Lionel locomotive, traction wheels in front or rear.

[Fordiesel69]

Really a dumb question but based on the body of the train, I cant; tell which is front or rear, it is a 1976 vintage Lionel Norfolk and Western and has the red, white, blue paint.  I just need to know if the motor goes on the front or rear.  The unit seems faster and better with the power wheels in the rear, but in my opinion the body looks backwards. 

 

This train:

http://www.youtube.com/watch?v=DO0aPz2QwJ0

[SleeperN06]

I would think that the traction tires should be in the back.

[8ntruck]

Your locomotive looks like a GP-9 as it flashes by in the video.  The real ones were operated either way - long hood forward, as yours was in the video, or short hood forward.

It is your railroad, so operate the locomotive the way it works best for you.

[hrin]

 LOL. That thing is going soo fast I cant even see it. Looks like its going good.

[Fordiesel69]

Yes it is a GP-9, I had to buy it so I could have my train this christmas.  My F3 is so sluggish and tired I could not use it this year.

 Anyways, looking at this train on ebay:

http://cgi.ebay.com/Lionel-28571-LRRC-2007-GP-9-Unctaloged_W0QQitemZ290384044684QQcmdZViewItemQQptZModel_RR_Trains?hash=item439c3ce28c

 Which direction is lionel intending it to go.  Cab part in the back with long hood forward, or hood in the back and cab in the front?  Which way did these travel in real life? 

[Anonymous]

Well LRRC is a railroading club not a real railroad so it really doesn't matter.  However, Lionel put engineer figures in this engine and if you look at the picture the figures are facing long hood forward so that is how I would run it. BTW - Lionel and MTH put engineer figures in most of their engines today, this helps to determine what the prototypical direction was for that railroad (but they have also been known to get these details wrong as well).

GP-9s, GP-7s and a few others were run either way by the real railroads so it depends on which railroad you are modelling what is prototypical.

[Fordiesel69]

Thanks, thats a relief.  The train performs so much better and draws much less current when the long hood is forward, and traction tires in rear.

[servoguy]

 If you are using switches with the non-derailing feature, you want the traction tires in the rear.  The truck that has the traction tires will not operate the non-derailing feature. 

[lionelsoni]

As far as tractive effort is concerned, the rear wheels tend to be more effective, but the situation is rather complicated:

Within each truck, there can be a transfer of weight to the rear wheels equal to the tractive effort of that truck, multiplied by half of the ratio of the height of the truck's center bearing to the truck's wheelbase.  Since that ratio is about 1/2 and the maximum tractive effort of steel wheels on steel rails is about 1/4, this all amounts to about 1/16 the weight on the truck.

It is possible, by using what are called "traction links", and by other equivalent means, to eliminate this weight transfer entirely; but this just shifts the problem to the locomotive as a whole.  The weight shift then occurs between, not within, the trucks, and depends on the ratio of the coupler height, which is about the same as the center bearing height, to the distance between trucks.  This ratio is about 1/10 instead of the 1/4 ratio that exists within the truck, so that's an improvement.

However, many prototype locomotives do not use traction links; and models certainly do not; so the weight transfer that occurs is completely within the truck.  But prototype trucks have the center bearing truly in the center, since they are expected to work equally well in both directions.  The toy-train trucks, on the other hand, may have their pivots considerably off center.  This is very much the case for the vertical-motor trucks used in Lionel F3s, GP7s, and "EP5s".  These are displaced substantially toward the middle of the locomotive.  The result is that the weight shift in the front truck tends to concentrate even more weight on the already more heavily loaded inboard axle, while evening out the weight distribution within the rear truck.

This situation is further complicated by the fact that, unlike prototypes, models are designed without much regard for distributing the weight exactly evenly between the trucks.  The bottom line is that it would be very difficult to predict which axles should have rubber tires to optimize traction for a particular locomotive and that any generalization among locomotives is pretty much hopeless.

[SleeperN06]

lionelsoni

It is possible, by using what are called "traction links", and by other equivalent means, to eliminate this weight transfer entirely; but this just shifts the problem to the locomotive as a whole.  The weight shift then occurs between, not within, the trucks, and depends on the ratio of the coupler height, which is about the same as the center bearing height, to the distance between trucks.  This ratio is about 1/10 instead of the 1/4 ratio that exists within the truck, so that's an improvement.

Do you have a photo of a  "traction link"? I did a search to see what it looks like and could not find anything.

[lionelsoni]

I can't find one on the Internet either; but perhaps I can describe it for you.  Traction links are used with a truck that lacks a fixed center bearing.  The truck usually supports the locomotive on resilient rubber blocks.  These can transmit vertical forces but not significant horizontal forces.  If they were the whole connection between the locomotive and the truck, the truck would simply run out from under the locomotive.

Instead, the truck pulls the locomotive through a traction link, which is a bar connected between the truck and the bottom of the locomotive's body.  The traction link slants diagonally down from the body to a point on the truck and is free to move around a little at each end.  If the link were extended in a straight line past the end that connects to the truck, that line would pass through a point at the height of the railheads right under the center of the truck.  It is because of this special location that the traction link eliminates weight transfer in the truck.

Normally there would be two traction links per truck, one on each end, so that the locomotive can pull in either direction and--also important--produce a braking force opposite to its traction force in whichever direction it is moving.

Here is a description that I wrote for another forum years ago describing why it works the way it does:

The traction link need not connect at the railhead level to do its job. If it is merely in line with the point at the railhead height at the center of the truck, it will be fully effective. (Of course, he closer one can bring the connection to that point, the less opportunity there is for truck pitching and spring action to misalign the link.)

To see how this works, consider first a truck without a traction link. At rest, there are only vertical forces on it, one downward from the center bearing and four equal forces upward, for example, from the points where the wheels contact the rails. Then start the motors. The wheels now have a horizontal component of force added, pushing forward; and the center bearing is pulled backward by the body bolster of the locomotive. To resist this torque, the vertical force on the rear wheels must increase and that on the front wheels decrease. This is the source of the well-known weight transfer.

Now add a traction link and redesign the center bearing to be free in the fore-aft direction so that it cannot be pulled on horizontally by the body; that is, make all traction forces go through the traction link. Now the horizontal component of the force in the diagonal traction link is the full traction force from the truck. But it can only support forces in the direction along its length; so there must be another, vertical force, which is equal to the traction force multiplied by the tangent of the angle of the link from the horizontal. Since the horizontal forces at the wheels and the diagonal force from the traction link all pass through the center at the height of the railhead, there is no net torque on the truck and therefore no weight transfer.

[SleeperN06]

lionelsoni

Now add a traction link and redesign the center bearing to be free in the fore-aft direction so that it cannot be pulled on horizontally by the body; that is, make all traction forces go through the traction link. Now the horizontal component of the force in the diagonal traction link is the full traction force from the truck. But it can only support forces in the direction along its length; so there must be another, vertical force, which is equal to the traction force multiplied by the tangent of the angle of the link from the horizontal. Since the horizontal forces at the wheels and the diagonal force from the traction link all pass through the center at the height of the railhead, there is no net torque on the truck and therefore no weight transfer.

You must an engineer.   I had to read it a couple of times and I had to make a little sketch, but I think I finally got it. It’s similar to my Weight Distribution system for my trailer hitch, except mine uses Spring Bars.

I take it that this has to be designed in and not something that I could just go out to buy.

 

[lionelsoni]

Right.