Talk:Center of pressure (fluid mechanics)/Archive 1

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In America, engineers use the abbreviations cg for center of mass (or gravity) and cp for center of pressure. Where are the abbreviations CoP and CoM from?--192.146.217.206 22:23, 25 August 2005 (UTC)

CoP and aircraft stability

Guys, there is no direct connection between the CoP position and aircraft stability! An airplane can have its CoP either ahead or behind CoM and still be statically stable.

As usual, CoP is confused with aerodynamic center. When I have time, I'll write an article about the aircraft stability and aerodynamic center, but so far — be alarmed.

P.S. A good starting point for those interested could be http://www.grc.nasa.gov/WWW/K-12/airplane/ac.html

Sergey Khantsis 11:40, 7 November 2005 (UTC)

There's no direct connection between AC and stability either. But certainly the comments about the relationship between CoP and CoG for basic flight is accurate. Additionally, if your CoG-CoP moment is beyond the control capabilities due to loading, you crash. That's close enough to direct in my books. And those books are pilot and failed physicist. I will agree, however, that a full explaination of stability would be a good addition. Maury 14:06, 20 November 2005 (UTC)

Well, in terms of control limits - certainly, the distance between CoG and CoP does have a direct effect. However, as long as there is enough control moments, stability is described by stability derivatives, most notably pitch moment by angle of attack (or CL), which is determined by the distance between CoG and AC (not CoP!). Yes, 'in general terms' CoP is required to be behind CoG; nevertheless, if, for example, wing CoP moves backward with the angle of attcak too fast (and this can happen in some circumstances, e.g. special airfoil), it can be easily placed in front of CoG without affecting the aircraft's static stability (because AC will be still behind the CoG). Sergey Khantsis 17:49, 27 November 2005 (UTC)

Aerodynamic center

The fact that this gives a moment which does not vary with AoA urgently needs more careful clarification, by a specialist (ie not me!) Bob aka Linuxlad 18:55, 21 January 2007 (UTC)

Definition

Contradictory. The intro does not make sense. Expert needed. `'юзырь:mikka 06:54, 31 May 2007 (UTC)

historical

The concept of center of pressure come from sailing ship design. sails share many aerodynamic properties with airfoils used on aircraft, and early airfoil science borrowed the term. But unlike rigid airfoils, sails do not have moment forces.

The center of pressure represents the point where the moment force is zero. This point is determined by dividing the moment force by the lift force to determine a moment arm which is added to the postition of the aerodynamic center to determine the center of pressure. Since the lift coefficient varies with the angle of attack, while the moment coefficient on a rigid airfoil is roughly constant, the length of the moment arm, and hence the center of pressure, varies with angle of attack.

Because the lift coefficent can be zero, the moment arm can be infinite in length. When considering a small change in the angle of attack from an angle that results in a slightly negative to a slightly postive lift coefficient, the center of pressure shifts from a position infinitely in front of the airfoil to one infinitely behind the airfoil.

While the center of pressure concept represents the lift force without the need to consider the moment force, the moment force produced by the airfoil is just one of several moment forces affecting the pitch characteristics of an aircraft relative to the center of mass of the aircraft. These other moment forces include the lift forces of both the tail and wing as well as the drag force of the wing. -- Gciurpita 01:09, 21 June 2007 (UTC)

Something missing?

The 'Aircraft' section starts thus: "A stable configuration is not only desirable in sailing, but in aircraft design as well". Presumably there was an earlier paragraph referring to sailing vessels, since deleted? As it stands, this makes no sense. AndyTheGrump (talk) 15:20, 23 August 2010 (UTC)

Yes, there was previously a section titled Historical usage which focussed on the use of center of pressure in the terminology of sailing vessels. It was deleted without explanation on 24 October 2008 in THIS EDIT. The concept of center of pressure is not unique to aviation so I think the nautical reference should be restored. Dolphin (t) 22:44, 23 August 2010 (UTC)

It has now been restored. Dolphin (t) 22:49, 23 August 2010 (UTC)

This article would be more helpful if it explained the centre of pressure mathematically as well as descriptively I think.--User:? 21.:45 November 2010 —Preceding unsigned comment added by 131.251.236.59 (talk) 21:45, 10 November 2010 (UTC)

'Center of Pressure in Biomechanics'

This is an entirely different subject to the one the article previously discussed, and accordingly should not be dealt with here. Perhaps we need a disambiguation page, with two articles - we certainly cannot have a single article on two unrelated topics, simply because they share the same name. I shall raise this matter at Wikipedia:WikiProject Organismal Biomechanics, and see how we can sort this out. AndyTheGrump (talk) 18:00, 24 March 2012 (UTC)

As I noted on WP:Biomechanics, I don't agree about them being separate - CoP is something that happens when force is applied over an area, whether it's a human foot on the ground or water behind a dam. I favor expanding the page to include solid mechanics. I'd be surprised if a similar concept didn't also arise in, say, civil engineering when dealing with the foundation of a building. HCA (talk) 18:40, 24 March 2012 (UTC)

No - you are incorrect. This article is about a specific concept in fluid mechanics, as it makes quite clear in the lede. The two subjects are unrelated, and they should not be discussed in the same article. However, as I've already indicated, this isn't the appropriate place to discuss this: please comment at Wikipedia talk:WikiProject Organismal Biomechanics#Center of pressure. AndyTheGrump (talk) 18:46, 24 March 2012 (UTC)

Having investigated further, and per the discussion in the thread linked above, I have now removed the 'biomechanics' section: it is clearly discussing a topic unrelated to that of the rest of the article. To avoid any further ambiguity, I intend to rename the article as Center of pressure (fluid mechanics). The deleted material may of course be used in a new Center of pressure (biomechanics) article. (If this is done, don't forget to indicate where it was copied from). AndyTheGrump (talk) 15:49, 28 March 2012 (UTC)

Center of pressure vs. Centroid

I am absolutely incredibly sorry for writing here but I don't know where to write this and I am not an expert so don't want to edit. I don't think that the "center of pressure" is the centroid - at least for a submerged plate such as a gate in a dam wall. The centroid is the "center of mass" and is called the first moment of area. The "center of pressure" is below the centroid and is called the second moment of area. I am sure I cannot put links in here but there are many references including wikipedia. Please delete this whether right or wrong :) lfahlberg — Preceding unsigned comment added by Lfahlberg (talk • contribs) 10:54, 11 May 2012 (UTC)