- #1
Murmur79
- 10
- 0
Suppose we have an infinite straight wing, using a given airfoil. Also, suppose for simplicity the B.L. is completely turbulent, and M<<1 (incompressible fluid).
As we know, the forces per unit length are: L=q⋅c⋅cl, D=q⋅c⋅cd, where cl and cd are the coefficients of the 2D airfoil for the given Re and α.
Now, if we rotate the infinite wing of an angle Λ, we have an infinite swept wing.
The theory says that in this case, the forces per unit length (parallel to leading edge) become: L=q⋅cos2Λ⋅c⋅cl, D=q⋅cos2Λ⋅c⋅cd.
Here is my question:
when looking up the cl and cd for the 2D airfoil, should we use:
.) the Re for the unswept wing: Re=U⋅c/ν
.) the Re normal to leading edge: Re=U⋅cosΛ⋅c/ν
.) the Re parallel to the flow: Re=U⋅(c/cosΛ)/ν
As we know, the forces per unit length are: L=q⋅c⋅cl, D=q⋅c⋅cd, where cl and cd are the coefficients of the 2D airfoil for the given Re and α.
Now, if we rotate the infinite wing of an angle Λ, we have an infinite swept wing.
The theory says that in this case, the forces per unit length (parallel to leading edge) become: L=q⋅cos2Λ⋅c⋅cl, D=q⋅cos2Λ⋅c⋅cd.
Here is my question:
when looking up the cl and cd for the 2D airfoil, should we use:
.) the Re for the unswept wing: Re=U⋅c/ν
.) the Re normal to leading edge: Re=U⋅cosΛ⋅c/ν
.) the Re parallel to the flow: Re=U⋅(c/cosΛ)/ν