On aerofoil section, the force of lift acts perpendicular to, and the force drags acts parallel to the :

A: chord line B: flight path C: aerofoil section upper surface D: longitudinal axis

  • 5
    $\begingroup$ Free stream flow. You should have a word with your instructor. $\endgroup$ – JZYL Sep 1 '19 at 19:29
  • 1
    $\begingroup$ why are you hesitating between all the possibility? It recommend you read the airfoil section of how it flies? $\endgroup$ – Manu H Sep 1 '19 at 19:51
  • $\begingroup$ I change the title of your question so that it looks like a question. feel free to edit again if it does not reflect what you wanted to know $\endgroup$ – Manu H Sep 1 '19 at 19:53
  • $\begingroup$ @Jimmy The instructor expects B (flight path) as the right answer. Which is correct if there is no wind. $\endgroup$ – Peter Kämpf Sep 1 '19 at 20:39
  • 1
    $\begingroup$ @PeterKampf Flight path is inertial. It has no bearing on aerodynamics. Even if we are talking about a wind tunnel case where the section is constrained, flight path is very poor wording; pitch attitude would be marginally better in that case. $\endgroup$ – JZYL Sep 1 '19 at 20:54

This is a basic question, and I give you the answer from the initial pages of a aerodynamic learning textbook.

The is presented in next figure:

Resultant aerodynamic force and the components into which it splits


  • L: lift: component of R (resultant force) perpendicular to air stream,
  • D: drag: component of R parallel with the air stream,
  • N: Normal Force: component of R perpendicular to chord,
  • A: Axial Force: component of R parallel with chord,

For further information you can refer to Anderson's Aerodynamic book.

  • 1
    $\begingroup$ Good diagram. This is very interesting as it presents a realistic representation of the forward component of lift (relative to perpendicular of wing) created by airflow over the leading edge curve at a higher AOA. This was noticed in drag studies, producing a negative drag coefficient! This is also a great illustration of areodynamic center through one point as AOA (potentially) changes. Correct answer - B. $\endgroup$ – Robert DiGiovanni Sep 3 '19 at 1:56

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.