by Dan Hampton
It was through his expertise in this area that Busemann developed the concept of a swept wing: one set at an angle less than 90 degrees to the fuselage. This had been done before as early as 1908, and J. W. Dunne, a British engineer, built a flying-wing biplane that made it across the English Channel in 1913. But Dunne and several others who used swept wings were concerned with pilot visibility and longitudinal stability, while Busemann was thinking in terms of speed.
The problem was air.
Or rather, how air reacts as a body moves through it at velocities approaching the local speed of sound. Remember that this varies with altitude as the higher one ascends, the lower the temperature; for standard conditions at sea level a body is supersonic at 1,117 feet per second, while 49,000 up to the speed of sound is less: about 968 feet per second. Amateurs and engineers alike, specifically ballistics engineers interested in improving artillery shells, understood that as a body approached this speed the drag acting against it increased. This observation was deliberately noted by Benjamin Robins, an accomplished British military engineer, in an article published in 1742.
But it was Ernst Waldfried Mach who first gave a numerical value for velocity as it related to the speed of sound; this was expressed in tenths, up to the whole number 1.0, which represented (and still does) supersonic flight. Mach was an Austrian, born in 1838 to a cultured, intellectual family who tutored him from an early age in geometry, algebra, and science. Mentally agile, Mach’s natural abilities in philosophy, music, medicine, and languages stimulated his creativity into many diverse fields.* Earning a PhD in physics from the University of Vienna, Mach served as a professor of experimental physics at the University of Prague for nearly three decades.
Then, in 1887, he saw the demon itself and, astonishingly, photographed it. A precise perfectionist and superlative experimentalist, Mach set up trip wires triggered by a passing bullet and then photographed the event. Well aware that air is disturbed by a body’s movement through it, he also knew that such a disturbance would refract light. Even in a transparent medium such as air, such a refraction would cause shadows, like sunlight striking waves, and these could be captured by photography—which they were. (The image appears in this book’s photo insert.)
Revealed to the Academy of Sciences in Vienna, the image of the shock waves surrounding the bullet was staggering. The bow wave is clearly visible just ahead of the bullet as was the turbulent, churned-up air in the wake. This point, Mach 1 as it came to be known in 1929, was where a body—projectile or plane—became supersonic. A further refinement became known as the Critical Mach Number, the lowest speed that some point on an aircraft becomes supersonic, but does not exceed it.
Mathematical calculations for supersonic flight were relatively straightforward, and now there was visible evidence of the shock wave, but very little was understood about air as it approached Mach 1. Termed the transonic region, this was a murky, ill-defined area where flows are locally lower or higher than the aircraft’s forward velocity. So while the trailing edge of a wing might be subsonic, the leading edge, for example, may have exceeded the speed of sound. Air behaved differently in these regions, and there were considerable problems, especially in a world of straight-winged aircraft.
Below the speed of sound, air is essentially incompressible (for our purposes) and cannot be “packed” any tighter than it is. In this region, a body or an aircraft disturbs the surrounding air, splits it, and sends out pressure pulses like a bow wave from a boat moving through water. As long as the aircraft remains subsonic there are no aerodynamic issues, and the flow remains relatively smooth with predictable actions. Now, we know that as air accelerates, its pressure changes, and as long as the speed remains well below the speed of sound, it does little more than generate the lift needed to fly. But when a body, or part of a body, accelerates into the transonic region, then different areas of it are now subject to erratic and variable pressures that subject the body to unplanned effects. The most severe of these was a slew of new aerodynamic challenges collectively termed compressibility.
Some of these had been identified as early as the Great War by engineers seeking to improve propellers, and it was well known at the time that even at a modest 130 mph aircraft velocity, the propeller tip speeds were well past the speed of sound. Essentially, air becomes “thinner” as it speeds up and the molecules spread out, which does a lot of bad things, aerodynamically. Pressure decreases, which simultaneously increases drag and decreases lift. This was confirmed during a series of experiments conducted under the auspices of the NACA by Hugh Dryden and Lyman Briggs of the National Bureau of Standards in the late 1920s. Courtesy of the General Electric Company, they improvised a wind tunnel and ran a series of physical tests to validate earlier American and British research.
Briggs and Lyman definitively proved that thicker wings at higher angles of attack were susceptible to transonic effects at lower speeds than a thin wing, or one at a lower angle. In addition to lift and drag, they also concluded that the center of pressure on a wing moved aft toward the trailing edge as speed increased. This was significant, though not realized at the time, because it would directly and often fatally affect controllability since the ailerons were located on the trailing edge. Also, remembering Mach’s photograph, that turbulent wake would subsequently flow over an aircraft’s horizontal tail and impact elevator effectiveness. Yet what could be done about it?
Air cannot be altered, so the answer had to lie with altering the effects air had upon a wing. In fact, the theme of the 1935 Volta Conference in Rome was “High Velocities in Aviation,” and specifically the properties of subsonic to supersonic airflows. Hosted by the Royal Academy of Science, the leading aerodynamicists in the world convened in Rome during September 1935. Among them were Gaetano Arturo Crocco, Eastman Jacobs of the NACA, Hugh Dryden of the Bureau of Standards, Theodore von Kármán, and Jakob Ackeret, who first articulated the “Mach Number” in 1929 in deference to Ernst Mach. Compressibility and its effects took center stage and Eastman Jacobs with John Stack of the NACA were the leading authorities on the subject. In addition to the precise, unambiguous findings, Eastman Jacobs also had a series of schlieren photographs, very much like Mach’s shadowgraph, which visually depicted the effects of the “compressibility burble,” a term coined by Stack.*
Adolf Busemann was certain he had the solution. A wing’s aerodynamic characteristics are dictated by a component of the airflow’s velocity perpendicular to its leading edge, so if the angle of the wing is decreased to less than 90 degrees (a straight wing), then the component striking the leading edge will also decrease. This would change everything. The critical Mach number would be higher, so the wing would fly faster before becoming supersonic, and the huge drag coefficient associated with this would be delayed. Even when it did occur, the severity of the increase would be much reduced. With a powerful engine, like a jet, the door could be opened for supersonic flight.
It is interesting to speculate how the air war over Germany might have played out if the potential of the swept wing had been grasped by the Allies in the mid-1930s. It is also tantalizing to picture the mating of Frank Whittle’s and General Electric’s jet engine research to a swept-wing aircraft in 1942, especially with the vast money and resources available to the Allies.
The presentation of the swept wing and a solution to this nasty aerodynamic dilemma should have been a godsend but, amazingly, it was virtually ignored. Those in attendance were focused primarily on theory, not design, and the evolutionary breakthrough was treated rather indifferently by von Kármán and others. The Germans, on the other hand, took it very seriously. Busemann confirmed his swept-wing data through high-speed wind tunnel testing in 1939 at Braunschweig, and this was subsequently used by Messerschmitt for development of the Me 262 and the next technical leap forward: Projekt 1101.
It was apparent to these men that the transonic region was the real danger, and if an aircraft could not be controlled as it transited the Mach, then it woul
d not physically survive to get through to the other side. The speed of sound was just a number, an artificial flag created by men and not a barrier at all—compressibility was the true gateway into the demon’s world.
Paradoxically, even as battlefield reverses accelerated German advanced technology development it had the opposite effect on the Allied jet program. With tactical and strategic successes, and in the absence of real threat, the Allies, particularly the Americans, rightly concentrated on perfecting and fielding proven technology that worked, rather than dissipating their efforts as the Germans did. Nevertheless, Major General Hap Arnold’s 1941 visit to Britain convinced him (and he convinced the U.S. government) that the technology gap must be closed. Just over ninety days prior to the attack on Pearl Harbor, the General Electric Company of Schenectady, New York, was contracted to build the initial American jet engine: the GE I-A.
In a surprising move, Bell Aircraft was asked to design the aircraft around General Electric’s engine, and the contract was signed on the last day of September 1941. The company’s efforts with the P-39 Airacobra and P-63 Kingcobra had been average, at best, and Bell’s reputation for building effective, frontline fighters was questionable. Yet they had a tolerance for unconventional ideas, and perhaps this was the reason behind the choice or, more likely, Bell’s Buffalo, New York, facility was the closest to General Electric, and this would help ensure secrecy for the project. In any case, the XP-59, America’s first jet program, was alive.*
By late summer 1942, as the Marines were landing on Guadalcanal, the first prototype was ready—but where to test it? Wright Field, though close to the engine and airframe manufacturers, was deemed too populated not only for secrecy but for safety in case anything went wrong. What was needed was a place no one would look, no big cities nearby and very little civilization. A place that was easy to secure, far from prying eyes, and with good enough weather to permit nearly constant flying. A place where nothing on the ground would be destroyed by falling aircraft because there was nothing on the ground to destroy. Such a place did indeed exist: Rogers Dry Lake in Antelope Valley, California.
Situated on the roof of the Mojave Desert, the lake bed was close enough to Los Angeles for convenience, but separated from the coast by the San Gabriel mountain range. It offered 120-degree temperatures, almost no rain, scorpions, flies, and snakes; combined with Rosamond Dry Lake, it also offered approximately 306,000 acres of flat, dry landing surfaces. Originally a water stop for the Santa Fe Railroad, the Rodriguez Mining Company had controlled much of the land, but in 1910, a few years after the Wright Brothers flew, Clifford and Ralph Corum arrived. The land was free, and the government was so desperate to attract settlers that it offered a $1 per acre incentive for every acre that was improved. The Corums called their new home “Rod,” short for Rodriguez, which means “Roger” in English, and the dry lake now had an Anglicized name.
The Corums went into business attracting other homesteaders to the area and helping them drill wells, clear the land, and ship in supplies. A general store was built, and also a church. To encourage growth and legitimize the little community, Effie Corum, Clifford’s wife, petitioned the U.S. government to name the post office after her family, but this was denied as a Coram, California, already existed and the similarity was too close. The Corums then reversed their name and suggested “Muroc,” which was accepted, and the area now had an official name.
In 1933 the Army Air Force, which had a penchant for desolate areas and decrepit, threadbare bases, sent a small detachment out from March Field to design a bombing and gunnery range. For the next eight years this was manned by a handful of Army personnel and used for aircrew tactical training while the government quietly bought up all the surrounding land it could. After the Japanese attack on Pearl Harbor, units of the 41st Bombardment Group left Davis-Monthan in Tucson for Army Air Base, Muroc Lake, as it was called. Joined later by the 30th Bombardment Group, the population of the dusty, obscure post went from dozens to thousands within days, and in 1943 was renamed Muroc Army Air Field.
Primarily utilized as an operational training base, Muroc and its satellite airfields existed to put the final touches on all sorts of pilots heading into combat: bomber crews in B-24 and B-25s; P-38 Lightning fighter pilots, and A-20 attack pilots. The ramshackle collection of buildings on the southern shore of the dry lake, called “South Base,” continued to grow. Bombing and strafing were the focus, and to that end the Army built a 650-foot-long mock-up of a Japanese Takao-class heavy cruiser.*
Muroc was perfect.
Yet by 1942 it was recognized that a remote test site was needed for the Army’s more exotic programs. Wright Field in Ohio and Florida’s Pinecastle were both becoming too populated, so a small highly classified annex was constructed on the north side of Rogers Dry Lake. Officially known as the Material Center Flight Test Site, the program engineers, technicians, and contractors called it “North Base,” and secrecy was so tight that the Army personnel on the south side initially had no clue what was happening. The XP-59 was taken west by rail in September, its jet engine covered with a tarp and a dummy propeller on the nose to allay suspicion. Robert Stanley, Bell Aircraft’s chief test pilot, first got the first XP-59A Airacomet (#42-108784) into the air from Muroc on October 1, 1942. It was underpowered and, like all jets of the day, prone to overheating. Cockpit visibility was poor, as was its acceleration compared to frontline piston-engined fighters.
Service test versions, now the YP-59A, were delivered to the military in June 1943, and even with 1,650 pounds of thrust each from more powerful GE I-16 engines the jet was still a dog. Despite its lackluster performer, controllability issues, and marginal engine response, the U.S. government ordered eighty of the new jets, though this number was eventually cut in half as the military correctly resisted expending time, money, and resources on unproven and, as they saw it at the time, unnecessary technology. Certainly the American attitude would have been different had the Luftwaffe fielded a jet fighter in sufficient numbers and early enough in the war to make a difference, but it had not. Yet there were those in Washington who could see, even in 1943 and 1944, that the next threat to emerge from the war would not be from Germany or Japan. The next threat would be as much a clash of ideals as of technology and it would be through technology, not numbers alone, that peace would be maintained.
Nevertheless, German technology was still fearful, and guided bombs were not the only new technology to appear during the summer of 1943. Wild rumors began circulating about strange German fighters with no propellers, and speeds no Allied plane could match. Some pilots were aware of jet engine technology, and some were not. It was certainly not new, nor was it particularly secret unless connected to a specific aircraft program. “We weren’t really worried about it,” Chilstrom recalls. “The Germans were at least six years ahead of us in this regard, and yet they hadn’t been able to put many into operation. From what I knew about jets they wouldn’t be much good at low-altitude operations . . . the engines weren’t made for it. And low-altitude ground attack was my life in 1943.”
The same month Ken Chilstrom entered combat during June 1943, Frank Whittle and Gloster’s E.28 second flying test jet logged over fifty hours in the air. Rolls-Royce had taken over production of the engine and Britain expected to field an operational jet fighter in 1944. The United States Army Air Force, thanks to a Whittle engine given to General Electric in 1942 and with vastly more resources available, rapidly caught up to the Royal Air Force.
June 1943 also saw Lockheed acceptance of a new government contract, and the legendary Kelly Johnson delivered his own jet fighter design proposal. Work commenced on the XP-80 just before the Allied invasion of Sicily and, realizing they were beginning at a disadvantage, Lockheed opted to build its own fuselage around an existing British jet engine: the Halford H-1B. Much of the initial design came from plans for a single-engine version of the XP-59 that Bell had provided. Johnson and his talented design team, the famous “Skunk Works,”
delivered their aircraft body in November 1943 after just 143 days.
Larger and heavier, the straight-winged jet sported tricycle landing gear and mounted the engine inside the fuselage, rather than in external nacelles. The new General Electric I-40 engine produced 4,000 pounds of thrust, more than double that of the I-16 in Bell’s Airacomet. To test and evaluate both jets, the Army Air Force formed the 412th Fighter Group, America’s first jet unit, and based it on the north edge of Muroc’s dry lake. Though the “Shooting Star,” as it would be called, did not fly until early 1944, it would outperform Bell’s Airacomet in every way, and become America’s first operational jet fighter, though too late for the Second World War.*
Though waning German fortunes of war accelerated the development and fielding of the Luftwaffe’s advanced aircraft programs, these efforts were too widely dispersed for real efficiency, especially under the current conditions. Still, they had not been idle, and were still well ahead in jet and rocket technology. Piloted by Heini Dittmar, the Messerschmitt Me 163 Komet flew in 1941, and the initial preproduction models were delivered to Erprobungskommando 16 (Service Test Unit 16, to EK 16), in July 1943, under the command of Major Wolfgang Späte, a ninety-nine-victory ace. Capable of flight past 600 miles per hour, the stubby little interceptor would remain the fastest manned aircraft of the war, and its technology would influence the future design of the Bell X-1.
Using detachable, dolly-type landing gear the Komet would roar off the ground and rocket up toward the belly of heavy bomber squadrons at an astonishing 11,800 feet per minute. Once in range of its two Mk-108 30 mm cannons, the pilot would open fire, then shoot vertically up through the bombers much faster than gunners or escorts could react. Apexing about 10,000 feet above the formation, the Me 163 would then dive down through them, firing again at the pass. Engagements were limited as the little interceptor had a short range, and eight minutes of fuel at best so once this was burned up the pilot would glide back to land. But the Komet was a rocket; true, it could fly extremely fast and hit hard, but it could never dogfight, perform close air support, or be taken seriously in an air superiority role at a time of flight measured in minutes.
