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What is the difference between centre of pressure, aerodynamic centre and neutral point?

At this link, there is an image used to explain the answer, but not much has been spoken about it. airplane holds disturbed position

I understand that the disturbance was caused by either the CG moving too ahead or too rear, or the CP moving forward of the CG. I would like to know that in the given image, how did the aircraft hold the disturbed orientation ? Was it perhaps by mechanically shifting the CP back again using some device ? Thanks in advance.

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  • $\begingroup$ I think you'll be interested by the section about pitchwise stability of how it flies $\endgroup$ – Manu H Apr 10 at 10:20
  • $\begingroup$ thankyou @ManuH sir, i will look at it $\endgroup$ – sahil saxena Apr 10 at 10:22
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Your own answer is correct. You "mechanically shift the CP (in relation with CG)" with a control surface.

Perhaps this is easier to see on the roll axis, where we use ailerons to laterally shift the aerodynamic CP. If the plane has dihedral, it will try to roll back up right, if not, it will remain in a bank, similar to your picture.

As a note to those "dihedral unbelievers", yes, a strong yawing or spiralling tendency will cancel dihedral stability, but that is an issue of the rudder.

A plane with "nuetral stability" stays where it is after control input or "external disturbance" is removed.

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  • $\begingroup$ Sir, may i ask you a similar question in the case of missiles or rockets ? A missile moving at constant velocity which has side thrusters at the nose and tail end in an X configuration, where vertically opposite thrusters are fired to cause a torque. We know that if the CP is aft of CG we will face a resistance from the body as in a resoring moment, but the CP also moves forward of CG with increase in AoA. So how much force/torque would the side thrusters have to use to be able to change the orientation of the missile ? And then how do we hold it in case of missiles ? $\endgroup$ – sahil saxena Apr 10 at 10:04
  • $\begingroup$ Keep in mind air friction will slow any rotation after control input is removed. But a missile, airplane, arrow, spear that is not directionally stable is difficult to control. The javelin solves this issue by spinning. $\endgroup$ – Robert DiGiovanni Apr 10 at 13:46

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