I'm working on planform and airfoil selection, and a question has emerged: at what AoA do we consider a wing to be stalled, since a wing does not have uniform C_l/C_lmax across its span? There is some range of AoA during which we first see the stall appear until all of the wing stations are stalled. After the stall is initiated, more AoA is required so that the unstalled portion of the wing can make up for the lost lift, increasing the area of the stalled region, until finally the entire wing is fully stalled and no lift is being generated.
Supposing we have a Hershey bar wing, the elementary method of determining area based on C_Lmax of the airfoil and desired V_s yields something like this:
So from the C_l distribution we know this wing should have a nice stall progression from root to tip as AoA is increased. Gudmundsson suggests (section 9.6.4), like most other sources, that so long as the outboard 30% remains unstalled and C_l is falling to zero outboard of this point, the stall behavior will be acceptable.
This rule of thumb seems to imply that in this example, while keeping our desired V_s fixed, wing area could be reduced to the point that the blue C_l curve moves up to intersect the red C_lmax line at 70% semispan like this:
What do you think? Is this an appropriate way to define the stall of a finite wing? Or is there a better rule?
After we've had some discussion of this validity of this conjecture, I'd like to go on to discuss how we might apply it to different planforms and to the inclusion of aerodynamic twist.
Supposing we have a Hershey bar wing, the elementary method of determining area based on C_Lmax of the airfoil and desired V_s yields something like this:
So from the C_l distribution we know this wing should have a nice stall progression from root to tip as AoA is increased. Gudmundsson suggests (section 9.6.4), like most other sources, that so long as the outboard 30% remains unstalled and C_l is falling to zero outboard of this point, the stall behavior will be acceptable.
This rule of thumb seems to imply that in this example, while keeping our desired V_s fixed, wing area could be reduced to the point that the blue C_l curve moves up to intersect the red C_lmax line at 70% semispan like this:
What do you think? Is this an appropriate way to define the stall of a finite wing? Or is there a better rule?
After we've had some discussion of this validity of this conjecture, I'd like to go on to discuss how we might apply it to different planforms and to the inclusion of aerodynamic twist.
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