G force and extreme aviation maneuvers

[cyboman]

I'm wondering what the potential benefit would be to having a fighter pilot surrounded by fluid in the cockpit on their ability to withstand high G maneuvers. How do the mechanics of fluid dynamics interact with the forces of gravity and the physiological stresses on the pilot during high G maneuvers? Hypothetically, if a fighter pilot was surrounded by a fluid in their cockpit, instead of open air, would this potentially decrease the physiological stresses on them when pulling high G maneuvers?

 

[Drakkith]

To my limited understanding, the g-forces on pilots are mostly those where the pilot is accelerated upwards or downwards, which forces blood out of or into their brain, resulting in redouts, greyouts, and blackouts. Since this is an issue of blood being accelerated parallel to most of the major blood vessels, being surrounded by fluid would do little or nothing to help. Fluid suspension is usually suggested in cases of high, sustained acceleration there the direction of the forces is from forward to back, where blood is accelerated perpendicular to the major blood vessels, which is much easier to tolerate.

Per the European space agency the main limiting factor in this latter type of acceleration is that air in the lungs prevents more than 24 g's of sustained acceleration. The lungs collapse because air is very low density and highly compressible. Breathing a breathable fluid and immersing a person in liquid inside a rigid container would possible allow accelerations upwards of 100+ g's.

Source: https://www.esa.int/gsp/ACT/projects/liquid_ventilation/

 

[cyboman]

Hypothetically, what if the fluid encompassing the pilot could change in density to potentially absorb or "buffer" the net g force acting on the pilot?

 

[Drakkith]

After reading the article and thinking about it a bit more, it might actually be beneficial even for maneuvers that force blood up or down. In a high-g turn, it is possible the water would be forced downwards, compressing the lower areas of the body, preventing blood from flowing into these areas.

But, as I said before, my understanding in this area is very limited.

 

[Filip Larsen]

Note that high-G maneuvering jets already have its pilots wearing G-suits which usually work by putting an external pressure on the pilots legs to reduce the amount of blood that can "pool" in the legs during high-G. Also, design of the seat can do much where even a 30 deg angle of the back can help reduce risk of blackouts and similar.

 

[jbriggs444]

Since this is an issue of blood being accelerated parallel to most of the major blood vessels, being surrounded by fluid would do little or nothing to help.

Blood, flesh and the hypothetical surrounding fluid have approximately the same density. Accordingly, the pressure gradient will work out just fine. Blood acceleration would not be problematic.

Consider by way of an extreme example, the following situation...

We have a water-filled tube immersed in a pool of water. The tube walls are thin and can support little pressure. The tubing is bent into a circle (doughnut or hula hoop shape). We insert a pump into the loop and task it with circulating the water in the tube.

The tube is under little stress. The pump can pump with little effort. The water anywhere within the tube is at approximately the same pressure as the nearby water outside the tube.

Suppose we increase gravity (put the pool into a centrifuge or rocket it off to Jupiter).

The tube is still under little stress and the pump still needs little power.

However, the body is not composed only of flesh. The lungs are a problem.

 

[A.T.]

Note that high-G maneuvering jets already have its pilots wearing G-suits which usually work by putting an external pressure on the pilots legs to reduce the amount of blood that can "pool" in the legs during high-G.

And some of them use a passive fluid for that, that increases in pressure under the g-load itself:
https://en.wikipedia.org/wiki/G-suit#History

The fluid could even drinkable as a survival ration:
https://www.key.aero/forum/modern-military-aviation/63082-simpler-is-better-the-dragonfly-g-suit
The liquid--housed in two-inch-wide channels that run the length of the arms, legs and torso--is harmless enough to drink, even serving as an emergency ration for a downed pilot

 

[A.T.]

Hypothetically, what if the fluid encompassing the pilot could change in density to potentially absorb or "buffer" the net g force acting on the pilot?

The fluid encompassing the pilot will automatically create the pressure gradient needed to prevent the body fluids from flowing down. But this works only if the fluid densities are approximately equal. Also note that this doesn't fully protect you from impacts (quickly changing accelerations) which produce shock-waves in the fluid.

 

[Vanadium 50]

This discussion is very 1980's. Today, if you can see your adversary, you are too close. Further, you are better off letting the weapon experience the forces, not the whole airframe.

 

[Filip Larsen]

Today, if you can see your adversary, you are too close.

However, Beyond visual range (BVR) engagements are effectively only a viable option during wartime with the targets clearly identified as hostiles by AWACS or similar long range radar system. In times of high tensions only pilots in interceptor roles are more or less required by ROE to eyeball potential targets first and must thus be prepared for some high-G maneuvers if that target turns out to be a (group of) hostile aircraft of similar maneuverability.

One can of course speculate that it is only a matter of time (a decade perhaps?) before pilots instead become drone operators who can initiate extreme semi-autonomous high-G maneuvers should the need arise while leasurly sipping their coffee 3000 miles away.

Later edit: My fingers wrote ROI instead of ROE.

 

[cyboman]

Breathing a breathable fluid and immersing a person in liquid inside a rigid container would possible allow accelerations upwards of 100+ g's.

That's incredible. Thanks for sharing.

 

[cyboman]

The fluid encompassing the pilot will automatically create the pressure gradient needed to prevent the body fluids from flowing down. But this works only if the fluid densities are approximately equal. Also note that this doesn't fully protect you from impacts (quickly changing accelerations) which produce shock-waves in the fluid.

What's also interesting is it could potentially be a game changer for counteracting negative g's. Which are very difficult for the pilot to withstand (max -3 as opposed to 9+). The G-suit as I understand it only provides pressure to counteract positive g's. A pilot within a significant mass of fluid would see buffering effects for negative g's as well.

 

[cyboman]

However, Beyond visual range (BVR) engagements are effectively only a viable option during wartime with the targets clearly identified as hostiles by AWACS or similar long range radar system. In times of high tensions only pilots in interceptor roles are more or less required by ROI to eyeball potential targets first and must thus be prepared for some high-G maneuvers if that target turns out to be a (group of) hostile aircraft of similar maneuverability.

One can of course speculate that it is only a matter of time (a decade perhaps?) before pilots instead become drone operators who can initiate extreme semi-autonomous high-G maneuvers should the need arise while leasurly sipping their coffee 3000 miles away.

I would add that additionally high-G maneuvers are required to evade missiles and other enemy fire. EDIT: and also for radar defeat like nape of earth tactics

 

[cyboman]

This discussion is very 1980's. Today, if you can see your adversary, you are too close. Further, you are better off letting the weapon experience the forces, not the whole airframe.

While having the smartest weapons is a big factor in mission success. So is having a better machine. Faster and more maneuverable. Current fighter pilots spend a lot of time training these high-G maneuvers, it didn't stop in the 80s. However, this is still a good point, having the smartest missile with the longest range is likely a big predictor of success in a lot of mission scenarios.

 

[berkeman]

That's incredible. Thanks for sharing.

They are lookikng for volunteers...

 

[Vanadium 50]

I (obviously) disagree. Stealth is an important factor today, one that is negated if you are close enough to dogfight. Further, pure fighters don't really exist any more - you see aircraft that combine the fighter and attack roles like the F/A-18 and F-35. The last pure fighter was probably the F-22, no longer in production.

Air combat is changing. And the solution to limitations imposed by acceleration of the squishy bits is "don't accelerate the squishy bits so much."

 

[cyboman]

I (obviously) disagree. Stealth is an important factor today, one that is negated if you are close enough to dogfight. Further, pure fighters don't really exist any more - you see aircraft that combine the fighter and attack roles like the F/A-18 and F-35. The last pure fighter was probably the F-22, no longer in production.

Air combat is changing. And the solution to limitations imposed by acceleration of the squishy bits is "don't accelerate the squishy bits so much."

So your position is that current fighter pilots are not at all concerned with executing high-G maneuvers? I never contended modern fighter aircraft are not multirole and only pure fighters. It seems you're not refuting any of the core hypothesis of the advantages of a pilot being suspended within a fluid to the physiological effects of high G maneuvers. Stealth tech is a big part of the race but is an entirely different subject that is not dealt with here. This is about high-G maneuvers. Talking about smart missiles and range is tangential too actually. Also, for clarity, what exactly are you disagreeing with?

 

[Filip Larsen]

Stealth is an important factor today, one that is negated if you are close enough to dogfight.

Absolutely, but today's aircrafts like F-35 is also a multi-role aircraft and if one of the roles require the pilot to be able to make high performance maneuvers then a G-suit and other measures to avoid G-LOC are still going to be relevant.

The Royal Danish Airforce, for instance, has a acquired a handful of F-35, but still has to use them to scramble for intercept and airspace denial (not sure what the English term is) when Russian aircraft routinely prod the airspaces over the Baltic sea. I understand it most often are larger bomber/recon aircrafts but once in a while it is a aircombat capable fighter.

Air combat is changing. And the solution to limitations imposed by acceleration of the squishy bits is "don't accelerate the squishy bits so much."

The low G-limits of the squishy bits are indeed a limiting factor and once one side in an arms race is moving towards "solutions" like drones that do not have such limit others will have to follow suit. To the extend you are saying that future air combat is not heading in a direction where more G-load are put on pilots, then I fully agree, but I would like to add that high G-load (up to the human limit) is as far as I understand it still going to a requirement for quite a while for some of the roles a modern fighter has to fulfill.

 

[Vanadium 50]

So your position is that current fighter pilots are not at all concerned with executing high-G maneuvers?

Why don't you let me state my position rather than putting words in my mouth,

My pointg is that of all the things you would like an aircatft to do - stealth, attack at longer range, multimission, etc. the ability to handle ever higher acceleration without damaging the squishy bits is low on the list and getting lower all the time.

 

[cyboman]

Air combat is changing. And the solution to limitations imposed by acceleration of the squishy bits is "don't accelerate the squishy bits so much."

This is essentially why I posed the hypothesis in the first place. If a more efficient anti-G system was developed this potentially wouldn't be a limit.

My pointg is that of all the things you would like an aircatft to do - stealth, attack at longer range, multimission, etc. the ability to handle ever higher acceleration without damaging the squishy bits is low on the list and getting lower all the time.

My post wasn't about how to improve the overall tactical ability of a fighter jet. Nobody said at any point g-suit or anti-G systems was high on the list of improving jet fighter performance. So again, I don't know what you're disagreeing with. I think you took the thread in your own direction but that's ok. Thanks for the contributions to the thread.

 

[cyboman]

but I would like to add that high G-load (up to the human limit) is as far as I understand it still going to a requirement for quite a while for some of the roles a modern fighter has to fulfill.

Exactly, and the more g's a pilot can withstand, the better their chances of success in a dogfight or other high-G mission scenarios.

 

[cyboman]

However, Beyond visual range (BVR) engagements are effectively only a viable option during wartime with the targets clearly identified as hostiles by AWACS or similar long range radar system. In times of high tensions only pilots in interceptor roles are more or less required by ROE to eyeball potential targets first and must thus be prepared for some high-G maneuvers if that target turns out to be a (group of) hostile aircraft of similar maneuverability.

One can of course speculate that it is only a matter of time (a decade perhaps?) before pilots instead become drone operators who can initiate extreme semi-autonomous high-G maneuvers should the need arise while leasurly sipping their coffee 3000 miles away.

Later edit: My fingers wrote ROI instead of ROE.

Thanks for your great contributions! I found this stackexchange thread that had some interesting replies that relate and builds on the points you've made. It's a bit tangential at times to the actual fluid immersed anti-G discussion but I thought I'd share as you might find it interesting. The posted question was: "Why are high-g requirements so important for training next generation of fighter pilots?" The highest rated answer is contributed by a user who was involved in training systems development, and training requirements, for US Navy fighter/jet pilots.

Here's an excerpt from his reply:

Two solid reasons: defensive and offensive ACM/BFM remain relevant​

I'll address the defensive issue first. Even if a pilot will never get into a dogfight, the pilot / aircraft still must defeat or evade a surface-to-air or air-to- air missile. This combines the use of both countermeasures and 3-dimensional maneuvering to cause the guidance system inside the missile to lose it's lock on the aircraft. To get the turn rate and axis-change-rate needed to deal with modern missiles requires the ability to pull a significant number of g's. You can look at is as a "purely defensive dogfight" technique. You fight the way you train, so you need to train for this likely situation.

The offensive high energy, high-g capability has to be retained because in real life, the rules of engagement do not always allow for a BVR (Beyond Visual Range) engagement. Further that point, even with BVR engagements allowed, if the opponent has good defensive technique versus your missiles you may still get into a dogfight-style of engagement in order to defeat or destroy that opponent. You have to know how to do that, and train for how to do that. It is an acquired skill. (The basics of the skill were eloquently laid out by John Boyd, which is where the OODA loop model comes from).

Both the offensive and defensive applications of these maneuvers require skill with and acclimatization with high-g maneuvering.

And a military text he quoted:

With the maturation of aerial warfare evolving into Beyond Visual Range (BVR), the decades that followed Korea exploded with the development and implementation of long range air-to-air missiles that could potentially eliminate the possibility of Within Visual Range (WVR) engagements. During the Vietnam conflict, however, aircrew often found themselves unable to employ their BVR missiles, forcing weapons employment into the WVR arena, ultimately relying on BFM skills to defeat their opponents. The days of Korea and Vietnam are long past, and we have achieved amazing successes with the accuracy and reliability of our current long-range missiles. As we, and our enemies, continue to improve our BVR capabilities, a combination of electronic attack, theater Rules of Engagement (ROE), switchology failures, or a momentary lack of attention to prescribed air-to-air timelines may ultimately bring us face to face with the enemy in a 1v1 engagement.

Another user:

Historically the maximum g-loads that fighter jets can take have increased over time. Only just recently the planes are truly 9g capable and can retain those forces for a longer period of time (except maybe F-35). To best use the capabilities of the aircraft, it makes sense to pull higher G-forces. Better anti-g suits would also make higher g-forces possible for the pilot.

Another reason might be that Stealth mostly only helps you against a less developed opponent. BVR-missiles are quite easy to evade for modern agile fighters and now that other countries are developing stealthy planes as well a shift to WVR-combat seems likely. The dream of making dog fights unnecessary failed once before when it was decided that fighters don't need a cannon when missiles first appeared. I believe it might be similar with Stealth technology.

Source: https://aviation.stackexchange.com/...rtant-for-training-next-generation-of-fighter