The War Against Gravity
ONLY 29 JAPANESE AIRCRAFT WERE SHOT DOWN DURING THE MASSIVE attack on Pearl Harbor on December 7, 1941, but enough bodies were recovered from the wrecks to reveal something very surprising. Many of the men had been wrapped almost mummy-style in tight, constrictive bindings, from the abdomen down to the ankles.
This was no ceremonial attire, nor was it insulation against the cold. It was a medical device intended to prevent the pilots from blacking out during high-speed turns or sudden climbs after bombing dives. It was a crude and ineffective forerunner of the antigravity suit the Allies would develop over the next three years.
That the Allies would get an antigravity suit developed at all before the war’s end is surprising, considering how many impediments there were, but the problem was hardly an obscure one. Pilot blackout resulting from centrifugal force had been experienced just a week after the Wright brothers first flew at Kitty Hawk. In late 1903 Hiram Maxim, a would-be inventor of the airplane, built a “flying machine” that was nothing more than a set of two-person cars at the end of rotating arms. Maxim’s chief engineer, Albert Thurston, took a test ride, lost consciousness, and fell to the bottom of the car when the force became 6.8 times gravity.
The dogfights of World War I demonstrated the problem in actual combat. British aviation doctors called it “fainting in the air,” and it eventually acquired an acronym, G-LOC , for gravity-induced loss of consciousness. In the civilian realm, pilots reported loss of vision while making sharp turns around pylons as early as the 1922 Pulitzer Trophy Air Race. A few years later planes had gotten so fast that pilots sometimes unwittingly flew extra laps after short blackouts interfered with their concentration.
What does G-LOC feel like? Imagine you’re a World War II combat pilot pulling out of a dive over Guadalcanal. At 175 miles an hour, your pullout may produce up to 9.3 times the force of gravity on the surface of the earth, or 9.3 g. As you reach 5 g, your arms become so heavy they’re a burden to lift. Your weight approaches half a ton, and colors fade, a phenomenon known as grayout. Tunnel vision prevents you from seeing cockpit instruments off to the sides. At about 6 g you can no longer move, your blood feels about as heavy as liquid iron, and you lose consciousness. For about 12 seconds after the onset of unconsciousness you are totally incapacitated. Either the plane flies itself until you wake up, or it crashes and you become a statistic in a ledger’s terrain-impact column.
One early theory was that blackouts were caused when a pilot’s blood got spun down to his legs and feet and pooled there as he whipped through a turn. The brain and eyes became starved for blood because little was left in the head. Aeronautical scientists called this “physiological decapitation.” This view was supported by the work of German researchers before World War II who spun apes in a centrifuge—a device like Maxim’s ride that simulated the effects of acceleration-and took X-rays that showed the apes’ hearts empty of blood.
The blackout problem was well recognized and earnestly investigated before the war began but was still frustratingly hard to solve. Why? One reason was pilots’ denial. Some airmen feared being grounded if they admitted to graying or blacking out, so they kept it to themselves. Or they didn’t even know. About half of those who experienced blackout also had amnesia and couldn’t remember it. Dr. W. K. Stewart, the head of a 1940 British research effort, made a flight expressly to experience blackout. Afterward he was disappointed that nothing had happened—until he saw photographs of himself completely unconscious. G-LOC was stealthy.
SURVIVAL OF THE FITTEST ALSO MAY HAVE PLAYED a gruesome role. Before the development of the antigravity suit, pilots who were more sensitive to g forces were more likely to crash and die, leaving behind a high proportion of g-resistant survivors who didn’t notice any major problem. Moreover, some military leaders thought anti-g suits wouldn’t be needed because the latest fighter planes were so fast they made dogfights obsolete, and when the Battle of Britain ended, in October 1940, leaving the skies over the nation relatively safe, the sense that high-g dogfights were unlikely only intensified.
But the biggest impediment to progress was the lack of a full explanation of the cause of blackouts. A Canadian cancer researcher named Wilbur Franks reasoned, typically, that in a high-speed turn, not enough blood returns from a pilot’s belly and lower extremities to his heart. To test the idea he developed a flying suit that was little more than a tight-fitting set of water-filled rayon coveralls.
The idea was to exert pressure on Iower-extremity veins to keep them from filling with blood from the head. As g forces made blood accumulate in the lower extremities, they would have the same effect on the water in the suit, increasing its pressure on the veins. But the suit offered insufficient protection. The British produced 800 Franks suits in September 1941, and the pilots who used them, during the North African landings of November 1942, found them wearyingly hot and heavy. Moreover, they imparted a disorienting feeling that the pilot was floating, so he couldn’t feel his aircraft maneuvering.
Germany, Japan, Italy, and Australia each looked into the problem, but none of them got very far. It was Americans who ultimately got the science right. In the spring of 1942 three research physicians, Charles Code, Edward Baldes, and Walter Boothby, formed a secret Aero Medical Unit at the Mayo Clinic, in Rochester, Minnesota, built a human centrifuge, and offered their services to the military for a dollar a year. “We were motivated by a high sense of loyalty to our country,” Code recalled nearly 40 years later. “We were driven by necessity. We agreed that our enemies were affronts to civilized man, and we were determined to do all we could to bring about their demise. None of us has ever felt that way about anything else since.”
Baldes recognized that they’d have to replicate actual flying conditions to uncover the physiological underpinnings of the blackout problem, and he designed his ingenious centrifuge to do so. It had an arm more than 20 feet long with a gondola at the end for a test pilot to sit in. The Japanese centrifuge had taken a full minute to get up to 5 g; Baldes’s reached 2 g in five seconds and added another 2 g each second after that, a rate of increase like that of real flying.
It achieved this by storing rotational energy in two 20-ton flywheels purchased from a brewery. Baldes connected them to the engine from a “reasonably priced” wrecked Chrysler automobile, driving the flywheels with a tire mounted on the drive train. Once the flywheels reached about 40 rpm, the operator popped a clutch to clamp the resting gondola (with the subject inside) onto the spinning wheels. “You’d take off with a tremendous zip,” Baldes said, “and the g would be applied almost instantaneously.”
Code, Baldes, and their colleague Ed Lambert recruited a young University of Minnesota Medical School graduate named Earl H. Wood to run experiments with the machine. After Pearl Harbor Wood had tried to volunteer for the Army Air Corps, but, he said, “They refused me, because I was considered essential to teach medical students.” He had wanted to fly since childhood, but “I didn’t have enough money to take flying lessons. Even if I did, I still didn’t have enough money to get something to fly.” He was now teaching at Harvard Medical School, and Code and Baldes lured him back to his native Minnesota with the promise that he could be in charge of their machine for studying the medical effects of flight.
Wood realized right away that no tests with animals could provide accurate enough information. In fact, “We had to experiment on ourselves,” he said, because “we would never do anything on any subject that we didn’t first do on ourselves.” In the end he rode on the centrifuge so many times that he is presumed to have had more blackouts in controlled conditions than anyone else ever. Code would later comment, “There wasn’t anything we did then that was safe.”
Dubious about the Franks flying suit, Wood set up an experiment in which he constructed a steel “bathtub” in the shape of a big backwardfacing shoe, mounted it to the gondola, and filled it with water. He had subjects ride the centrifuge while up to their chests in the water. This proved that water could not provide enough protection. When he shared this finding with Air Marshal Sir Harold Whittingham, of the Royal Air Force, Whittingham replied: “Gentlemen, I have enjoyed your presentation. The only thing I can report is that if you’re shot down over the ocean or desert, it’s a handy thing to have a little fresh water along.”
Wood, realizing how incomplete current scientific explanations for the blackout problem were, quickly ascertained the true major problem. By comparing blood pressure at heart and head levels in the centrifuge, he learned that the heart couldn’t generate enough pressure to pump blood made heavier by extra g’s to the head. At 5 g, blood weighs five times as much, overwhelming the heart’s ability to move it, so blood pressure in the head at 5 g is virtually zero.
No wonder a water-filled suit to compress veins wasn’t the answer. What was needed instead was a pneumatic suit that could also compress arteries, which would increase blood pressure. Compressing arteries would be like putting a thumb over a garden hose, sending out a jet spray instead of a dribble.
THE MAYO AERO MEDICAL UNIT TEAMED UP WITH A master weaver and a corset manufacturer to design an arterial-occlusive suit. In essence it was a series of five interconnected air bladders, much like the ones in blood-pressure cuffs, sewn into high-waisted trousers. Two air bladders fitted around the calves, two around the thighs, and one around the abdomen. At 1.5 g they would begin to inflate and compress the arteries in the lower half of the body, increasing the blood pressure in the upper half almost instantaneously. Inflation took less than a second, and the pressure would keep increasing as the g’s increased.
The bladder around the abdomen was the fruit of another of Wood’s discoveries. He had found that the force exerted by a tight turn or a dive recovery could drive the diaphragm and the heart down toward the feet as far as two inches. That meant the heart had to generate even more pressure to pump blood up to the brain. The abdominal bladder in the arterial-occlusive suit was there not to compress abdominal arteries but to reduce the downward shove of the diaphragm and heart by supporting the abdominal wall.
The suit worked well. Tests showed it could increase the pilot’s threshold for blacking out by up to 3 g. Now Wood focused on a curious ancillary phenomenon he had observed. Fighter pilots claimed that screaming or yelling inside the cockpit during an especially tight turn seemed to increase their g tolerance. What could be the science behind that? In 1943 Wood and Baldes took that question to the Mayo centrifuge. Their experiments quickly yielded the answer: Yelling tightened muscles on the chest wall, increasing the pressure the wall could exert on the heart. The chest squeezed the wall the way a hand squeezes a plastic ketchup bottle, and that meant more blood coming out. It also turned out that if a yell was good, a grunt was better. Wood says that his favorite accomplishment is his invention of the grunt that came to be known as the “M-I maneuver” ( M for Mayo).
As taught to pilots, the grunt approximates the physical effort of lifting a heavy barbell. The pilot puts his head down between his shoulders; tenses the muscles in his chest, belly, arms, and legs; and slowly and forcefully exhales through partially closed vocal cords—that is, grunts loudly. Lowering the head decreases the pumping distance between heart and head, grunting increases chest pressure, and tensing the muscles compresses arteries—all in one package. Expert grunting could add another 3 g of protection beyond the pilot’s blackout threshold, on top of the effects of the arterial-occlusive anti-g suit.
After all this Wood finally got to fly. To confirm some of his findings, the Army lent him a noisy and drafty Douglas A-24 Dauntless dive-bomber, which Mayo’s Aero Medical Unit named the G-Whiz . The plane’s pilot, Lt. Ken Bailey, flew more than 700 dive maneuvers and high-speed turns with 43 different test subjects in the rear gunner-observation seat. Often the test subject was Wood himself, and sometimes Bailey let him take over the controls. Wood said of flying, “It’s easy once you are up there.”
American scientists had managed to develop an anti-g suit in just two years. Now a batch of obstacles arose to delay the acceptance of their invention. As Code later recalled, a few powerful officers were suspicious of the scientists and dismissed the centrifuge experiments as poor imitations of actual cockpit experience. But Code and Wood responded by stepping up the pace of the experiments with the G-Whiz and confronted their detractors with reams of cockpit data.
Pilots didn’t like the suit itself; many preferred blacking out to wearing it. “Pilots are just that way,” Wood said. “They don’t think they need anything.” On the ground the suit was uncomfortable and hot, and in tropical climates crew rooms without air conditioning felt like saunas. In combat the suit could actually be painful. In high-g maneuvers of long duration, the pneumatic bladders could stay inflated for up to a minute and feel like forgotten tourniquets. Blood circulation to the legs would be cut off, and the legs would ache with the pain of ischemia, like that of a heart attack. If the abdominal bladder inflated too quickly, it gave not the usual hugging feeling but something like a punch in the stomach.
Pilots also found the M-I maneuver distracting. After all, they needed to use it at the most dangerous moments, when escaping a pursuer during a dogfight or recovering from a dive after dropping a bomb at low altitude. “Pilots worried about attention and concentration,” Wood said. “‘How could I do all that and fly a plane?’ was their question.” The two main concerns fliers always face are safety and performance. In peacetime the two receive equal emphasis; in war it might seem natural to discount safety. After all, war is expected to be dangerous, and fighters are always choosing among risks.
The suit became operational in the fall of 1944, and data soon came in showing that blackout and grayout were happening much less frequently to pilots who wore it. The Australian air force became convinced that a pilot wearing an anti-g suit could make a pursuer crash just by putting his own plane through very highg maneuvers that would force the enemy to black out. (The Japanese and Germans never successfully developed anti-g suits.) None of these safety issues won over pilots, but performance data finally did. A P-51 Mustang fighter group of the 8th Air Force reported that pilots wearing anti-g suits shot down 67 enemy aircraft per 1,000 operational hours, compared with only 33 aircraft for suited pilots. A doubling of the kill rate was persuasive.
Meanwhile, since the mid-1930s, fliers and engineers had been developing a different type of pressure suit for a different purpose, allowing flight in the thin air of the upper atmosphere. (See sidebar below.) Such suits were indispensable with unpressurized planes, and even when the fuselage was sealed and pressurized, a leak, malfunction, or enemy attack could cause a sudden pressure loss. Prototypes of this kind of suit were developed in a variety of laboratories, in the United States and elsewhere, during World War II.
They were all bulky and uncomfortable, and none made it into production during the war. But as pressure suits became more streamlined, it was natural to combine them with g suits. The first effort of this type was the S-I, designed by James Paget Henry of the University of Southern California. It was a partial pressure suit, with bladders to compress the abdomen and limbs, an airtight helmet with a mask and tube for breathing, and air cooling for comfort. The S-I was completed just as the war ended. With the arrival of jet propulsion, it was blended with design concepts from other pressure-suit projects and revamped as the T-I. Chuck Yeager, who had worn an early g suit as a P-51 pilot during the war, used a T-I in his X-I experimental plane when he broke the sound barrier in 1947. Beginning in the late 1950s, the technology branched off in another direction as pressure suits were adapted for use in the space program.
Meanwhile, airplanes have gotten even faster and more adept at maneuvering. The increased agility of such advanced models as the F/A-22 Raptor means that a pilot will be subjected to higher g forces in sharper dives and turns than ever before. Extremely rapid acceleration means that G-LOC may come on virtually instantaneously, without any of the useful warning signs such as grayout. Thus, the well-dressed Raptor pilot will don several new pieces of gear. A face mask called the Combat Edge forces pressurized air into the pilot’s lungs to make the grunting maneuver more effective and less tiring. And the old “speed jeans” have been updated as the Advanced Technology Anti-G Suit, or ATAGS, which completely envelops the legs and buttocks. A pilot wearing both the Combat Edge and ATAGS can withstand rates of g onset faster than 5 g per second.
Today, anti-g protection is just one of many things a flight suit provides. But the basic techniques discovered by a small, dedicated group of Mayo Clinic researchers more than 60 years ago are still in use, allowing the human body to routinely handle conditions far beyond its design limits.
IN 1978 THE MAYO CENTRIFUGE WAS DISMANTLED, THEN dragged through a hole cut in the wall of the clinic’s Medical Sciences Building, ponderously lowered onto a trailer, and hauled away. It was stored on a nearby farm for several years in case a museum wanted to claim it, but none ever did, and it was ultimately cut up for scrap. No one knows what became of the 20-ton flywheels. Nor does anyone know what happened to Lt. Ken Bailey, the Dauntless pilot who made so many mock strikes on Rochester, Minnesota, with Earl Wood in the back seat.
Wood, now 92, lives in a retirement high-rise in Rochester. He has three, perhaps the only three, remaining pieces of the centrifuge: two rollers and one ball from the fly-wheel bearings. They’re mounted with epoxy on a small mahogany plaque inscribed with his name. It’s a scant monument to the prodigious work that so many dedicated scientists and inventors did. But the important monument is the lives they saved.
