Positive G-Force is centrifugal forces acting on you, the pilot, and your aircraft, while moving together through the sky in a given direction and then you suddenly and strongly pull back on the the control stick straight aft, creating a massive amount of lift from the top of the wings. This rapid rate of change in the the amount lift being generated results in a violent high G-onset and a rapid rate of directional or heading rate of change. This huge increase in the turn performance of an aircraft that is traveling at high speed then asked to turn a fast tight circle causing the occupants of these high performance aircraft to feel the punishing effect of G-Force, or centrifugal force, pushing you down into the seat.
The sensation is that of a person your equal size and weight sitting on your lap at 2 Gs or 2 times the normal body weight . It’s very much the force that holds the water in the bottom of a bucket as you swing it around in a circle like a Ferris wheel. Depending on the speed that you and your aircraft were traveling at the moment you pulled back on the stick and the rate at which you pulled (the quicker the pull; the higher the G-Force) will determine how many Positive G’s you and your aircraft will experience. The higher the speed, the higher the potential G-Force capability will be. The more abrupt the pull, the more punishing the G-Force experience will be.
So what happens to you, the pilot, when all this takes place? Here’s how it works. Pulling Gs is like power lifting at the gym. If you are about to lift 5-9 times your body weight you would have to do to get your body ready for a strenuous and extreme lift like that. If you don’t get your heart pumping by taking a few big and quick breaths to get your blood pressure up in anticipation of this very strenuous task, the blood pressure in your body most likely will not be sufficient to perform the lift. After you have attempted it, you will probably feel a bit weak, dizzy, queasy, light-headed and you might even feel like you might pass out. This is exactly what it feels like when you don’t tense up soon enough or strong enough prior to pulling a back on the stick from high speed and sustain high G-Forces in an airplane. Taking several deep breaths, and then simultaneous tensing and holding your stomach muscles (like someone is about to punch you in the stomach), tightening your leg muscles and your neck muscles and straining enough to turn your face red, will dramatically improve your G-Tolerance and minimize our your chances of a G-LOC or G-Induced Loss of Consciousness event. This is a very crucial habit to get yourself into as you learn to fly. It is a matter of life and death for all fighter pilots and airshow performers around the world who fly aircraft that are capable of pulling 6-12 Gs instantly.
If the G-Forces come on quickly enough, are strong enough (anything over 3.5 Gs can do it ) and sustained long enough the pilot must perform the above mentioned physical preparation maneuver. The US Navy calls it the “HOOK” maneuver. As the blood in your head, which is vital to you keeping your conscious, is drawn down from the upper part of your body to your lower half, during the next 3-7 seconds, you will begin to suffer from the effects of “graying out” which is your first sign that you are now behind in your battle to remain conscious. You must have either forgotten to tense up your body, or didn’t tense up soon enough, or held it strong enough before the onset and for the duration of the the high G-Force event, which is the best way fight off the affects of the G-Forces.
You will then begin to see the “tunnel vision” effect setting in where your peripheral vision will fade out and you will only be able to see straight ahead. Then if you don’t tense up really hard and/or relax some of the back pressure on the stick, to relieve you of some of the G-Forces, you will be well on your way to “blacking out” or G-LOCing yourself. Once the tunnel vision is allowed to manifest itself, you will then see the “Black Curtain” come down you are very close to actually “blacking out” at this point. You can still think and hear but you cannot see. This is your final warning sign that unconsciousness is near. If this final symptom is ignored, you, the pilot will become unconscious and you could remain asleep for up to 30 seconds. This could be very bad if you are in close proximity to the ground and you are alone as in a fighter or air show stunt plane.
Learning your G-Limits, honoring your warning signs and when in doubt, by relaxing the back pressure on the stick and/or tensing up your stomach muscles as soon as you realize that you are about to pull some Gs, will always put you 1 step ahead of the effects of the G-forces at all times. Fly Safe! Watch this entertaining and educational video to see it in action. Centrifuge Training Video on YouTube