IM003506

This pict has duct 90 degrees to cowl, notice how much less exit area can be seen compared to next shot that is 90 degrees to gills. With duct 90 degrees to cowl, exit air was 1500FPM, (Feet per minute), with duct 90 degrees to exit of gills, 1550FPM. True that this is not an ideal ducted fan, and the prop is a bit too close to lip that hurts things, but restriction of gills slows flow and prop somewhat stalls and cavitates. No duct allows air to spill out and sounds much better. No duct it tis. Acid test if proves want to suck air in gills, then will add duct, easy to do on completed aeroplane.