true Capabilities of US steam engines(and which was actually the fastest in the world) cause a lot of this Information was kept from the general public's access to know.
Well there weren't slow by any means but they didn't recorded it official with a dyno cart so it is just saying hearing and after almost 100 years it is a bit of a stretch to say they were the fastest but I would say that they were competitive if they had picked up on the record hunt
@@TheLtVoss If the records are to be believed there were many who would of smoked Mallard for sure. The problem was a similar issue like what happen with the Twitter files ex posse also happened for the American Railroads between WW1 and WW2.
@@TheLtVoss I dont under stand how its a stretch that American locomotives truly held the record when they where substantial more powerful than british locomotives relative to their size. If the FEFs could reach 120+mph do you really think engines like the T1, or the MILW 4-6-4s, couldn't go faster?
@@whispofwords2590 you know why they used biger engines to pull more load that counters the max speed since you need more power to keep more load at speed and it needs a engineer with balls of steel and a great knowledge of the track to do any speed record and to be fair the A4 had many clever and for speed practical advances especially in efficiency too make up same power But it is what it is the record lays in the UK by the A4 since nobody challenged it
THANK YOU HYCE! I’ve been trying to grip my head around the horsepower v. tractive effort argument for years! This makes way more sense, and at least gives me a place to start in making my own calculations.
You can have all the horsepower in the world but TORQUE wins races. Think of torque as leverage and horsepower as the means to maintain it. Maintaining delivery is the limiting force.
The biggest consideration for diesel vs. steam was personnel costs as well as the cost to maintain, coaling and water towes, every 100 to 150 miles you hd to get water and grease the rods. It was the manpower requirements to maintain the steam engines, the cost of the manpower was alleviate by the arrival of the diesel option, less people required, plus the maintenance on diesel was greatly reduced compared to steam engine. Steam engines had no dynamic braking, diesel like the EMD FT had it for day one, the requirement to use car/train brakes was reduced. Depending upon load and grade drives the assignment engines and type AC or DC locomotives. Most trains on use two diesels along with THE DIESEL ENGINES comes the ability to be use a DPU either in mid train or end of train. Steam engines could be used in double header operation as well as helper, but they required full crews for each engine, again personnel costs. Great video thank you!
Thanks so much sharing this Hyce, always wondered how engines with 40,000lbs of tractive effort pulled cars that were 200,000lbs or more and never quite understood it but now it makes sense.
Moving a 100 ton car is actually fairly easy. Because of the extreme low rolling resistance of the car, a single man could move that car. I once saw a three year old girl move a four ton freight car truck.
@@FS2K4Pilot I think I saw a video of it somewhere. A local railroad actually used to use a tractor to push freight cars around. They finally got an old switcher locomotive but they used that tractor for years. Wasn’t even a really huge tractor, they used the bucket to push them.
Hi Hyce, I have been trying to explain this to my family and friends for years, but no one understands me or they want to argue about it. I really love this because you explain with science, math and excel time tables. Very cool, man!
This is a very interesting subject on the power output of railroad locomotives. We have an old saying that a steam locomotive can pull anything it can start and a diesel can start more than it can pull. On the subject of tractive effort for steam locomotives the constant in the formula is not always 0.85 as this depends on the maximum cut off a particular locomotive design. Older locos had a maximum cut-off of about 90% whereas later designs had shorter maximum cut-off to give better valve event openings at higher speeds. A constant of 0.85 for a 90% maximum cut-off is okay, however for a maximum cut-off of say 75% it would be necessary to reduce the constant hence reducing starting tractive effort for that particular loco design.
The railroad is a business, and the metric that matters is cost. The steam locomotive will pull a train from Point A to Point B at a certain cost. In the Post-War era, a new technology became available in quantity, which did the same job for around 85% of the old technology cost. So the steam technology built up over a century disappeared in less than a decade, because it was no longer competitive in the transportation marketplace.
I’ve heard an old saying, “a diesel can start a train it can’t pull, and a steam can pull a train it can’t start”. After you went through the math of everything that pretty much checks out.
You sir are excellent at explaining engineering concepts. This video is fascinating and quite a relief to finally learn this essential life information.
I’m more of a car guy than a train guy, but it is amazing how people underestimate the importance of Torque and the “power ban” (basically the relation between RPM, horsepower and torque). Also drivetrain loss, yeah you might have 1000hp, but you might lose 20% of that in the drivetrain while the guy next to you with 900hp might have a 10% drivetrain loss.
I have a book that has an interesting chart in it. The NP did a test comparing a 4 unit FT set (4500hp and 240,000lbs TE starting) with a Z5 2-8-8-4 (effectively 0 hp (starting) and 140,000lbs TE) The diesel set began to loose TE as soon as it started moving. Steam stayed level out to 12mph it was equal at 7-8mph, and from then on the TE war was won by steam. The gap closed a little, but clear out to 50 mph the Z5 had more TE, and at speed, vastly more HP. Another interesting story came from the Burlington Route. They tested a new 1500 hp F3A by coupling it to 10,000 tons. It actually was able to get this train moving, but it was unable to exceed 4 mph doing it.
It is worth mentioning that in any system power generated is determined by the load, or work being done. The engine determines the maximum power available. You can also calculate the power being used by multiplying the drawbar force over a distance and dividing by time in either minutes or seconds. Divide that result by 33000 (for minutes) or 550 (for seconds). The result is the net power being used.
So the current running of the 4014 & it's diesel would be the ultimate power setup for starting & speed. If it wasn't for the maintenance cost of the big boy, UP would probably try it. That reminds me, they used to do some crazy lash ups into the 50's when diesels we're taking over and the steam engines were being phased out. I seen a few historic videos of oddball big boy & challengers being paired with diesels, both as head end & pushers. Some of them for sure had 3 separate locomotive crews to move.
I love that you are a younger guy learning how this stuff was accomplished in the past. I grew up not too far from Mears Junction and worked at the Monarch Quarry in the 70s and 80s suppling limestone for CF&I Steel. I didn't know the Gunnison Museum existed until I saw your channel. I hope you have a wide following and I am impressed with the amount of knowledge you have accumulated. I hope kids today find your channel and learn lots. I love you and Kan's shenanigans!
Well I'm just a model railroader, collecting mostly stream locos of the PRR. They were gorgeous looking machines and heavy duty to survive the very long distances. I always thought that the only reason steam locos were eventually ditched was the high maintenance and the (supposed) fuel inefficiency, translates to $$$. I also know that Electro Motive Division was the only diesel loco manufacturer allowed to produce during WW2, that's why companies such as Alco and Baldwin came into financial trouble and the EMD E- and F-units almost single handedly replaced steam. Steam locos had a lot of problems such as wheel slipping and being hard on the tracks, but clever designs, cross balancing and superheating solved a lot of these.
Hyce, thank you so much for being the guy to explain this to me. I'VE BEEN SUFFERING WITH THIS TOPIC FOR MONTHS XD but all in all thanks for making great videos and I cant wait to see more from you man! Also give the K-37 a good run! Roll on Hyce, Roll on!
I really enjoyed your explanation on horsepower and Tractive Effort. I am researching information for one of my upcoming videos on Queensland Rail's C19 class steam locomotive. I qualified as a Fireman and Driver on Steam in 1999, so I have a reasonably good knowledge on their operation, but I never knew how train loads for each locomotive class were calculated. Thank you for filling in the blanks. QR had so many restrictions, it hampered their locomotives from reaching their full potential. Light line, wooden bridges and steep inclines with, at times 5chain curves. Not to mention we have a narrow gauge of 3ft 6". Cheers from Emerald Queensland Australia.
We have tractor pulls on RU-vid showing steam engines out pulling diesel engines. Now this also comes down to traction on from the tires but that steam engine never bogged.
I was expecting another chocho fanatic and I get somebody who's done his homework. Good job! Several points to consider: firstly the engine builders present all of this information in ways that make their product look good and the other guy's look worse. During the great pull off celebrated by electro-motive in the late 30s they knew that their diesel could outpull the steamer at 15 mph but the steamer would win at 25 so they loaded both trains to hold the speed down. Diesels have an advantage in that all of the locomotive weight is on the drivers just like Thomas the tank engine and it doesn't have to drag a 50 ton tender behind. (unlike some ladies who appear to have a 50 ton behind that's somewhat tender). Getting a steamer to start a train takes experience, less so for the diesel, and even less for modern ones with slip/slide controls. I used to marvel at the new GEs on the CSX pulling the night coal trains thru Pt of Rocks, MD as the computer calculated just how much each axle could pull without slipping. There are other reason why the railroads went diesel, a good short course in this is offered at Steamtown in Scranton PA allowing the spectators see them prepare a steamer for the day's tourist run. It takes a mechanic and his helper about FIVE hours to put this show on the road and they earn their money. If they used a diesel, the engineer would walk out to the yard where the locomotive was parked, he'd check the oil in the crankcase, then climb aboard and push the start button, when he had sufficient air for the brakes he'd drive off to pick up his assigned train. Tourist railroads that have any kind of mountain to challenge them will sneak a diesel into their consist, not to help on the way up, but to stop the damned thing on the way down, love those dynamic brakes. My father apprenticed as a draftsman with American Locomotive, Patterson Works (about 1910), so I got my training early on. The diesel engine is the most efficient means of turning fuel into power, even long ago it was about 30% (the rest is either radiated as heat or goes out the exhaust), the steamer struggles to make 10%. Everybody wants to paint the diesel as dirty and evile when in fact it is one of man's greatest inventions. Too bad it ain't sexy, that's why we love our chochos.
When I worked for the B&O many of the guys I worked with were veterans, both of WWII and Steam. The saying goes that a steam engine could pull a train it can't start, and that a Diesel can start a train it can't pull. That may have had something to do with the fact that older Diesel electrics use DC to power the motors and there was such a thing as "short time ratings," a limit of the time one can run in notch 8 below certain speeds without damaging the traction motors. On of my jobs as a yard clerk was figuring the tonnage of the trains we made up. After using an adding machine to determine tonnage (this was early 1970's and most of the tech was 1920's vintage) an additional seven tons per car would be added. I was told that was to account for the effort to overcome the frictional starting resistance.
This is so fascinating. Steamers and diesel-electric both have their functions but one lacks the other. Putting them together may result in getting what you'd need out of what the other is lacking. Not suggesting it always should be done. Diesel-electric and steamer personalities and functions are amazing even if the math melts brains
Great video! The exact same things apply to electronics and power grids. I am an amateur radio operator (ham). I currently have four radios hooked up to my 12 volt power supply. This power supply can provide 50 amps of 12 volt power. But since I am typing on a computer and not talking on my radio, my power supply is only drawing 1 amp of power while idle. If I were to key all four radios at the same time, the safety would kick in and I would blow a fuse. But luckily, I can run all four radios at the same time because I only have one mouth. The same goes for all of our power in our homes. I also have an extensive wood shop, but again, I am only typing on the computer and when I am outside, I can only run one device at a time (ok, 3, but...). Also, I am not in the kitchen so the toaster and microwave are not on, nor is the dishwasher (my stove, water heater, and furnace run on gas). So the same thing is with steam. There is a lot of potential power that is not actualized because of the innate inefficiency of the system (the exhaust and released steam while idle is a product of the inefficacy).
This is my first time here, and all I can this guy looks more like a gamer than someone going to teach me about mechanical engineering. The info is good though.
As a gamer I had to explain to several engineers why hydrogen can't economically compete with battery passenger cars, you have to judge people by how they talk about a Subject.
It begins to be really interesting when you introduce the adhesion into the math... I studied and transformed the formulae to derive the formula for the maximum gradient of adhesive railway in the introductory chapter of my master thesis about cog railways 👨🏼🎓
Love the background. I have a railroad lantern just like the big black one. Mine is red and needs a ton of work. I have a similar one to the smaller ones but mine has a solid base that you would fill with fuel. Also great video. I will probably watch it again for awhile because this reminds me of trying to figure out music. One day it just clicks. Great video Hyce it’s very educational it is wonderful
Most powerful locomotives ever built, if they had ever been fitted with the booster engines that they were designed to accept they would have also had the most tractive effort.
No, the 2-6-6-6’s, even if fitted with a booster, would not have had the most tractive effort of any steam locomotive. They had, if memory serves, 110,000lbs TE. A Northern Pacific Z5 2-8-8-4 had 140,000, PLUS a booster. The Alleghenies were very good engines, and certainly had tremendous HP, but they were never going to be the most powerful engine out there. What was tragic about them was that they were terribly misapplied. If assigned to flatter county with time freight, they would have been superlative! They were simply out of their element pulling drag freight in mountain country.
Holy arithmetic Batman ... I asked this question on one of your newer vids, and thank you for answering my question here. Now I can sleep at night :) I think I am going to call you the Professor of trainomics! Cheers!
I noticed that in the big table, the rolling resistance etc is already calculated in, so the result should be the weight of the cars already (17:10 - 3.8 million pounds of car weight).
This reminds me of a story Rich Melvin one of NKP 765s engineers. The 765 was on an excursion out of Corning, NY (I think, I may be wrong). The Conrail Road Forman who rode along with him kept suggesting to add a diesel to the train since there was a nasty grade out of Corning that the diesels kept stalling on. Melvin say no, and they start going up grade, and the Forman is worried so he suggests giving 765 more power. She was already doing 30, and now they are up to 32. The Forman keeps this act up until he realizes 765 wasn’t slowing down, but going faster.
I always enjoy when someone enters a steam traction engine in a tractor pull. There is a 150 horse Case tractor that typically pulls the sled clear through the course and only stops when it runs out of track. Super diesel tractors only make it half way.
That steam tractor was built by a young fellow from original blueprints. When he built that there were none of the original 9 that case built in existence.
@@dannthenitromanSteam engined vehicles are inherently heavier but the extra mass gives them more traction hence why those super old tractors do so well in pulling competitions despite their age. Same thing applies to locomotives: more weight means more tractive effort.
Another way to look at it is that power is the ability to keep producing tractive effort at higher speed. Two locos, same tractive effort but different power ratings will both start the same train on the same gradient, but one will pull it up the hill faster than the other. A few other points: the 'foot-pound' of work we're talking about is a pound of tractive effort, pulling a train forward one foot. One foot-pound of torque per second doesn't make sense - there's no change or movement in that second (or at least, you haven't defined how much movement). Although electric motors do reduce their torque at speed due to back-EMF, the main reason the torque falls, at least on diesel-electrics, is that the engine can't produce any more power so the torque must reduce as the speed increases. In crude terms, current creates torque but voltage drives speed, so you would have to supply the same current at increasing voltage which equals increasing power. In essence, remember that force × distance / time can be read both as work / time and as force × speed.
Very cool to actual see how the things do the things which I've always had a lose understanding since I know how a steam train works off a line and working at a grade with big load and always knew steam has a lot of torque which most people don't understand torque is what is more useful than horsepower which does get weird at the extreme ends
I always heard this explained as: Steam locomotives are constant tractive effort machines (provided ample steam production) but variable horsepower. Diesels are constant horsepower but variable tractive effort. As a result a steam locomotive can pull a train at speed which it can't start (due to static friction), and a diesel can start a train which it can't pull at speed.
The tractive effort curves I've seen for steam locos show the TE more-or-less decreasing linearly with speed. Incidentally, that puts maximum power output round about the point where TE is half the starting value (and in theory half the maximum speed!)
I remember having this discussion in 7th grade engineering, back when phones still had cords and attached to the wall. My teacher had the ever-popular tagline "Horsepower is what you see, Torque is what you feel." I then applied some 7th grade math for that to mean "So to get 8000hp it takes a minute, but I can have 8000ft pounds of torque right now?" Future genius moves evidently. 😁
I`m not a math guy but I wish we could have had these kinds of interesting kinds of practical problems when I was in university. I might have found mathematics more fun. Good presentation.
My preferred method for Railroads Online is to just hope for the best. Which sometimes leads to the unfortunate reality that my train of 12 loaded tanker cars cannot be pulled up the 2% grade I have to the refinery even with the Class 70. I don't want to have to buy the Climax for 2% grade though, I'd rather wait for an update with a bigger engine. For now I just get the class 48 I have at the refinery anyway to help out
I have won many a beer posing the question "what engine has 100% of its torque at zero RPM"? The pause can be almost painfully awkward when talking to a Gearhead. Torque is locked up in the boiler pressure.
Also, your RR Online sheet is better than my kludged together mess I use for Train Sim Classic, now I at least have some better math to throw at it. I can't wait for dovetail physics to cruelly betray me.
Your Excell spreadsheet is beautiful because it is simple to understand. Your explanation of the math is excellent. I think many people do not want to accept the validity and truth of equations like the ones you provide here. Instead, they make decisions based on emotions and can not figure out why things don't work out the way they willed them to.
The way I've always had the difference between them explained to me is "Diesel can start anything but steam can keep anything moving" and I think that's probably explained by all this.
Another reason why you typically see more than one diesel locomotive on a freight contest is actually because of redundancy purposes. The consist that the Challenger was pulling back in 1991 was brought in by three General Electric locomotives and while on relatively flat ground they can be pulled by just one of those locomotives at speed. I've actually seen it firsthand actually. I mean look at Amtrak. Do you really think they need to locomotive at 4200 horsepower each to pull 10 superliner cars? Descendants and it was also the same in the steam are not where they would try to make sure that they had enough power to get over the grade if one or more locomotives gave out. So in a way it's as much of a horsepower issue as it is a reliability issue.
@@Hyce777 Yes, I suppose not but it IS fascinating stuff - many people board aircraft and don't give a thought as to how the pilot has to calculate the load and balance for a safe flight (I'm also a pilot) on even a large airliner.
Brilliant explanation of who it all works. I learnt a quite a few things. And presented well. Hope your channel keeps growing, might make enough to buy your own engine :D p.s. Be interesting to see the numbers on the Garrats the NSWGR ran, they where mighty powerful units
This was awesome. Operationally, I understand why you need engineers - just in the mind set alone. Not only do you have to work out whar you can pull up an arbitrary grade, but what kind of forces are you dealing with as a train crests and part of it is still pulling backwards, and then more starts pushing down the grade more and more as more of the train crests. And that's not including a flat portion if any, No wonder you need calculus to figure out physics. Different forces with different vectors - ARG! Mind needs rebooting!. Naw, really, this is something that makes learning fun. I took me three times to get a C in my calc I class. I know what a limit is conceptually, but ask me to figure it out or apply it, much less figuring out integrals, I'd need to go back to school. A lot more to it than pull lever, make train go fast.
I saw something recently on the BR standard 9F where they were originally rated for pulling 900 tons but on the final run for the class they pulled 2200 tons... Now that is a locomotive I would love to see in Derail Valley
They could also easily do 90mph in service, and some even went the ton. It was advised against because of the small drivers, but it could be done. And I still don't fully understand how it did it. It had no right to be as good as it was, but it just worked.
That’s one time when being small and light is an advantage, because it makes your connecting rods smaller and lighter, and thus easier to balance. The Pennsy had a 2-10-0 that made 96,000 pounds of tractive effort, but it had to have side rods that were so massive that you couldn’t properly counterbalance them on a 63” driver (I believe the same size as those on the 9F), so they rode like shit. If you went 90 in one of those, you’d get drawn and quartered by the track gang, right after the Road Foreman of Engines skinned you alive. This, of course, assumes you didn’t derail your engine and kill yourself and your crew.
This was really an insightful video man! Thank you for the technical aspects which are so obviously overlooked in many instances. My dad and grandfather always bragged on the power of steam. My grandfather was on and around them in the 40s. The airplanes, cars and trains were so interesting then. They weren’t such a standard unit. There were all sorts of clever thoughts and engineering to compromise on a myriad of aspects in these vehicles. I love mechanical linkages and really anything mechanical that has now been replaced with non moving electronics. I understand the parts that don’t move don’t fail so often but preventative maintenance and inspections well also. Great info bud!! Keep it up 💪🏻✌🏼
is there a reason why the formula uses bore diameter instead of radius? pi is canceled out by wheel diameter, but area of a circle is still pi*r^2, so where does the extra coefficient of 4 come from to make it d^2 instead of r^2?
great explanatiom. however, I did catch one error in your description of work. work is force applied over distance, for instance you push a box across the floor. you push with a force of 10 lbs, and you push it 10 feet. that is 100 foot-lbs of work. however you descirived touque for instance you apply 10 lbs of force on a 10 foot lever, you also get 100 foot-lbs of torque, but if it takes 200 ft-lbs to turn the nut (or whatever you are turning) no work is done, and it gets more confusing because a simular unit of energy is used in balistics to the energy of a projectile.
They need more horsepower to overcome the lack of inertia at the start of a pull. As the engine gets up to speed the kinetic energy of the train’s weight also plays into the equation.
My man you must be doing something right cuz I'm a car guy, never really found trains that interesting personally, but I saw this video, it caught my eye, and kept me til the end. Great video and really interesting math related to these engines, didn't realize steam was that powerful!
2:34 Ft·lb is energy and lb·ft is torque. Dimensionally, they're the same, but are not interchangeable. Power is torque times angular velocity, or energy (work) over time. Conflating the two is understandable but won't work for calculations.
You know hyce, every time I am out railfanning with my dad, when the train is about to thunder by us standing beside the tracks, I always say what you said in the Horn battle video:
Something I have been wondering for a while is when you go to measure the diameter of the Driving wheel, do you include the tire or is it just the wheel? Also I love how you know the math about Tractive Effort, I need to see what Jupiter's and #119's are, thanks Hyce!
Of course you need a lot of horsepower for acceleration and to go uphill at substantial speed, which might be less important for bulk freight but when travel time counts it's important. It also improves line capacity greatly if freight trains go almost as fast as passenger trains, so they fit better between them.
Another great one, Mark! You also just reminded us all why automotive horsepower ratings, although impressive in TV ads and in product brochures, offer no tangible effects that the occupants of the vehicle can realistically feel. Applied torque in big numbers and at the right spot in the power curve, however, is what puts the big, satisfying smile on your face and pisses off your wife when you stand on the accelerator pedal. Well done.
I've found it frustrating trying to compare the pulling power of steam and diesel engines, since Wikipedia gives steam engines' tractive effort in pounds of force and kilonewtons, while diesel engines' tractive effort is given in horsepower.
An engineer on the old Pennsylvania RR told me that a diesel electric (or pure electric) can start a train it can't pull, and a steam loco can pull a train it can't start. Easy peasy!
Thank you, great summary, As a ship conventional steam chief engineer both reciprocating and turbine plants. I always wondered how a locomotive engineer could gauge power/speed/ efficiency. I understand comparison like this are kind of like are apples to oranges. I always assumed regulator on a steam locomotive acts like a throttle valve on a ship, keeping boiler pressure constant and regulating the amount of steam admitted to the steam chest for a requested speed? I get the concept of tractive effort (assumption, weight on the driver wheels= or slip or ship cavitation of the propeller) . Unlike Locomotives(except dessert service) shipboard we recover the exhaust steam as condensate to send back to the boiler and used fuel consumption to calculate efficiency. great presentation, thanks.
Congratulations, you've almost rediscovered what engineers have known for a long time. HP is an important number. It tells you how much work something can do per unit time. Torque (what tractive effort substitutes for) is also an important number, including the RPM at which that torque occurs. Hence, both are usually specified. In general it's also important to understand how those numbers vary with RPM. in the case of a locomotive (or car, truck etc) that needs to operate over a fairly wide RPM range you would much rather see a lower peak HP and torque and have it produce a usable amount over a wide operating range. On the other hand, you might be looking at a Genset that operates at just one specific RPM. In that case you'll be more than happy to optimise for an extremely peaky output at that specific RPM. It might be absolutely useless as a traction motor but exceptional numbers at that one RPM are what count cause you're not using the rest of it anyway. So no, HP isn't bad. Far from it. The whole thing comes from the blatantly stupid idea that this is a dichotomy. You don't want HP or torque. You want HP _and_ torque and your application decides how you want both of them delivered. It's really not a difficult concept. The issue is simply the prevalence of scientific illiteracy, idiots in marketing departments and fools with soapboxes and an agenda.
Odd for a person standing on a soapbox to speak negatively about others and their soapboxes. Try not talking down to people who are probably just as smart, if not smarter than you, in other areas and maybe the public as a whole would be more informed. I.e. try to stop coming across as a self involved asshole
Steam engines should have maximum torque at zero RPM, supposing that you have a two cylinder with dual acting cylinders. A 4 stroke ICE needs 5 cylinders or more to not have dead spots, but a dual acting steam cylinder is essentially a 1 stroke engine, since every stroke is a power stroke. Two cylinders 90° out of phase means that you always have a cylinder able to generate torque(not at top or bottom dead center) on its power stroke. That isn't totally true however. Maximum filling of the cylinder can be achieved at zero rpm, but the pressure wave of steam filling the cylinder is higher pressure than the steam is. Here is further explanation. Steam engines are similar to gasoline engines, in that they can use timing advance. For a steam engine, typically there are two extra linkages attached to the valve gear, one can reverse the valve timing to reverse the engine, the other one can advance or re t ard (that word gets auto flagged) the valve advance. On a gasoline engine, the spark plug ignition timing is advanced as the rpm increases. With steam, there is a delay, the speed of sound in steam at x temperature, for the steam to fill the cylinder, so it is beneficial to begin filling earlier as rpm increases. With both engine types, ICE and Steam, there is zero torque while the engine is at top or bottom dead center, and maximum torque when the connecting rod is tangential to the crankshaft rotation, in other words the connecting rod is at 90° to a line drawn from the crankshaft center to the rod journal. This angle for maximum torque would only be 90° ATDC with an infinitely long connecting rod, and before then with a finite length connecting rod. Rod-Ratio is the measure of connecting rod length divided by piston stroke length, this ratio tends to be between 1.5 : 1 to 2 : 1 on gasoline engines, and around 3 : 1 on steam engines. Both Steam and combustion flame front can only travel at the local speed of sound, and both act as a sonic pressure wave as they propagate through the cylinder. That pressure wave is itself energetic, and higher pressure than the volume behind it, it is helpful to think of it as a tidal wave of sound. So, peak torque on an internal combustion engine, and a steam engine, occurs when the engine speed is such that: the sonic pressure wave of steam filling the cylinder or combustion propagation strikes the piston near peak torque crank angle, 40°-50° ATDC in Gasoline and later in steam, and the piston speed is close enough to the local speed of sound that the piston rides the pressure wave on its downwards stroke. If the piston speed is faster or slower than the speed of sound inside the cylinder, you lose torque, and also if the timing isn't properly advanced such that the pressure wave strikes the piston near peak-torque crank angle, you lose torque.
