Athearn recently sent me three of their new 2600 cubic foot Airslide covered hopper cars to take a look at. One was a GATX modeled after the late version of the cars (built after 1965) and the other two, Union Pacific and Burlington Northern, were "early versions" built between 1955-1965. You can see images of those two cars below.
Airslide hopper cars were developed in the 1950s as a way to improve the unloading of fine granular and powdered materials from hopper cars. Originally, items such as flour and sugar were shipped in bags inside of boxcars. Hopper cars make for far easier unloading of bulk materials like that, but commodities like flour and sugar can easily cake up inside a hopper car, particularly if any moisture is present, and don't flow out as easily. The Airslide hopper contains an air-permeable membrane along the bottom sides of the hopper, through which pressurized air can be pumped through at the unloading station via connections on the bottom side of the car. The air flowing through the membrane flows through the material inside of the hopper, fluidizing the material, and allowing it to flow out very easily. Airslide hopper cars have been the primary means of transporting bulk goods like flour, sugar, corn starch, plastic pellets, and the like since the mid-1950s.
These Athearn cars are great models, and are similar in size to a 40' box car.
Here you can see what the ends of the late version cars look like (in the top image below) and the early version cars (bottom).
Here is a look at the car underside. Note that these models all contain body-mounted couplers which improves reliability, especially when pushing long strings of cars through turnouts.
These models all weighed in at 1.1 oz, slightly heavier than NMRA recommendations. I prefer N scale cars to always be overweighted, and generally weight my cars around double the NMRA recommendation, sometimes even more, which helps them track through turnouts better, especially when being pushed through turnouts. Heavier cars also couple and uncouple easier.
These Athearn cars look and run great, and are worth considering if you are looking for some Airslide hopper cars to run on your layout.
Here is the model info from the Athearn page. Note this will vary somewhat depending on what specific model you are looking at (early or late versions of these hoppers mainly):
MODEL FEATURES:
Three road numbers
Early GATC Airslide body: no angled end gusset plates; channel-section vertical posts at bolsters
Detailed underbody including outlet piping
Rectangular or oval shaker brackets
Gravity or gravity-pneumatic outlets
See through metal roof walk
Factory installed wire grab irons and brake piping
Separately applied round roof hatches and brake wheel
Roller bearing or Bettendorf trucks
Fully-assembled and ready-to-run out of the box
Accurately painted and printed
Highly detailed, injection molded body
Machined metal wheels
Weighted for trouble free operation
Body mounted McHenry® operating scale knuckle couplers
Clear plastic jewel box for convenient storage
Operates on all popular brands of track
Minimum radius: 9 ¾”
You can pick up these great looking hopper cars from Horizon Hobby here: https://bit.ly/3wxDDWy