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After reading this question and the linked article, I had some more questions about G-Forces on pilots.

The article says:

The average, fit aviator has about a 3g "naked" limit, which comes from automatic tightening of blood vessels forcing blood to the brain.

I'm a private pilot, with no training with G-forces. I'm average fitness (maybe even a little below average).

For the big 40th Birthday, I went to the Sky Combat Ace experience, doing simulated dog-fights in Extra 330LCs.

The instructors said that both my brother and I pulled in excess of 7G. (with no G-suits or anything beyond some grunting).

I'm not so sure I believe that now. Were they blowing smoke to give us a fun experience? Or could I have credibly pulled 7G for 10-20 seconds without prior experience?

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  • $\begingroup$ Their site makes similar claims, and says that a regular healthy person will lose consciousness at around 5-6 Gs (which they can do in the Extra). $\endgroup$ – fooot Feb 23 '15 at 20:30
  • $\begingroup$ It depends on which axis you receive the Gs $\endgroup$ – Antzi Feb 24 '15 at 2:41
  • $\begingroup$ On a similar topic, how does negative G forces affect our bodies? $\endgroup$ – Firee Feb 24 '15 at 5:39
  • $\begingroup$ Incorrectly performing a G straining maneuver, AGSM, will actually decrease your G tolerance. Forcing blood to your head actually over pressurizes your brain and causes your veins to open up and dump the blood. Your brain is much more sensitive to extra blood pressure, vice less blood pressure. Think positive vice negative G's. The dump valve, so to speak, is a safety mechanism. $\endgroup$ – Rhino Driver Feb 25 '15 at 21:43
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    $\begingroup$ 7G for 10-20 seconds sounds unlikely to me! Human can resist way more then that but only for a very short amount of time (car crashing into a thick wall goes up to more then 30G...) but only for a very very short time. As soon as you have a longer time the Gs affect your blood flow. This will lead to unconsciousness. Fun fact: Astronauts have to resist about 3G during launch and/or landing. (Thanks to @SHAF for correction) $\endgroup$ – Maverick283 Feb 25 '15 at 21:47
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The G-limit for the Extra 300 (the parent airplane to the 330):

The Extra 300 is stressed for ±10 G with one person on board and ±8 G with two

So it is certainly possible from an airplane perspective that you pulled that many Gs - in an aerobatic airplane, it's not unheard of to pull 1G less than the aircraft limit (usually there is a large margin of safety built into that number before a catastrophic structural failure).

Now did you pull 7Gs? As others have noted, 7Gs for 10-20 seconds seems very unlikely. But it is not out of the question your peak instantaneous G load was 7.

From a human factor standpoint, G-suits typically don't increase the max G-load, but rather increase the sustained G-load and the time period it can be held for. G-suits do very little to actually decrease blood flow (pooling in the legs) - they primarily serve as a reminder to the pilot to perform an AGSM.

A g-suit does not so much increase the g-threshold, but makes it possible to sustain high g longer without excessive physical fatigue. The resting g-tolerance of a typical person is anywhere from 3-5 g depending on the person. A g-suit will typically add 1 g of tolerance to that limit.

Now there are a vast array of factors affecting this resting G-tolerance. I flew a military high-performance trainer, and my resting G-tolerance was around 3, or the lower end of the spectrum. One of the other pilots I knew had a resting G-tolerance of about 7.5. The primary difference is blood pressure. I am 5'10" and only 145 pounds, with a resting blood pressure of about 90/60-100/70. He was 6'0" and about 215 pounds, with a much higher blood pressure. Tall, skinny, nonsmoking runners have actually the worst resting G-tolerance while short, stocky, sedentary or heavily muscled smokers have much higher tolerance. Other factors, such as how hydrated and rested you are and how much stress you are feeling, can vary vastly your daily G-tolerance.

All of those numbers I just listed do not take into account the pilot performing an AGSM (Anti-G Straining Maneuver). This can add several Gs to the pilot's tolerance, and is one of the biggest things taught in physiological training for high-G maneuvers.

So TL; DR: could you have pulled 7Gs without prior exposure? It is possible, depending on varying personal factors and body type, but it is not likely. However, with a little training, 7Gs is perfectly attainable.

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    $\begingroup$ Its been my experience that a gsuit will increase your max resting G by at least 1-2 G's--which is significant if your resting G is 3.5, you perform a G warmup, you don't squeeze and your hose comes undone. There have been several times I've had to squeeze the black out when I've noticed a faulty hose and was expecting my suit to inflate. I can easily reach 5 G's without squeezing when my suit is inflating. $\endgroup$ – Rhino Driver Feb 25 '15 at 21:38
  • $\begingroup$ Why the downvote? $\endgroup$ – SSumner Feb 25 '15 at 22:22
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A normal acrobatic ride experiences 3-4 G's for a few seconds. Competition acrobatic pilots will pull up to 5 Gs for 2-3 seconds, which is risky. It is difficult to do more than this in a piston-powered aircraft. 5 Gs for more than 5 seconds will present a significant risk of a blackout or loss of consciousness in an inexperienced person. From a textbook on aeronautical medicine:

G-force table

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  • $\begingroup$ Its entirely possible that what felt like 10-20 seconds was actually only a few seconds. It certainly felt longer. :) But somewhere I have a video of the ride. I'll have to re-watch that with a stopwatch. (It still won't tell me how many G, but it should give me a solid idea of duration) $\endgroup$ – abelenky Feb 23 '15 at 22:47
  • $\begingroup$ Look closely. The cockpit will be fitted with a G meter. You might be able to see it in the video? Oh, and 7g for even a few seconds is blackout for all but the most fit and well trained. $\endgroup$ – Simon Feb 24 '15 at 7:43
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    $\begingroup$ 5Gs for more than 5 seconds is blackout. This is not at all true the way you said it, though perhaps you meant some qualifiers in there you didn't type. And competition pilots pull instantaneous G-forces in excess of 9 and several-second G-forces easily in excess of 5. Most of this is done without G-suits $\endgroup$ – SSumner Feb 25 '15 at 12:20
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    $\begingroup$ The top number represents the average resting G rate (just prior to light loss) of 1,000 people. Its not uncommon for shorter people to have resting G rates much higher. I personally know a woman whose resting G is higher than 5. However, even a moderate amount of squeezing can make 5 G's completely tolerable for an extended amount of time. Furthermore, more important than the max G's sustained is the G onset rate. An extremely high onset rate to 5G's can easily black a person out, even if they are wearing a G suit. Also, a push-pull (negative to positive G's) is GLOC inducing. $\endgroup$ – Rhino Driver Mar 25 '15 at 21:32
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    $\begingroup$ Certainly the operator is well versed in his own G Limits. Anyone that constantly flies in that regime of flight is more than capable of sustaining 5 Gs. Furthermore, that article you cited with 4.8 is resting GLOC, with no squeezing. Id be surprised if the operator didn't know to squeeze his legs. If the passenger GLOCs, who cares? Aside from doing the funky chicken when he wakes up, and having some wicked awesome dreams, it's a non event and he's got a cool story. If he doesn't LOC, then he's still got a cool story. Sounds like a win win to me. We put people to sleep all the time. $\endgroup$ – Rhino Driver Mar 26 '15 at 0:03

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