COMPOUND CURVE C049
A compound curve bends in two directions at the same time.
Compound curves are desirable in impeller design because they can reduce the amount of impeller wear in abrasive service by allowing the abrasive particles to fall off the vane as it turns.
Notice that the impeller blade bends from the eye of the impeller towards the outside diameter, but also slopes or bends from the near side of the vane towards the back plate.
Compound curves can be formed in investment cast parts, but not sand cast parts.