First, every airplane has to be trimmed, so it flies straight (not up or down) when you let the controls go. Normally for that you set small trim fins on the elevator. On passenger planes you move the horizontal stabilizer. Normally that is done in the cockpit by turning a wheel forward or backward.
When you fly mach speeds of more than 1 mach that means you are going faster than sound. The air behaves very different, when it hit´s the plane with more than speed of sound, than below that speed.
When you go through the sound barrier, the point of lift moves backwards on the wing, that causes a nose down effect. So you have to trim to counter that effect.
When you fly mach speeds of more than 1 mach that means you are going faster than sound. The air behaves very different, when it hit´s the plane with more than speed of sound, than below that speed.
When you go through the sound barrier, the point of lift moves backwards on the wing, that causes a nose down effect. So you have to trim to counter that effect.