PEI_3721
The pressure differential AOA measurement is very simple: as the AOA changes the pressures change as well. At low AOA mainly the pitot hole is effected and the pressure at the 45 degree hole is less. At large AOA the pitot hole will "rotate" out from the airstream (decreasing pressure at it), and the 45 degree hole will be effected more by the airstream. Continuous processing of these two pressures will give an AOA.Yes, Aspen's system surprised me too, especially the use of GPS data. But the engineers of this big company must be skilled enough, they now what they're doing, I guess.
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Thank you the explanation. Actually the "bending" of the airstream is not the classic up/downwash yet, because this bending will occure already at a 2D profile, but the acutal up/downwash is related to the finite 3D wing. BUT you are right, the probe definitely meausre the higher AOA because of this phenomenon. But in the aviation literature I have not find any theory on how much is this bending of the freestream related to the camber of a profile, what is the aerodynamic correlataion? There are a lot of material on up/downwash, but as I wrote it is not THE up/downwash.
I think the bending of the free airsteam is related to the absolute angle of attack (angle from zero lift and this way to the camber). For example a manufacturer of an AOA isntrument especially calls the user attention to forget the classic concept of AOA, because the instrument actually reads the absolute AOA (angle from zero lift). And with a more cambered wing, I mean with flaps the absolute stall AOA will be always higher compared to CLEAN. And the instrumens definitely work in this sense.