Tuck Under (Mach Tuck)

Mack tuck is an effect to cause an airplane to pich down as it accelerates in transonic flight (0.72 ~ 1)

 

1) Shock waves moves after and gets stronger as the airplane accelerates --> CP also moves after and this increases a moment of force that makes the airplane to tuck under

 

2) Reduced downwash on the tailplane 

 

At normal speed, the tailplane provides downwash that stabilizes the airplane

 

Changing airflow from the wing reduces the tailplane effect downwash, consequently resulting in a stronger nose down moment