John Carbon, a Sophomore student at the University of Southern California, has never flown a plane. Yet he is helping the Navy improve its air arm by making aviation better and safer for those who man fast-flying planes.
Between classes, Carbon sets aside his books, runs his hand through his crew cut, hitches up his faded corduroy breeches, and heads for the Navy’s research center in the middle of USC’s fifty acre campus. The Trojan statue before the Administration Building should doff his helmet to Carbon, for, like a hundred other student volunteers in the university, Carbon is a friend of naval aviators whom he has never met. He helps accumulate data for scientists to work out means of controlling the harmful effects of the G-force that is an inherent part of fast flying.
A couple of years ago, prior to enrolling in USC, Carbon would have favored you with a blank inquisitive look if you had asked him to define the G-force. He never heard of it, at least by that name. Having completed high school physics, he could tell you something about centrifugal force: that it is the resistance of moving objects to change of direction, and he might have illustrated it by mentioning that cars skid at turns on wet pavement, that railroads are banked at curves, and that ships heel over in fast maneuvers. He might have gone further to say that you can swing a container of water overhead rapidly without spilling water over the brim because centrifugal force pushes the liquid toward the upturned bottom more than gravity pulls it out the open top.
Today, however, if you ask Carbon about the G-force, he will give you an enthusiastic reply and go on to show its effects on pilots of high speed aircraft.
The G-force, he will tell you, causes pilots to blackout or to red-out in the middle of fast maneuvers, and that it is one of the most important physiological and psychological problems that must be faced as the speed of aircraft goes higher. “G” is a term which expresses the normal pull of gravity, an accelerative force equal to 32 feet per second. One G, that is, normal gravitational pull, is exerted upon everyone.
Flying personnel, however, zooming through the air in tight turns and steep dives have additional accelerations exerted upon them from the centrifugal force of their maneuvers. These added forces are expressed in multiples of normal pull—2G, 3G, and so on. Plus description is given to the G-force when it pulls blood from the head. Minus description is given to the G-factor when blood is pushed toward the brain. Carbon illustrates plus G-force by mentioning the bucket of water swung overhead. When flyers execute an inside loop, they give plus G to the gravity load of the body. Centrifugal force pulls blood from head to seat exactly as water clings to the bottom of the bucket. The lack of blood in the head first causes the pilot to see grey mist before his eyes, then everything turns grey, and finally it may cause him to blackout. If the force is prolonged, he loses consciousness completely. Blood is pulled down to his lower extremities and at the same time the blood pressure in his head drops. Pooled blood in the lower part of his body becomes quite viscous, like Mississippi sorghum; solids are in higher proportion and flow less freely, sometimes resulting in blood stagnation. The brain gets insufficient oxygen, in effect suffocating it. Unconsciousness and permanent brain damage can follow long-continued brain anoxia, the technical description of the occurrence.
On the other hand, Carbon will tell you that when flyers maneuver in outside loops, the opposite holds true. A minus G-force is exerted upon the pilot, pushing blood from the lower extremities of the body toward the head. At minus 5G, for example, blood pushes so hard against the brain that capillary walls may be ruptured and brain hemorrhages may occur. The pilot sees red. His head aches violently. If protracted, the force can cause death. Humans generally cannot stand more than minus three G’s. Throbbing headaches and nausea usually follow minus three G runs. Symptoms are much more severe from negative G effects than from positive G, but to military pilots both are a pain in the neck. And G’s pile up on aviation personnel every time a plane flying at high speed is put into a loop, tight turn, spiral, dive, or pull-out. The number of G’s piled up depends upon the speed of the plane and the sharpness of the maneuvers; how the pilot fares under the G-factor depends upon his physical condition, how long the force grips him, and upon what protective devices he uses.
Naturally the harmful and sometimes fatal effects of the G-force were a matter of concern to designers of aircraft and flight surgeons as well as to the pilots who flew the planes. The Office of Naval Research wanted to do something about them.
The Navy’s research agency contracted with the University of Southern California to provide scientific personnel for studies that may answer some of the questions that the G-force poses. What are the full effects upon the bodies of aviation personnel? What about reaction time—can pilots and gunners operate their instruments as efficiently under the effects of the G-factor? Should instruments be relocated to make flying safer? These and other questions were to be studied by USC scientists.
Possibly the most obvious place to study the effect of the G-factor would be in a plane operating at high speed in the air, cutting capers like free style trapeze artists. As a matter of fact, some of the earliest research in the field of radial accelerations had been performed under actual operating conditions. Scientists found, however, that a looping plane is no place for study. Besides being unable to carry proper recording and testing equipment, the scientists themselves were subject to redding out or blacking out at the same time as their subjects who manned the controls of a flying laboratory.
To perform experiments properly, then, the physiologists and psychologists needed equipment which would duplicate, under controlled conditions, the effect of maneuvering aircraft.
Since centrifugal force is the result of an acceleration acting on a body moving in a circular path, a gigantic arm swinging in a horizontal circle would copy the effect. Furthermore, the operators of the arm could, by setting its speed, control the number of G’s to be developed.
Such a device, similar to a huge butterfat tester, was built during the war on the USC campus three miles from downtown Los Angeles. The largest in the world at the time of its completion, the centrifuge is capable of developing twenty G’s when loaded with a human subject and five hundred pounds of testing apparatus.
A building which looks like the top of an astronomical observatory houses the device; offices and laboratories adjoin the hemisphere building. The centrifuge itself— variously referred to as the Merry Go Round and the Whirling Dervish—consists of a fast-moving boom which swings in a circle. At the end of the boom a seat with testing equipment is mounted in gimbals twenty- three feet from the center of the circle. The tilting seat may also be equipped with simulated aircraft controls.
To make tests, Carbon or another of the USC student volunteers climbs into the cockpit. A control operator rides the boom at a shorter radius. The USC centrifuge is powered by a gasoline motor which operates a sixteen foot flywheel. A clutch arrangement on the flywheel sets the boom in motion with a quick start and—blooie—G’s start piling up on the subject. The device has a steady controlled speed which, along with quick starting, is essential because volunteers take G’s for only about fifteen seconds at a time.
About a hundred volunteers, all students at the University of Southern California, have participated in experiments since the first call for help was sent out on the campus. After a rigorous physical examination, subjects take indoctrination rides of first two, then three G’s. If results are satisfactory, the volunteers go on to experiment with five G rides. Each appointment lasts a total of about twenty minutes with eight 15 second spins at G levels between two and five. Two to five minute rest periods are allowed between whirls because taking G’s is a strain. The muscles of Carbon’s lean face sag as G’s mount, and he appears to have jowls and a double chin as centrifugal force pulls his blood and muscles down. Because centrifugal force is apparent as weight, the merry go round could, if operated at full speed, multiply Carbon’s hundred and fifty pounds to exactly a ton and a half. At slightly less than half speed a very strong man might raise his arms above his head only with extreme difficulty; and at a little more than half speed, his eyelid muscles would not be strong enough to lift his eyelids. Though Carbon and other volunteers are not subjected to such tremendous accelerations, five G runs make rest periods advisable. Five G runs, you will remember, increase Carbon’s effective weight to seven hundred and fifty pounds.
How many G’s can a man take? For fifteen seconds, the upper limit of a relaxed subject —one wearing no G-suit, not straining, sitting as in an armchair reading the comics— is considered to be three and a half to four G’s. The relaxed subject usually blacks out if the force increases. Some people, of course, can take more than others.
With a G-suit, the average individual can take five positive G’s without blacking out; some can take up to nine. One of the great advantages of the anti-blackout suit is that strain is taken off the pilot during his fast maneuvers.
The next best thing to a G-suit is called the Val Salva maneuver, a conscious protective reaction in which the flyer tenses his abdominal muscles to try to prevent blood’s pooling in his abdomen. Some pilots yell bloody murder to tense the stomach as they begin taking G’s, and it helps.
As mentioned previously, humans generally cannot take more than three negative G’s for any appreciable length of time. For this reason flyers often turn the plane on its back or slip off into a dive, and thus they take positive rather than negative G. Physiologists are studying the effect of minus G and means of overcoming it. The G-suit serves as protection, but only to the lower part of the body; it does not stop blood’s being pushed directly from the heart to the head. One can stop blood from flowing with great force to the brain simply by putting a noose about the pilot’s neck and pulling it tight. This, however, is considered a rather drastic means of stopping the flow of blood, and scientists are searching about for some way that might be looked upon with more favor by flying personnel. The Val Salva maneuver has little effect in controlling minus G.
In order to make accurate measurements on subjects, physiologists use electronic equipment to record blood pressure charts on subjects undergoing minus G experiments. Pulse, respiration, and blood analyses complete the physiological data. USC scientists use animals to make experiments that might be dangerous for human subjects under the influence of minus G factors.
All of the information tabulated by Dr. Charles F. Lombard and his assistants might have a tremendous effect on the appearance of the aircraft of the future. The greater the speed the more intense is the physiological problem when a plane changes direction, even easing up, down or around. It is significant that designers in the West Coast aircraft industry consult frequently with Dr. Lombard and study the scientific papers that result from research undertaken at the university. Human research, the Navy’s operational experience, and projected design will be balanced in aircraft which are yet to come. The physiological studies made by Dr. Lombard, Dr. L. E. Morehouse, and Dr. Robert S. Pogrund constitute roughly half of the research work done on the centrifuge at USC. In addition to other Navy project assignments, numerous technical reports have resulted from the tests undertaken at the university.
Psychological studies—reaction time, manual operations, spatial orientation, and speed of perception—are being made under the direction of Dr. Neil D. Warren.
Graduate students in experimental and quantitative psychology develop and administer psychological tests. Albert A. Can- field, A. L. Comrey, Robert C. Wilson and W. S. Zimmerman, candidates for doctoral degrees, carry out psychological experiments to determine, for example, how quickly volunteers can perceive minor differences in the visual field. Taking positive G’s, subjects wearing anti-blackout suits seem able to see these differences about as quickly as those at one G.
Another test-— one calculated to find how much strength pilots would have for pulling on the stick—yielded surprising results. Psychologists expected an increase in pulling power when G-force was applied. In practice, however, it was found that subjects had actually pulled less than before the G-factor entered the picture.
In spatial orientation to determine how well one may interpret motion, subjects wearing G-suits were not influenced by positive G. It may be that without artificial protection, the volunteers would be able neither to see nor to think as well under positive G because of reduced oxygen’s reaching the brain. The psychological staff will make further studies for comparison in the near future.
Speed of reaction to various light patterns before the revolving volunteers is now being tested. Results will be tabulated after the series is completed.
Other psychological tests will be conducted to learn everything possible about pilot posture and performance. As aircraft become faster and faster the location of the pilot in the plane and his position while operating it may be affected. If speeds increase to the point that G-factors severely limit the motion of his arms and legs, it is possible that basic aircraft control devices may have to be altered. Since at eight G’s a strong man can lift his arms only with intense effort, it may be that buttons on an armrest, or some other modification, will replace conventional controls. Exact changes affecting pilot posture and location of control mechanisms will depend largely upon conclusions derived from work on the Whirling Dervish and from the willingness of flying personnel to adopt them.
Until research develops the full pattern of bodily function and behavior, therefore, these are matters only for speculation.
The thousand mile per hour plane may be just around the corner. At that speed, a pilot making a 180° turn over a two mile area would throw perhaps 12 G’s upon himself. Any appreciably tighter turn would almost certainly black out any pilot. Nothing more than shallow glides would be advisable at such speeds, then, because of tremendous minus G-effects on the push-down and positive forces on the pull-out.
While we are crowding speeds higher and higher, the Navy is not neglecting the human element. Not only at USC, but also at Pensacola, the G-force is being investigated. A new and larger human centrifuge is being built at Johnsville, Pennsylvania, and will soon be in full operation. With a fifty foot arm, it will be capable of developing forty G’s for the most complex research studies.
Additional studies over the country in vibration and heat effects are being made under the direction of the Office of Naval Research in order to protect flyers from ailments that supersonic flying might bring on.
Conceivably we could build a plane that flies faster than even the most rugged man could stand. Scientists over the country are delving deep into the unknown in order to devise means of protecting earth dwellers whose design, it seems, cannot be altered as quickly as that of aircraft. Taking the human design as it is and placing more artificial protection about it, one day, by virtue of scientific effort, earth dwellers may without ill effect screech through the air with their own noise trailing far behind.