The problem with alcohol-based fuels (so far) is not that the energy they hold is less than gasoline, but that their internal pressure is much higher: they start to boil at much lower temperatures, or much higher atmospheric pressure, than either avgas (aviation gasoline, for piston engines) or avtur (aviation kerosene, for turbine engines). Practical ceiling is much lower.
There is a way round the problem: pressurised fuel tanks. I don't know of any aircraft to have these- they would be heavy...
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