His method goes a little like this; 1. Design/modify ducts 2. Test results 3. Evaluate results 4. Go back to 1.
After making 7 revisions of the 5 inch version, the design generates at least the same amount of extra thrust as the ducts weigh. Which is a very promising results.
To achieve better efficiency and more thrust he’s now moving to a 6 inch propeller setup.
But why on earth does ducts generate more thrust from the same power setup? Mainly 2 reasons. When a propeller spins around the airfoil on the propeller creates lift by generating low pressure on the top of the blade. Nature hating differentials the high pressure air on the bottom wants to flow to the top of the blade and equalise the system. This results in a spiral vortex forming at the tip of the blade which induces drag and ruining lift. By adding a shroud/duct with a very small clearance between the propeller and the duct wall the high pressure on the bottom can’t flow to the top which almost completely kills the vortex at the tip of the blade. The second reason for the additional lift is the lip of the duct. This is designed to have a soft edge that rolls over the and down the outside of the duct. In fact it’s shaped like an airfoil! The air being sucked into the propeller rushes past this aerofoil lip, which generates a low pressure zone just like a wing, which we know generates lift! Pretty clever stuff.
Keep up the great work Eric!