Was Ludwig Wittgenstein's aircraft propeller ever built?
Ian Lemco of the Royal Society published a note on this in 2007. He described the invention more as a jet engine than anything, as it featured a central compressor feeding tip-jet nozzles. Burner position varied during development of the design, from central to blade tip. A patent dating from 1910 shows jet combustion at the tip. One central compressor was of the centrifugal type. Thus, it is seen in some ways as foreshadowing the Whittle jet engine.

Lemco found sources to be scarce, mostly anecdotal, and unreliable. Certainly Wittgenstein constructed various experimental devices and tested them, both in the lab and on a railway track. Some may have been rockets. One source remarks in passing on the engine that he constructed, but the reliability and context are far from clear. There is no confirmation that he ever built a complete jet engine.

It seems to have been fundamentally workable, as compressor-driven tipjet rotors were indeed later flown, but it was probably beyond the technology of Wittgenstein's day.

Ian Lemco; "Wittgenstein's Aeronautical Investigation", Notes and Records of the Royal Society of London, Vol. 61, No. 1 (Jan. 22, 2007), pp. 39-51. Stable URL: http://www.jstor.org/stable/20462605