Originally Posted by
Rarife
Is it possible to achieve flying at negative angle of attack? Let's skip the part where it would be more like fall than a flight.
Sure in theory it is not a problem. I have airfoil, I put it into a wind tunnel and I can have any aoa I want.
But in reality? Let's asume I have normal real aircraft with some normal angle of incidence. My point is that even if I nose dive the flight path vector will be always "under" the airflow. I can imagine reaching negative alpha during the pushing. For a while but once I fly down it gets and stay possitive.
Even if I look at aoa indicators they have mostly only possitive values and books or so show you lift coeficient curve but I have not seen anything which shows how alpha changes in real flight.
I know it may look simple or ridiculous but I'm really not sure.
The two cases I can come up for sustained negative AOA are inverted flight and multiple outside loops (a loop made by pushing the control while in level flight and keeping the input until you are level again).
Also parabolic flight can have a temporary negative AOA, as long as you push enough.
Most wings are designed to give positive lift at 0 AOA, but exactly at what (negative) G-load your AOA becomes negative is above my pay grade.
(I think the angle of incidence isn't relevant, the AOA is the angle between wing and air, the angle of the fuselage really doesn't matter for this...)