A propeller blade, like a wing, need only have an aerofoil section to minimise drag. Both could be made from flat planks, set an an angle to the airstream, given a big enough driving force.
Today’s invention is to make an aircraft propeller of strips of transparent plastic. Each strip would be essentially a plank, set at an angle to to axis of rotation and petal-shaped. These blades would sweep out a volume exactly like that of a large, bi-convex lens.
Rotating at speed, persistence of vision would cause it to act as a solid lens in front of the pilot of a single-engined plane.
When atempting to spot missing people on the ground, or a distant landing strip, the pilot could look forward and see a magnified view of reality.