Angle of Attack-which cord

[dimsp81]

Hello to all!
This is my first post,even though I have started to read this forum a long time ago.
I am a student pilot for ppl,who likes to learn,not only to pass the exams.
So,I like to search everything I can't understand.

One of the things I can't understand is the angle of attack.

I have read most of the topics here refering to the aoa.
Some of them say that by deflecting flaps,we take the chord that connects the leading edge with the trailing edge that is deflected down,so the aoa is increased (effective angle of attack).
Others say that we take as a reference the chord of the unflapped wing.So,due to the increased camber,we have a faster separation and the wing stalls at a smaller aoa.

What of these things happens?


Does the same thing happens with the ailerons?I mean,by deflecting the aileron down,the aoa of the wing will increase?

I know that there are here some aerodynamists,so,I would appreciate if someone who knows much about aerodynamics can answer.

P.S.IF my thread is in the wrong section,please change it!Thanks!

[abgd]

It's an interesting question...

You could also ask 'which section of the wing is used to calculate angle of attack?' as in a wing with washout (change in the angle of incidence from the root to the tip) the angle of attack will differ from root to tip. Even without washout, most planes don't have full length ailerons or flaps (or flaperons) so it will be rare that a wing has any single angle of attack.

Practically speaking, we're probably most interested in the angle of attack at the wingtips, because a stall here is most likely to lead to a stall/spin accident.

[Tay Cough]

Always thought it was "Mean Aerodynamic Chord".

[S-Works]

It's normally the mean chord line or the chord of the root if the wing. It's just a reference point chosen by the engineers.

[bravobravo74]

Some of them say that by deflecting flaps,we take the chord that connects the leading edge with the trailing edge that is deflected down,so the aoa is increased (effective angle of attack).
Others say that we take as a reference the chord of the unflapped wing.So,due to the increased camber,we have a faster separation and the wing stalls at a smaller aoa.

What of these things happens?

The deployment of flap increases the camber of the wing, which increase the coefficients of lift and drag. A wing's resistance to flow separation is inversely proportional to the downward acceleration that it imparts to the oncoming air, therefore the greater the camber the lower the critical angle of attack.

Despite the flapped wing having a lower critical angle of attack than a clean wing, the flapped wing has a greater coefficient of lift at the critical (or indeed any) angle of attack than the clean wing.

It's worth remembering that the increase to the coefficient of lift that results from increasing the angle of attack is caused by the increased effective camber. As angle of attack increases, the stagnation point moves down the underside of the wing, thus reducing the length of its lower surface and increasing the length of its upper surface.