Il2 DD Update Dev Blog 263 "G-Load"

[+76.IAP-Blackbird 3,557]

Salute pilots! 

It’s been a year since we introduced a detailed human physiology model in our simulator. The model which takes into account the limits of human’s G-load tolerance, as well as a number of other factors affecting pilots in flight. This, of course, immediately and greatly changed the dynamics of air battles. They became much more realistic. After all, now, when performing an attack or a defensive maneuver, you have to take into account the fact that a living person with his natural physiological capabilities and limitations is sitting in the cockpit. And that any pilot, of course, gets tired of constantly maneuvering at high Gs. And in the end, there comes a moment when he just needs time to catch his breath and recover.

 

We were interested in your opinion

 

Over the past year, we have read a lot of your comments on the forums and collected a lot of feedback about this model. We have seen that this new and exciting aspect of dogfight has been very warmly received by the bulk of our community, and it's encouraging. While another part of the players asked us to make some changes to this model.

 

In order to understand the situation, a month and a half ago we conducted a poll among players on the  .com and .ru forums.

 

What did the poll show?

 

The poll results showed that 60% of players are quite happy with the current model (494 out of 821 unique users on both forums, excluding the extra 31 votes of those who voted twice, i.e. on two forums). And 40% of players would like us to make adjustments to this model.

 

I had carefully read all your comments on the polls. In general, there were more players satisfied with the model on the Western forum, so I conducted a more detailed analysis of that thread and found that 63 out of 381 Western users who chose option 1 (“leave everything as it is”), nevertheless, in comments have written a number of requests for changes in the model.

 

Thus, it became clear to us that the community was divided in opinions approximately 52/48. This means that we cannot leave this situation unattended and we need to think carefully about what can be improved in our model.

 

Collecting new scientific data

 

Over the course of this year, thanks a lot to you, our community, we have collected a large amount of new data from the field of aviation medicine and human physiology under extreme stress conditions (I would like to express special thanks to comrade @Floppy_Sock for the materials he found). This allowed us to take a fresh look at our physiology model and find ways to improve it.

 

For example, a year ago, in my work on a physiology model, I relied mainly on the well-known monograph of the Russian scientist, professor, doctor of technical sciences Boris Abramovich Rabinovich “Human safety during acceleration (biomechanical analysis)”, 2007, where while talking about the duration of the G-loads a human can sustain, he refers to the famous article by Anne M. Stoll, "Human tolerance to positive G as determined by the physiological endpoints." ), published in The Journal of aviation medicine in 1956. This article provides a graph of time to loss of consciousness versus G-load. It is compiled on the basis of the results of 40 experiments,13 of which ended in loss of consciousness by attendants.

 

However, recently we learned that in 2013 there was another article published on the BioMed Central portal in the Extreme Physiology & Medicine section: “The +Gz-induced loss of consciousness curve ”. Its authors, Typ Whinnery & Estrella M Forster, prove there the fallacy of the conclusions from the article of 1956, relying on much broader statistics: now they had already 888 cases of loss of consciousness by testees. These statistics were collected from 1978 to 1992 at a number of US research centers (USAF School of Aerospace Medicine, Brooks AFB, Texas and the Naval Air Warfare Center, Warminster, Pennsylvania).

 

In particular, in their article Tip Whinnery and Estrella M. Foster argue that at high +Gz (that is, acting on the pilot in the "eyeballs down" direction), up to +11.7G, the subjects never lose consciousness earlier than 5 seconds after the start of acceleration, and on average statistically - only after 9 seconds after it.

 

While in our current model, built on the basis of data from the sources published above, loss of consciousness occurs within 3-5 seconds at acceleration of more than 6-7G.

 

Authors of the study explain this difference by the presence of a certain “functional buffer” of the brain, which prolongs the activity of the brain for a few seconds after the arterial systolic pressure at the level of the eyes (brain) drops to zero under the influence of extremely high Gs.

 

In addition, many players asked us to reconsider the pilot's tolerance to large negative Gs (assuming that the deteriorating effect of negative Gs should be more pronounced). They also asked us to implement the so-called push-pull effect (PPE), which manifests itself in a noticeable and very dangerous short-term decrease in the +G tolerance immediately after a negative one. Many aviation accidents on maneuverable aircraft are associated with this notorious effect. Over the past year, we managed to find scientific materials about this effect, too: for example, an article published in 2011 on the scientific, technical and medical portal Springer, co-authored by a number of Chinese scientists “A centrifuge simulated push-pull manoeuvre with subsequent reduced + Gz tolerance ”.

 

This and over three dozen other publications, NASA reports, scientific dissertations, and unique test materials that we have collected, gave us a large amount of numbers that we could rely on with greater confidence. And the need to simulate the above-mentioned phenomena presented me with the fact that it is not just about readjusting the coefficients of the current model. It became clear that the model would have to be built anew, with a more detailed account of all factors acting on an individual and an even more detailed simulation of physiological processes in his body.

 

Today I am glad to tell you about the results of this work.

 

First impressions

 

The new pilot physiology model is currently undergoing a detailed and meticulous beta test.

 

The first impression it invoked in our testers, and which, most likely, it will invoke in you, is “it became more forgiving”. After all, due to the appearance of the “functional buffer” of the brain, quick and short-term maneuvers at very high Gs have now become possible without immediate loss of consciousness.

 

More details...

 

For example, if by a one second long jerk one pulls +7-8Gs, then visual disturbances in the form of a "gray out" (which is loss of color perception) will now occur only 3.5 seconds after the beginning of acceleration. After another 1.8 seconds, the peripheral field of view (the so-called “tunnel vision”) will begin to narrow. The vision will be completely lost (“black out”) after another 2 seconds, that is, only 7.3 seconds after the start of the maneuver. And after another 1.6 seconds, G-LOC (G-induced loss of consciousness) will occur.

 

It has also now become possible to perform, for example, a loop or a split-s with the initial and final G-loads of +5...+5.5Gs without loss of peripheral vision. But if these Gs are maintained during the maneuver for longer than 25 seconds, the “blacking out” will nevertheless begin to happen, and consciousness will be lost 32 seconds after the start of the maneuver.

 

In general, at first you may really think that the pilot has become more resilient, and it has become easier to fight.

 

Has it really become easier?

 

But already after 2-3 days of “test flights” our testers found that the first impressions were somewhat optimistic. Yes, you can now actually “kink” the trajectory more sharp. Once, twice ... but you won't be able to maneuver for a long time, while constantly holding high Gs. You will have to reckon with fatigue and a decrease in the pilot's tolerance to G-forces during the battle, just as before. And just as before, you will have to plan well the trajectories of the fight, choosing the moments when to “pull” and when to let yourself catch your breath.

 

About endurance and fatigue

 

As I wrote above, we have collected a large amount of scientific data on a human's tolerance to +Gs and -Gs of different magnitude. Unfortunately, some of them are contradictory, and there is no one single model of the “average person” that would reliably describe our “average” endurance. In one source, you can find information that an experienced aerobatic pilot can withstand +2Gs only for 13 minutes, while in another source, you can find a figure that the + 3Gs are quite normally tolerated within an hour. At the same time, when we talk about larger Gs values, the numbers from different sources become closer to each other. But still, this subject has some field open for discussion. 

 

Therefore, the endurance of our pilot to long-term G-loads, as well as to cyclic G-loads in the new model is adjusted both taking into account reliably known data from various publications, and based on the impressions of real pilots with aerobatic experience. We have involved military pilots and pilots flying on sports aircraft in testing. They all praised the results achieved, and admit that the model reproduces their own feelings quite closely.

 

What else

 

I think that many players will be especially pleased with the fact that the new model now contains several interesting phenomena that have been simulated thanks to a more detailed calculation of physiological parameters.

 

PPE

 

For example, the push-pull effect. If you pull a high positive Gs immediately after the action of any prolonged negative Gs (of which only three to five seconds is enough), then visual impairments will come faster than usual, at noticeably less G-load. To the extent that such a maneuver can lead to an unexpected LOC. The greater the negative G was and the longer it lasted, the more noticeable this effect will be. But just a few seconds of a pause after a negative Gs is enough: the cardiovascular system will have time to adjust and will be ready again to normally sustain positive Gs. This effect is due to the fact that with a negative G, blood intensively rushes to the head, and the body reacts to this by rapid vasodilation, seeking to reduce cerebral pressure. And if, in such a state, a large positive G is immediately pulled, then the vessels will take time to narrow again and maintain the now falling blood pressure at the level of the brain. At this moment, a quick crisis comes.

 

Warming up effect

 

Also, thanks to the improved calculation of vascular response, the new model has a “warming up” effect. It is when the first short maneuver at high +Gs is tolerated worse than the subsequent ones. It is also related to the compensatory response of the cardiovascular system, which needs time to “warm up” in order to maintain sufficient blood pressure in the head. If you pull, for example, +6G in one-two seconds, withstand it for five seconds (this is when you will get the partial “tunnel vision” effect), then reduce to 1G, pause for five seconds, and then create the same +6G for the same five seconds again at the same rate, then in the second case there will be no “tunnel vision” effect. But the same maneuver made third in a row will again lead to a partial "tunnel vision". But this is already because of a decrease in the tolerance limit due to excessively intense load without sufficient recovery time.

 

Backrest angle

 

Over the past year, there were many attempts by some players to prove that there are differences in the endurance of the pilots of one or another coalition. Although the physiological model of a pilot was the same and did not depend in any way on the plane in which he was sitting. However, now in the new model of physiology, while still remaining the common model for every pilot, the peculiarities of the aircraft cockpit in which the pilot sits are taken into account. Namely, we are talking about the backrest angle. As you know, tilting the seat back significantly increases the pilot's tolerance to G-load. This is due to a decrease in the difference in hydrostatic blood pressure between the heart’s level and the head’s (eyes) level. For example, tilting the seat back by 30° increases the maximum G-load-sustaining capacity by about 15%.

 

Many researchers also attach importance to the position of the legs. For example, the Spitfire even had two pedal positions: a lower one for normal flight and a higher one for aerobatics. It was assumed that in the elevated position of the legs, the outflow of blood from the head to the legs decreases under the action of +Gs. However, a number of experiments have shown that this effect is negligible, and, nevertheless, the angle of inclination of the pilot's upper body plays a much larger role. The new model takes this angle into account, which on all highly maneuverable aircraft in our simulator ranges from 0 ° (MC.202 series VIII) to 22.5 ° (MiG-3), averaging about 10-15° for different planes.

 

AGS

 

In the current physiology model the effect of the anti-G-suit (AGS) was simulated empirically, based on statistical data. In the new model, a detailed calculation of the suit’s pressurisation dynamics and the effect of this boost on the hemodynamics of the pilot's blood pressure is performed. Several mathematical models of this phenomenon can be found in scientific research, and all of them give, on average, results that are in good agreement with the tests for modern AGSs. In our new model, we used the characteristics of suits from the 40s, which gives us confidence that this aspect is now modeled even more authentically.

 

AGSM

 

In the scientific literature, the term "anti-g straining maneuver" (AGSM) refers to a set of special measures that a pilot applies in order to temporarily increase his tolerance to G-load. This is a special type of breathing (you are familiar, of course, with it from the current version of the simulator), as well as tension in the muscles of the legs, butt and abdominal press. A well-trained pilot who has undergone special training in a centrifuge, using AGSM, is able to increase his G-load tolerance limit by 2 to 4G! It is not easy and requires a lot of physical effort. If the AGSM is performed incorrectly, then the effectiveness of such a technique is sharply reduced.

 

As you know, during the World War II, pilots did not undergo special training on centrifuges, and were not trained to perfectly perform AGSM as modern fighter pilots are. But even then it was known that the tension of the muscles of the press and legs together with strained breathing allows one to endure higher Gs.

 

Taking these facts into account, the pilot in our game (just as before) performs the AGSM not “excellently”, but “somehow”. This increases his tolerance limit for prolonged G-loads from 5.5G in a relaxed position (statistics are on the chart below) to 6.7G. This is about 0.4-0.5G more than in the current model. Such a slight increase in the limit of the maximum tolerated long-term positive G-load, however, will now make it possible to maintain a g-load of +6G with a partially narrowed peripheral field of view, up to a complete loss of vision within 18 seconds. Loss of consciousness under this Gs will occur in another 2 seconds.

(all pictures are clickable)

 

At the same time, I hasten to inform you that the annoying bug of “double breathing” (duplicate overlay sounds), which sometimes appeared in our game, will now be fixed.

 

Visual effects

 

I would especially like to mention that the effects of visual impairment have also been readjusted.

 

I personally have been flying aerobatics in ultralight and light sport aircrafts for many years, but over the past year I got a new aerobatic experience, now with high G-loads on the Yak-52 sports airplane. Therefore, I now know firsthand what all phases of visual impairment look like from the beginning of the “gray out” appearance, then through a “tunnel vision” and, as a result, almost to a “blacking out”. As they say, a real picture is worth a thousand words. So now in the new model the manifestation of such effects as loss of color, “blurring”, “tunnel vision”, - very accurately correspond to what I see with my own eyes in real flights, if I perform a maneuver with a long-term 5.5 to 6Gs. Other pilots who have tested the new model also agree with this visualization.

 

 

The red-eye visual effect under the influence of negative Gs, has also been slightly enhanced:

 

 

 

Visual disorders dynamics

 

Additionally, in our new model, the delay between the moment the G-load is reduced and the restoration of vision after visual disturbances will be shorter. From my own experience, I would say that now this delay in visual reactions better corresponds to reality.

 

Also, the time between the complete loss of vision (“black out”) and the loss of consciousness has been brought into better agreement with the research results, and now is about 2 seconds, in rare cases reaching 8-9 seconds. By the way, in the current (older) model, this time ranges from 0.2-0.8 seconds under 6G  and higher to dozens of seconds under less Gs. As you can imagine, this change will allow you to better anticipate the moment of G-LOC and to fly near this border with more confidence.

 

I also corrected the effect of temporary and more severe visual impairment, which happens if you pull a high +Gs on the first maneuver with an abrupt jerk (when the pilot was not "warmed up" yet). This effect is associated with the already mentioned above feature of the cardiovascular system hemodynamics. It takes some time for the vessels to "mobilize" and respond to the sudden increase in G-load with an increase in blood pressure. After 5 to 7 seconds from the start of such an abrupt maneuver, while the blood pressure is still "lagging" behind the G-load, the pilot gets a more apparent temporary visual impairment. But after another 3 to 5 seconds, the blood pressure rises enough and the visual function improves.

 

If the Gs are not pulled abruptly, but are rather gradually increased over 5 to 7 seconds, then such a temporary "crisis" of vision can be avoided. This is exactly what is implemented in the new model more clearly than in the current one.

 

Disorientation effect

 

We already have implemented in our older model the "motion sickness" or disorientation effect which was happening in the case of frequent changes in the Gs direction or sign-changing angular velocities. Now this effect will come even faster in order to better imitate the discomfort pilot suffers under alternating positive and negative G-forces. I will not say that the “wobbling” or "dolphin" is physically unbearable. I myself tried to do it in real flight. But it's really damn unpleasant, and I prefer to not do that anymore.

 

Also, this disorientation effect will now come along with the period of recovery after G-LOC (the so-called period of relative incapacitation). It will also manifest itself when approaching the border of LOC, foreshadowing it. Taking into account that, in the new model, loss of consciousness under prolonged G-loads of less than +4..+4.5G will now occur without an obvious tunneling effect, this “dizziness” together with “defocusing” of vision will become a good indicator for you that you are already on the edge.

 

Fatigue indicator

 

By the way, about the fatigue indicator. We decided to heed the popular request and add a G-load induced fatigue indicator to the simple instruments in GUI. When you set the difficulty to “Normal”, you will see a small white triangle in the lower left corner of the G-meter in the GUI. The more your pilot is worn out by the G-forces, the smaller this little triangle will become. Thus, it will give you a rough idea of your current state.

 

As I have repeatedly written on our forum, a real pilot cannot predict in advance what Gs he can sustain during the next maneuver and for how long. He, of course, roughly understands how tired he is. Therefore, this indicator will give you only an approximate idea of the current physical condition of the pilot. When you set the “Expert” difficulty, you will not have this indicator.

 

As a result

 

Ultimately, the new improved version of the pilot's physiology model turned out to be more interesting, detailed, taking into account new important factors and, as a consequence, more “vital” and corresponding to reality. All tests, including the ones with the participation of real pilots, indicate that this model will be the next important step in the development of our simulator, and the realism of air battles will again be raised to the next step with it.

 

This model will get to your computers very soon, along with the next update of the game.

 

Sincerely,
Principal software engineer
Andrey (An.Petrovich) Solomykin