Anyone flying with us – in any type of aircraft actually – will experience G force. We commonly refer to G force as “times” body weight when doing evolutions. When flying in our fighter jets, you may experience up to 7Gs. But what is G force exactly ? The gravitational force, or g-force, on something is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces. Accelerations not produced by gravity are termed proper accelerations, and cause stresses and strains on objects. Because of these strains, large g-forces may be destructive. A light plane doing extreme maneuvers may break in two due to G force.

The standard gravitational acceleration at the Earth’s surface produces g-force only indirectly. The 1g force on an object sitting on the Earth’s surface is caused by mechanical force exerted in the upward direction by the ground, keeping the object from going into free-fall. An object on the Earth’s surface is accelerating relative to the free-fall condition, which is the path an object would follow falling freely toward the Earth’s center. It is thus experiencing proper acceleration, even without a change in velocity (the familiar “coordinate acceleration” of Newton’s laws).

Objects allowed to free-fall under the influence of gravity feel no g-force, as demonstrated by the zero-g conditions in spacecraft in Earth orbit. This is an example of coordinate acceleration without proper acceleration. The g-force felt is a measure of proper acceleration (in this case, zero), not change of velocity.

In a fighter jet, one can feel positive and negative Gs. Positive, or “upward” g, drives blood downward to the feet of a seated or standing person (more naturally, the feet and body may be seen as being driven by the upward force of the floor and seat, upward around the blood). Resistance to positive g varies. A typical person can handle about 5 g (49m/s²) before G-LOC, but through the combination of special g-suits and efforts to strain muscles—both of which act to force blood back into the brain—modern pilots can typically handle 9 g (88 m/s²) sustained for a period of time.

Resistance to “negative” or “downward” g, which drives blood to the head, is much lower. This limit is typically in the −2 to −3 g (−20 m/s² to −30 m/s²) range. The subject’s vision turns red, referred to as a red out. This is probably because capillaries in the eyes swell or burst under the increased blood pressure.

In aircraft, g-forces are often positive (force blood towards the feet and away from the head); this causes problems with the eyes and brain in particular.

As g-force is progressively increased the pilot may experience:

Grey-out, where the vision loses hue, easily reversible on leveling out.
Tunnel vision, where peripheral vision is progressively lost.
Blackout, a loss of vision while consciousness is maintained, caused by a lack of blood to the head.
Redout, a reddening of the vision while consciousness is maintained, caused by an excess of blood to the head.
G-LOC a loss of consciousness (“LOC” stands for “Loss Of Consciousness”).[9]
Death, if g-forces are not quickly reduced, death can occur.

The ultimate tester of G force was John Stapp. John Stapp was subjected to 15 g for 0.6 second and a peak of 22 g during a 19 March 1954 rocket sled test. He would eventually survive a peak of more than 46 g, with more than 25 g for 1.1 sec.

When flying with us, you may experience up to 7Gs, but you will handle it well as we use G suits.