Which prop creates more lift? Leading edge or blown flap?
In distributed propulsion there seem to be 3 prop locations: leading edge (NASA X57, blackfly), blown flap (Lillium), and pusher prop (Kittyhawk).
Which would create more lift, leading edge or blown flap?
Leading edge: The entire wing chord sees about 50% of prop exit speed (turbulent though), the prop pushing 50% of the air under the wing (although it would create lift by hitting the flap (assume 45-90 deg flap position)
Blown Flap: wing sees 100% of prop exit speed but only on about 45% of the of the chord ( assuming 50% chord flap), but the first 45% of the wing sees non turbulent air. Blown flap has the advantage of providing vertical thrust.
See pictures below.
Lillium - blown flap ( assume props, not the actual electric turbines it uses)
Kittyhawk - pusher prop
Nasa X57 - leading edge/tractor prop
Below are 3 Cp plots from xflr.
First plot has no flap, but has a roughly 30 deg angle in (-) pressure drop.
Adding a 50% chord flap, increases the suction at 0% chord???
Was surprised to a spike in negative pressure at 0% chord from a 50% chord, 45 deg flap!!! Would have thought there would be a negative pressure spike at 50-60% chord....
What would the shape of the pressure plot be when distributed propulsion is added to the flap? See plot below.