Airscrew Smoketrails, Single-Surface Flat & Cambered Sections Vs Helically-Pitched Low-Drag Aerofoil

Not the first time I've attempted to capture the differences between Bad & Mediocre Sheetmetal Fans - a 5-Bladed unit with Cambered (Curved) Blade-Sections, and one with with a slightly larger Diameter (7.5 inches rather than 6.5 inches ; both of them up against the freshly recarved and reprofiled 8-inch Diameter by 6-inches Pitch Laminated Wooden "First Attempt", at making a proper Propeller - with Pure Helically-Pitched Blades all the way from their Tips in to 1/2 an inch Diameter, at the Hub...

Both the Flat-Pitch units attempt to produce a thin-walled Torus of Airflow, located halfway from their Tips to their Hubs, radius-wise ; with their Tip-ends being somewhat "over-pitched", a ''Magic Doughnut" where the airstream is advancing at a speed which matches the actual Incidence carved into the Blades...,
And inside that Torus is a stagnant Plug of Air being held back by the flatly underpitched Inner ends of the Blades.


And the Marketing Jism, driven by Production Engineering ; would have people
believe the thin bent Sheet Sheetmetal Blades are "perfectly fine" in real life, when sold in a Box with Promises printed on Paper.

Whereas in real life,
Thin Sheetmetal "Propellers" merely
look good on the
manufacturer's
Balance Sheet.

Such is Life,

Have a good one...

Stay safe.

;-p

Ciao !