MarkBolton wrote: ↑
Mon Nov 16, 2020 2:46 pm
Regarding induced drag, I understand where it comes from-the horizontal element of the resultant lifting force due to the rear facing lift vector.
But what is this 'horizontal' element in relation to? The ground, mean chord line or the direction of travel?
What is the correct term for this plane?
Is it possible to have a 3D lifting aero shape (not something symmetrical) in which all the lift is perpendicular to the 'horizontal' plane, so that there is no induced drag?
Turning the air requires energy, the manifestation of that energy conversion is drag. You cannot eliminate drag if the shape creates a pressure differential as it cuts across the air, you can minimize extra drag only, never zero drag. Only way to have no induced drag is to not have bodywork in the path of the air.
"Is it possible to have a 3D lifting aero shape (not something symmetrical) in which all the lift is perpendicular to the 'horizontal' plane, so that there is no induced drag?"
Yes to the former, no to the latter. It only matters which way the air is flowing on the trailing edge that determines the force vector on the surface.
Look at the bargeboards, they're a perfect example of this. The airflow hits it dead on, but is pushed out and up, so the force vector is still towards the ground. You can see the way the floor flicks up aft of the side pod undercut, to understand where the force vector of the bargeboards is.
The air flows freely under the bargeboards, while over them, the air turns out and up, which slows it down increasing its pressure which comes to a head when that air interacts with the sidepod undercut.