HIGH-ALTITUDE GIRDLES

Pressure suits, more often called "space suits" by the public, are essentially taken for granted today. Fifty years ago they were still the stuff of science fiction. These suits serve several necessary purposes, with supplying the correct partial pressure of oxygen being the most obvious (although masks or full-face helmets can also accomplish this). The most important purpose, however, is to protect the pilot against the increasingly low atmospheric pressures encountered as altitude increases—pressures that reach essentially zero above about 250,000 feet. At high altitudes, the blood and water in the human body want to boil—not from heat, but from the pressure differential between the body and the environment.-1771

A distant precursor of the full-pressure suit was, arguably, the dry suits used by turn-of-the – century commercial salvage divers, complete with their ported brass helmets and valve fittings. In 1920, renowned London physiologist Dr. John Scott Haldane apparently was the first to suggest that a suit similar to the diver’s ensemble could protect an aviator at high altitudes. There appeared, however, to be little immediate need for such a suit. The normally aspirated piston – powered airplanes of the era were incapable of achieving altitudes much in excess of 20,000 feet, and the major concern at the time was simply keeping the pilot warm. However, the increasing use of supercharged aircraft engines during the late 1920s led to the first serious studies into pressure suits. Suddenly, aircraft could fly above 30,000 feet and the concern was no longer how to keep the aviator warm, but how to protect him from the reduced pressure.-1781

During the early 1930s Mark E. Ridge determined that a suitably constructed pressurized suit would allow him to make a record-breaking altitude flight in an open balloon. His efforts to interest the United States military in this endeavor failed, and instead he contacted John Haldane in London for help. At the time, Haldane was working with Sir Robert Davis of Siebe, Gorman & Company to develop deep-sea diving suits. Together, Haldane and Davis constructed a hypobaric protection suit for Ridge. For a number of reasons, Ridge was never able to put the suit to actual use, although he tested it in a pressure chamber at simulated altitudes up to 90,000 feet.-1791

In 1934 famed aviator Wiley Post commissioned the B. F. Goodrich Company to manufacture a pressure suit of his own design. Unfortunately, the rubberized fabric suit did not work all that well. The basic design was modified by B. F. Goodrich engineer Russell Colley, and after some trial and error, Post was able to use it successfully on several record-breaking flights to altitudes of 50,000 feet.1801

While work on derivatives of the Ridge-Haldane-Davis suit continued in England, the U. S. Army Air Corps finally recognized, somewhat belatedly, the need for a pressurized protective garment for military aviators and started the classified MX-117 research program in 1939. This drew several companies into pressure-suit development, including B. F. Goodrich (with Russell Colley), Bell Aircraft, the Goodyear Rubber Company, the U. S. Rubber Company, and the National Carbon Company. From 1940 through 1943, engineers produced a number of designs that all featured transparent dome-like plastic helmets and airtight, rubberized fabric garments that greatly restricted mobility and range of motion when fully pressurized. The development of segmented, bellows-like joints at the knees, hips, and elbows improved mobility, but still resulted in an extremely clumsy and uncomfortable ensemble. The striking visual aspect of these suits resulted in their being called "tomato worm suits," after the distinctive tomato hornworm.[81]

By 1943 the Army Air Corps had largely lost interest in the concept of a full-pressure suit. The newest long-range bomber, the Boeing B-29 Superfortress, was pressurized and seemed less likely to require the suits than earlier aircraft. As Scott Crossfield later opined, "During World War II the armed services, absorbed with more vital matters, advanced the pressure suit not a whit."-82

After the war, Dr. James P. Henry of the University of Southern California began experimenting with a new concept in aircrew protection. The capstan-type partial-pressure suit operated by imposing mechanical pressure on the body directly, compressing the abdomen and limbs much like the anti-g suits then entering service. The compression was applied by inflatable bladders in the abdominal area and pneumatic tubes (capstans) running along the limbs. A tightly fitting, rubber-lined fabric hood that was fitted with a neck seal and a transparent visor fully enclosed the head.-83

In Worcester, Massachusetts, a small company named after its founder, David Clark, produced anti-g suits for the Air Force and experimental pressure suits for the Navy. Scott Crossfield described Clark as "one of the most interesting men I have ever met in the aviation world." Although Henry had approached the David Clark Company for assistance in developing his suit concept, contracts for anti-g suits between David Clark and the U. S. government made direct cooperation appear to be a conflict of interest. Instead, Clark sent materials and an experienced seamstress, Julia Greene, to help Henry continue his development in California. Just after the war, the Air Force asked Clark to observe a test of the Henry partial-pressure suit in the altitude chamber at Wright Field. Henry demonstrated the suit to a maximum altitude of 90,000 feet, and remained above 65,000 feet for more than 30 minutes; everybody was suitably impressed. The Air Force asked David Clark to produce the Henry design, and all parties soon reached an agreement that included Julia Greene returning to Worcester. David Clark produced the first suit for Jack Woolams, a Bell test pilot scheduled to fly the XS-1, and made additional suits for Chalmers "Slick" Goodlin and a little-known Air Force captain named Chuck Yeager.-84

These early partial-pressure suits did, in fact, work. On 25 August 1949, Major Frank K. "Pete" Everest was flying the first X-1 on an altitude flight when the canopy cracked and the cockpit depressurized. The laced partial-pressure suit automatically activated, squeezing Everest along the torso, arms, and legs, supporting his skin and keeping his blood from boiling. He landed, uncomfortable but unhurt. This was the first recorded use of a partial-pressure suit under emergency conditions.-1851

Continued improvements resulted in the T-1 suit, the first standardized partial-pressure suit used by the Air Force. The Air Force used the T-1 suit in a variety of aircraft, including the stripped-down "featherweight" versions of the Convair B-36 intercontinental bomber that frequently flew missions lasting in excess of 24 hours at altitudes above 50,000 feet. Unfortunately, the T-1 suit was not a particularly comfortable garment.-861

The discomfort of the so-called "Henry suit" was an unfortunate aspect of the fundamental design of partial-pressure suits. This was at least partially eliminated in the subsequent MC-1, MC-3, and MC-4 series (the MC-2 suit was an experimental full-pressure suit to be discussed later) by the placement and adjustment of panels during customized fitting. However, the suits did accomplish their main purpose: to protect the wearer from the effects of emergency decompression at altitude.-1871

Taking a different route, after the war the U. S. Navy began investigating the possibility of developing a full-pressure suit in cooperation with B. F. Goodrich and Russell Colley. This led to a progressive series of refinements of the basic design that resulted, in the early 1950s, in the first practical U. S. full-pressure suit. At the same time, the David Clark Company was also experimenting with full-pressure suits under Navy auspices. On 21 August 1953, Marine Corps Lieutenant Colonel Marion E. Carl took one of the D-558-2 aircraft to an unofficial record altitude of 83,235 feet while wearing a David Clark full-pressure suit.-1881

The Navy’s adventures in full-pressure suit development took some intriguing turns, and Scott Crossfield covers them well in his autobiography. The Navy ended up concentrating on the Goodrich designs. One of these was the Model H, an early developmental suit that the Navy considered unacceptable for operational use but showed a great deal of promise. Consequently, in a perfect example of interservice rivalry, the Air Force and Navy began separate development efforts—both based on the Model H—to perfect an operational full-pressure suit. By the early 1960s the Navy had progressed through a series of developmental models to the Mark IV, Model 3, Type 1, a production suit that Navy aircrews wore on high-altitude flights for several years.-1891

Air Force experience at high altitudes in the B-36 confirmed the need for a full-pressure suit to replace the partial-pressure suits used by the bomber crews. In response, the Air Force drafted a requirement for a suit to provide a minimum of 12 hours of protection above 55,000 feet. The goal was to construct a "fully mobile suit" that would weigh less than 30 pounds, operate with an internal pressure of 5 psi, and provide the user with sufficient oxygen partial pressure for breathing, adequate counterpressure over the body, and suitable ventilation.1901

Whatever the political nuances involved, in 1955 the Air Force issued a request for proposals for a full-pressure suit. Several contracts were awarded and the two leading designs were designated the XMC-2-ILC (International Latex Corporation) and the XMC-2-DC (David Clark Company). The ILC approach resulted in an unwieldy garment that used convoluted metal joints and metal bearing rings, and had limited mobility under pressure; it was known, however, to provide the required pressure protection. Unfortunately, the joint bearings produced painful pressure points on the body and were hazardous during bailout or ejection—hardly an ideal solution.1911

On the other hand, the David Clark suit featured a major breakthrough in suit design with the use of a new "distorted-angle fabric," called Link-Net, to control inflation and enhance range of motion. This eliminated the need for the tomato-worm bellows at the limb joints. David Clark had been developing this same basic suit with the Navy before that service opted to go with the Goodrich design. The Air Force selected the David Clark suit for further development.1921

The new Link-Net fabric was the result of an intensive effort by the company to develop a new partial-pressure suit fabric using both Navy and company money. Originally, David Clark had constructed several torso mockups using different unsupported sheet-rubber materials, but quickly discarded these when it became evident that a rupture in the material could cause the entire suit to collapse. The company began looking for a supported-rubber material that would meet the sealing requirements but would not collapse when punctured. Ultimately, David Clark selected a neoprene-coated nylon. A puncture in this material would result in a small leak, but not a sudden expulsion of gas.1931

The enormous advantages offered by the Link-Net fabric were hard to grasp. Coupled with advances in regulators and other mechanical pieces, David Clark could now produce a workable full-pressure suit that weighed about 35 pounds. Previously, during the early X-15 proposal effort, North American had estimated a suit would weigh 110 pounds.[94]

Further tests showed that two layers of nylon marquisette arranged with opposite bias provided the maximum strength in high-stress areas. This improved Link-Net material consisted of a series of parallel cords that looped each other at frequent intervals. The loops were interlocked but not connected so that the cords could slide over each other and feed from one section of the suit to another to allow the suit to deform easily as the pilot moved. The main characteristic required of the Link-Net was the lowest possible resistance to bending and twisting, but the elasticity had to be minimal since the suit could not increase appreciably in volume while under pressure. The use of a relatively non-elastic cord in the construction of Link-Net made it possible to satisfy these seemingly contradictory requirements. Clark chose nylon for the Link-Net because of its high tensile strength, low weight, and low bulk ratio.-195

The X-15 provided the first impetus to develop a workable full-pressure suit, and Scott Crossfield and Dr. David M. Clark were instrumental in the effort. The first X-15 full-pressure suit, the XMC – 2 (S794-3C) was demonstrated by Scott Crossfield in the human centrifuge at the Aero Medical Laboratory on 14 October 1957. Two 15-second runs were made at 7 g, and the following day an additional 23 tests were conducted to demonstrate the anti-g capability of the suit. (U. S. Air Force)

The first prototype David Clark Model S794 suit provided a learning experience for the company. For instance, the initial anti-g bladders were fabricated using neoprene-coated nylon, but failed during testing. New bladders incorporated a nylon-oxford restraint cover, and these passed the pressure tests. Materials evaluated for the gloves included leather/nylon, leather/nylon/Link-Net, and all leather. Eventually, the company found the best combination was leather covering the hand, a stainless-steel palm restrainer stitched inside nylon tape supported by nylon tape around the back, Link-Net from the wrist up to the top zipper, and a black cabretta top seam. However, pilots quickly found that gloves constructed in the straight position made it impossible to hold an object, such as a control stick, for more than 15-20 minutes while the glove was pressurized. When the company used a natural semi-closed position to construct the glove, the pilots could hold an object for up to 2 hours without serious discomfort. Perhaps the most surprising material used in the prototype suit was the kangaroo leather for the boots, which turned out to be soft and comfortable as well as sufficiently durable."

The construction of two "production" full-pressure suits (S794-1 and S794-2) followed. These suits were an improvement in terms of production and mobility but were, in reality, still prototypes. One of the major changes was extending the use of Link-Net material further from the joints to increase the amount of "draw" and provide additional mobility. Eventually David Clark concluded that the entire suit should use Link-Net. David Clark delivered these two suits to the Aero Medical Laboratory at Wright Field for testing and evaluation, and used the lessons learned to construct the first X-15 suit for Scott Crossfield."