GMD Portager car

I am on a roll with 3D modeling lately. I wrapped up the A-Stack kits last night, so unless I get some print errors on Shapeways, those files are solid.

My latest project is the GMD Portager car. Like the A-Stack, these were an experiment in intermodal shipping. They were designed to compete with the Flexi-Van system, but Canadian Pacific was the only buyer. Based on photos, the trailers they carry seem to retain their landing gear legs with only the wheel bogie separating from the body. That would limit them to overhead loading rather than the Flexi-Van system where the trailer rotates to the side. The cars bear a resemblance to the later Front-Runner spine cars in the fact that they are short cars with single axles trucks on the end. While the Front-Runner had outside bearing wheels, the Portager had inside bearing axles mounted on a swing hanger system. Later car phases returned to outside bearing axles on an I-beam assembly. The suspension for these later cars was not on the trucks, but under the trailer. The fifth wheel was equipped with coil springs, while the skid for the rear of the trailer was on a leaf spring.

The early phase cars had a tube spine while the later phase cars had a more traditional I-beam. I am working on the early phase car with the tube spine right now. According to blueprints, the canisters the transverse spring hanger is mounted to are torsion springs and appear to be the only form of suspension these early cars had. The bearings should be able to fit 33" NWSL or JB flush-axle wheelsets (3/32" diameter axle).

 

Here is a final color-coded model that shows some extra parts I added. The beige side skirts are not included with the print just because I think they are easier to make out of styrene sheet. That way there are no thickness or warping issues; and plus, styrene does not have any layer lines. The model will be smoother and more realistic that way. I think including accommodations for aftermarket parts makes 3D printed trains feel more like real models and less like novelty blocks of plastic. The red wheelsets are just stand-ins to make sure the inside bearings meet minimum NMRA clearances: getting a real 3D printed wheelset to run smoothly sounds like a nightmare.

 

Do you happen to have a 1:1 scale pic of this for reference, really curious what this looks like now!

Don't think I've ever seen one.

 

I hadn't seen them either.

My first reaction was, when did General Motors get in the car business? That sounded like an incredibly stupid question, so I tried again. Since when does GM do non-powered rolling stock?

Could this be an attempt to re-purpose the Aerotrain cars, and get some of the development cost back? But didn't they have outside bearings?

 

This wasn't GM proper, rather General Motors Diesel, the Canadian subsidiary of EMD. (GM-owned) Rapido has done models of their GMD-1 as well as some of the Canadian F units. In recent years with international shipping and with all buyouts (CN and Illinois Central, CP and SOO, etc.), the line between the American and Canadian divisions of the company have become blurred. They used to operate relatively separately in order to avoid tariffs on importing locomotives to Canada. Caterpillar now owns EMD through Progress Rail and the GMD plant is actually closed, so it doesn't even truly exist anymore.

There seems to be very little information available on these cars, or it was all taken over by GM car sales ads. Searching for "GMD car" or Portager Trucks" was fruitless because all I got were road-going cars and trucks, not results on the railway use of the same words.

I have seen no connection to the Aerotrain, so it seems this car was new from the rails up. The Aerotrain was based on their buses, which I doubt had any chassis similar to this. I got most of my information from this website, which in turn might have taken information from an old Trains article. http://www.trainweb.org/oldtimetrains/CPR/intermodal/pioneer.htm. The way some of the photos are scanned with their included captions makes me believe they are from the "Railroad News Photos" section at the beginning of the magazine. I don't know their source issue, but it must have been published close to the introduction of the real cars.

The first (2 at least) prototype cars had those inside bearing axles, although the ten production-style cars had the outside bearings seen in some of the darker photos on that page. The photos show a few different variations of trailer mounting equipment, but I have no numbers on how many of each type were made. Their relatively low scan quality make me leery of taking on a model of the late cars. I can't see a lot of the details and I don't want to make an inaccurate model because I was guessing at all of it.

 

Yes, thank you, I know.

Relatively is the word. GM may have rearranged hoods and such for the Canadian market, but they didn't reinvent the wheel for it. Pontiac of Canada may have had different engines than Pontiacs sold south of the border, but they didn't have different engines than Chevrolets. Likewise, GMDs had 567 and 645 prime movers, and rode on Blomberg and Flexicoil trucks.

The New Look bus had no chassis at all. Aerotrain cars did.

Now that's interesting. The chassis of the Aerotrain cars had the bus-based bodies bolted on, so they could be replaced when they--well, I don't know what they were thinking. Maybe they hoped to sell new bodies when the seat upholstery wore thin. In any case, they didn't even sell the chassis, except for the demonstrators. They flopped. If those late production units used leaf springs, I'm inclined to like my theory that this is GM trying to find another way to sell these chassis they designed at some expense.

It would certainly explain why GM tried to get in the car business.

 

I didn't realize the New Look was monocoque, and indeed the Wikipedia page specified that as a special characteristic of the model. They were lighter than competitors' traditionally constructed vehicles. I found a drawing of the Aerotrain, which shows it having a 25' 3" wheelbase. The Portager drawing has a 31' 6" wheelbase. It could have been modified from Aerotrain use, but now the big question: Was the Aerotrain frame a spine or a traditional automobile ladder frame? (I'll see what I can find). Comparing the axle mounting systems reveals more differences though. It may have those pedestals the Aerotrain has, but all you can see in the photo is the bearing cap. Everything else is too dark.

My initial understanding based on this photo is that the axle was rigid to the Portager carbody and the suspension was under the container (leaf to rear and coil on the sides of the fifth wheel frame). I can't really see anything around the axle spring-wise. The Portager may be a derivative of, or uses information from the Aerotrain program, but I think there are too many differences for it to be a drop-in fit. There are some surviving Aerotrain cars, but all that shrouding makes photos of the inner workings of the frame non-existent.

 

I suspect you're right. I hadn't seen a pic of a later, outside bearing car de-skirted until now; thanks for posting it. Clearly the differences were many.

But I still can't help but wonder if GMD would have tried it without the Aerotrain research in hand. Sometimes GM tried to repurpose something existing, and found it didn't work. So being in for a penny, they went in for a pound, and the tail wound up wagging the dog.

It would explain how General Motors got in the car business for a little while.

Man, it most surely does look that way. But that couldn't possibly be true. That's too rigid, and too much unsprung weight. One dip in one rail and one wheel's hanging above the rail, skewing, its flange useless to guide it. That's a recipe for disaster. There's some suspension hidden somewhere. Has to be.

 

Usually when I think of individually sprung axles, I think of Napoleon hat-style blocks like on modern GE trucks. Obviously the Portager is not like that. What if those I-beam angles are somehow linked to the opposite side with another transverse beam? While the beams are rigid to the axle, an entire axle assembly may be sprung since the individual bearings are not. It would be a different and less traditional approach, but it may make sense because they are single-axle trucks. Locating the suspension between the truck and the car, rather than the truck bolster and sideframe, would be possible since there is no kingpin: the trucks don't rotate.

 

That's sure what it looks like. The chassis (if you can call a single beam that) doesn't carry any weight. It pulls plenty of weight when the locomotive pulls the cars ahead of it. But it doesn't carry any. The springs only have to keep it upright enough for the couplers to stay level.