Pitching Moment Acting on a Wing

  • Thread starter fog37
  • Start date
860
42
Hello, I am learning about the pitching moment acting on a wing that is immersed in an airflow hoping to clarify some key concepts. In general, the moment of a force depends on:
  • Location of moment reference point ##o##
  • Force magnitude
  • Lever arm (distance between force application point and moment reference point ##o##)
A positively cambered wing always experiences a nonzero, constant, pure and negative (nose-down) moment ##M_{camber}## even when the net lift force ##F_{lift}=0##. However, when the lift force ##F_{lift}\neq 0##, which happens for increasing angles of attack ##\alpha##, an extra moment ##M_{lift}\neq 0## due to ##F_{lift}\neq 0## must be included and the total pitching moment ##M_o## about the arbitrary point ##o## is equal to: $$M_o = M_{camber}+M_{lift}$$ When ##M_{lift}=0## then ##M_o = M_{camber}##. I think this discussion presumes that the lift force ##F_{lift}## is applied at the aerodynamic center ##a.c.## and generates a moment ##M_{lift} = F_{lift} x## where ##x## wis the distance between the moment reference point ##o## and ##a.c.##. When the moment reference point ##o=a.c.##, the total pitching moment becomes $$M_O = M_{a.c.}= M_{camber}$$ since ##M_{lift}=0## because the lever arm ##x=0##. So ##M_{lift}## is always zero when either ##x=0## (which happens when ##o=a.c.##) and/or ##F_{lift}=0##. Is that correct?

The same total moment ##M_o## should be obtained when, for a certain angle of attack ##\alpha##, when we consider the force ##F_{lift} \neq 0## and to be applied at the center of pressure ##c.p.## instead of at the aerodynamic center ##a.c.##. I can see how the total moment ##M_o## about a reference point ##o## would be nonzero when ##F_{lift} \neq 0## since $$M_o =F_{lift} x^{*}$$ where ##x^{*}## is the distance between ##c.p.## and the point ##o##. The moment can be positive or negative depending on if ##o## is before or after ##c.p.##.
But when ##F_{lift} = 0##, the moment ##M_o=0## always regardless of the lever arm ##x^{*}##. However, the total moment ##M_o## should always be nonzero due to camber moment contribution ##M_{camber} \neq 0## existing even when ##F_{lift} \neq 0##....
 
1,416
9
Thanks for the thread! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post? The more details the better.
 

Want to reply to this thread?

"Pitching Moment Acting on a Wing" You must log in or register to reply here.

Related Threads for: Pitching Moment Acting on a Wing

Replies
4
Views
17K
  • Posted
2
Replies
34
Views
3K
Replies
3
Views
15K
Replies
7
Views
713
Replies
4
Views
977
Replies
1
Views
759

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top