G-LOC
G-induced Loss Of Consciousness (abbreviated as G-LOC) is a term generally used in aerospace physiology to describe a loss of consciousness occurring from excessive and sustained g-forces draining blood away from the brain causing cerebral hypoxia. The condition is most likely to affect pilots of high-performance fighter and aerobatic aircraft or astronauts but is possible on some extreme amusement park rides.
G-LOC incidents have caused fatal accidents in high performance aircraft capable of sustaining high g for extended periods. High-G training for pilots of high-performance aircraft or spacecraft often includes ground training for G-LOC in special centrifuges, with some profiles exposing pilots to 9 Gs for a sustained period.
Nevertheless, only a few fighter pilots have experienced G-LOC incidents.
Pulling 9Gs
But what’s it like to pull 9Gs?
Adam Daymude, former US Navy EA-18G Growler pilot, explains on Quora;
‘Oh boy, does it hurt!!
‘Empirically, I, as a 220 lb man, will weigh close to a ton at 9Gs. That alone would make it hard to sustain that pull but there are other things going on that make a 9G pull a VERY temporary state.
‘First for the blood. Since your G vector is down, that’s where your blood is being pulled; your feet and legs swell very quickly with all the blood rushing in. That’s a problem because you need to be able to think but the blood is being pulled away from your brain. The first thing that typically goes before you lose consciousness is your peripheral vision (the photoreceptors in your periphery are more oxygen sensitive) and so we’re taught to do some clenching moves with our legs and stomach to try and push the blood back up before G onset (our G suit also offers about 3 additional G tolerance compared to resting state). But no G clenches in the world are going to keep you going for long at 9Gs. You’re going night night (GLOC…G induced loss of consciousness) if you don’t stop pulling fairly quickly.’
G cough and G measles
He continues;
‘G cough. These are fun. If you pull too long, some of the delicate tissue in your lungs get damaged and you’ll begin literally hacking up a lung. Doesn’t happen all the time but if you’re in a prolonged fight, be prepared.
‘And finally, my favorite: G measles. I only got these in the centrifuge and that was only because I was at 9 Gs for about 15 seconds (that’s a lot longer than it sounds). What happens is that some of your capillaries (mine were in my arm) burst and you get splotches on your skin from the burst capillaries. It looks like you have measles, hence the name. And they itch like crazy! And to make matters worse, they do what always happens when you have blood leaking out of the veins/arteries: they turn into bruises. After my trip through the centrifuge, my arms were all bruised up for about 4 days.
Pulling 9Gs feels like an elephant is standing on your chest
‘So, to summarize, pulling 9Gs feels like an elephant is standing on your chest and it very quickly begins damaging your body. Reversible damage, but damage nonetheless.’
Daymude concludes;
‘About G tolerance: I’ll preface this by saying the values I’m giving you are based off a cardiovascularly fit aircrew. Just sitting there in your ejection seat, you’ll typically be able to handle 3Gs. That means you shouldn’t experience any of the high G symptoms at 3Gs, like greying out. As I said above, our G suit will get us an additional 3Gs of tolerance. Squeezing your legs and doing what’s called the “hick” maneuver (you actually say “hick”, pause on the k, and bear down on your abs and chest) will get you at best another 2Gs. That puts us at 8Gs the average aircrew can handle without fighting a losing battle. There are very few people that can get that extra G of tolerance to safely hold a 9G pull.’