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Pilots since world wars have been wearing g-suits in fighter planes to minimize the effect of high g encountered by them during close maneuvers.

  1. How do g-suits help in minimizing the effect of high g's on the pilots?

  2. What is the maximum g that a g-suit could handle properly?

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How do g-suits help in minimizing the effect of high g's on the pilots?

G-suit create extra external pressure on the limbs (legs in particular) to prevent the blood to stagnate far from the heart. In normal conditions specific biological systems automatically return the blood from the extremities to the heart, but when subjected to high G loads these systems fail, as they are not designed for such conditions.

By creating pressure on the body the G-suit alleviates the G load perceived by the body.

What is the maximum g that a g-suit could handle properly?

The main limitation is not only the amount of Gs, but for how long the human body can sustain them (spoiler alert: not much)

enter image description here

Image source

As you can see the Gs usually experienced in a fighter aircraft (blue line, see diagram on top right) cannot be sustained much beyond 3 seconds if they are of even moderate intensity. The G-suits help the body resist slightly longer.

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  • $\begingroup$ What's interesting to me here is how the F-16 seat (and less so the F-22) is tilted back to turn some of the Gs experienced in the blue direction into Gs in the more forgiving red direction. $\endgroup$ – Todd Wilcox Jul 13 '15 at 19:13
  • $\begingroup$ @ToddWilcox please don't get confused by the diagram: to "convert" blue into red you should tilt the seat forward, not backwards. $\endgroup$ – Federico Jul 13 '15 at 19:18
  • $\begingroup$ Blue is positive Gs driving blood towards the feet, right? Wouldn't that make red indicate Gs driving blood towards the back/spine (eyeballs in)? $\endgroup$ – Todd Wilcox Jul 13 '15 at 19:22
  • $\begingroup$ @ToddWilcox blue (up) drives the blood down, I then understand that red (back) would drive the blood in front. $\endgroup$ – Federico Jul 13 '15 at 19:31
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    $\begingroup$ @Sean yes, it is missing, I could not find one with that included. For the why part, I think you better ask on biology or health, I cannot answer that. $\endgroup$ – Federico May 6 '18 at 6:43
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Additionally to what @Federico wrote, g-suits press the legs by using inflatable sacs sewed in the suit. The suit is connected to a valve on the aircraft (or spaceship). When g forces increase, the valve pushes more air to the sacs and inflates them.

As for the limit, I think it is 9 g's but I don't have any citations. Also bear in mind that g limit has to do with other parameters as well, such as cockpit and seat design like HAC (high acceleration cockpit).

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  • $\begingroup$ More primitive suits use liquid or gel; as Gs increase, the gel is forced downwards toward the legs. It's also interesting to note that they can't always be used; the inflation of the leg cuffs in the G-suit can restrict movement of a center stick, so the Blue Angels famously do not wear them, and "graduation day" involves staying awake through a max-G 360 turn. The Thunderbirds do use them, as the F-16 has a side stick. $\endgroup$ – KeithS Jul 14 '15 at 3:28

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