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Originally Posted by nosehair  "rolling" stability (around the longitudinal axies) is designed into the airplane by "dihedral". The wings are slanted up slightly. When a gust of air causes a wing to go down, this downwaed motion causes a slight increase in angle of attack which increases lift which brings the wing back up level with the other. Think exagerated. Think of a boat in water. The sides of the hull of the boat are like the dihedral of the wing. Think of a boat or wing at 45 degrees. If the airplane or boat is pushed over, the pressure on the down-going wing or hull against the airplane or boat will push it back towards equalibrium so that the boat or airplane 'floats' upright in the air/water.
"pitching" stability (around the lateral axies) is designed into the airplane by designing the center-of-gravity in front of the center-of-lift. By having a designed nose-heavy airplane, it will always fall nose first when it stalls.
When it is level the CG is pulling the nose down at all times, so the horizontal stabilizer (hmm...horizontal stabilizer..) is designed to produce a down force equal to the down force of the CG. So the center of lift is between the down force of the nose and the down force of the tail. You are balancing this stabilizing force when you trim to the exact nose down weight of the airplane.
These are the two main stabilizing forces; there are others, but this will
satisfy the initial inquiry. |
Yup - knew that stuff, but how does that make the dynamic stabilty positive, rather than neutral? Something must gradually dampen the oscillations so the aircraft settles back to equalibrium. What provides that damping effect? Is it just that, when an oscillation starts, it gradually loses energy?