ClipArt ETC
"The chamber (curvature) of the blades should be (1) equal, (2) decrease evenly towards the tips of the blades, (3) the greatest depth of the curve should, at any point of the blade, be approximately at the same percentage of the chord from the leading edge as at other points." —Barber, 1917

Aeroplane Propeller Balance Chamber

"The chamber (curvature) of the blades should be (1) equal, (2) decrease evenly towards the tips of…