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Drag is aerodynamic force component parallel to the direction of motion.

Lift is aerodynamic force component perpendicular to the direction of motion.

Direction of motion with respect to what?

1) The instantaneous local atmosphere (the air)? If the wind suddenly changes, does the displacement angle (below) change because the rocket keeps going in one direction, but the aerodynamic force changes because the air is now moving differently?

2) Earth-centered, Earth-rotating frame?

3) Earth-centered, inertial frame?

I'd like to write a few lines of code, but I was stopped cold when I realized that a (very strong) gust of wind can induce lift - depending on how the vectors are defined.

Image from https://spaceflightsystems.grc.nasa.gov/education/rocket/rktstab.html

NASA Rocket Forces

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As I believe you suspected, it is based off of the local wind direction. Changing winds will affect the way that lift affects the rocket. As specified at Wikipedia

Drag ... is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid.

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  • $\begingroup$ Afterward, it seems obvious - a no-brainer. But only after someone who knows what they are talking about confirms it. Retroactively-obvious I think it's called. Thank you! $\endgroup$ – uhoh Jul 9 '16 at 13:56
  • $\begingroup$ Where "wind" includes relative motion due to the flight of the vehicle, and not just wind relative to the ground. Shuttle mostly used the body frame. $\endgroup$ – Organic Marble Jul 9 '16 at 17:43
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    $\begingroup$ Hence the use of the word "Local" $\endgroup$ – PearsonArtPhoto Jul 9 '16 at 17:46
  • $\begingroup$ As one who dealt with meteorological winds during launch, it was an important distinction for us. $\endgroup$ – Organic Marble Jul 9 '16 at 17:51
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Offered up as a supplement to the accepted answer, since I like pictures.

enter image description here

enter image description here

From Coordinate Systems for the Space Shuttle Program.

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  • $\begingroup$ I like them too! The linked document is a fun read as well. Thanks! $\endgroup$ – uhoh Jul 10 '16 at 1:23

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