What do we mean by G's in aircrafts?

Answer 1

Multiples of the force of gravity--a three-G turn puts three times the force of gravity on the plane and everything in it. When you are sitting or just standing, you are experiencing 1G of gravitational force. You don't notice it but you should feel it on your feet or your seat. When a plane makes a 3G turn while banking(so the force acts without any side loads) then you will feel as though you weigh 3 times your normal weight. This G-force also pulls on your arms, face, and blood. A 5-G force or greater is about the level where it pulls the blood from your brain and causes it to go to sleep. This is referred to as "black-out" because the first sign is your vision gets dark and you pass out. Fighter pilots wear G-suits that help squeeze the body and keep pressure on the blood so it will not leave the brain. Pilots also learn the techique of grunting (as if you are trying to go to the bathroom) and this forces blood to the head. If the aircraft dives rapidly such that you experience a Negative G-force, this will cause things in the aircraft to fly up into the air, such as your tray table or drink. In a jet fighter, this will cause the blood to rush to the brain and result in what is called a "red out".