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Founder
26th Nov 2006, 12:32
What is the difference between the Aerodynamic Center and Center of Pressure?

/Tim

AirDawg
26th Nov 2006, 13:25
iirc:
c.p. is the point along the chord where the distributed lift is centered.
a.c. is the point along the chord where lift changes (or the sum of lift changes)take place

c,p. is rather static and a.c. will move depending on aoa, dyanmic pressure (q), and other variables.

Hope this helps as a starter, someone else I'm sure can expand and/or clarify further.

Founder
26th Nov 2006, 13:29
iirc:
c.p. is the point along the chord where the distributed lift is centered.
a.c. is the point along the chord where lift changes (or the sum of lift changes)take place

c,p. is rather static and a.c. will move depending on aoa, dyanmic pressure (q), and other variables.

Hope this helps as a starter, someone else I'm sure can expand and/or clarify further.

Ok... That clears it up a bit...

but...

I'm a bit confused... according to my books the CP moves with AoA as well as TAS. As an example when accelerating through the transonic region, the CP shifts from about 25% chord to 45% chord...

And the CLmax vs AoA diagram, doesnt it show the CP movment compared to AoA?

pstaney
26th Nov 2006, 15:28
iirc:
c.p. is the point along the chord where the distributed lift is centered.
a.c. is the point along the chord where lift changes (or the sum of lift changes)take place

c,p. is rather static and a.c. will move depending on aoa, dyanmic pressure (q), and other variables.

Hope this helps as a starter, someone else I'm sure can expand and/or clarify further.

Other way around. Center of pressure will change with mach and aoa. It is aerodynamic center that really doesn't change, theoretically calculated at exactly 25% MAC, but typically between 23 and 27%. There was a very informative thread on this a year or 2 ago. Keith Williams explained it well.

Founder
26th Nov 2006, 15:35
Other way around. Center of pressure will change with mach and aoa. It is aerodynamic center that really doesn't change, theoretically calculated at exactly 25% MAC, but typically between 23 and 27%. There was a very informative thread on this a year or 2 ago. Keith Williams explained it well.

Thanx =)

I tried to find the thread but was unable to do so by searching for posts with his name... :(

pstaney
26th Nov 2006, 18:48
You're right, quite hard to find. Not much on C of P, but has AC info. Here it is, should work.
http://www.pprune.org/forums/showthread.php?t=130098&highlight=Aircraft+C+of+G+wing+pitching+moment

Founder
26th Nov 2006, 18:53
You're right, quite hard to find. Not much on C of P, but has AC info. Here it is, should work.
http://www.pprune.org/forums/showthread.php?t=130098&highlight=Aircraft+C+of+G+wing+pitching+moment

Thank you very much =) I'll read through it tomorrow =)

Again PPRuNe proves to be the place to find answers to most questions, I'm very impressed with this forum and the people here =)