Improving physiology model : push-pull effect (loss of pos G tolerance)

[Blackhawk_FR]

Hello, 

 

I open this thread to start talking about this particular physiological effect: negative to positive G tolerance (push-pull effect). 

It's just a start as I don't have much data right now, except my experience of professionnal aerobatic pilot. 

Anyone is welcomed to add arguments and links about datas and studies about that. I will gather them in the first post. 

 

 

The loss of positive G tolerance after negative G (or just severals seconds of inverted flight at -1G) is a real, well known effect, and it affects every pilots, whatever his training and accomodation to G. 

In summary, when flying under negative G, blood vessels in the upper part of the body get wider. If you immediatly pull positive G in that condition, the enlarged blood vessels are litteraly highways for the blood that will flow faster out of the head to the legs. Resulting in positive G symptoms (black out, G lock,...) appearing faster and with less G than usual. 

Another symptom is that the heart rate slow down under negative G. While you need a high heart rate to counter the positive G. 

 

It would improve the physiology model and add more realism to combats. Knowing the first version of this model is already an amazing improvement. 

 

It seems very clear this effect is not modeled in the game. Unfortonatly there is no accelerometer indicator available in game [not anymore], and I don't have tacview (anyway many are saying it's not reliable). 

I just made a lot of tries and never noticed any changes in G tolerance. 

For example, I pushed a lot of negative G to the limit of the pilot (before the loss of consciousness) then pull about the same amount of positive G. The pilot clearly seem to handle positive G in the same way. 

Anyone who has tacview is welcomed to share his results, to have a stronger proof. The most simple would be to have a confirmation from the dev team that the alternative negative to positive is not modeled.

EDIT: Thanks to 4.006 update, we have an accelerometer. I'll do my best to make proper tests to see if push-pull effect is present or not. 

 

 

 

Links with datas/studies/anything about the push/pull effect:

https://www.ncbi.nlm.nih.gov/pubmed/11542365

http://medind.nic.in/iab/t01/i1/i1/iabt01i1p8o.pdf

 

2 hours ago, 1PL-Husar-1Esk said:

"Remember that I said that there are individual variations in a person’s G 
tolerance depending upon a number of physiological factors? Well one factor 
which affects G tolerance in all pilots at any instant in an aerobatic sequence is 
what the preceding manoeuvre was. If the preceding manoeuvre involved  zero 
or  negative G for longer than about 3 seconds the heart will have responded to 
an over pressure signal from the brain and begun slowing down!  If at that point 
the pilot slams on +4G, he/she is ‘flirting’ with instantaneous GLOC, because 
the slowing of the heart rate can drop the entire ‘G tolerance chart’ down about 
2G!
It seems that the heart is capable of responding faster to ‘over pressure’  signals 
from the brain than ‘under pressure’ signals. Trials of heart rate versus G on 
advanced aerobatic pilots have shown that the heart slows down faster  than it
can speed up when going from high +G to high –G. In one trial a transition from 
175 beats per minute to 40 beats per minute occurred within 5 beats! That is, the 
heart rate dropped from 175 to 40 in 2 seconds!
This combination of manoeuvres, from negative G to high positive G, has been 
nicknamed ‘sleeper’ manoeuvres because they are going to put the pilot to sleep! 
Sleeper manoeuvres have caused the death of a number of aerobatic pilots over 
the years, which is the main reason I am giving this lesson. If those pilots had 
attended such a lesson I am sure they would be alive today."

 

source : 'Noel Kruse, the creator and Chief Flying Instructor of the 'Sydney Aerobatic School'

 

Edited May 22, 2020 by JG300_Faucon

[VR-DriftaholiC]

I think tacview is free to try. I'm curious your take on the in game pilots ability to handle positive G especially without a suit. I've head some say a young WW2 pilot could handle a bit more then the in game counterparts.

[VR-DriftaholiC]

41. A G-load indicator is added to the HUD. When simplified instruments are switched off, G-load is indicated without a fractional part;

 

Part of your wish.

[Blackhawk_FR]

3 hours ago, ShadowFrost said:

http://medind.nic.in/iab/t01/i1/i1/iabt01i1p8o.pdf

 

I figured this would be good to add. 

 

TL:DR If you pull negative g's, expect positive G tolerance to be significantly reduced for a duration afterward. 

[ZachariasX]

How much would „significantly“ be then?

Personally, I hate negative g maneuvers because they hurt much before I‘d pass out. But I find the onset as we have it implemented now rather soon. I‘m not asking to increase limits here, as I do like the play style it enforces. But adding further reductions in tolerance would probably overdo it. But one had to try.

 

Why I‘m saying that the onset of g effects might be a tad soon is that in non-competition aerobatic biplanes, it is not easy to do maneuvering (you also ruin the aircraft) that you get even near a g-loc. I’d stall out way before that. Yet in our WW1 crates, it is a rather easy thing to do. You can tighten your circles as if you‘d be in an aerobatic glider. In the B-4, I‘d pull 6 g‘s with one finger after getting it to 200 km/h. But other aircraft?

 

I mean, is there an 800 kg aircraft with 150 hp where you can sustain such 4+ g-loads that easy?

[ShadowFrost]

36 minutes ago, ZachariasX said:

How much would „significantly“ be then?

Personally, I hate negative g maneuvers because they hurt much before I‘d pass out. But I find the onset as we have it implemented now rather soon. I‘m not asking to increase limits here, as I do like the play style it enforces. But adding further reductions in tolerance would probably overdo it. But one had to try.

 

Why I‘m saying that the onset of g effects might be a tad soon is that in non-competition aerobatic biplanes, it is not easy to do maneuvering (you also ruin the aircraft) that you get even near a g-loc. I’d stall out way before that. Yet in our WW1 crates, it is a rather easy thing to do. You can tighten your circles as if you‘d be in an aerobatic glider. In the B-4, I‘d pull 6 g‘s with one finger after getting it to 200 km/h. But other aircraft?

 

I mean, is there an 800 kg aircraft with 150 hp where you can sustain such 4+ g-loads that easy?

Out of curiosity what is your resting G-load IRL? 

I would say mine is around ~3.5 Gs depending on how accurate the gauge is of course. 

Though I agree with you, significantly is a bit vague but unfortunately they do not list a large variety of tests/scenarios, so data is somewhat limited with this source. Though, in their conclusion, 5gs was about the limit with "near maximal strain" after "less than 1g for a few seconds". Which, 9gs is being used as a baseline for normal maximal pull in this document. So approximately a ~45% reduction in overall positive G capacity can be inferred from that statement. Though, a curve in terms of how harshly you are affected under different negative G-loads in respect to positive may be harder to obtain due to the somewhat limited examples/tests provided. 

 

I will also say, I don't have many issues with the g-model in terms of normal pulls (IE no negative slamming/pushing/weird stuff before hand). I find it to be more than fair for a person like me, in decent shape, with minimal aerobatic training/ AGSM practice. Though one can make the argument if this should be more than it is currently, that is not the argument I am after nor do I believe the OP is.

 

The argument is against, slamming/pushing negative without consequence to how well you can pull positive g's afterward. Which there seems to be no downside in IL-2 currently for performing negative maneuvers and then returning back to positive g's immediately. Which is not the case IRL. And then lastly, most maneuvers in the negative aspect are done quite aggressively online (in such a way I wouldn't dare IRL) that I would imagine the penalties to be more drastic than if you eased into negative gs and back out to positive gs. 

Though I understand what I think (assume) has no or minimal value, as changes should only be made based on good evidence. I see no reasonable way to test the extremity of negative pushes like we see in the game. As I don't dare do the same in a T-6 (the most comparable aircraft available to me, and even then the negative G limit is lower than 3) and as reported in the document, centrifuges are unable to recreate the scenarios we would want to verify from the game as well. 

 

Edited May 22, 2020 by ShadowFrost
Grammar

[ZachariasX]

8 minutes ago, ShadowFrost said:

Out of curiosity what is your resting G-load IRL? 

I couldn't really tell, but when doing longer term increased g-loads (spiral flight) it might be somewhere near 4 g (that I consider a lot when sustained). I haven't done many maneuvers where I would have impaired vision during the turns, and so far never in aircraft that can sustain this load. Really getting a grey out would be *maybe* be somewhere above 5.5 g. Most likely my limits in this regards would be somewhat similar to yours, if I was being told that 3.5 g is my resting limit, then that still makes sense. Toward 4 g sustained, I feel more just uncomfortable than anything else which convinces me to go and to another maneuver. Still, I have the impression that the load where vision finally gets shrouded is higher. But as we have it in game, I'm generally happy about it.

 

I'm not saying that I'm more g-tolerant than reference (certainly not) but I cannot reconcile how easy it is to black out in turns in out biplanes, whereas in a real biplane, blacking out is about the least of my worries in such coarse maneuvers.

 

Thus, there is and probably will alwys be a difference of "the real life" and permissive gameplay derived form a simulation of "real life". In the end, what we implement should ideally enforce gameplay to be in line with what was done. But often one can ony say ex post if a change to the simulation brought gameplay closer to the real thing. In this sense, it might be worth trying to reduce g tolerance after negative g maneuvers. There would probably be a lot of lawn darting (as when g effects were introduced) but maybe players adjust.

 

 

[ShadowFrost]

1 hour ago, ZachariasX said:

I couldn't really tell, but when doing longer term increased g-loads (spiral flight) it might be somewhere near 4 g (that I consider a lot when sustained). I haven't done many maneuvers where I would have impaired vision during the turns, and so far never in aircraft that can sustain this load. Really getting a grey out would be *maybe* be somewhere above 5.5 g. Most likely my limits in this regards would be somewhat similar to yours, if I was being told that 3.5 g is my resting limit, then that still makes sense. Toward 4 g sustained, I feel more just uncomfortable than anything else which convinces me to go and to another maneuver. Still, I have the impression that the load where vision finally gets shrouded is higher. But as we have it in game, I'm generally happy about it.

 

I'm not saying that I'm more g-tolerant than reference (certainly not) but I cannot reconcile how easy it is to black out in turns in out biplanes, whereas in a real biplane, blacking out is about the least of my worries in such coarse maneuvers.

 

Thus, there is and probably will alwys be a difference of "the real life" and permissive gameplay derived form a simulation of "real life". In the end, what we implement should ideally enforce gameplay to be in line with what was done. But often one can ony say ex post if a change to the simulation brought gameplay closer to the real thing. In this sense, it might be worth trying to reduce g tolerance after negative g maneuvers. There would probably be a lot of lawn darting (as when g effects were introduced) but maybe players adjust.

 

 

Yes, and the argument against whether the pilots in sim should be able to take more positive g's is understandable. I am unable to recreate the conditions to a comparable enough level I would feel confident saying definitely otherwise, but potentially IL2's positive g tolerance is slightly low but nothing too far off IMO. I don't know if in WW2 they had as good as a understanding of AGSM or etc. I would like if someone would inform me more on whether or not they had the same tolerance as of today or if we've made improvements in technique/understanding to better compensate for it. 

 

Agreed, it would take time for people to adjust but IMO that is no reason not to pursue a more realistic interpretation of the pilot physiological model. As it would likely put a stop to people slamming negative which is unrealistic in my opinion (at least in the extreme examples commonly seen). Not to say negative maneuvers aren't used, they just likely weren't used in the extremes seen currently. Though they have their time and place, they should have the proper consequences as well which would hopefully push Il2 to be a more realistic representation of air combat of WW2. 

Edited May 22, 2020 by ShadowFrost
grammar

[Aurora_Stealth]

This is a great point and a very overlooked one, switching from positive to negative G's (or opposite) definitely has an additional effect on the pilot.

 

Perhaps a second wave review of the pilot physiology could be planned by the dev. team to dive deeper into his?

 

From my experience in aircraft seating design and testing (including support of 16g dynamic / 14g dynamic - sled testing).. there should also be an effect modelled for the pilot seating angle as this is also a major factor and is why side facing seats and other types of non-standard seat design are quite difficult to certify in practice alongside stricter regulations and head injury loads.

 

I'm wondering if you are situated at a flatter angle, would that lessen the shock from switching loads from positive to negative G (or opposite)?

 

Food for thought.

[Blackhawk_FR]

I started some testing.

 

First results to give an idea:

 

Sustained 5Gs with fast onset (3/4sec to start the turn and stabilize 5G):

A strong but short grey out (almost black out) appear very quickly, then it return into a normal grey out.

Grey out increase at 40sec. 

G lock will occur between 1min and 1min15. 

 

Sustained 6Gs with quite fast onset (8-10sec to start the turn and stabilize 6G):

G lock between 25 and 30sec.

 

6G with instant onset:

G lock after 7sec (+/- 1sec).

Edited May 22, 2020 by JG300_Faucon

[FTC_Kongoo]

1 hour ago, JG300_Faucon said:

I started some testing.

 

First results to give an idea:

 

Sustained 5Gs with fast onset (3/4sec to start the turn and stabilize 5G):

A strong but short grey out (almost black out) appear very quickly, then it return into a normal grey out.

Grey out increase at 40sec. 

G lock will occur between 1min and 1min15. 

 

Sustained 6Gs with quite fast onset (10sec to start the turn and stabilize 6G):

G lock between 25 and 30sec.

 

6G with instant onset:

G lock after 7sec (+/- 1sec).

which aircraft was this done with?

[1PL-Husar-1Esk]

"Remember that I said that there are individual variations in a person’s G 
tolerance depending upon a number of physiological factors? Well one factor 
which affects G tolerance in all pilots at any instant in an aerobatic sequence is 
what the preceding manoeuvre was. If the preceding manoeuvre involved  zero 
or  negative G for longer than about 3 seconds the heart will have responded to 
an over pressure signal from the brain and begun slowing down!  If at that point 
the pilot slams on +4G, he/she is ‘flirting’ with instantaneous GLOC, because 
the slowing of the heart rate can drop the entire ‘G tolerance chart’ down about 
2G!
It seems that the heart is capable of responding faster to ‘over pressure’  signals 
from the brain than ‘under pressure’ signals. Trials of heart rate versus G on 
advanced aerobatic pilots have shown that the heart slows down faster  than it
can speed up when going from high +G to high –G. In one trial a transition from 
175 beats per minute to 40 beats per minute occurred within 5 beats! That is, the 
heart rate dropped from 175 to 40 in 2 seconds!
This combination of manoeuvres, from negative G to high positive G, has been 
nicknamed ‘sleeper’ manoeuvres because they are going to put the pilot to sleep! 
Sleeper manoeuvres have caused the death of a number of aerobatic pilots over 
the years, which is the main reason I am giving this lesson. If those pilots had 
attended such a lesson I am sure they would be alive today."

 

source : 'Noel Kruse, the creator and Chief Flying Instructor of the 'Sydney Aerobatic School'

 

Edited May 22, 2020 by 1PL-Husar-1Esk

[Blackhawk_FR]

2 hours ago, ACG_Vietkong said:

which aircraft was this done with?

 

Tempest. I choosed this one as it's one of the easiest to take a lot of G. 

Departing from 3k and holding the number of G wanted in a spiral descent. 

 

 

2 hours ago, 1PL-Husar-1Esk said:

because 
the slowing of the heart rate can drop the entire ‘G tolerance chart’ down about 
2G!

 

Forgot it was also (and may be mainly) about heart rate. Thank you. 

[Floppy_Sock]

I think the tail limits to the tolerance curves are reasonable in the current model. 

 

I two very large gripes though:

1. as faucon pointed out, the lack of push pull induced tolerance reduction. 

 

2. This absolute incorrect use of onset rate dependence on non-relaxed g tolerance. Yes, relaxed g tolerance is dependent on onset rate, to a degree. However, the fact that onset rate is the paramount dictator in g-loc is false. I'm not trying to make the devs look bad here but the paper the devs used used that made this claim (Stoll AM: Human tolerance to positive G as determined by physiological endpoints. Aviat Med 1956, 27:356–367.) was from 1956. This is the paper where this image comes from:This conclusion was based on only 14 loss of consciousness events. It's been critically reviewed multiple times by different authors and subsequent studies. 

 

There is a much more recent study from 2013 which compiles over 800 loss of consciousness events with which the following conclusion is made:

The two new G-LOC curves differed significantly from previous curves in temporal characteristics and key aspects underlying neurologic response to acceleration. The new acceleration onset rate curve reveals that for onset rates ≥ 1.0 G/s, G-LOC will occur in a mean time of 9.10 s and is independent of the onset rate. The new +Gz-level curve demonstrates that G-LOC will occur in a mean time of 9.65 s for rapid onset rate exposures to +Gz levels ≥ +7 Gz. The minimum +Gz-level threshold tolerance was defined as +4.7 Gz. When +Gz onset rates are gradual, ≤ 0.2 G/s, G-LOC occurs in a mean time of 74.41 s. G-LOC did not occur earlier than 5 s for any acceleration exposure

Whinnery, T., Forster, E.M. The +Gz-induced loss of consciousness curve. Extrem Physiol Med 2, 19 (2013). https://doi.org/10.1186/2046-7648-2-19

 

It was found that onset rate is not a factor above 1 G/s. Find this study here: https://link.springer.com/article/10.1186/2046-7648-2-19

 

This explains the apparent weakness in our pilot's ability to handle "short" but high ROR maneuvers with or without a g suit. There is a deadband, where regardless of onset rate or final g, a human, in the average, will not lose consciousness. This paper reports the deadband to be a staggering 9.1 seconds after acceleration begin. This has to do with the short term oxygen stores in relevant brain tissue.

 

As a comparison, here's a horizontal max performing break turn in the spit mk9 - 3.66 seconds to gloc. Fresh pilot. 

 

Edited May 23, 2020 by Floppy_Sock

[1PL-Husar-1Esk]

I had long break (year or more ) fighting in ww2 planes, but what I found recently,  that now the best throw off fast comming enemy from 6 is not break but other maneuver - slow down and do oscialation maneuvers up and down by pushing and  pulling stick ... how artificiali it looks and work fine without penalty   from  negative to positive G just to game the game. He overshoots and you are behind ready to pull the triger, espiecialy if you are in high power/accelaration plane.

Edited May 24, 2020 by 1PL-Husar-1Esk