So, how possible would it be for aircraft to be invented early enough (say, 1870s/1880s) to have to be steam-powered? OTL, there were some designs for such aircraft, and some were even tested, but none were successful. If at least one had succeeded, then what would the immediate effects of heavier-than-air craft being developed early be on the world? How long would steam power last for aircraft, at the longest, before eventually being replaced by internal combustion engines? And what would be the effect on aviation history?