A long time ago - a very long time ago! - I recall my father telling me this: If you take a standing steam locomotive of any wheel configuration and wedge a single penny tightly fore and aft between the track and each driver (8 drivers = 16 pennies), it will not be able to move.
Can somebody please confirm for me whether this is a fact based on engineering calculations or one of those recurring myths we often encounter in our journey through life. [%-)]
i don’t know about pennies but i’ve heard that a single spike is hard to climb over. always wanted to try it with a diesel but never had the nerve. if something went wrong then the road foreman or traveling engineer would have a calf.
Well, first presuming dead-level and rock-solid track that isn’t deflecting at all under that load:
Probably fact for rolling under gravity per condition 1 as stated above - as you’ll see below, that’s the equivalent of an adverse approx. 2.9 per cent grade.
But Myth for moving under its own power per condition 2, unless it is dreadfully underpowered.
Short mostly non-mathematical analysis follows - for the full version, I’d want to be able to draw a diagram with all the force vectors:
Think about a Shay - the geared locomotive. Anybody who’s ever seen one in operation on rough track would have no doubt that it could climb over the pennies. Yes, you probably presumed a rod-type locomotive, but the example helps to illustrate the qualitative analysis process here, as you’ll see in a moment. The characteristics of a Shay that enable it to do that are small wheels, hence a lot of leverage to get over the penny; and the tremendous gear reduction ratio, which generates very high tractive effort.
Only the pennies in the direction of motion make a difference - the other ones will just be left standing there as the wheels roll away - squashing the other pennies to a mere fraction of their original thickness in the process. Of course, in a very short time those ‘left behind’ pennies will also be flattened, except for the last if the locomotive has no trailing truck, tender or following cars.
I might ask the folks at the Nevada State Railroad Museum, or the V&T crew, if they can test this under real world conditions. Proof positive would be worth the eight to sixteen pennies, and their flattened remains might make interesting gift shop items (with certificates of authenticity that would cost more than the pennies…)
Being made of steel, chains won’t get squashed, nor will spikes.
Chuck (Modeling Central Japan in September, 1964 - in a Nevada garage)
I’ve heard something similiar, only with nickels instead of pennies. I think it was only two, one on either side of a drive wheel, tight up against it.
I too have thought it would be good for Mythbusters.
I’m no steam expert, far from it. But I know over at the Boone & Scenic Valley I’ve heard some of the steam crew say if the stop with the drive rods just right, they have trouble starting. They usually have to let it roll just a wee bit to reposition the rods. I know I’ve read of that problem elsewhere, but I think it was in a situation where one side of the steam engine was totally disabled. Again, that’s what I’ve been told. I’ll leave it to our resident steam gurus to weigh in.
“But, there must be some validity to the general idea of a chock - elsewise, why did they old-time crews drape a heavy chain fore and aft of a single driver to keep the rod-type steam locos from rolling away, even when some steam would leak into the cylinders ?”
anytime a steam locomotive was left standing the cylinder cocks were opened so any steam leaking by the throttle would not pressurize the cylinders. failure to do this was like getting out of your car and leaving it in drive.
every enginehouse i remember being in had short lengths of heavy chain to throw across the rails even when the engine was dead.
While Paul North’s analysis was great fun to read, I’ll advocate for a physical experiment–even more fun! I’d like to suggest to the experimenters that you try, besides the pseudo-copper of today’s pennies, an equal thickness of steel. If the “copper” penny just sort of oozes out of the way, is it really testing the ability of the locomotive to climb over it? Might as well just try a .050" thick piece of styrene, for that matter.
Now, the owners of the locomotive might balk at placing a bit of steel under the wheels, because they might fear putting a “dent” in the surface of the tire.
So, it appears that you want a material that will not deform from the weight of the loco, but will also not damage the loco either. Perhaps it’s a matter of shaping the “chock” just right.
After reading this thread, my head hurts. And I would go to the medicine cabinet for two Excedrin but my grandson put pennies under the sole of my slippers and I can’t move.
Not really. There’s no doubt a steam engine rolling along will easily roll over and flatten a penny on the track. The issue is that a steam engine, unlike a diesel, doesn’t have it’s full potential power available at start up. The theory is that because of this, if you put the pennies right up against the drivers of a standing engine, the engine wouldn’t have enough power to lift it’s massive weight up the grade caused by the pennies or nickels or whatever coin.
I suspect if Mythbusters did do this one, it would turn out the engine would be able to start OK, however sometimes these myths turn out to have some truth to them so it would be fun to test.
Let’s not confuse 'power ’ - as in horsepower = the rate or speed of ‘work’, in ft.-lbs.[force] lifted per second or similar; with ‘momentum’ = the tendency of a body in motion to stay in motion, which can also be measured as Mass x Velocity in seemingly those same units of lbs.[but of mass instead]-ft. per second, or similar; or with force = the push on the mechanisms, esp. the tractive effort or force, usually measured in lbs.
That said, stix is right that steam locomotives usually did not develop their maximum horsepower at starting - that typically did not occur until mid-speed range. Likewise, at starting a steam locomotive would have no velocity and hence no momentum. However, I believe that raw tractive effort or tractive force was a maximum at starting - full undiminished and undepleted boiler pressure bearing on the piston area for the entire stroke (unless the cut-off was limited in some way). As such, whether the locomotive at rest could slowly lift its massive weight over the pennies boils do
This topic brought back some memories of an article in an early 60s TRAINS mag discussing the Bud RDC. Someone being interviewed claimed that because of the type of power transmission, an RDC could be prevented from starting up by a single penney on the track wedged against a single wheel. Apparently, there was considerable slippage in the fluid coupling in the diesel-hydraulic drive under this particular situation. Sounds questionable, since with each truck powered by a separate system, and RDCcould start and accelerate on grades steeper than any other self-propelled car of their time.
All that math confounds me. I figure that even a light 120 ton Mikado would have to develop 240,000 lbs of tractive effort, sustained, no slipping, to lift its weight up over a diamond penny, or maybe a neutron density penny…something that wouldn’t compress worth a darn, but retain its integrity. Or do you only have to take the weight sustained by the one driver? In that case we’d be down to 20 tons…give or take, and that would come out to a required tractive effort equivalent of only 40,000 lbs. I would guess a Mike could come close to that for tractive effort. All the penny needs to do is to compress the one spring or suspension element…right? That seems doable.
Paul, you better pass around a tray of Advil next time you drop in an lay it on us.
First - your 20 tons/ 40,000 lbs. may be per axle, not per driver, for a 120 ton gross weight ‘light’ Mikado - that would be 80 tons on the drivers, and the other 40 tons either on the pony or trailing trucks and/ or the tender trucks, etc. Because if it’s 20 tons per driver instead, then that would be 160 tons on the driving wheels, which is a pretty surprising feat for a 120-ton loco, don’t you think ? [%-)]
But let me try again, with the benefit of some time to think about this more clearly. The key to this is to realize that the locomotive is not lifting its weight directly upwards - like me doing a vertical rope climb in gym class or as part of PT. Instead - mainly due to the horizontal distance between the bottom center of the driving wheel and where the penny is wedged in against the wheel tread and the rail head - the locomotive is effectively moving itself up an inclined plane with its own power. That incline has a slope - per my previous example - of about 1 in 35 = what we call a grade 2.89 %. As such, the locomotive just needs to be able to exert a little more tractive force than that percentage of its weight which is being blocked by the pennies. Using your example, that would be 2.89
Actually, that helped a lot…or maybe it was the Advil I took. [(-D]
Seriously, Paul, I can see my error, forgetting that there are two wheels per axle, so thanks for pointing it out as you did. And the rest seems very reasonable and intuitive, and I offer my thanks for taking the time to explain it without geometry.
So, even a neutron density penny would be hardly noticed by the engine? Huh…it’s all in the angles.
Perzackly ! [as would have been said in the old Pogo comic strip]
It’s basically related to the height of the chock - that’s why the 2’’ or 3’’ chains worked so well.
We office engineer-types sometimes can get all worked up and involved in the theory and method of analysis and all to make sure something would work. Meantime, the shop guys would just throw a chain across the rails 'cause they knew from experience and intuition that’s all that was needed to work, and then went for a beer before going home. [8D]
I can’t tell you about a steam loco, but put flat washers in front of and behind the wheels of a GP-40 and it is stuck there. It can not roll over the washers. The washers behind it keep it from rolling backwards and getting momentum to roll over the ones in front. I have also seen a stuck sander for the front wheels keep it from going forward.
Richard looking at MP 242 while working for the FEC Rwy.