Originally Posted by
FCeng84
The shape of a commercial airplane wing (twist, sweep, variation in cord and camber along the span, etc.) is very complex. As such it would be quite a trick to define a true "zero AOA" reference. What ever metrics used for such a calculation would undoubtedly be impacted by flap position and wing spanwise droop that is a function of payload/fuel distribution and wing lift loading. AOA as determined from the body mounted vanes (with correction for known local flow distortion) is presented with respect to the fuselage.
Exactly, and this is the flip side of all the non-wing "total airframe" components I mentioned that make any zero-AOA datum, arbitrary. So you might as well choose a convenient one, that is not separated, as you note, by the AOA vanes by a floppy piece of structure (and, I'll add, from the IRS).
As has been mentioned, transport aircraft that are optimized to maximize L/D are designed to fly with a small, positive pitch attitude. To design an airplane to fly with deck angle of exactly zero in cruise would be to leave unrealized performance on the table!
This I disagree with. Why can't a plane be designed for the cruise condition with an exactly-level fuselage attitude (least drag) and wing incidence set for an AOA that yields best performance?
(I understand that after the basic design is "locked in" and it would be too time consuming and expensive to change the incidence, customer requirements or fuel prices or max gross weight or many other factors could change the cruise condition, and therefore the AOA, and therefore fuselage attitude; but I'm talking about the design process at the very beginning, before it's molested by such changes.)