Speaking of scary props...

[Eric Viglione]

If you are afraid to run that vintage walnut prop in the other thread, this ought to give you chills! Heh...

On my shelf for proud display in my study is the: Dynamic Models Hi Johnson Auto-Pitch! I am guessing it's intended victim would be an old ignition engine I suppose, being a 12x 5 to 7 pitch!  

Check out the sales pitch lingo ad copy! This text appeared in American Modeler, October-November, 1964:

"...Still stocked is the Auto Pitch prop; however, replaceable blades with considerably more area are now made for this unit. The hub is sold separately, blades in several sizes are extra. This is not a variable pitch prop; it is intended to operate at only two pitch settings, one for normal flying, one for low speed.

Latter will allow "idling" at 5,000 to 6,000 RPM so no fussy carb settings are required. When in low pitch (can be adjusted to suit your plane and engine) the prop offers considerable air resistance—you can even set it to give negative thrust. This produces a steep glide, can take the place of flaps on an R/C plane—but does require a different landing technique."

Umm... yeah, ok, you first! I'll pass!  
EricV

[JoeJust]

Eric, back in the late 80's I built a number of fiberglass props for the Hi-Johnson hub a friend of mine used in several of his R/C ships.  They worked very well, and he told me that he had used this arrangement in a Navy Carrier plane. as well.  His comment to me was that the variable pitch props felt like the engine had downshifted to a lower gear. He also told me the advantage was not too great as the hub weighed a ton! Like you though, I would not risk running any old wood blades using this devise.
Joe