A previous poster mentioned an exhibition airplane running on ethanol. I also recall
this bird and it seems I saw it fly at Oshkosh, circa 1997. It seems that
it was a black fabric biplane with green trim?

The State of Illinois flew a yellow and green aircraft around the
airshow circuit to promote ethanol. I always suspected Archer Daniels
Midland was the wizard behind the curtain, but I never saw any credit
claimed in print.