Was wondering if the pilot would faint, could g-force be enough to maybe break the neck bone with the head and weight of a helmet being pulled downwards. Another relay to this is the effects on the inside of the body, more specifically, the brain. Like a boxer, after taking a few too many knockouts. Is there a limit, or an event horizon to permanent brain damage and bone structure deterioration concerning g-force and pilots in aircraft maneuvers?
Can excessive G-force break or dislocate bones during pilot maneuvers?
Even if the pilot remains conscious.
For example see http://medind.nic.in/iab/t00/i2/iabt00i2p1o.pdf which describes compression fractures suffered by pilots.
No, the moment consciousness is lost, the body will go limp and the hands will release the controls and the aircraft will naturally seek 1g flight. However, several cases exist where pilots have awoke in a supersonic, or near supersonic, dive and sustained massive flail injuries after ejecting.
Its also important to note that simply jumping in the air will exert your body to instantaneous G-forces well above what you'd experience in a fighter aircraft. If such G-forces were capable of causing injury then you'd hardly be able to get out of bed without causing grievous injury.
The danger to high G-forces in the vertical axis is that the blood is pulled from the brain to the lower extremities causing a form of hypoxia commonly referred to as GLOC, or G Induced Loss of Consciousness. For what it's worth, skeletal injuries due to G forces are so rare that they aren't even briefed during training.
Yes, there have certainly been cases in which fighter pilots break bones while performing high-G turns. Unfortunately, the bone most susceptible to injury is the spine because that is the one of the few structures supporting real weight other than itself.
...pilots of high-performance aircraft frequently sustained cervical spine injuries due to their exposure to high gravitational forces (5), these investigators measured accelerations about the head of an F-16 fighter pilot during simulated air combat maneuvers. With the aid of a spine model, they calculated the forces on the lower cervical spine and noted that the forces were of the same order of magnitude as failure loads of cervical vertebrae and estimations of maximum cervical spine muscle forces.
In one miraculous instance, a USAF pilot was able to land after pulling a 9G turn and breaking his back. I currently cannot find a source for this but I remember listening to my dad's friends (USN) talk about visiting the pilot. I believe he was disabled in a leg or maybe both but he did not fly again.
Less severe maneuvering will not break bones very easily, but they can produce neck injuries.
There are many safety features built into aircraft that can maneuver into such high-G turns, however. The earliest example of this is the G-suit, which pushes blood that pools in the lower half of the body back up to the brain using air pressure lines and sacs. In addition, some aircraft set artificial limits on how tight a pilot can turn to prevent pilot injury and airframe stress (The F-14 could survive much more than 6-7Gs but that limit was set on the controls to reduce wing stress and failure). More recently aircraft have adopted digital systems that will right an aircraft if the pilot fails to respond to an alarm within a certain period of time. If a pilot is in blackout or prolonged greyout, the aircraft ignores pilot input and tries to fly straight and level. This is mainly to prevent unconscious crashes into terrain, but it also prevents pilots from entering tighter and tighter turns that they cannot leave.