Effective angle of attack

[Craig Toutolmin]

I'm under the impression from a source I can't recall, that the effective angle of attack of a wing varies with aspect ratio. At the same angle of attack a wing with a higher aspect ratio will fly at a higher effective angle of attack.

If this is infact true, are aspect ratio and lift distribution tied together so that past a point of optimum aspect ratio, lift distribution suited for the design task begins to suffer?

Is this solely due to the fact that a higher aspect ratio wing has a higher effective span from lower induced drag?

Does the lower average chord of the high aspect ratio wing affect this scenario or is it accounted for by selecting proper foils for the Reynolds numbers and local Cl during the designed task?


TIA,

Craig

[Sail 'n Soar]

The lift-curve slope per degree alpha for an elliptical wing is:


a = ae/(1+(57.3*ae/pi*AR))

Where:

ae = section lift-curve slope
AR = aspect ratio

This relationship is very close for straight taper ratios between .2 and .6 ct/cr.

[Sail 'n Soar]

If this is infact true, are aspect ratio and lift distribution tied together so that past a point of optimum aspect ratio, lift distribution suited for the design task begins to suffer?

Is this solely due to the fact that a higher aspect ratio wing has a higher effective span from lower induced drag?

The reduced effective angle of attack is directly linked to the finite wing shed vortex fenomina, which creates induced drag. Ignoring wash-out, the lift distribution is driven by the planform shape and not the aspect ratio - for a given total lift the spanwise lift distribution will be the same, only at aspect ratio dependent effective angles of attack.