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G Induced Loss of Conciousness Part 1
#1 Posted : Monday, April 11, 2011 11:10:03 AM(UTC)
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This is a good introduction to G-LOC for all acro pilots.
Steve Johnson

A Plain Pilots Guide to GILOC - part 1

Part 1 - Basics of G-Induced-Loss-Of-Consciousness

1. Definition of GILOC: A pilots Loss Of Consciousness caused by sustained high +Gz.

This separates our subject from the acceleration-induced unconsciousness produced by head injury and, for the moment, the effect of “hyper-G” – that is, sustained Gz beyond +12 Gz / -9 Gz, which may be an operational requirement in time years ahead. For the moment we are dealing with the problems associated with the +9 / -7Gz domain of competition aerobatics.

2. Human Design Limitations.
One of our biggest problems is that The Almighty, having done so good a job on the first five days of Creation, obviously went off on the first Long Weekend in History and left the design of the Mark 1 Human (Man) to a second line design team, in which an apprentice named Satan was a prominent lay-about. Their efforts are characterised to this day by haphazard arrangement and botched improvisation. Sadly, when He Himself, suitably refreshed, returned to the No.1 Design Bureau to produce on the second Tuesday of Creation the up-rated Mark II version (Woman), many of the basic faults persisted.

3. Brain Energy Requirement
Our Brain is the organ with which we worship our Maker (and also pay our taxes). It is therefore the most important part of the body (as well as being its most essential aerobatic component). One would reasonably expect it to work when all else had failed. To do this it should have a copious energy store to keep it independent of lesser organs and tissues. This simple requirement was quite overlooked by that First Saturday Morning, second league design squad. And the later, uprated (female) version got no better kit (though admittedly ONLY in this respect). Our brains carry only enough energy reserves to function for 5 seconds without a continuous supply of oxygen and glucose, delivered by the blood pumped continuously into the brain by the heart - the CBF (Cerebral Blood Row). Stop the CBF for 5 seconds only and the brain instantaneously switches OFF completely. One is immediately, completely and instantaneously rendered unconscious. And there is nothing one can do about it. Even if the CBF is immediately totally restored, it takes the brain <15 second to get started again, <15 seconds more to begin to get its act together (we are now passing 30 seconds), 3 minutes to do much that is useful and maybe <30 minutes before we can fly a passable instrument approach. That’s plenty of time to scare the hell out the Judges, and get uncomfortably acquainted with the horizontal feature 100 metres below the bottom of the box.

4. CBF - Cerebral Blood Flow.
This is maintained at about 1 lit/min by the CO, Cardiac Output of the Heart. This is no problem in the First Friday Series of animals, particularly the Quadrupeds. They were designed with their heads at the same level as the heart. The significance of this was lost on the on-duty Archangels beavering away on our design early the next morning, thinking only of how quickly they could knock off to get to the First Football Game, starting at noon. They were familiar only with a 0Gz eternal environment, whereas the Almighty was designing our species for the 1Gz Eden Garden operational area. Problems really started when our quadruped spine was racked through 90° to satisfy an erect postural requirement, without the trouble of designing a vertebral column for the job. One result is that commonest of all human ailments – “back trouble” - but that’s another story. For our purposes the heart now has to pump the blood 35cm or more up into the head. This is bad enough with blood weighing what it does under +1Gz Eden conditions. Usually we get away with it, if we don’t we faint. But out in Eden, if we faint, we fall to the Good Earth, which gets our head back into the relationship it should have - with the heart at the same horizontal level - and the heart can still push some +1Gz weight blood along to the brain and presto! we wake up in time (lady heroines always take longer).

5. Effect of +Gz on CO and CBF.
Increasing +Gz increases the weight of the blood. The strength and ability of the heart remains the same. Eventually the heart just is not strong enough (even, unbelievingly, in Swedes!) to pump the blood up into the head and so the CBF, upon which the brain constantly and continuously depends for its function, ceases. No problem for 5 seconds, but after that the brain turns off, like a light. Like someone pulling the plug on a computer.

6. Brain Recovery from no CBF.
Our brain can survive <4 minutes of cerebral “ischaemia” (no CBF), though only one group has ever tested this (convicted murderers) and its unlikely that well get ethical approval to try it again. The aerobatic problem is the <5 second ischaemic (no-CBF) consciousness limit. Cross that boundary and you are OUT for <15 seconds, and in the reality of aerobatic flying practice, likely to be well through the Pearly Gates by the time you wake up. Even if the +Gz is let off immediately (because, being unconscious, you’ve let off the control input to maintain the pitch-up which has generated the high tGz).

7. G-warning, “grey-out”.
The old hands among us will by his time be muttering “wot about grey.out”? What about it, indeed? If you pull on +Gz gently and slowly (taking in most of Northern Europe to do a 360° turn, or the further stratosphere for a loop), then you can titrate your cerebral blood flow against the weight of your blood and the strength of your heart and enjoy the dubious pleasures of borderline CBF: first tunnel vision, then lost of colour vision (“grey out”), then vision itself while hearing remains, then oblivion. This is what crafty old flying instructors used to rely on to make sure we did not “pull a fast one” on them, to render them unconscious so one could enjoy a little freebie aerobatics whilst the “old Man”, usually all of 26- 28, slept. The sure-fire method is to wait until he is distracted then immediately pull +8Gz and in 5 seconds he’s with his fathers (but so will you if you don’t get your ASM, Anti-G Straining Manoeuvre, in first!). The explanation of this little paradox lies in Fig. 1 below. You can pull as much +Gz as you like for <5 seconds or until your brain shifting down into your neck spoils your pleasure! Hold that Gz a nanosecond longer and you’re OUT for a count >10. And it won’t be the canvas that you’ve hit.

Creep up slowly and savour marginal CBF if you will, but you won’t get many points from the judges, even if they have powerful enough glasses still to see you! The little “kink” after 5 seconds of playing with +Gz is the effect of the rise in One’s blood-pressure brought about reflexly, but all too slowly (how long does YOUR girlfriend take to make your hair stand on end? Even Nottingham girls lake >5 seconds! And even if you took HER along in your Su 29, she still could not get your blood pressure high enough to get your blood up into your by-this-time-overloaded-with-delight brain.

8. The “G-free Window”.
The reason why those of us who have had the fun and good fortune to aerobat high performance aircraft and survive are here, is that so far our aircraft have generated huge G-induced drag, burning off energy and preventing us from sustaining high ±Gz long enough for our ischaemic brain to run out of their strictly limited energy stores. Alternatively we have got around the corner and there’s no need to continue to pitch up and maintain the high +Gz. We have been skirting coma and disaster without knowing it. Saved by those very aircraft limitations which have frustrated us for so long. However, better aerofoils and more installed horsepower now means that we have the means (like the military with advent of the F-l6) to wreck ourselves if we continue in ignorance and operate our new gear with the intellectual blinkers of yesteryear.

John Firth, Queens Medical Centre, Nottingham

A Plain Pilots Guide to GILOC - part 2

Part 2 - “Of Gas and Gaiters”

GILOC - Facts and Fable

1. Introduction.
In part 1 we dealt with the basic problem of G-induced-loss-of-consciousness (GILOC): keeping a continuous supply of blood, oxygen and glucose to the brain with never >5 seconds interruption when pulling +Gz we can render our blood as heavy as lead and yet out hearts can be only just so strong. The next question to be addressed is: what has been happening since Kitty Hawk? Why all the fuss, now? These are reasonable questions and it helps ones understanding of the subject to recall what our predecessors thought and did about it.

2. 1914-18: LOMF - “Lack of moral fibre”.
A number of British fighter pilots had the courage to report what they took to be a form of fainting when exploiting the capabilities of the new generation of fighters introduced (especially by Tommy Sopwith and his chum Harry Hawker) to counter German Air Superiority over the Western Front in 1916. Tough, externally braced (like a Pitts) and with plenty of elevator authority, the Sopwith Pup and its more aggressive successor the Camel could not only be flicked using the torque and precession of their (relatively huge) rotary engines, but they could also maintain the tightest of spiral dives to exit the unattractive attentions of the various German “circuses” of the time, of which Maestro Richthofen’s was the worst. However such tactics, thought cowardly by some, were appropriately rewarded by attacks of the “vapours”.

Now no True Brit could admit to feeling faint in the Face of the Enemy (however much +Gz had been pulled for however long). Obvious cowardice! Better stand and be shot like a man, or so the Earth-bound critics of these pilots insisted.

One answer was to go to Gosport for the weekend (rather than spend it more pleasantly in Paris) and get a wierdo Canadian to teach you what we would now call spin recovery. Spinning was held greatly in awe and anyone surviving had to be a bit of an ace (so much so that Prof. Lindemann was still conducting profound and serious research at Farnborough on how one might recover from a spin years after the operational squadrons at the Front were using it routinely!). I had two old uncles who seem to have spent the entire War spinning out of trouble (no “fainting” and no medals, but they always got back for their beer).

The other answer was a sufficiency of brandy (which, of course, the proverbial uncles could not take, being good, abstemious, Calvinistic, tea-totalling whisky-drinkers) and an immediate return to the air. This ensured that one was promptly shot down by the ever present Richthofen and Co. - which neatly disposed of the problem. l9l8 and the end of the War allowed the whole un-savoury subject to be conveniently forgotten.

3. Dolittle who did Much
The annoying matter next raised its unwelcome head in no less inappropriate (for Lack of Moral Fibre, that is) a place than at the Pulitzer Trophy Races - The True Home of the Fast and the Great: Cleveland, Ohio. The Great Fainter now was none other than the All American Hero of the hour, James Dolittle, Himself (no less). He commanded the highest fees to fly the hottest and fastest ships that the American Aircraft Industry could produce during the frenzied height of the Boom before the 1929 Slump. Of all people, James the Great reported that when turning pylons, flat-out (he only removed the throttle from the firewall to land), he lost first vision, then hearing and then, he alleged, ‘sensibility’ itself. Panic! Uproar! If young Jim said so it had to be so. There had to be a problem (especially when he might “blow” all that sponsorship in front of every cinema audience on Earth). First the dread Dr. Bauer was called in. Confusion! Next the even more dreaded Dr. (Capt.) Armstrong (Harry to his friends, though he was particular about those whom he so numbered). He Who Always Had The Answer (but not on this occasion for a long, long time to come). Collapse of worthy parties with retirement to furthest, deepest, most Southerly and remotest Ohio (that is to Wright-Patterson Field, and was).

4. “Deutschland űber alles”.
Meanwhile the fiendish Col. Prof Dr von Diringshofen (of that ilk) was not pleased. An impudent young whelp (later to be the even-more fiendish Gen Prof. Dr. Bruno [von?] Műller, but for the moment Luftwaffe Leutnant Műller) had been having some fun with the new-fangled Ju-87 Stuka. Just like an F117A in the middle of a Baghdad night, you could really wake up the Mess by putting a 500lb bomb down the chimney when they least expected it. But there was a nasty snag. One usually ended up in a heap about 200m away, and could not remember why. Those vapours again? Surely not? In the Master Race? No less. Now this Műller character, later good friend and fellow West German FAI-CIMP Delegate, was no ordinary Flying Medical Officer. He had the guts to stick to his guns and insist that the lily-livered Limey Disease could even affect the Herrenvolk, given the right conditions.

Consternation! How could the Stuka strike terror throughout Degenerate Europe when the Super Race suffered from so demeaning a condition? What’s more the Reichsbank insisted that each Stuka was to be used at least TWICE! But take thought. If even the Great Bruno could have the odd faint, where was all his blood going? Speedily a Ju-87 was equipped with:

i. An automatic, pre-set, altimeter-driven, pitch-up device (we call it auto- recovery these days) which would recover the aircraft to the Straight and Level whether the pilot was compos mentis or not.

ii. An X-ray machine (get a load of this for carrying capability: it needed more than the curvature of the Earth to get off the ground, but the North German Plain and half the Baltic was just enough), mounted in the fuselage firing forward to irradiate the pilot and see what was going wrong.

iii. Even more extraordinary: a proof radiographer who squeezed into the rear cockpit (or sat astride the fuselage) and was not allowed to pass out. Even though the pilot had GILOC-ed seconds before and they were still screaming downhill straight at Eternity’s Eye, this imperturbable radiographer was required to attend to his massive, steam-driven apparatus and continue to serially X-ray the slumbering (and, no doubt by this time, convulsing) pilot in record events. If anyone ever deserved the “Pour La Merité” it was that, alas unrecorded, radiographer.

The upshot of all these antics was (surprisingly) not to put everyone off the Stuka (that was left to the RAF), but to show that on the pull-out, under high +Gz, Bruno Műller’s heart disappeared. Not because it had migrated somewhere below his lower pelvis (though he recalled it often felt so!), but rather that the blood appeared to have pooled down into his legs (the fact that the valves in the leg veins would not allow this was conveniently overlooked). This was then investigated on the first operational centrifuge outside Berlin and vast expense and effort was most laudably diverted from more sinister activities to devise ways to get the blood back to the heart. For some reason it was assumed that if the heart could be made to look alright on the high +Gz X-rays then by some magic all would be well. In the event the work was overtaken by the success of the auto-recovery device and Galland et al’s adoption of a neo British attitude to aviation fainting which was to cost them dear in the closing days of WWII. For the moment the Luftwaffe was all-conquering and needed little help from the faint-hearts of the Luftmedezin brigade lurking in their cozy dens around Berlin.

5. Schneider and all that.
The success of Dolittle in the Schneider trophy races flying Curtiss (seaplane) Racers and the obviously impending success of the Italian Marchetti machines eventually stirred-up even the Brits to take note. Mitchell and Supermarine came up with the airframe, but no one had an engine. The Napier Lion series produced the poke, but usually blew up before lift-off (which, admittedly, did use most of the English Channel and a sizeable chunk of the North Atlantic as well). Their opportunity came when Curtiss went broke in The Slump of ‘29. Hallelujah! Curtiss even had a straight twelve on the stocks which could be bought for a song and disguised by Rolls-Royce as the greatest thing in new, innovative, true-Brit aero-engines - the “Merlin” (even better, poor old Stanley Baldwin, the Prime Minister who was trying to raise enthusiasm for rearmament against Mr. Hitler and being hammered at every bye-election, was persuaded to put up the tally, from his secret rearmament fund, on the assurance that this would power the first of his great new super-weapons, the 8-gun monoplane fighter which artful Sopwith and the mischievous Camm had convinced the Cabinet, but not Whitehall, would keep the evil Bosche out of English skies, hotly supported by the other Baldwin secret wizzo weapons: Death Rays [which produced Radar, and later the Laser] and Regional Neurosurgical Units. Great thinking these bureaucrats!

However, horror of horrors, the faints struck again, even in the creamiest of the creamy, the RAFs vaunted High Speed Flight. In the event they did win, but not before one pilot continued to hurtle around the course long after the race was over, apparently totally GILOC'ed and oblivious to the outside world. If he had not run out of fuel he would be up there yet, or until his beard got entangled in the rudder pedals. This was too much. Col. “Flat-belly” Flack. RA. (Royal Artillery, not Royal Academician or an artist, aviation matters were far too important to leave to aviation people) was summoned to sort them out. He concluded that whilst it was, indubitably, a very bad case of LOMF and must be stopped, immediately, there was a problem. Presumably this reflected the slouched style and unmilitary bearing fashionable in the RAF at that time. Tightening up their belts and flattening the abdominal (no doubt accompanied with an adequacy of senna and bromide) was what was necessary, hence his nick- name.

6. The Gaiter Brigade.
By this time the buzz was out. Sherrington the physiologist had shown that fainting was accompanied by a fall in blood pressure in the erect posture. One’s blood pressure “fell into one’s boots”. Obviously as soon as one collapses into a (horizontal) heap the blood flows back into one’s head and you wake up. The long feverish work was in progress in Australia, Canada and the United States as there was now real prospect of a Second War. Air Power would decide it and the side that fainted would definitely NOT deserve to win. The plan was, initially, to force the blood back from the legs to the heart which would then obligingly pump it up to the head. The possible inability of the heart to pump lead-weight blood 35 cm uphill to the head was ignored. This work produced the familiar “G-suit”. Starting with gaiters to squeeze the legs, abdominal-squeezing bladders rapidly followed as the gaiters did little more than could be achieved by flexing the leg muscles (which normally squirt the blood up and back into the body each time we move them). The gaiters worked best in those whose varicose veins were so bad that they could accommodate the individual entire circulating blood volume. However not many such pilots in this condition were to be found in the front line squadrons.

The first operational suits were water-filled, gave about +1 Gz advantage and impressed the girlfriend if they caught you letting it out (Gen., then Lt. Yeager, impressed most by reportedly being able to micturate through four orifices simultaneously).

In the event Allied success in the air and the arrival of the P51 in sufficient numbers to swamp the Luftwaffe allowed bouncing to become the all-pervading tactic (and certainly much more safe than becoming entangled in a dog- fight with some hoary, old, ex-Spanish Civil War, 350+ victory ace from the Eastern Front). Interest in Aerobatics, the key to dog-fighting survival, and its associated equipment waned.

7. A Voice in the Wilderness (Wood)
Though von Diringshofen’s team had indicated the importance of the reflex responses in Gz tolerance (they make the “hitch-up” in the GILOC part-1 graph) only one man was really out of step with the orthodox concept of blood pooling being the important factor. Dr. Wood at the Mayo Clinic in Rochester, Minnesota, was (still is) a clinical cardiologist whose primary interest was Cardiac Output and Cardiac Failure (when the CO, Cardiac Output, fails). His approach was entirely different. He was impressed by the induction of acute, at high +Gz complete, Cardiac Failure on the centrifuge, where Failure was defined as the inability to get the blood up into the brain. The problem was that the hearts, even of Mayo men (and there are plenty of good Swedes in those parts), were not strong enough to pump >+10Gz blood up 35 cm to the brain. The only way to overcome this was to put the brain down at the same level as the heart (so that the heart has only to pump blood “sideways” into the brain, abolishing the effect of +Gz altogether. This led to two alternative strategies:
i. Positioning the pilot horizontal (like getting the bomb aimer in a Lancaster to do all the flying, on his belly: hellish for neck-ache!). The RAF and its Institute of Aviation Medicine did not, as that time, believe in centrifuges. So Farnborough constructed and flew a prone-position Meteor in which the ‘safety plot, who was normally seated and meant to look after his chum flying in front on his belly, in fact spent his time continually GILOC-ed, oblivious to the acute embarrassment and discomfort of his colleague, who had then to get the contraption back on the ground, head first and scraping his nose and even more important parts of his equipment along the runway at 160 kts.

ii. Anti-G Straining Manoeuvres. These involve tightening the leg muscles to squirt the blood into the abdomen. then squeezing the abdomen (not to pass a motion as if one were constipated, but keeping one’s sphincter clamped shut) to shunt the blood up into the chest and to the heart, and then in turn squeezing the chest to squirt the blood from the pressurised heart up into the head and brain. This is a tall order when working hard to tweak the oppo in a dog fight or even keep up with one’s leader in high Gz formation aerobatics (if you got a canny leader he uses all the heavens and keeps the +Gz down low). Ml and LI, the two popular manoeuvres are based upon the time-honoured Valsalva Manoeuvre (which is what one does if your XVIth Century Package Tour has left you high and dry on the inside of the Siege of Padua, with nothing better to do than express one’s disinhibition at the situation, by disposing of your surplus-to-requirement salmonella upon the encircling French below, the meanwhile sitting backwards over the walls using Italy’s answer to Messrs. Doulton or American Standard). The Chinese have a further variant. As we will discuss in the next article, they need careful instruction and plenty of practice, but they don’t cost anything and anyone taking the trouble can increase their
+Gz tolerance by at least +2 Gz. Positive Pressure Breathing, PPB, getting the gear to do the work for you, is much easier (though hideously expensive if it is to be reliable). The airways, legs and trunk are all pressurised to squeeze the blood like toothpaste up into the head. It’s great, except for two things:

a) It also squeezes the blood back down one’s anus and does wonders for one’s intervertebral nerve roots in the thoracic inlet at the base of the neck.

b) If you have got on top of your oppo’s 6 o’clock and he has any sense, providing he does not have PPB, has his G-strap done up tight, his cockpit well-hoovered and a -Gz capable aircraft (like any aerobatic machine, including Mig 29 and Su 27), he will use the old Daimler-Benz injected engine 1940 trick and immediately PUSH negative, across your firing gate and away before you have realised it. If you, PPB-equipped you, follow from high +Gz, HOLD YOUR HEAD ON tightly. Of course, you won’t, you’ll execute an elegant roll and pull-through, see nothing (he’ll be halfway back to Abbeville for his tea) and report another success. Such a success that the RAF usually shot down more Me l09s every day than could be found west of the Weser.

8. Small Fry
The last ‘school’ of thought on GILOC resided in the Tiger Club (in those halcyon days when it was still based at Redhill and before it fell out with Alan Bristow) in 1968, using a Zlin 526 provided by Players of Nottingham and equipment developed with and loaned by Dr. (now AVM) Peter Howard of IAM Farnborough fame (and all the time angling for a NASA grant before they got to the Moon and high -Gz was unfamiliar territory). A principal area of concern was whether under high +/-Gz the Brain itself could be induced to move around enough inside the head to alter consciousness. It became apparent that using high -Gz at low level in turbulence could generate high Gz transients of sufficient amplitude to induce the phenomenon of Brain Stem “Sleeving” described the previous year by Prof. Lindgren (Gothenburg) in acceleration head injury In the event it was not until l975 when Curtis Pitts allowed us to use the S-IT prototype to explore up to +15 Gz at Sherman, Texas, that we found that one had to use this order of +Gz to induce significant subjective sleeving, way beyond the useful +Gz envelope for the aerofoils then available or projected. It was also very energy-inefficient as one merely burnt-off speed, rather than squaring the corner or stood on one’s own tail in a turn. Brain Stem shift is a potential hazard, but only at present in two domains that have no competitive usefulness:

i. Low-level, high -Gz in turbulence. World Championship and CIVA Regulations mean that this is outside competition meteorological limits. Experience is limited to ill advised bravado, trying to put on ‘flat’, low-level aerobatic displays in bad, turbulent weather. The answer is DONT - you have been warned.

ii. Using more than +10Gz. This is getting into “hyper-G”. It is unnecessary competitively in the standard of the 1km International ‘Box’. The International Judges have the answer and ate the best influence here: Don’t mark-up lunatic corners. Reward intelligence and good aircraft handling (or you may have no competitors to judge.

9. Conclusion
GILOC has been around since Peter Nestorov looped the first loop and tail-chasing began. Fortunately today we have a clearer understanding of what is going on. It is a problem which we all skirt all the time in Unlimited Aerobatics and one which we can all encounter at any level of flying. We are all susceptible to the circumstances of GILOC because we are all either Mk I or Mk II (improved, female) humans and we all like to get the most out of out aircraft.

In the next article (part-3) we will consider what the prudent pilot does to recognise the First Law of Aerobatics: you have to be alive, well and in one piece after the Last Flight of the Last Championship in which you ever compete - to pick the First Prize. You cannot do this in Heaven. There God always wins, and the angels have had more practice. The first rule is to stay alive and win the lot, right there, this side of the Great Divide. There are no prizes for dead acrobats. Sorry. Next time we will discuss what we can do to stay awake and alive.

John Firth, Queens Medical Centre, Nottingham
Steve Johnson
Nashville, TN
1 user thanked Gjunkie1 for this useful post.
MX2FLYR on 4/11/2011(UTC)
#2 Posted : Thursday, April 14, 2011 5:32:40 PM(UTC)
Rank: Newbie

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Joined: 4/14/2011(UTC)
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Location: Verona,NY 13478

A lot of great info. Thanks a lot. Dick.
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