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The wikipedia page on G-forces, https://en.wikipedia.org/wiki/G-force, lists that WW1 aircraft encountered 4.5-7g during dogfights.

This made me wonder, how did pilots in the early days of aviation handle the g-forces? G-suits were not invented until 1940s.

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    $\begingroup$ The Wikipedia page doesn't cite a reference for that figure, nor does it appear on the page linked to as the main article. I find it difficult to believe that WW1 fighters could sustain g at that level, let alone the pilots. $\endgroup$ – user27769 Jan 6 '18 at 5:11
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This interesting British document on the G loads sustainable by German WW1 fighters pegs the highest G factor for a British fighter at 5.5G for reference, with the SE5. German fighters examined and tested by the British after the war didn't fare quite as well, with max G tending to be in the 2-3 G range, beyond which the rear wing spar would fail.

What is also important to consider is that WW1 aircraft on both sides were not capable of sustaining those G's for very long, due to the low airspeed and rather underpowered engines of that day. An aircraft sustaining very high G's bleeds off quite a bit of speed in the process, due to the increased drag.

A WW2 fighter capable of 300-350 knots with a 1500-2000 hp engine, can pull a lot of g's for a long time, before scrubbing off enough speed to be in danger. A WW1 fighter at 80 knots, with a 150-200 hp engine, would only be able to sustain high G's for a few seconds, before they lost enough airspeed to risk stalling.

The few motion pictures of dogfights of that era, presumably re-enacted, tend to reinforce this: the planes appear to make a series of brief sharp turns interspersed with returns to level or near level flight, sort of a jerky movement as opposed to the long high G turns of WW2 fighters.

Finally, there were techniques some pilots used to avoid blacking out. Major Greg Boyington, who had been a boxer before the war, reported withstanding more G's longer by tightening his neck muscles up.

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    $\begingroup$ The document is indeed interesting. It describes calculated stresses though, not actual destruction tests. $\endgroup$ – Koyovis Jan 6 '18 at 8:51
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    $\begingroup$ They would use up their altitude to make up for the energy loss in turns. Von Richthofen writes in his biography that dogfights invariably ended in ground level chases after a few turns. $\endgroup$ – Peter Kämpf Jan 7 '18 at 1:01
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Typically the human heart can produce enough head to keep the blood flowing to around +5g. So sustained maneuvering at those limits should not pose a problem. Proper breathing, body position and flexure of the skeletal muscles in the legs and stomach combined with physical conditioning with weightlifting and experience can allow a pilot to pull sustained loads in excess of +10g without the use of anti g suits. Remember, at their best an anti g garment will only offer an extra g or so of enhanced tolerance.

There is also the issue of instantaneous vs sustained load factors while maneuvering. While a WWI fighter might be capable of pulling 4-7g instantaneously, sustained loading were probably more in the area of 2-3g - early engines just didn’t produce enough power to allow for hard sustained maneuvering. So risk of s G-LOC was minimal in early fighters.

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The phenomenon was first observed in WWI but was poorly understood. The most likely flew up to their personal limits using their body as a queue.

G-LOC of pilots, then called "fainting in the air," first occurred in World War I and may-have been, the cause of some military aircraft accidents

Head, H, The sense of stability and balance in the air, Chapter 11. In The medical problems of flying. H. Milford (ed.). London: Oxford U-siversity Press, 1920.

They may have just passed out and recovered...

According to this account, the pilot passed out in one dog fight although in this case it may have been from either the spin or blood loss in the leg.

...but succeeded in driving down two of the enemy in a spin. He lost consciousness after this, and his machine fell out of control. On recovery he found himself being again attacked heavily by a large formation, and singling out one machine, he deliberately charged and drove it down in flames.

This article would make it seem like red-out may have occurred in some maneuvers but due to a lack of understanding of what was actually happening they just flew through it.

This aircraft was designed to undertake a controlled bunt, with structural limits of -5G! Those pilots surely would have had “Red out” during those -Gz maneuvers. It could perform a U-Turn in less than 200 yards of air space, clocking up almost 8 G in the process. Since those brave hearts did not know anything about G-LOC, neither were there any anti-G suits designed then, so they flew on

It seems that little was done (or at least little was documented) during the first world war on this front as the first actual technique for G tolerance increase was not used until 1933.

A type of AGSM useful in flight was first the discovered as a method to increase G tolerance by Stainforth of England in 1933. He found that straining the abdominal muscles increased G tolerances 2 G, from 4 to 6 G.

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    $\begingroup$ AGSM - Anti-G- Straining Maneuver, Performing a isometric strain or tightening of all abdominal and leg muscles, puts muscle pressure on arteries in lower part of the body, minimizing tendency of blood to pool there in high- G maneuver, thus keeping more blood available for eyesight and brain function, and can increase G-tolerance by 1-2 Gs. $\endgroup$ – Charles Bretana Jan 6 '18 at 14:16
  • $\begingroup$ Something very interesting is that the fluid inside the eyeball is under very slight pressure (to keep eyeball inflated), and because of this, the blood pressure inside the eye is very slightly higher than the blood pressure outside the eye in the arteries which feed it. The upshot is that as G load increases, the blood pressure inside the eye goes to zero before blood pressure to the brain goes to zero. So Vision fails at a very slightly lower g-load than where GLOC occurs. Hence the "red-out" before "black out". $\endgroup$ – Charles Bretana Jan 6 '18 at 14:20
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    $\begingroup$ @CharlesBretana I understand red-out to be a reddening of vision under negative G's. The visual phenomenon under positive G's is, I think, an increasingly narrow tunnel vision, and/or graying of vision. $\endgroup$ – Wayne Conrad Jan 6 '18 at 19:53
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    $\begingroup$ @Wayne, sorry, you are correct, it has been a while since I got out of service. "red-out" is the phenomena (seldom experienced except by aerobatic pilots) when under negative Gs. "Grey-out" is what I was referring to $\endgroup$ – Charles Bretana Jan 8 '18 at 15:45
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The same article cites:

A typical person can handle about 5 g0 (49 m/s2) (meaning some people might pass out when riding a higher-g roller coaster, which in some cases exceeds this point) before losing consciousness...

So they could just pull g's until their personal limit of consciousness - natural selection would then weed out the pilots with the lowest tolerance.

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