Doubleheading, why does it work?

Perhaps not completely germane to the conversation but I have used TMCC to  double-head a pair of Williams PRR K4s steam locomotives (photo below).  

I have also created and run a train using a snapper (pusher for you non-Pennsy types).  Both scenarios worked very well.  Keep in mind they were identical locomotives.  Kids - you should try this at home! 

George

Depends on what you mean by "effects" - the final speeds and direction of motion of each object is one way of looking at it.

But, the total kinetic energy before the collision is dissipated in many places.

Some is evident as the kinetic energy of the objects after colliding, but the rest is distributed within the colliding bodies and surrounding environment causing deformation of materials, heating effects, etc. This is where the coefficient of elasticity and numerous other factors (always ignored in basic physics) comes in.

However, describing exactly where all the energy goes is what most people mean by "how bad was the impact". That's where crash testing comes in. Hopefully, the design of the auto dissipates this energy by crumpling unimportant things and keeps it away from the important things (people).

Now, I'm going down to run trains!

Jim

Stan2004

   To offset the lazy horse theory that is why the wagon driver has a whip. The horses are not given a vote about how hard to pull.

   Same thing in real railroading today. All the engines are MUed so they all pull at the same speed even if the power ratings are different.

    In O gauge trains you could have engines that run at different speeds even when using TMCC or Legacy. At this years open houses at the Back Diamond Society of Model engineers I ran a MU of three Lionel Legacy SD70ACe engines. It pulled 15 intermodal cars all but two being die cast up and down 2.5% grades. All engines were powered and they pulled the load with no issues. Do a search on Black Diamond Open House to look at the video or look at my posts by clicking my name.

JohnB

While at my train club, I tried to double head a long 50 container train with a rear helper...

With a 3% grade, my train was being derailed on its tight curve and I could not make the GRADE....I had them all under one controller...so i ended up taking the rear engine out of que and decided to control both sets of locos independently.

couple of things i noticed, first, the two lead engines pulled so hard once they arrive to the top of the hill that it still derailed them...the curves were a bit tight...so i tried again..this time once the lead engines were on top of the hill, i slowed them down but kept the rear engine pushing at the same rate....to my surprice..it worked every time...

so in short, i did what real locos do in real life...control the lead and rear depending on the the power being exerted...

going down  the grade made the opposite where the rear was pushing more than the front engines...i simply slowed the rear...

anyhow..just my 50 cents... 

Caesar

  Were you running TMCC, Legacy or DCS? I can bearly manage one engine or one MU set. Did you use two remotes? Hope you got it on video.

JohnB

hm...we were talking about lashing up locomotive...did i mention it as an HO latch up?  

Different scale, but similar concept.

Wow.  Line me up with the guys with advanced degrees who think two 50 mph cars colliding are a lot more like a 100 mph collision with a stationary auto than they are whatever Dennis was asserting.

I run what you would call "conventional", with minimum radius 64" ( or O-128).  I often have up to four steam locomotives of different types on the point, and have run pushers.  With broader radius, the pushers work just fine, and right now I have Four very different 0-6-0s pulling a very heavy freight.  Remove any one of those four locomotives, and the three remaining switchers will just sit there and spin drivers.

My grand parents used to tell me about seeing doubleheaders during ww2.You get an incease in pulling powerit works.If it didn,t work the railroads would never do it.I have done it with my trains.Mth and kline steam locomotives.The last one here is a mth mohawk ps2 and a kline mike working together.

When two or more locomotives are lashed up together, this increases the amount of horse power. True enough, but it is the tractive effort that needs to be examined. Take my favorite locomotive, the AC6000 by GE. She is, perhaps the quintessential example of brute power. Both in scale and in the real world. She can out pull just about anything out there. Yet, in scale and in reality, even she has her limitations. She must pull, not only her own weight, but also the weight of how ever many cars are lashed up to her. This is where the tractive effort comes in. She must also get things moving and that requires huge amounts of tractive effort.

By lashing up two and typically three locomotives together, the tractive effort is increased greatly. This not only helps in a smooth start, but also assures that the locomotives themselves will actually help each other out.

I am not using numbers here for simplicity, but when three AC6000's are lashed up together, nothing on heaven and earth will stop them from moving the gargantuan load(S) behind them. Obviously, each locomotive has its own power curve. Thus, the engineer and freight conductor must configure the whole affair so that there is not only enough horse power, but tractive effort available when the time comes to push the throttle.

One of the reasons Union Pacific designed and built the DD40AX locomotive was because of the lack of any real high horse power locomotive out there back in the 60's. Mating essentially two of the same locomotives together meant massive power for one locomotive. Lashing two of these beast together meant that UP could move far more freight/loads then any other rail service.

Today, everything is about "green" locomotives. Less pollution and greater pulling effort, but with a smaller more up scaled type configuration. GE has led the way with this technology by employing some rather specific principles to modern railroading. One being that a locomotive need not be huge to move allot of freight. Two being that a locomotive need not use a diesel engine which puts out massive amounts of pollution. Lastly, railroads need locomotives that are capable of going great distances on the least amount of fuel possible. Thus saving all involved allot of money. Lashing up three ES44AC's or two SD90's can accomplish allot with less fuel.

In scale, the reason I believe we use this, is primarily for looks. Yes, the theory holds that even in scale, two or three AC6000's or what ever you are using on your layout, when they are lashed up together, they can pull tremendous amounts of cars all around the layout until you decide to pull power on them.

Pete

So, how is all this "lashing together" accomplished, i.e. what sort of ropes or chains do they use?

OK, back to the two colliding automobiles.  I am saying that if two identical cars of the same weight, with the same engines, the same crash dummies or same weight people are in an exact head-on collision, at 50 mph, the damage to both cars and its innards will sustain exactly the same damage as if they had run into an immoveable concrete wall at 50 mph, no more, no less damage.

.....

Dennis

If you want to discuss lashing, ropes and chains, I understand that there are forums for that. 

 OP-Why does a engine work when it pulls on cars? Whatever answer you prefer, multiply it by 2 for double heading.

 They fact none of you changed the subject to train cars colliding is beyond me.

I knew what you were all trying to basically say the same thing in different ways.

Train Yard Pete, you left your firebox wide open!

You can lash a load to a flatcar, but only Lionel "lashes" railcars together. Most here hate the term, especially Rich our host Better off to limit its use to use and programing posts for Lionel remote equipment. Welcome to the "learn it the hard way" club.

The way I think of it is if a train requires 3 lbs of force to overcome static friction, and one locomotive is pulling with 2 lbs of force it will not move it (it will most likely start spitting out traction tires if you let it try long enough). Add a second locomotive, and now you have 4 lbs of force and the locomotives will together be able to move the train. Typically with command control lash ups the rear engine will do most of the work, until the need for help arises. Say I have an SD40-2 lashed up with a GP9 leading. The SD40-2 will be doing most of the work, but the moment it fails to maintain the speed the lash up is set to the GP9 will start to work harder to try to get the lash up back to the set speed.