Acceleration in Aviation G-Force (the gravitational force equivalent). People with the highest g tolerance are known as “g-monsters”. There are people who have been perfectly conscious at 6 g. Others pass out at 3 g.

The swooping, sickening sensations you experience on a roller coaster come courtesy of brief g-forces of up to 5 g. Rides have to be designed so people don’t black out.

The force of gravity on earth causes a constant acceleration of 32 feet-per-second squared. An object in freefall will accelerate at an ever-increasing speed toward earth until it impacts the earth or reaches terminal velocity, the point at which the force of aerodynamic drag acting on the object overcomes the force of acceleration induced gravity. Acceleration is described in units of the force called “Gs.” A pilot in a steep turn may experience forces of acceleration equivalent to many times the force of gravity. This is especially true in military fighter jets and high-performance, aerobatic aircraft where the acceleration forces may be as high as 9 Gs.

Our tolerance of g-forces depends not only on the magnitude and duration of the acceleration or deceleration but also on the orientation of our body. We are most vulnerable to a force acting towards the feet, because this sends blood away from the brain. Five to 10 seconds at 4 to 5 g vertically typically leads to tunnel vision and then loss of consciousness.

Fighter jets can pull up to 9 g vertically, and the more a pilot can take without blacking out, the better their chances in a dogfight. Human beings are adapted for life at 1 G on the surface of the earth. In the aviation environment, any maneuver has the potential to expose the human body to more than1+ Gz of acceleration force. This can be particularly hazardous for pilots in the Gz axis. The heart and cardiovascular system must respond quickly to G acceleration to keep blood flowing to the brain and maintain consciousness. Physiological response to +Gz causes the heart to beat harder and faster with an increased vascular tone to keep the blood flowing “northward” toward the head.