The Brotherhood of Yellow Pads

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The story of Frank Whittle and the invention of the jet engine would make a great B movie, and probably has. I can just see all the mustachioed boffins of the Air Ministry conferring in their offices about how to rid themselves of this pestilential fellow obsessively slaving away in a brick basement in the countryside, while we in the audience, knowing that the jet age is just around the corner, cluck over their folly. The obtuseness of military bureaucrats harassed poor Whittle for a time into a diet of amphetamines and barbiturates, but he still managed to die at 89 - good news for worried substance-abusers.

His German counterpart, Hans Joachim Pabst von Ohain, seemingly had quite a different experience. Von Ohain, who worked for bomber manufacturer Ernst Heinkel, seems to have sailed from paper sketches to an airworthy jet engine in the space of three or four years, while poor Whittle, who had a head start, took a dozen.

Whittle had begun thinking about jet engines in 1928, when he wrote a college thesis on future developments in aviation. He was prescient, considering that this was the heyday of the biplane and Lindbergh had only recently crossed the Atlantic. "It seems," he wrote, "that, as the turbine is the most efficient prime mover known, it is possible that it will be developed for aircraft, especially if some means of driving a turbine by petrol could be devised." At first he was thinking of a turboprop, but by 1930 he had realized that an airplane could be propelled by the fast-moving gases of the turbine exhaust alone, and that thrust obtained in that way had advantages, for high speed flight, over thrust obtained by means of a propeller. In that year Whittle took out a patent on an engine design consisting of an air compressor driven by a gas turbine, with a gas-generating burner between them. This was, in general outline, a complete jet engine. Mechanically, it had much in common with the turbosupercharger, which had been developed for aircraft use during World War I, a principal difference being that the heat source for the turbosupercharger - what we now call a turbocharger - is external.

Whittle's first operable engine was a crude lash-up that resembled a large model of the cochlea. It was intended only to test the feasibility of the idea - of which I'm sure he had, in his heart, no doubt - and Whittle experimented with alternative designs before arriving at the one that actually propelled an airplane on May 15, 1941. The physical arrangements of Whittle's first flight engine and Ohain's, which had already flown, unbeknownst to the British, on August 27, 1939, were not greatly different. What strikes the modern eye about both engines is that they were so short and fat, as though the designers had wished to imitate as closely as possible the proportions of a conventional radial engine.

The large diameter of these primitive jet engines was due to their use of centrifugal compressors, which take in air at a central point and sling it outward through a narrowing passage. (If you've seen a turbocharger dismantled, you've seen a centrifugal compressor.) Though mechanically robust, aerodynamically undemanding, and able to produce compression ratios of 3:1 or better in a single stage, the centrifugal compressor has the disadvantage of a large diameter and a tortuous airflow path if two of them are used in series to achieve higher compression.

The extreme stubbiness of Whittle's and Ohain's early engines was probably due to a desire to control structural weight and to keep the main shaft, which carried thousands of horsepower from the turbine to the compressor, as short as possible. The 10 burner "cans" in Whittle's engine, which were longer than the whole rest of the engine together, were disposed around its perimeter, with airflow reversing direction to enter them and reversing yet again on the way out into a turbine located just a few inches behind the compressor. The large size of the burner cans was due to the difficulty of getting the fuel to burn completely before reaching the turbine. In a modern engine, the burners, which are highly efficient, occupy relatively little space, while the compressor, which develops pressures 10 times higher than Whittle's did, is proportionately much larger.

A third jet-engine pioneer, Anselm Franz, a turbocharger specialist at the Junkers engine works, recognized the drag implications of the bulky centrifugal compressor and created an axial-compressor engine. His relatively long, slender Jumo 004, which first flew in 1942, was only about 30 inches in diameter. Accurately anticipating the future evolution of the turbojet, its compressor consisted of eight fanlike stages alternating with flow-straightening stationary blades. Mounted in nacelles below the wings, two 1,980-pound thrust 004s powered the world's first operational jet fighter, the Messerschmitt Me 262. (Actually, Heinkel had built a similar twin-jet fighter, the He 280, in 1941, but the Luftwaffe, certain of early victory, wasn't interested.) But for Hitler's fortuitous insistence that the Me 262 be developed as a bomber-he was vengefully obsessed with the idea of dropping bombs on England-this historic airplane could have nullified the Allies' air superiority at the end of the war.

Early in the war, before the entry of the United States, England had turned over Whittle's designs-the poor inventor protested in vain as his life's work was wrested from his control-to NACA, the American National Advisory Committee for Aeronautics, which contracted with General Electric to build several examples of his W2B engine. After the war ended, Whittle himself traveled to America to consult with General Electric; eventually he emigrated here, and took up a professorship at the Naval Academy at Annapolis.

A set of notebooks, their lined yellow pages filled with notations in Whittle's compact, orderly hand, also found its way to America and was acquired two decades ago, along with a lot of other papers from Whittle's company, Power Jets Ltd., by General Electric. The notebooks were logs of his engine tests during the period from October 1938 to October 1941, when he was testing the so-called "third experimental engine." These historic materials languished in obscurity until last year, when four of the test logs came to light. None the worse for six decades in darkness, the Whittle logs evoke a remarkable period in aviation history: The birth of the jet age.

It was, he would later write, a "heartbreaking period." Two great difficulties bedeviled Whittle. One was making the turbine survive in the stream of hot gas from the burners; this was partly a matter of high-temperature metallurgy, which, fortunately, was making strides; and partly one of finding how best to use bleed air from the compressor to cool the hollow turbine blades. The other was establishing and maintaining stable and complete combustion in the burners themselves.

The combustion problem was the more difficult one. Von Ohain had temporarily circumvented it by using hydrogen as a fuel. Hydrogen burned rapidly and evenly, and it was relatively easy to maintain a uniform flame throughout the combustor; but it was not a practical fuel for an airplane. Petroleum fuels, on the other hand, delivered to the burner in liquid rather than gaseous form, required fine atomization and a suitable proportion of fuel to air, and it was difficult to distribute the droplets uniformly and to burn them completely during the short time it took the moving air to pass through the combustor. If fuel arrived unburned at the turbine, as often happened during early tests, it could overheat the turbine blades and the tailpipe or, at the very least, produce an impressive, but from the propulsive point of view useless, roostertail of flame.

The third experimental engine incorporated, for the first time, multiple separate burners rather than a single annular one. The "can-type" burners had the advantage of being easier of access, modification and repair, and they allowed easier control and observation (through quartz windows) of the flame. Many later engines would incorporate some variation on the can-type burner.

Whittle appears to have used a two-page form for each log entry and, in the absence of copy machines, to have filled out the headings throughout each book - date, time, run time, reason for stopping, remarks, repairs and modifications, and so on - in advance in small, neat lettering. Engine runs took place at irregular intervals: sometimes two days, sometimes a month. "Unsatisfactory combustion" was his constant refrain. "Vibration due to irregular combustion could be felt throughout machine," he wrote on December 14, 1938, after a 10-minute test run. "Flashes of flame at intervals from end of exhaust pipe. Exhaust adjacent to No. 8 combustion chamber red hot." The red heat was less disturbing, in itself, than the fact that it appeared only at isolated locations, indicating non-uniform combustion.

He tinkered continually with fuel manifolds and jets, swirl baffles, and the perforated flame holders in the centers of the burners. Gradually he increased the engine speed from 6000 rpm - hardly more than an idle - toward the design value of 16000 rpm. Always the same problems pursued him. "Severe maldistribution of heat … fuel surging between combustion chambers … unsteady combustion … ." But by mid-1939 the engine was running for more than an hour at a time at up to 14000 rpm. "Vibration much reduced," he wrote on June 19, when the engine had built up a total of more than 14 hours. But combustion was still not satisfactory; three days later a test ended prematurely owing to "explosive combustion" after vibrations that shook the massive test truck. By August, however, test runs were generally lasting for the planned duration, and the reason for stopping was simply, "End of test."

And so it went through 1940. "Measured thrust readings were unusually high," he noted in June, when the engine had accumulated a total of 48 hours. By late in the year, the engine had over 60 hours and was running reliably. Oddly, Whittle's handwriting had changed; earlier neat, erect and disciplined, it had become, whether from elation or exhaustion, swift, slanted and irregular.

The engine flew five months later in a specially designed airplane, the Gloster E28/39, which, in spite of the immaturity of the engine, and after minimal ground testing, attained over 350 knots and climbed to 42,000 feet, outperforming all contemporary fighters. The Air Ministry finally took notice. These yellow pages, resembling a student's exercise book, evoke an era, within the lifetimes of many who are still around today, when one person with a fixed idea, a tiny budget, and a small and shabby workshop could defy conventional wisdom and eventually triumph. The first 40 years of aviation were like that; many of the great companies bore the names of their founders, and airplanes reflected the personalities of their designers. Then consolidation came, and the progressive absorption of the pioneering individual by the corporation, and of the corporation by the holding company, or the state.

Is the age of Whittle really gone? Or is there perhaps a Whittle today, somewhere, scribbling notes on a yellow pad about some invention, unimagined by us, that will soon change aviation forever?