Definition
An uncommanded nose-down pitching tendency that occurs as an aircraft approaches transonic speeds, caused by the rearward shift of the center of lift as shock waves form on the wing. The shifting pressure distribution reduces downwash over the tail and produces a nose-down pitching moment that the pilot may be unable to counter with normal elevator input.
Plain English
As an airplane gets close to the speed of sound, the lift on the wing shifts backward. That makes the nose drop on its own, and the pilot may not have enough elevator authority to pull it back up.
Context Anchor
Seen in high-speed flight discussions, especially when learning how shock waves affect airplane control and stability.
Derivation
The phrase pictures the nose 'tucking' downward, the way a diver tucks their head and body forward into a dive. It is a plain-English description of what the aircraft does, not a technical coinage.
Why Pilots Care
If not corrected promptly it can lead to a rapid increase in speed and loss of control, especially in aircraft not designed for transonic flight.
Grounding Statement
Picture an airplane near its high-speed limit beginning to lower its nose even though the pilot did not command a nose-down pitch.
Intuition Check
Tuck under does not mean part of the airplane is folding under. It means the airplane has a nose-down pitching tendency caused by high-speed airflow effects.
Example Sentence 1
As the jet accelerated past its critical Mach number, the crew felt a slight tuck under and the Mach trim system automatically applied nose-up trim to compensate.
Example Sentence 2
Reducing power and applying nose-up trim helped stop the tuck under and return the aircraft to stable flight.