Question about NACA airfoils

[philthepile]

I recently found a site with a lot of NACA airfoil profiles given as coordinates. When I looked at the NACA 0008 and 0009 profiles I found that they were symmetrical about the horizontal (they had no camber). Is there something I'm missing or did early airfoils have to be angled to provide lift?

[drgondog]

Originally Posted by philthepile

I recently found a site with a lot of NACA airfoil profiles given as coordinates. When I looked at the NACA 0008 and 0009 profiles I found that they were symmetrical about the horizontal (they had no camber). Is there something I'm missing or did early airfoils have to be angled to provide lift?

Many of the early airfoils started with flat bottom surface and curved top surface as these airfoils were more efficient in low speed. Both symmetrical and cambered airfoils give lift but a cambered airfoil may give lift at zero angle of attack with freestream, whereas a symmetrical airfoil requires a finite angle of attack to generate lift.

Additionally the Theodorsen Transformation yielded a forward solution, using a complex variable mapping of a rotating cylinder immersed in an airflow (think curveball), to design an airfoil with a specific velocity distribution target. - Its immediate application was cambered wings.

Theodorsen and Von Karman were the leading intellects in the US driving theory and knowledge of thin airfoil theory.

[philthepile]

Thank you for the quick reply. I was not aware that airfoils relying on a non zero angle of attack for lift were so common.

[drgondog]

Originally Posted by philthepile

Thank you for the quick reply. I was not aware that airfoils relying on a non zero angle of attack for lift were so common.

Any symmetrical airfoil, absent flaps, etc would fit that bill. You have to have airflow faster over one surface than the other to achieve a 'lower' pressure compared to the other surface - inverted or upright.

At zero angle the symmetrical airfoil has equal velocity over both top and bottom surfaces - no lift until AoA changes one direction or the other

[drgondog]

Originally Posted by philthepile

Thank you for the quick reply. I was not aware that airfoils relying on a non zero angle of attack for lift were so common.

Any symmetrical airfoil, absent flaps, etc would fit that bill. You have to have airflow faster over one surface than the other to achieve a 'lower' pressure compared to the other surface - inverted or upright.

At zero angle the symmetrical airfoil has equal velocity over both top and bottom surfaces - no lift until AoA changes one direction or the other.

As to examples - think of most all USAF fighter a/c since Mustang

[Ivan1GFP]

The tail surfaces of most planes are symmetrical airfoils.

- Ivan.