Well, I think I can pur your mind at rest. They are about a decade to early to be driven by rotary engines. Judging by the cylinder heads, little two-strokes as used in mopeds or lawnmowers, or maybe even model planes, boats, cars…
(Cue Hardy Krüger explaining that model planes are “real planes”.)
Yes, that invention of Professor Calculus is from “The Red Sea Sharks”, which was first serialized from 1956 to 1958. The time frame matches well to the assumption that the skates in the picture were Herge’s inspiration for it.
I saw the nsu-skates and this was immediately in my head. very strong imprint in my brain.
left a big impression for me as a child, I always thought of this tintin-adventure as an apology and form of “reparation” from herge for his mean and racist as fuck early tintin in the congo.