G-lock is the source of most of accidents in military aviation, people lose their lifes because of that.
When in a tight turn, the blood goes from your brain into your legs.
LuftWaffe pilots (especially Stuka pilots) noticed that short people have better tolerance to G force, so women and short men are the best jet crews cus they can handle the Gs much better than taler people.
Why ? you ask, simple, cus the way for the blood from the legs to the brain is shorter. Simple isn't it
The blackout, it's when you loose consciousness, is called "G-lock".
The symptoms of G-lock:
-you start loosing focus
-your field of vision will become smaller and smaller (like looking through a soda straw)
-you will loose the ability to see colours
-everything goes black and you loose consciousness