RE: Why are helicopter glow engines so smoky????
The oils used in Heli specific fuels tends to be higher in nitro and oil content, and viscosity. I know someone who flies Helis and he runs 23% synthetic oil in his fuel. He has said its also a bit unconventional to set the needles on a heli. It seems to be common for helis to have no castor in the mix, so that lends to the smoke as a portion of the lubricating oil also burns. Synthetics tend to smoke more in my experience.