The speed at which the main gear touches the ground is known as what?

The term for the speed at which the main gear touches the ground during landing is referred to as "touchdown speed." This speed is critical as it represents the aircraft's velocity just as it makes contact with the runway, and it is a key factor in ensuring a safe landing.

Touchdown speed is determined by several factors, including the aircraft's weight, configuration (such as flap settings), wind conditions, and airspeed prior to landing. Knowing the touchdown speed helps pilots manage the landing process effectively, ensuring they have the appropriate speed to maintain control upon contact with the runway surface.

Other terms like relative ground speed and reference ground speed do not specifically define the moment of main gear contact with the ground, while landing ground roll speed refers to the speed during the aircraft's rollout after touchdown, not the moment of touchdown itself. This distinction is important for pilots as they prepare for a safe landing approach.