http://www.jaylenosgarage.com/video/ericsson-hot-air-pumping-engine/1241133/
Despite several science degrees and a few thermodynamics classes, I still really don't understand how these things work in practice; but work they do. The advantages of a hot air engine is durability, simplicity and longevity: they will run until the fire runs out. The disadvantage is that they are very weak, which is why you never see them powering a locomotive. Except here.
Ernst Plank was the only company that I know of eccentric enough to sell hot air trains. They only made two types; this locomotive and a tram based on the same chassis.
Because of the weakness of hot air propulsion, they needed large engines. Therefore these trains are Gauge 3 (67 mm, or 2.5", or Gauge 2.5 in some catalogs which reserve "Gauge 3" for 75 mm gauge). Although the locomotive pulls a gauge 3 train, due to the poor pulling power Plank actually used a gauge 1 tender and gauge 1 cars made out of the thinnest tinplate imaginable. The tender and cars look horribly disproportionate with the loco in pictures, and in fact the engine doesn't look like much in pictures either, but in person it has presence. Unfortunately, my engine is frozen up. It looks like the copper pistons have welded themselves to the tinplate sleeves through galvanic corrosion, so I can't really confirm or deny that these have decent pulling power. A word of warning: the tram has been faked; so much so that there probably are more fake trams out there than real ones. Allen Levy wrote about a pair of them way back in the mid seventies in "Century of Model Trains". Its one of the highest items on my want list to get, but I am very nervous about buying one. The locomotive's value is probably as much for pilfering the chassis to fake a tram than in the loco itself.
