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Have there been any known tests or prototypes of variable-diameter propellers?

There's this paywalled paper from 2014 that seems to have made a virtual prototype model, have there been any physical tests or practical builds, before or since then? Are there other documentation about this topic?

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    $\begingroup$ I found some gorgeous old patent drawings from 1964: patents.google.com/patent/US3128829A/en Would be very interesting to learn if/when any pratical trials were undertaken! $\endgroup$
    – Wasserwaage
    Jun 15 at 19:14
  • $\begingroup$ great find, this is elegant and frightening at the same time! $\endgroup$
    – jkztd
    Jun 16 at 8:32
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    $\begingroup$ Do folding props on motorgliders count? ;) $\endgroup$
    – quiet flyer
    Jun 16 at 12:45
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    $\begingroup$ If you go back to literature in the early 1930's, variable diameter propellers are discussed as an equally credible alternative to constant speed props and propellers with variable ratio gearboxes (some CVT). Constant speed props were developed and the others never really were. $\endgroup$
    – Rob McDonald
    Jun 17 at 5:10

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The 1994 NASA report Wind tunnel test of a variable-diameter tiltrotor model documents wind tunnel tests of a 1/6th scale variable-diameter tiltrotor. Fig. 3 on p. 4 (p. 12 of the pdf) shows the mechanical design of the blades.

Fig. 2, below, shows the blades extended in hover to increase thrust, and retracted in horizontal flight to not hit the fuselage. [Edit: Also, Wasserwaage's comment's patent description notes that horizontal flight's higher airspeed demands more RPM, which demands smaller diameter, both to not overload the engine and to avoid sonic booms at the tips.]

figure 2 of nasa paper

Page 79 (p. 81 of the pdf) of Winning indoor designs, 1987-1989 U.S. indoor championships reports that the winner of the 1998 F1D world championship used a variable diameter propeller. It used a rubber band to retract the blades toward the hub as the load changed through a flight. Its design is meticulously explained on pp. 8-17 of Indoor News and Views, #121, Spring 2007.

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    $\begingroup$ great content thanks a lot! these F1D variable diameter props mechanisms are amazing $\endgroup$
    – jkztd
    Jun 16 at 8:28

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