The "Universal" adjustable and reversible propeller built by Paragon Engineers, Inc., Baltimore, Md

Bacon, David L
naca-tm-155
November 1922


A device which does for the aircraft what change speed gears do for the automobile is the invention of Spencer Heath. It comprises a system of special blades and a mechanism for varying the pitch of the blades from zero to 360 degrees, while in flight or otherwise.

An Adobe Acrobat (PDF) file of the entire report:
http://naca.central.cranfield.ac.uk/reports/1922/naca-tm-155.pdf