Uncoupling cars on the fly

[Gunneral]

From memory the GWR slip coaches had special slip coach bays at particular stations and they would coast into them under their own momentum under the control of the brakeman. The slip coaches were generally picked up for return to London by a stopping passenger train as required. Gunneral

[NorthWest]

Euclid

That sounds like a drop.

Yes, just different terminology for the same thing.

[Euclid]

I wonder how fast they were going when the pin was pulled.  I assume they would have slowed way down from passenger train speed; maybe down to 15 mph or so. 

[Ulrich]

Last coach was probably filled with third class passengers...back then if a few of them got banged up in transit it wasn't that big of a deal. 

[schlimm]

BaltACD

cefinkjr

Then there were the British "slip coaches" described by the late John Armstrong several years ago.

An "up" train (from London) would approach a rural station at a fairly high speed. Brakes would be applied for a second or so and a brakeman on the last coach on the train would uncouple it. The train would then accelerate; allowing the coach to drift into the station where it would be shunted onto the arrival track. And, yes, this was apparently done with passengers aboard.

I am wondering what sort of hand brake test was performed before the drop to ensure that the brakeman could actually stop the car at the station - who was handling station switches?

Probably pre-Beeching era or earlier, when the British system had a far bigger labor force to check things and all stations were manned, often with a staff of 2-4 people.

[BaltACD]

cefinkjr

Then there were the British "slip coaches" described by the late John Armstrong several years ago.

An "up" train (from London) would approach a rural station at a fairly high speed. Brakes would be applied for a second or so and a brakeman on the last coach on the train would uncouple it. The train would then accelerate; allowing the coach to drift into the station where it would be shunted onto the arrival track. And, yes, this was apparently done with passengers aboard.

I am wondering what sort of hand brake test was performed before the drop to ensure that the brakeman could actually stop the car at the station - who was handling station switches?

[Deggesty]

I have wondered how the cars were taken back to London; I doubt it was on express trains.

[Euclid]

cefinkjr

Then there were the British "slip coaches" described by the late John Armstrong several years ago.

An "up" train (from London) would approach a rural station at a fairly high speed. Brakes would be applied for a second or so and a brakeman on the last coach on the train would uncouple it. The train would then accelerate; allowing the coach to drift into the station where it would be shunted onto the arrival track. And, yes, this was apparently done with passengers aboard.

That sounds like a drop.

[54light15]

In a recent  "The Railway" magazine, a British publication, there was an extensive article about slip coaches and how it was done. Seemed to be a common practice. Don't know if it was done anywhere else.

[daveklepper]

If your car bumps into another in front, the acceleration of that car in front will only occur during the period the two cars are in contact and your car is thus applying force to that car.  Once your car slows down enough so that the car in front moves away from your car, no further acceleration will take place and that car will also begin slowing down, with whatever rate its conditions impose on it.

NOTHING ACCELERATED WITHOUT A FORCE BEING APPLIED

[Randy Stahl]

sandiego

"Can it be that all these people (except Ed) have forgotten about all the buff compression springs in the draft gears, which are compressed to some degree while the shove is going on, but that provide mutual recoil between cars"

Sorry, but that's not how draft gear works. Draft gears are designed to dissipate impact energy by first compressing (assuming forces in buff) and then slowly expanding back to normal, with retarding force generated by friction between rubber and metal elements (for conventional draft gear), or by hydraulic fluid forced through a small orifice (for hydraulic end-of-car cushioning units). This is the same principle used on automotive "shock absorbers" (more properly described as shock dampers). Any system with springs will oscillate wildly when perturbed unless some form of damping is provided. If you've ever had a vehicle with "bad shocks" that bounces you up and down repeatedly after hitting a bump you've encountered a perfect example of this.

So, a cut of cars will run in or run out depending on whether they are pushed or pulled, but they won't keep going back and forth like a weight suspended by a spring.

Kurt Hayek

 

I still remember riding cabooses and I know for a fact that cushioned cars stopped bunched will accelerate themselves when the brakes release and the cushions decompress. Even with the head end stopped the rear will get going pretty good even on flat track. It's really quite a hit and you can't let your guard down until the slack settles.

 I think overmod is right, I have some old bruises to prove it.

 

Randy

 

 

[oltmannd]

sandiego

"Can it be that all these people (except Ed) have forgotten about all the buff compression springs in the draft gears, which are compressed to some degree while the shove is going on, but that provide mutual recoil between cars"

Sorry, but that's not how draft gear works. Draft gears are designed to dissipate impact energy by first compressing (assuming forces in buff) and then slowly expanding back to normal, with retarding force generated by friction between rubber and metal elements (for conventional draft gear), or by hydraulic fluid forced through a small orifice (for hydraulic end-of-car cushioning units). This is the same principle used on automotive "shock absorbers" (more properly described as shock dampers). Any system with springs will oscillate wildly when perturbed unless some form of damping is provided. If you've ever had a vehicle with "bad shocks" that bounces you up and down repeatedly after hitting a bump you've encountered a perfect example of this.

So, a cut of cars will run in or run out depending on whether they are pushed or pulled, but they won't keep going back and forth like a weight suspended by a spring.

You are both right.  Modern draft gear uses rubber pads, not springs.  That's true.  But the rubber pads are really just springs with a lot of hysteresis. The are capable of storing and releasing energy.

Hydraulic end of car cushioning is a different animal.

[CSSHEGEWISCH]

Chuck is right about slip coaches.  Passengers were aboard each coach since the concept allowed an express train to serve selected intermediate stops without making stops.  The brakeman aboard the slip coach brought the car to a stop using only the hand brake.

[cefinkjr]

Then there were the British "slip coaches" described by the late John Armstrong several years ago.

An "up" train (from London) would approach a rural station at a fairly high speed. Brakes would be applied for a second or so and a brakeman on the last coach on the train would uncouple it. The train would then accelerate; allowing the coach to drift into the station where it would be shunted onto the arrival track. And, yes, this was apparently done with passengers aboard.

[cx500]

Thanks for that story, Jeff.  I was very aware of the sloshing action of tank cars.  You don't want to get too close to either end of a string of those cars until you are certain they have come to a complete rest.  But I had never heard of it being used to advantage.

John

[jeffhergert]

BaltACD

And if you really want a wild ride - flat switch a cut that has a number of loaded tank cars in it!  Can you say slosh slack!

When I was training (no pun intended) at Beverly Yard, one of the yard foreman would use the sloshing of tank cars to pin them off when switching.  Beverly is downhill, west to east.  Most switching was done from the west end. 

When cutting off tank car(s), he would bring the move to a stop.  The slack ran out, but the slosh would bring the slack back in enough to pull the pin.  The sloshing then would cause the car(s) to move away from the rest of the cut and down the yard track.  I can't remember if it worked for all the tracks (north side of the mains) or just the first three or four tracks.  It seems we were up around yard #1 switch when we did this.

I don't know if the other foremen back then, or now, used this trick.  Maybe some of our Cedar Rapids area friends might be able to check it out some nice afternoon.

Jeff 

[BaltACD]

And if you really want a wild ride - flat switch a cut that has a number of loaded tank cars in it!  Can you say slosh slack!

[sandiego]

"Can it be that all these people (except Ed) have forgotten about all the buff compression springs in the draft gears, which are compressed to some degree while the shove is going on, but that provide mutual recoil between cars"

Sorry, but that's not how draft gear works. Draft gears are designed to dissipate impact energy by first compressing (assuming forces in buff) and then slowly expanding back to normal, with retarding force generated by friction between rubber and metal elements (for conventional draft gear), or by hydraulic fluid forced through a small orifice (for hydraulic end-of-car cushioning units). This is the same principle used on automotive "shock absorbers" (more properly described as shock dampers). Any system with springs will oscillate wildly when perturbed unless some form of damping is provided. If you've ever had a vehicle with "bad shocks" that bounces you up and down repeatedly after hitting a bump you've encountered a perfect example of this.

So, a cut of cars will run in or run out depending on whether they are pushed or pulled, but they won't keep going back and forth like a weight suspended by a spring.

Kurt Hayek

[tree68]

Overmod

...the buff compression springs in the draft gears...

That would be those "outside forces" at work...

[Ulrich]

You're welcome!  

[gardendance]

Ulrich

Acceleration. What if I drive my car at 90 mph and rear-end yours at a red light? Your car will definitely accelerate,  I assure you of that. My car will lose some of its momentum in the process (not that it would matter much to anyone inside). Would not the same effect apply for a locomotive bumping some rail cars? 

Thank you for offering me another opportunity to say what I and others have said already, just slightly rephrased. Yes, the other car will accelerate, but no more than 90mph minus whatever energy's lost in the collision, minus the difference between your car's and the other car's masses, minus friction. The other car will NEVER accelerate more than 90mph, just as the railroad cars cut free from a trailing locomotive will never accelerate as that locomotive slows down.

[BaltACD]

Ulrich

Maybe. I'm pretty sure I saw them accelerate.. but who knows, maybe my mind was playing tricks on me. 

Watch 'Your Bleeped Up Mind' on History or Discover Channel's - to understand how really bleeped up our minds are in the way they work and 'fill in the blanks'.

[Overmod]

Can it be that all these people (except Ed) have forgotten about all the buff compression springs in the draft gears, which are compressed to some degree while the shove is going on, but that provide mutual recoil between cars ... all the cars in the cut ... when the locomotive decelerates?

[Euclid]

Ulrich,

When I refer to it as an optical illusion, I am not discounting the appearance.  It does indeed look like the kicked car speeds up as it leaves the cut. 

[Ulrich]

Maybe. I'm pretty sure I saw them accelerate.. but who knows, maybe my mind was playing tricks on me. 

[Euclid]

Ulrich

Acceleration. What if I drive my car at 90 mph and rear-end yours at a red light? Your car will definitely accelerate,  I assure you of that. My car will lose some of its momentum in the process (not that it would matter much to anyone inside). Would not the same effect apply for a locomotive bumping some rail cars? 

I don’t see the comparison.  The car that gets let go was accelerated only by the locomotive.  It is not “bumped” into action.

Actually, I would say that the appearance of acceleration of the kicked car is an optical illusion.  As the engine brakes, the slack in the cut runs out.  The deceleration in that runout increases as it moves from car to car.  By the time it gets to the last car that is still coupled, the slack runout has become most abrupt; so it decelerates that last car at the fastest rate compared to all of the other cars in the cut.   

Railcars are amazingly free-rolling.  So when the kicked car rolls free, there is no perception of its speed slackening.  And yet the last car in the cut abruptly decelerates in a way that is visually obvious.  This creates the illusion that the kicked car actually sped up.  I don’t believe it can.   

[tree68]

Ulrich

Acceleration. What if I drive my car at 90 mph and rear-end yours at a red light? Your car will definitely accelerate,  I assure you of that. My car will lose some of its momentum in the process (not that it would matter much to anyone inside). Would not the same effect apply for a locomotive bumping some rail cars?

The car you hit will definitely accelerate at the time of impact.  After that it will decelerate, unless other forces act upon it (gravity:downhill, wind).  Other factors will also determine how quickly it decelerates:  friction, mass of the car, air resistance, brakes.

So it will be with the railroad cars being kicked.  Barring gravity or wind (ask Carl about that), it will begin to decelerate as soon as it is uncoupled from the locomotive (or other cars).

To do otherwise would be counter to the laws of physics.

[switch7frg]

Reading the Kurts post ,I recalled my younger years in Dayton , Ohio. Remembering the sound of the car hitting the string  as it bunched up the slack, then stretching out for the next car to hit.  We lived on Huffman Av. at the bottom of "Eastern Hills" on the PRR. The switch yard was east of Smithville Rd. The other yard was on Findley street and ran from there to Irwin street. That main track was the Big 4 RR.There is where I learned about  track torpedoes from switchmen.They sure were loud when hit .  That was in a time  much nicer. I met two friendly "Bulls" , William and  Arnold  at different times and they told me where I could go  and could not go on rail property. This was in the 1940s.  My how times have changed.

                                                               Cannonball

[Ulrich]

Yes, the operative word being "after". Likewise,  the freight  car too slows down for coupling.