based on what I know -- this from some unofficial conversations with Boeing types a few years ago -- there is NO safe and practical ethanol equivalent of jet fuel (nor can there ever be due to absolute limitations imposed by molecular chemistry), and efficient carburetion of ethanol in piston engines is impossible at altitudes much above about 10,000 feet. The 21st Century version of a Boeing P-12 (or the comparable Polikarpov I-5) would be just as vulnerable to interdiction by ground fire as were the originals. But the whole discussion is moot due to the lubrication problem detailed in the next paragraph.
The ultimate barrier to ethanol is the absolute limit imposed by the fact there is NO -- I say again NO -- non-petroleum substitute for lubricating oil. Without adequate lubrication -- no matter what fuel might be discovered to replace petroleum derivatives -- any and all internal-combustion engines will grind themselves into scrap within minutes. And without petroleum-based insulation for electronics, there will be no electronics. Period. (The original Edison-era wire-insulation was a combination of rubber and cloth, the former impossible to obtain without re-colonizing Southeast Asia, the only place rubber plants grow, or paying definitively hostile nations whatever price they choose to demand.)
I don't hold to the back-to-the-stone-age scenario for the post-Peak Oil scenario, but I do recognize how dependent we are on petroleum for everything from fuels and lubricants to packaging and the insulation on electrical wiring, and I recognize that once the oil runs out, technology will at the least be very quickly reduced to a 19th Century pre-flight level. World population will be reduced by plague, famine and war accordingly.
Given these horrific realities, the United States faces two -- and only two -- alternatives. One is already being imposed on us: the emergence of an ultimate fascist state based on a corporate economy similar to manoralism in which one is either part of the ruling class or is a neo-serf literally owned by (and therefore totally enslaved by) the corporations -- a kind of degradation literally too horrible to contemplate, especially since we already see how it will be enforced: by Abrahamic theocracy (whether Christian or Islamic) and therefore by a New Dark Age that will literally last until humanity itself is extinct. The other alternative -- unlikely at best -- is the triumph of a global socialist revolution (whether via the ballot box or other means) that will (1) ensure that the residual wealth of the old USA is equally divided among all its surviving residents while (2) ensuring that our nation takes its place in a world that shares the remaining resources equally while (3) doing whatever possible in terms of re-forestation and de-industrialization to restore the global ecosystem. Here is a living portrait of how such a society might look:
http://www.globalpublicmedia.com/articles/657The shape of the future and what it will be -- fascist savagery or socialist humanitarianism -- is in fact the ultimate stake in the political struggles of today.
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Edit: addition of link and revisions necessitated thereby.