G AND YOU

[Music] [Applause] [Music] [Applause] an aeroplane in flight is packed with power large forces have gone into making it fly at high speeds to change either the direction or the speed of its flight requires equally strong forces these forces affect both the plane and its pilot when the changes of speed or direction are sudden the accelerative forces called into play may be so large that the human body cannot function properly blackout is one of the results in flying there are two important kinds of high acceleration and aft or linear accelerations are caused by sudden changes of speed without turning you all know how a catapult takeoff flings you backward against your seat if you don't brace your head you'll bump it a crash landing throws you violently forward against your shoulder harness your plane has stopped suddenly but your momentum makes you keep on going that's why your harness is there to protect you from the effect of linear acceleration the other kind of high acceleration is the one in which fighter and dive bomber pilots are most interested it occurs whenever you change the direction of your flight centrifugal force arises whenever a moving body changes its direction remember when you were a boy how you used to swing a stone on a string and how the pull of that stone got greater the faster you whirled it you didn't care then but that was centrifugal force pulling on that stone now you care a great deal because when flying you are like that stone if you push your stick forward centrifugal force lifts you up against your seat belt if you make a flipper turn it drives you down hard into your seat every time you pull back on the stick your weight increases just the way the weight of that stone used to increase as it tried to fly away from you you and your plane grow heavier due to centrifugal force it's your extra weight during prolonged high speed turns which makes you black out the normal weight of anybody is due to the force of gravity because centrifugal force changes your effective weight we measure it in terms of the pull of gravity and use the expression g i'm a g-man i stand for the force of gravity i am one times gravity i am one g one g is normal you're withstanding one g right now sitting in that chair g can be positive or negative depending on its direction in level flight you still have one g acting on you downward g in this direction is called positive in a 60 degree turn you have 2g on you and on your plane the extra g hops on while you're changing your course an 80 degree flipper turn suddenly calls out six g all this g is positive inverted flight puts one g on you but in the opposite direction g acting in this direction is called negative an outside turn will put even more negative g on you and on your plane we can measure the amount of g by an accelerometer a simple one is a weight supported by a spring like a fish scale a pointer on the weight moves down a scale calibrated in multiples of g if 5g comes on during a pull out the weight becomes five times as heavy and the spring is stretched accordingly with the resumption of level flight the pointer returns to one g or the normal force of gravity the navy kosman accelerometer works on the same principle there are three hands one for maximum positive g one for maximum negative g and one for active g you can reset the hands by turning a knob when they all now indicate the normal force of gravity or positive one g when the accelerometer is turned upside down it shows negative one g when it's sideways of course it doesn't show any g because it wasn't designed to work sideways when you maneuver an aircraft the g alters with every change in direction a sharp nose over may lift you out of your seat with a force equal to twice that of gravity or negative 2g a pull out from a dive may increase the g acting downwards as much as seven times or more this means that you and your plane will weigh seven times normal in this state you will weigh over half a ton and your blood will be heavier than iron if you stay this heavy for more than a second or two your blood will not circulate and you will black out what determines the amount of centrifugal force first the radius of the turn the tighter the turn the more g is developed by halving the radius and maintaining your speed you turn in half the time but the g is doubled if you pulled 3g at first you now pull six the other factor is air speed g varies as the square of the air speed if you double your speed you again get around in half the time but the g is multiplied by four instead of three g you and your plane now have to take twelve and twelve g is unhealthy it is obvious therefore that the more g you can stand the tighter and faster you can turn now what does all this g do to your aeroplane it makes it heavier 7g will increase its weight and therefore its wing loading seven times and your fighter will be as heavy as a b24 but you still have the same ship with the same wings and the same engine naturally you can't expect it to fly the same stalling speed is increased you may put it into a high speed stall if you haven't enough air speed so you need more power to keep your heavier kite in the air fighters and dive bombers are designed to stand fairly high loadings of positive g seven eight or nine but negative g is another matter high loadings of g in this direction can more easily strain your plane and anyhow it doesn't fly as well it was built to stand stress as you were in the normal direction navy fighters cannot take more than four negative g and you yourself can't take that much for long g does things to the pilot as well as to the plane we can find out what they are in flight tests but on a human centrifuge they can be studied more conveniently this centrifuge which you may think looks like a rube goldberg nightmare can develop high g with both the amount of g and the length of time controlled records are made of the g and of the pilot's reactions during a run the subject sits in a car suspended on the end of a long arm and is whirled around in this merry-go-round by means of a system of signals and answers he can record the point at which he blacks out the controls work accurately and the subject is under continuous careful observation a movie camera photographs his reactions during a run so that what g did to him can be studied later under g the car banks properly in its turn on top of the instrument panel is a clock which measures the time in seconds just below it are two lights a green one and a red one which are also flashed on the dashboard in front of the subject by the observer when he sees these lights he turns them off one with his thumb and one with his throttle hand if he can't see them anymore he doesn't turn them off and we know he's blacked out below is an accelerometer now at 4g the two lights beneath it show his pulse rate and time in seconds now let's take him on a 5g run for 10 seconds and see if we can black him out as the car starts and the g comes on his face is pulled down like every part of him it has become five times as heavy see how old he looks there he goes going gone blacked out and more how do you feel pretty woozy eh okay pal you're all right now bet you don't even remember what happened although your weight may increase to many times normal during a turn in either the centrifuge or an aircraft your bones can easily support this extra load but there are other parts of your body which can't principally the blood circulation blood gets heavy too when g increases by centrifugal force it acts on blood to produce its well-known effects on the pilot that is gray out and blackout how is the blood normally circulated a diagram of joe's insides will give you an idea of the way it works normally the heart pumps fresh blood carrying oxygen obtained in the lungs rapidly and under considerable pressure through the arteries to all parts of the body in the tissues the oxygen is released then through the thin walled veins the used blood is returned slowly under a low pressure this is just enough to push it up from the lower parts of the body against the force of gravity on reaching the heart it is pumped through the lungs here it absorbs fresh oxygen before it is again pumped out to the body during level flight gravity is acting in its normal direction on the blood that is downward the one g therefore affects the blood flowing uphill through the soft walled veins back to the heart and to less extent the blood pumped from heart to head when g increases in tight maneuvers the blood gets heavier this extra weight drives it downward in the pilot's body just as he is driven down into his seat heavy blood tends to pool in the legs and abdomen here the soft walled veins stretch under their increased load this makes the blood flowing back to the heart slow up although the heart is strong enough to pump blood which is heavier than normal the heart like any other pump can deliver only the blood it receives as the pump starts to run dry the blood pressure falls and the circulation to the head decreases if the vital oxygen supply to the brain is cut down often enough by tight maneuvers fatigue results if a turn is too prolonged or too tight the senses fail altogether first sight fades leading to blackout then hearing goes and finally consciousness may be lost why do these things happen loss of vision or blackout is caused by the lack of circulation of blood through the eye the eyeball has a water pressure inside it to keep it rigid this internal pressure tends to obstruct the flow of blood to the light sensitive parts the normal blood pressure overcomes this resistance easily and so supplies the oxygen necessary for sight when however the blood pressure falls during increased g the pressure inside the eye slows up the blood flowing through it and vision is great because the eye doesn't get enough oxygen at 5g the blood pressure may fall too low to force any blood at all through the eye the result is blackout some blood can still enter the brain however because there is no internal pressure there to obstruct its flow that is why the pilot stays partly conscious even when he can't see if the g is increased still more his blood pressure may fall too low to supply even the brain with oxygen hearing is lost and the pilot becomes very groggy finally he loses consciousness altogether as the g falls off blood begins to return to his heart his blood pressure rises bringing oxygen again to his head as he wakes up he may think he's been dreaming as the circulation comes back to normal he goes through the same sensations but in reverse order he may stay a bit confused for a moment afterwards because blood gets moving slowly it takes time for these changes to occur blackout does not come on until blood has had time to collect in the veins you don't black out therefore until a couple of seconds after you have entered a turn similarly you stay blacked out until after the turn is over that is why mental confusion lasts a few seconds longer the g at which your vision fails is called your blackout threshold you can estimate it by noticing at what amount of g your vision starts to fade during a maneuver but your threshold is not necessarily the same as that of the fellow next to you a force of 6g lasting for five seconds may have little effect on some people but can produce momentary unconsciousness in others still most pilots will black out at 6g the g at which you black out also depends on the rate at which g comes on a high value of g developed rapidly as in a snap maneuver may not even make you gray on the other hand the lower value acting for a longer time may cause blackout it takes time to produce blackout don't forget though that snaps can be dangerous to your aircraft and may make you walk home so far we have considered positive g only now let's see what negative g does negative g acts on the blood in the same way but in the opposite direction although you may not run into large forces from outside maneuvers so often their effects on you may be greater blood is forced towards the head causing congestion this makes your face feel full your stomach is shoved up toward your chest pardon me with more negative g you may get a headache spots before your eyes and your vision may read out negative g causes more mental confusion what is more important even a little of it relaxes your blood vessels if you fly on your back for a short time and then make a diving pull out as in a split s more blood will rush downward there'll be more pooling of it and you will black out at a lower level than usual the amount of g you can take depends on the position of your body in relation to the direction of g obviously standing is the worst position because the blood must be forced directly against g all the way from feet to head lying down is of course best because g is then acting at right angles to the flow of blood but can you fly a plane lying down crouching is a compromise it reduces the vertical distance from heart to head making it easier to pump blood to the brain also by crouching you increase the pressure in your abdomen squeezing blood up to the heart and thereby helping to prevent blackout raising your feet on extensions of the rudder petals or by lowering your seat also helps the blood to flow from your feet to your heart although you won't black out as easily when you crouch a lot of strain is put on your lower back if you have any tendency to a weak back don't crouch besides of course you can't see to fly very well with your head between your knees physical condition is another important thing that affects the amount of g you can take if you keep yourself in good physical condition your own black out threshold will be at its highest you can take much more g if you're fit you can also definitely raise your threshold by tensing your muscles and fighting against blackout before the g comes on if you relax g will get in its dirty work your blackout threshold will be lowered by anything which makes you less fit to fly this includes failure to use your oxygen flying on an empty stomach lack of exercise and particularly lack of sleep in your off time it's nice to relax but too much relaxation doesn't help to keep you in good flying shape [Music] the g-man will get you if you don't watch out for too late hours too much alcohol too much tobacco and too many other interests [Music] even if you're in the best of condition and your threshold is at its highest a lot of tight maneuvering is bound to have an effect on you if you take g too often you'll get tired and if you take too high g you'll black out because both fatigue and blackout are caused by pooling of the blood they can be prevented if the veins are not allowed to expand one way to prevent pooling is to oppose the downward pressure of the blood with an equal and opposite force against the lower half of the body to keep the blood where it belongs what happens to poor old joe when this is done suppose we build a bathtub around him and turn on the tap oh gee as the water fills the tub the veins are compressed to their normal size under the force of g water increases in weight just as blood does since both way about the same the pressure on the outside of the veins equals that within at any g therefore pooling is prevented and the heart gets enough blood to pump to the head when the brain is again well supplied with oxygen the pilot regains consciousness his vision returns and he can now fly his f4 ub all over the sky without getting tired he doesn't however need a whole bathtub full of water to be protected all he needs is a thin layer to provide the proper pressure around his body and it isn't necessary to use water pressure any form of pressure will do he doesn't need to walk around with his pants full of water air pressure is just as good if applied to the right places an anti-blackout suit designed on this principle has been made for you it has an outer covering of cloth which doesn't stretch the idea is that graduated air pressures inside this non-stretchable covering are automatically applied to places on the lower part of the body when g is on squeezing the veins partly shut and so preventing pooling of blood in them a lot of rubber sacks or bladders which fit around the legs and thighs provide the pressures when they are filled with air there are eight of them on each leg if a pressure gradient is built up in this way going from a given pressure on the thighs to higher ones on calves abdomen and ankles blood cannot collect in the lower part of the body and blackout will be prevented the bladders are connected to the source of air pressure by three rubber tubes running along the outside of the suit in zipped up channels each tube is connected to several bladders at different levels so that air under various degrees of pressure can be supplied to the right places at the right time a kind of girdle goes around the waist and not only will give you a good figure if you need it but the after part is reinforced like a motorcycle belt and will keep your back from getting tired there's another bladder in front to prevent pooling in the abdomen sort of a g-spray no interruptions please the six tubes from the leg bladders and the one from the belt all pass through a flat plastic manifold this manifold fits in the small of the back and you never know it's there this distributes air to the proper sections in the legs and abdominal belt at the various pressures required all these tubes are connected to an air inlet plug which comes out of the side of the suit this fits in the socket beside your seat in the plane it goes in in only one way if you should have to bail out it will pull out easily the plug is connected by three pipes to three g valves each valve is so designed as to automatically deliver a certain air pressure to a part of the suit when g comes on there is no pressure in the suit during level flight in a turn the amount of pressure delivered depends on the setting of the valve and on the g each valve is set for a different pressure the main air line runs through an oil vapor separator so that oil thrown by the air pump will not come into the suit and rot the rubber the pump uses the ordinary b3 pump which is standard equipment on your plane when you use this apparatus the great force of g now works for you instead of against you g controls the air valves sections of the suit fill with different pressures the ankles fill under a high pressure the thighs fill under a low pressure and the calves and abdomen fill under a medium pressure when the suit takes hold this setup is found to work best if we fill the whole suit with compressed air we can see how the bladders are blown up the whole outfit works automatically the more g the more pressure but the gradient remains the same you put on this g suit like a winter flying suit don't get worried by all the zippers you won't get mixed up the crotch strap hooks on the top of the suit and one zipper goes all the way down the leg to the ankle there it locks it has a gadget to keep it from sliding loose the other side works the same way it takes about half a minute to put the suit on the whole outfit weighs about six pounds which isn't too much for you to carry on top you can put on your coveralls or heavy winter gear and you're all set to take g it's not uncomfortable is it look at the docs figure now let's see how it works first we'll take this pilot for a run in the wily gig and find out what his blackout threshold is he's going to take 6g for 5 seconds look at him being pulled down the old heavyweight can he do it no i would like a light didn't expect that did you come on old man wake up you're having a nice dream his true blackout threshold is 5g or less now we'll try the suit the g valves are mounted in a single unit behind the seat and the pump has been installed the plug fits into a socket in this unit g-valve number one supplies the high pressure for the lower leg g-valve number 2 supplies the medium pressure for the calf and for the abdomen and number three the low pressure for the thighs with the suit on the story's different we'll take him up to eight and a half g for five seconds there he goes look at him pull down see how his face sags but now he's perfectly conscious he still seems to get 30 years older in a few seconds but he doesn't even gray out the suit has protected him against g he can take more g now than his f4f and still fly it these g suits come in four sizes when a suit is issued to you it must be adapted to your individual shape so that it will fit you and you alone once properly fitted the suit is yours and needs no further change the correct fitting is therefore very important start with a belt it is hooked on loosely zipped up and then tightened by three straps on each side it should fit over the middle of your abdomen and reach the edge of your ribs we make it snug but not tight we then zip the suit on with all the lacings loose so that we can make the suit fit you more or less permanently this is necessary because if the suit is too loose it will take too much air to fill it and it won't squeeze your legs equally all around when g comes on we adjust the elastic suspenders to keep the whole suit well up on the body there is a zipper in the middle for loosening the suit in the ready room and for other obvious purposes the lower leg section is supported from the shoulders by a strap going to the knees this keeps the pressure units in the right spots it should be fairly tight but ought not to bind your shoulders then we lace up the different sections first the lacings along the side are tightened after they are tied in a square knot what isn't needed is cut off because this is your personal suit the thighs are adjusted by lacings to make them fit snugly but not so tightly as to be uncomfortable when fitted properly we make a permanent job of it and cut off what's left the lower legs are molded to your body the same way so that when the pressure comes on it will be applied immediately and distributed evenly over the whole surface of your leg the correct and comfortable fitting of this section takes some care because the pressures are highest here now it's your suit and will fit only you how's it feel pretty good is it too tight if it is it hasn't been fitted properly but even if you do find it a little snug at first like a new pair of shoes it will loosen up with use once it has been fitted you can zip in and out of it quite easily wear it over your under clothes you'll find it a little warmer than the summer flying suit some pilots like to wear it just as it is raw others to put coveralls over it but whatever you do take care of your suit it has been issued to you for your personal use hang it up carefully when you take it off don't let the rubber deteriorate try to keep it dry if it gets a puncture you won't be as well protected it's no good driving in a flat tire you're quite right but don't interrupt take care of your suit and it will take care of you when it gets dirty your suit can be easily cleaned you can take it apart and remove the 16 rubber bladders in the legs and the one from the abdominal belt in a single unit the bladder slip out quite easily through the holes where the tubes are connected you then take the whole thing apart removing the manifold tubes and bladders all in one piece and get the outer covering cleaned now let's take a flight test we fitted up the plane with a movie camera so that we can see what happens the poor old dock has a low threshold and he has no suit on to protect him so at four and a half g [Music] out he goes what a pilot he'd make now he's just plum g-roggy maybe he was up too late last night but let's see what the suit will do for him there is no pressure in it during level flight when the g comes on the suit fills it once with air notice how normal he is at six and a half g he has no tendency to black out or even gray in fact he's okay now repeated casts made in fighters and dive bombers have shown that the suit will protect you up to about 7g possibly to eight but above these levels you may still black out the suit raises your threshold by several g what is equally important it lessens the fatigue which often follows exposure to moderate g in long gunnery passes even if your blackout point is high you will find that the suit keeps you from being so tired after your flight when you're wearing the suit don't forget that although you are protected your plane isn't your plane has no suit it is still the same aeroplane the fact that you have a suit on doesn't change the plane's loading limit although fighters and dive bombers are designed to stand fairly high loadings of positive g you may be tempted to exceed their limits if you are protected by the suit this is especially true if you are used to judging the g you pull by your greying if you fly by the seat of your pants or rather by the sight of your eyes you may wrinkle your wings with the suit on so don't take chances with your plane furthermore just because you're wearing the suit you yourself are not completely protected you can black out at a high g the main advantage is that the suit will make you as good in withstanding g as your aeroplane in some cases even better in general fighter planes f4 f's and f4us will take seven to eight g without difficulty dive bombers are designed to stand nine g these limits of course depend on the load in the airplane at the time g is put on if you have a big load of gasoline and ammunition your fighter will not take as much g as if you were flying empty seven g is about the limit for a loaded fighter these restrictions are really very high when you compare them to a tbf which will take only 4g or a pby which will take only two and a half that's why you can't do a snap roll in a p boat when you first try out the suit it is a good idea to take an accelerometer along so that you can tell what g you put on the plane in maneuvers you have to learn all over again how hard to pull the ship around this is important don't forget it your plane is not wearing a suit remember that at high g your plane flies differently its stalling speed is increased at 4 g it will stall at twice the air speed at 9 g its stalling speed is 3 times that at one g this means that you need more power to make it fly it means that you have to open your throttle when you're trying this suit out do it at safe altitudes there's no future in low altitudes and high g you ought to know by this time that your suit will give you an advantage over the fellow who hasn't got one you know that the tighter and faster you turn the more g is produced therefore you can turn tighter and faster with the suit on because you can take more g a blacked out pilot is no good to anybody least of all to himself know your own threshold and know your plane's threshold without the suit the plane has the edge on you with the suit you have the edge on the plane be careful remember this here zoot suit ain't infallible it don't mean you can get in lousy shape you gotta keep fit to take g suit or no suit keep your belly muscles in trim get enough sleep don't fly on an empty stomach don't smoke too many cigarettes don't drink too much liquor the night before flying the suit won't cure a hangover use oxygen above ten thousand feet blackout is caused by lack of oxygen and if you already are low you'll black out sooner be careful of negative g it will lower your blackout threshold don't make snap pull outs if you can help it a snap pull out may put much more g on your plane than it will stand your plane won't fly without wings that is it will fly but only in one direction what a streamlined job it makes one point landings gee whiff but don't be afraid of g use your brains you know how to protect yourself against it with your knowledge of g and with your suit you'll have an edge on the jab unless he gets a suit too oh so sorry please that means secrecy don't talk keep it dark keep it very dark keep it blacked out you have an advantage over the jab and the nazi use it be intelligent about your flying so that you can do a good job so that you can get on your target and still see to shoot [Music] you