I wonder if he has thought it through as to were all that burning hot gas will be venting, or how hot those arm rests are going to get?
Yes.
This is not a jet engine or a rocket engine; it is a turbofan.
That means a small turbine is providing the motive force to turn a large fan, which in turn propels ambient (i.e., cool) air through the propulsion ducts ("armrests"). I didn't study the design closely enough to determine where he is routing the exhaust from the gas turbine, but if it goes through the propulsion ducts, it will be diluted enough by the large volume of air provided by the fan that excessively high temperatures will not be a problem.
While the whole project seems to my (admittedly untrained) eye to be of no great usefulness, I would not characterize it as being crackpot. There is obviously a great deal of quite competent engineering and construction here. Even if (as is likely) it never leaves the ground or is even completed, it is quite a showcase of skill, perseverance, and dedication.
tanstaafl.
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