## Forum

# Angle of attack calculate

Quote from robytian on 18. March 2024, 10:19Hi David

I recently encountered a problem regarding finding the effective angle of attack. I hope you can help me answer it.

I took the blade tip segment based on the airfoil in the qblade and wanted to verify the angle of attack calculation to determine whether my theory is correct. But the angle of attack I calculated was as high as 89 degrees. The qblade calculation shows that the angle of attack of the blade tip is about 5 degrees. I gave a simple small program based on the method given by A. van Garrel by solving the normal vector a3 and the tangential vector a1. The resultant velocity is obtained by using the inflow velocity

V0minus the linear velocityomega*rplus the induced velocityVind, although here I didn’t give an induced velocity, but I’d like to know, where is my problem that causes the angle of attack to be so large? Did I overlook something?Thank you

BR,

Roby

Hi David

I recently encountered a problem regarding finding the effective angle of attack. I hope you can help me answer it.

I took the blade tip segment based on the airfoil in the qblade and wanted to verify the angle of attack calculation to determine whether my theory is correct. But the angle of attack I calculated was as high as 89 degrees. The qblade calculation shows that the angle of attack of the blade tip is about 5 degrees. I gave a simple small program based on the method given by A. van Garrel by solving the normal vector a3 and the tangential vector a1. The resultant velocity is obtained by using the inflow velocity **V0** minus the linear velocity **omega*r** plus the induced velocity **Vind**, although here I didn’t give an induced velocity, but I’d like to know, where is my problem that causes the angle of attack to be so large? Did I overlook something?

Thank you

BR,

Roby

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Quote from David on 19. March 2024, 11:28Hi Roby,

even without any induced velocity you should not get such high angles of attack in the tip region, see the velocity triangle below:

Most likely there is an error somewhere in your vector operations or AoA evaluation.

In QBlade the AoA is obtained in the folowing way through a projection of the total velocity into the cross sectional plane of an aerodynamic panel:

m_AoA = atan2((m_V_total.dot(a3)),(m_V_total.dot(a1)))*180/PI;where

a3is the normal vector in the chordwise direction anda1is the normal vector in the direction of the airfoils suction side.BR,

David

Hi Roby,

even without any induced velocity you should not get such high angles of attack in the tip region, see the velocity triangle below:

Most likely there is an error somewhere in your vector operations or AoA evaluation.

In QBlade the AoA is obtained in the folowing way through a projection of the total velocity into the cross sectional plane of an aerodynamic panel:

m_AoA = atan2((m_V_total.dot(a3)),(m_V_total.dot(a1)))*180/PI;

where *a3* is the normal vector in the chordwise direction and *a1* is the normal vector in the direction of the airfoils suction side.

BR,

David