- #1
NBAJam100
- 146
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Hey guys,
I current picked up Fundamentals of Aerodynamics by John D. Anderson Jr. and am having a little bit of trouble understanding some of the equations i am given. This is the first aero book I've picked up so I am not too familiar with aero concepts or terms yet.
On page 20, they break down the Lift and Drag components geometrically. The symbols below are as follows: A= axial force and N=normal force. [tex] \alpha = [/tex] angle of attack.
They have:
[tex]L=N\cos \alpha - A\sin \alpha [/tex]
[tex]D=N\sin \alpha + A\cos \alpha [/tex]
I am having trouble understanding why this is true, and why they put the +/- where they did. I see that [tex]N\cos \alpha [/tex] is equal to L, so why are we subtracting the [tex]A\sin \alpha [/tex] ? Same goes for the equation for D. I am sure I am overlooking something very obvious here, but id appreciate someone helping me see it.
Thanks.
I current picked up Fundamentals of Aerodynamics by John D. Anderson Jr. and am having a little bit of trouble understanding some of the equations i am given. This is the first aero book I've picked up so I am not too familiar with aero concepts or terms yet.
On page 20, they break down the Lift and Drag components geometrically. The symbols below are as follows: A= axial force and N=normal force. [tex] \alpha = [/tex] angle of attack.
They have:
[tex]L=N\cos \alpha - A\sin \alpha [/tex]
[tex]D=N\sin \alpha + A\cos \alpha [/tex]
I am having trouble understanding why this is true, and why they put the +/- where they did. I see that [tex]N\cos \alpha [/tex] is equal to L, so why are we subtracting the [tex]A\sin \alpha [/tex] ? Same goes for the equation for D. I am sure I am overlooking something very obvious here, but id appreciate someone helping me see it.
Thanks.