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Colyn! The prop scales up or down. I recently did a design
for a four-blade CS, 55" diameter, 500+ hp, 400 mph. Very high efficiency. Prop
tips are mounted on a long lever. One lb of drag at the tip of a 3 ft radius
consumes three times as much hp as one lb at 1 ft radius. There is no lift at
the tip, but the drag, which is proportional to chord, is still there! Sweeping
the tip doesn't get rid of the drag, nor does making the blade thinner, which is
also what sweeping a blade does; it makes the blade look thinner. Thinner blades
also have lower L/D! Keeping tip chord at zero and tip Mach at or below
0.85 is the ticket! In my equations I compare thrust-to-torque ratio
every inch along the blade. On my designs it decreases somewhat near the tip,
but stays fairly constant all the way into the root. On standard
wide-chord blades, it really goes to Hell at the
tips!
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