Adhesion is Adhesion !!


M

MarkInLA

Guest
Though most of us subconsciously already know this from day 1 in the hobby, it's still something when you actually ponder it; the very fact that our model locos adhere to the rails thru thee very same science/mechanix as the 1:1 scale to gain traction and overcome inertia !! Big or small, it's the same !! That's so cool when ya really think about it, huh ?! M
 
Also the reason, as a 12yr old, with my first OO loco, with a cast metal shell, I liked the weight to size ratio in my hand. Felt like a real minature of a full size one. And of course, weight is the deciding factor (unless it has rubber tires) to how well it pulls loads up grades.
 
MarkInLA said:
Though most of us subconsciously already know this from day 1 in the hobby, it's still something when you actually ponder it; the very fact that our model locos adhere to the rails thru thee very same science/mechanix as the 1:1 scale to gain traction and overcome inertia !! Big or small, it's the same !! That's so cool when ya really think about it, huh ?! M
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I remember an article a long time ago (late 1960s I believe) that had the actual math for adhesion of steel wheel on steel rail. They went on to contrast that with the formulas for that various model railroad wheel types on brass and nickel silver track.
 
I have a copy of the 1930 locomotive Cyclopedia. There are many formulas including calculating TE and factor of adhesion. If you have 2 steam locos that are identical except for wheel diameter, the one with the smaller drivers will pull more! Same weight, but less contact on the rails.
 
The loco with the smaller drivers has the same weight on the drivers as the larger loco. No difference there. The difference is an almost negligible difference in 'footprint' on the rails, even with the smaller angles of the smaller drivers,...almost... But generally, two steamers with the same weight born by the drivers, but where one of them has more drivers making contact with the rails, that loco will have more traction on the rails. Each axle, if we ignore bearing resistance/inefficiency, has less rolling resistance due to the deformation alluded to in the previous post. This stands to reason because there are more wheel rims bearing the weight of the same tonnage on the two locos, one with six drivers and one with eight drivers (times two engines in the cases of the articulated engines). This is demonstrated by the Y6 Mallets and Big Boys with their eight drivers per engine versus the H-6 which is a 2-6-6-2. But smaller drivers' leverage between the rim of the tires, where the 'work' takes place, and the end of the crank pin on the main rod where the effort takes place, is what makes the difference in tractive effort. Smaller drivers have better leverage. It's that simple.

Here is something longish and bookish to stew over with a cup of coffee:

https://www.scribd.com/doc/281070303/Tractive-Effort-and-Train-Resistance
 
WOW -- I was doing pretty good until Page 9:
Then my head exploded!
I think I will go and find my B-707 manual and put myself to sleep.
 
Yikes ! Where did my OP go ? Didn't mean to start all this ...I merely meant the phenomenon itself; that whether it be 1:1 scale, 1:87, 1:160 or any scale, the physics are the same, causing us to deal with the same challenge that adhesion dictates, and how much cooler that makes the hobby !....Datz it...M
 
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MarkInLA said:
Yikes ! Where did my OP go ? Didn't mean to start all this ...I merely meant the phenomenon itself; that whether it be 1:1 scale, 1:87, 1:160 or any scale, the physics are the same, causing us to deal with the same challenge adhesion dictates, and how much cooler that makes the hobby !....Datz it...M
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Discussions tend to take on a life of their own Mark, I'm always being accused of having an excess of locos in a train for it's length, but I just do what the real RRd's do, if 1 or 2 won't pull the train up a hill, stick another 1 (or 2) onto it. Looks good anyway. I'm with Tim Allen, more power, raof, raof.
 
Edited later: Question: Toots, when you do double or triple head your engines, assuming you're DCC, what is your sequence of starting each loco rolling ? I meant with steam (which of course can't be MU-ed like diesel.), and also not in digital-consist, either. Put another way, to mimic the 1:1 scale steam activity, what would be your way of starting to move 2 or more engines ? Just a little puzzle to see if you too came to the same conclusion as I.
 
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MarkInLA said:
Edited later: Question: Toots, when you do double or triple head your engines, assuming you're DCC, what is your sequence of starting each loco rolling ? I meant with steam (which of course can't be MU-ed like diesel.), and also not in digital-consist, either. Put another way, to mimic the 1:1 scale steam activity, what would be your way of starting to move 2 or more engines ? Just a little puzzle to see if you too came to the same conclusion as I.
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I can't see why steam engines with DCC can't be consisted just as diesels can, they're all electric motor and fitted with digital decoders. I use NCE as my control system, as does my club, so I use it's "Advanced consisting" method. I believe most DCC control systems have something similar, but there may be some differences in the setting up. The alternative method provided for is what NCE call "Old style" consisting, where it is just a matter, basically, of adding the loco addresses together in no particular order. Their Advanced consisting identifies a consist by the lead loco's address and the rear loco's address, others get added as extras to that. There are advantages to this method, not available in the "Old" one.

What I do, I start up each engine I want to consist in their respective positions (uncoupled, with a bit of space between) by each ones own address. I then select and enter the Advanced option on my Cab. This then gives me a consist number, starting at a high of 127 and going backwards from there if any are already occupied by another operator e.g. say, 124 if 3 others are already assigned. I then get asked on the Cab's screen for the address of the lead loco, which I type in and press enter. Then I get asked for the direction in which the loco is facing and will normally be running F or R, select and enter. Then I am asked for the rear loco's address and go through the same process. Adding more locos is just a matter of doing the same thing with their addresses.

Normally after setting up the consist in this way the display will change the loco address in the display to the lead loco's number and change from LOC to CON, but I have had to remind it which one by selecting and re-entering it.

I then, while they are still uncoupled, test the consist, to make sure it's all working as required. After that, it's away you go.

I do have a problem at the club, because my Cab is radio connected to the base station, of as yet, a positively unidentified interference that can scramble the display. I believe it's because the building is metal framed as is also much of the layout's frame, the main reason I go through all the checks, the other is that the loco's I usually use in consists have had CV's modified to act in certain ways in the consist (lead, rear or mid) as I choose, with the functions that that loco would have alone, something that you can't do with the other method of consisting.
 
I think he's talking about the REAL prototypes where steamers were not MU'ed. When I did steam I used both engines and never MU'ed them. More fun to just add more throttle on the pusher.
 
Toots, yes, Y3a [above] is correct ! Acting like separately controlled engines of the steam era, I'd run 2 -3 together by myself by ping ponging from one address to the other, slowly getting faster, until the train is rolling along smoothly. But since you likely have never dealt with that, I will answer the puzzle.. With steam, double/triple headed, the rearmost engine begins first..Why? To prevent coupler knuckles from being ripped out. If front were to roll first, that potentially could happen (second engine not rolling yet).. So, 3 steam on the point, they'd go 3, 2, 1 in order to commence rolling..Sorry you didn't get my meaning and wound up typing so much. Yes, of course diesels are MU-consisted to be run under one crew, 1:1 scale or model...
 
Ah, I see. Not having any experience with 1:1 steam (or diesel for that matter) and as steam always had a crew in each loco, I would say that the rear engine would start moving first, to remove the slack between the couplers to prevent them slamming against the jaw and possibly breaking some. Where I lived as a child, we were in earshot of a long tailed wye, where trains could change direction from north to south or vice-a-versa. When the wind was right, you could hear the slack rattling through the length of a train as it began to leave the wye after having pushed it's load in. Running multi engined consists in the steam era, must have been a very tricky business. It may be, with diesels, MU'd, their electronic controls can automatically adjust the throttles to compensate.

It's is probably pretty similar to modelling helper consists. I have found on the club layout, which has reverse grades on the opposite sides of a couple of the peninsulars, that because there is no practical method of controlling lead and helper sets individually, but still in unison, except by the method you describe, when one set is going up and the other is going down, other than keeping the overall speed, low, so as to limit the effect on the couplers.

Don't worry about me writing long posts, you might notice I tend to do that ;)
 
When steam was king on big hills that were designated helper districts, there would rarely be no more than (not never, just rarely) be two pullers on the head end and one pusher. The pusher would signal with two long blasts of its whistle and wait to hear a faint acknowledgement from the head engine. When the acknowledgement came, it meant the pusher could open its throttle and bunch up the slack on all the couplers ahead of it. Powerful pushers like the Y6b Mallets were capable of crushing wooden-framed cabooses, so if any were present, they would have been shunted to the rear of the pusher's auxiliary tender.

When the slack was bunched, accompanied by banging, the second engine would open its throttle, followed by the lead engine...all via hand signals and experience.

When the pusher had done its job atop the 'Big Hill', it would cut off from the still-moving train and let it gain speed. It would either back down the same track if told to, or move to an adjacent track (if the line were doubled, and it often would be on a helper district to allow faster trains to move past the coal drags, as was the case on the Blue Ridge for the Norfolk & Western) and back down the hill on that track.

I have a BLI Class A 2-6-6-4 and a BLI/PCM Y6b. I put the Mallet on the rear, shoving, and the A is the road engine. I start the Y6b with three or four speed steps, wait a few seconds because I have a lot of inertia programmed into CV3, and then give the A a couple of speed steps. By the time I have the consist doing 15 mph, the typical coal drag speed up the Blue Ridge, the Y is at speed step 17 while the A is at about 8 or 9. The difference lies in the diameters of the drivers. The drive mechanism is assumed to be about the same, but the voltages need to be different due to the driver diameter disparity. I have only done this twice, about 2 months ago, by now 14 years into the hobby! But, it worked, and no stringlining took place. Whew!! There were 20 BLI H2a coal hoppers between the locos.
 
I used to do it in a similar fashion, but Since I modeled N&W in the 1930's I was using weighted, detailed Powerhouse Y3'a from Oriental. The consist was usually 45 Athearn BB 2 bay hoppers with a few others mixed in (Like a few HP's from Westerfield) I used vacuformed sheets with a thin layer of real coal to imitate the full hoppers, while having very little weight. I would use just the front engine going up a 4 percent grade until it was just slipping. Then the Y3 pusher with modified front coupler would compress the rear of the consist. Then I'd click the pusher up 2-3 notches and then the front engine. When it got up to about 7 mph I would let it go over the top of the grade, where it would start to speed up, leaving the pusher behind. Never did video of it. I did do an A & Y6b and a long string of hoppers on youToob that had Mobile Fidelity sound syncronised to the video.
 
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