Reference Area for Cl & Cd with changing Alpha
 

Hi all,

I have so far assumed that the reference area (and thus chord length/frontal area) for calculating Cl and Cd are taken constant as the 0-degree Alpha values for an airfoil. In principle, the plan and frontal area change with alpha - is this ignored normally or should we account for this when doing an alpha sweep to generate Cl and Cd vs Alpha plots? Plan area of a wing doesn't change much with alpha (with typical low alpha values) but frontal area does change significantly... This would also tie in with calculating Re Numbers... So with high Alpha they would change significantly...

It gets tricky when comparing with experimental data as I don't believe in published historical data accounts for changing chord length/frontal area - or am I wrong?


Thanks for any thoughts,


Kai.