RE: : Prop construction

Neil,

Two things should be noted.  A true flat airfoil or wing (no bumps, like the spars, on the leading or trailing edges) produces lift when the angle of attack is positive (and oppositely, too).  Second, a "flat" wing with spars for the leading and trailing edges and the tissue on the top is not truly flat.  That wing has (positive) camber so that (positive) lift is produced at a zero angle of attack.  One can look at it, in a simple way, as slowing down the air on the underside.  In an observational sense, such a wing has a leading edge slat and a trailing edge flap just like a commercial jet airplane uses when landing.

This is also why a wing tip that uses a "flat rib" on the outside (tip) still is a cambered airfoil.  It is just less cambered (at the tip) than a tip that as a curved outer rib at the tip.

Leo