Lift and Drag Which frame of reference?

AI Thread Summary
The discussion centers on the definitions of lift and drag equations in different frames of reference, specifically the stability frame and the wind frame. It highlights that while the equations for lift and drag are valid in both frames, the choice of reference area significantly influences their application. The dynamic pressure remains consistent across frames since it relies on the relative velocity of the air to the body. The main concern is how the coefficients of lift and drag (C_L and C_D) are derived, as they can vary based on the frame used. Ultimately, the direction of the force vectors is what changes depending on the chosen frame of reference.
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Lift and Drag...Which frame of reference?

Hi,

When expressing the Lift and Drag acting on an airplane as:

F_{lift}=qSC_L
F_{drag}=qSC_D

where q is the dynamic pressure, S is the wing ref. area, and C's are the lift and drag coefficient.

My question: Some sources, like this one, claim these equations are 'defined' in stability frame {S}, while other claim they are in wind frame {W}. In either case you'll use a rotation matrix to go back to body frame {B}, but this matrix will differ whether going from W->B or S->B, wo which is correct?
 
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I'm sorry you are not generating any responses at the moment. Is there any additional information you can share with us? Any new findings?
 
Not really. I still do not have answer.
 
It all depends on how CD and CL were calculated in the first place. The equations themselves are valid in either frame since the dynamic pressure is not frame dependent in the sense that it uses velocity magnitude of the air relative to the body. The only thing that really matters is what reference area was used. The only place the frame would matter is in determining which direction the vector for each force points within each respective frame.
 
Well, C_D and C_L are Taylor expanded into many components which are usually obtained from a CFD software, so I am not sure.
 
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