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How private philanthropy, inventive engineers and a courageous pilot put the “I” in IFR.

Airmen of all nations faced a common problem in the 1920s: flying safely when darkness, clouds or fog obscured their way. In an era when IFR flying literally meant “I Follow Railroads,” it constituted the greatest of all flight safety challenges. By day, pilots typically followed roads, rivers and railroads. At night, they relied on moonlight, easily recognized stars and, after the creation of lighted airways, evenly spaced rotating beacons and flashing markers between major cities. But rapidly forming fog and clouds could quickly rob them of these references. If they became trapped in clouds or fog, potentially fatal vertigo often swiftly followed. Uncertain of the airplane’s attitude, many pilots crashed, driven out of control by their own confused senses and impulsive control inputs. Even if they did not crash, fog and clouds often forced them to chance risky emergency landings. In one year, the U.S. Post Office recorded nearly 800 such landings by its airmen, approximately one for every 20 flying hours, a national average of more than two a night.

Disorientation and subsequent loss of control made any long-distance flight potentially hazardous, for in the course of a journey of several hundred miles an airplane was likely to overfly clouds or enter obscuring conditions. In May 1919, the crew of the U.S. Navy’s Atlantic-crossing Curtiss NC-4 encountered disorienting sea fog broken occasionally by a hazy sun. The NC-4 slipped into a spiral dive, prelude to a fatal spin. Fortunately the pilot, Coast Guard Lieutenant Elmer Stone, aided by providential glimpses of the solar disk, recognized the direction of rotation, and recovered control.

A month later, it was the turn of Britain’s John Alcock and Arthur Whitten Brown. Flying through clouds between Newfoundland and Ireland, they lost control of their twin-engine Vickers Vimy, which abruptly stalled, mushed oceanward and began a slow spin. Luckily the cloud deck did not descend all the way to the sea, and they spun out of the base of the clouds with barely enough altitude to recover.

In 1927, flying from New York to Germany, Clarence Chamberlin and Charles Levine became disoriented in clouds, stalled their Bellanca WB-2 and then lost 17,000 feet before safely recovering and continuing onward. Later that same year, Hermann Köhl took off from Dessau, Germany, attempting the first east-west airplane flight to America. As he was passing over Ireland in thick weather, a rising howl warned him that his Junkers W33 monoplane had dropped into a spin. He recovered as much by luck as skill, decided he’d had enough for one flight and flew back to Dessau.

Existing instruments were of little help, so imprecise that instructors told students— Charles Lindbergh among them—to trust their senses instead. Such advice constituted a death sentence for many airmen, for if instruments could mislead a pilot, reliance on “seat of the pants” feel certainly did mislead them.

In 1926 extensive Air Corps tests of hooded pilots sitting in rotating gimbaled chairs proved that the mind, its perceptions governed by the inner ear, is notoriously unreliable in the absence of visual cues for judging motion, acceleration and position. No matter how great their previous skill and experience, with their vision obscured all the pilots routinely mistook rates and directions of rotation, missed reversals of direction and changes in seat angle or could not even tell if they were moving at all. Under such conditions pilots risked not only losing control but, miscued by their senses, actually putting their airplane out of control. What was to be done?

The answer came from a remarkably energetic, conscientious Swiss émigré family, the Guggenheims. After arriving in America in 1848, the family had made millions in mining and mineral investments, turning much of it to public benefit by supporting various charities and foundations. Such generosity, combined with scrupulous honesty, earned the family high marks from reformers.

Daniel Guggenheim and his son Harry were responsible for the family’s interest in aviation, the former because he saw its business potential, and the latter because he enjoyed flying and thought it could help bring the world’s peoples together. Plagued by heart problems, Daniel had retired in 1923, at age 67, establishing The Daniel and Florence Guggenheim Foundation for “the well-being of mankind throughout the world.” Daniel’s son Harry, born in 1890, had studied mining at Yale and political science at Cambridge. In World War I he became one of the first naval aviators. He returned afterward to the family’s business, building a sprawling mansion on the north shore of Long Island, and flying with a local aero club.

In 1925 Daniel Guggenheim had given $500,000 to New York University to create an aeronautics program and educate “highly trained engineers capable of building better and safer commercial aircraft.” The school opened a year later, a two-story building with a 9-foot wind tunnel, classrooms, laboratories and an initial enrollment of 57 students. So great was the aviation community’s reaction that the Guggenheims immediately began considering a larger effort. On January 16, 1926, the elder Guggenheim announced The Daniel Guggenheim Fund for the Promotion of Aeronautics, a $2.5 million (roughly $30 million today) fund. It subsequently undertook a wide and influential range of educational grants, scientific research, technical evaluations and practical commercial aircraft demonstrations.

While on a European study trip immediately after establishing the fund, Harry Guggenheim emphasized to a British acquaintance that “safety was the vital necessity to civil aviation.” To that end, the fund’s trustees hoped (as one announcement read) to convince the public “not by statistics, but by actual demonstration that airplanes are inherently no more dangerous than steamships or railroads.” In 1927 this led to a West Coast “Model Air Line” experiment with Western Air Express, using three new Fokker F-10 trimotors. (The F-10 was a development of Tony Fokker’s popular 10-seat F.VIIb/3m, but powered by Pratt & Whitney Wasp radial engines, with Dutch-built wings and larger American-built steel-tube-framed fuselage capable of carrying a dozen passengers).

The Model Air Line included an experimental radio and weather service along the route. A chain of reporting stations issued bulletins and weather updates, and balloons were launched at various points to measure winds aloft. Telegraph, telephone and teletype machines speeded surface communications across the airway and airport network. The Guggenheim weather-reporting network greatly influenced the federal airways system and the Weather Bureau’s reporting network. Still, the blind-flying challenge remained. Pilots could navigate cross-country using radio aids and informed of weather hazards en route, but how could they fly safely, in all weather, day and night, if they couldn’t see the ground?

In June 1926, fund trustees had agreed to finance an effort to overcome the challenges of “fog flying,” but only after first executing a series of grants creating widespread national aeronautical engineering education. Two years later, with this endeavor well underway, they announced a switch in emphasis from education to research,“particularly meteorology and the problem of fog-flying.”

Shortly after that, however, their confidence was dashed when Jerome Hunsaker, a leading aeronautics authority, concluded that “safe landing in fog is not today possible, and no means are in sight to make it so.” His discouraging views recalled an episode in the Wright brothers’ career: In 1901 Wilbur Wright exclaimed that man wouldn’t fly for 50 years—but then in two years the brothers achieved success at Kitty Hawk. Now the emerging technology of radio navigation, coupled with new cockpit instruments, would soon make fog flying a practical reality.

The Bureau of Standards’Aeronautical Research Division had developed radio beacons enabling long-distance navigation. Though these were not perfect, they had already proven their value. The bureau’s beacon design incorporated two antennas to transmit the Morse letters “A” (u -) and “N” (- u). Flying in a particular quadrant, the pilot would hear one of these two letters. But where the A and N signals overlapped, the pilot would hear a steady tone, the “equisignal” (—). As the pilot approached the beacon, the signal would build in strength until the airplane passed directly over it. Then it would enter a “cone of silence”: The signal would abruptly end, then resume again as the pilot flew away from the beacon. Knowing the location of the beacon, the plane’s course approaching it and the distance and direction of an airfield in relation to the beacon, a pilot could use a combination of maneuvering and timed turns to precisely position his aircraft for landing.

In the summer of 1927, barely a month after Charles Lindbergh landed at Le Bourget after flying the Atlantic, Air Corps Lieutenants Lester Maitland and Albert Hegenberger flew the Fokker trimotor Bird of Paradise from California to Oahu, navigating some 2,400 miles across the Pacific by using (in the words of the flight report) “the most precise and complete equipment for astronomical, dead reckoning, and radio navigation.” Bird of Paradise had left Oakland on June 28, carrying voice radio, a homing receiver, compasses, drift meters, sextants and navigational references. The radio beacons worked only sporadically; updates from passing ships, classic dead reckoning and sun-and-star sights proved more reliable. Radio played one important role: Nearing the islands at 10,000 feet, Maitland and Hegenberger used signals from a beacon on Maui to make final course corrections.

The Dole Air Race fiasco a month later underscored the risk of not having radio. Woolaroc, a big high-wing Travel Air 5000 monoplane flown by Art Goebel and William Davis, won largely by simply surviving. Since their plane was equipped with a radio,Goebel and Davis were able to take bearings from Maui, confirming a hunch that the winds had changed. They survived—but seven other fliers vanished over the unforgiving Pacific, lost in three planes without radios. Radio navigation clearly saved lives. By the end of the year, the Bureau of Standards had equipped an airway between Cleveland and New York with radio beacons for civil trials.

Preparing to tackle blind flight, the Guggenheim Fund turned to the Air Corps, Navy, General Electric, MIT, AT&T and the Bureau of Standards for assistance in establishing a laboratory, as well as acquiring airplanes and experts. All furnished equipment, support and staff. Air Corps chief Maj. Gen. James Fechet authorized the use of Mitchel Field on Long Island and detailed two pilots, including Lieutenant James H. Doolittle, and a mechanic to work on the problem. Then just 31, Jimmy Doolittle was the archetype of the scientific test pilot, possessing both extraordinary piloting skills and an MIT Ph.D. in aeronautical engineering.

The fund spent $26,000 to purchase two small biplanes: a Consolidated NY-2 trainer and a Vought O2U-1 Corsair observation plane, the former for research and the latter for fast transport. Mitchel already had a 125- mile-range radio beacon, and in January 1929, Bureau of Standards technicians installed two others: a short-range “localizer” indicating the landing flight path, and a “marker” designating the airfield’s boundary. By month’s end, the Full Flight Laboratory was ready to begin its work.

Hardly had flight operations begun when, on March 15, Doolittle experienced firsthand the serious threat posed by fog. After a day of meetings he left Buffalo in the Corsair, flying east to Albany and then turning down the Hudson River valley. By the time he reached New York City, fog shrouded the entire East River, making a return to Mitchel impossible. Nearing Elizabeth, N.J., and able to catch only fleeting glimpses of the ground, he crash-landed in an impossibly small clearing, where trees tore off the wings. If Doolittle was not immune from such danger, what chance did an average pilot have?

Some sort of extremely precise, perhaps gyro-stabilized instruments were clearly vital to any solution. Pilots flew primarily by measuring airspeed, altitude, direction and turn rate. In 1921, piloting a de Havilland DH-4 equipped with a turn indicator, Lieutenant John Parker Van Zandt had crossed the treacherous Allegheny Mountains from West Virginia to Washington, completing a 90-minute flight in weather so foul that two other aircraft not so equipped turned back. But a turn indicator could lag by at least several seconds behind what a plane was actually doing, potentially misleading a pilot. Moreover, it only indicated turning motion, not angle of bank—little use if a pilot was fighting vertigo, which was common in fog or clouds.

Doolittle’s baseline flights revealed equally serious deficiencies with altimeters and magnetic compasses. The former lagged badly enough to prevent his accurately knowing the airplane’s height above ground, very dangerous when flying in fog at low altitude. The latter lagged too, particularly during gentle turning, sometimes indicating a false course for many seconds and rarely an exact course unless the pilot held to the same one for several minutes. Finally, no instrument existed that could furnish an artificial horizon and indicate whether a plane was flying nose-up or -down. Perhaps Hunsaker had been right after all, and flight science had reached an insurmountable technology barrier.

The fund had previously awarded study grants in America and Europe to encourage new instrument development. But Doolittle himself proved to be the catalyst in finding experts who could actually do the work. Learning of a new altimeter concept that had been submitted to the Bureau of Standards, Doolittle arranged to meet the designer, Paul Kollsman, and they immediately bonded. Just 29, Kollsman was a German native who had come to America in 1923, briefly working for the Pioneer Instrument Company before leaving in 1928 to found his own firm. The secret to his design was extremely precise and fine gearing far beyond that of conventional altimeters. Tests showed Kollsman’s altimeter was 20 times more precise than others.

But what about indicating course, bank and pitch? Doolittle believed a gyro-stabilized compass superimposed over an artificial horizon could furnish all that data. He turned to the masters of the gyroscope, the Sperrys. Elmer Sperry and his sons Elmer Jr. and Lawrence had demonstrated the world’s first practical autopilot in 1914. Elmer had a special interest in bad-weather flying, having written Lawrence in 1920, “We have absolutely got to solve this problem; if we die in the attempt and could have registered a single notch in advance, it seems to me that it would be well worth while.” Sadly, his words turned out to be all too prescient: Lawrence died just four years later, crashing while crossing the Dover Straits in bad weather.

The elder Sperry recommended separating the artificial horizon from the directional gyrocompass. After convincing Doolittle that two instruments would do what one alone could not, he assigned Elmer Jr. to work with the fund. The younger Sperry brought in company engineer Preston Bassett. They soon created an artificial horizon, using a movable airplane symbol superimposed over a gyroscopically stabilized horizon bar. If the plane banked, the bar remained horizontal while the plane symbol rotated to indicate the bank angle. If the pilot climbed or dived, the horizontal bar descended below the symbol or rose above it. Young Sperry next designed a directional gyrocompass, attaching a compass card to a gyroscopically governed gimbal. The pilot would use a magnetic compass to establish the course, then set the directional gyro, which—unlike the lagging magnetic compass—would immediately show any off-course deviation.

Together with radio navigation, these three instruments promised to make blind flight both practical and safe. Thanks to the artificial horizon, the pilot would know precisely what the plane was doing, without relying on “feel.” Radio navigation enabled precise cross-country flight, and the directional gyrocompass gave the pilot a means of precise navigation. The precision altimeter allowed a pilot to let down with assurance even in the most extreme weather. But as promising as each new device seemed, only when they were evaluated in actual flight, as an integrated navigational and flight safety system, could their true worth be evaluated.

The fund outfitted its NY-2 with all the instruments plus nearly 80 pounds of communications equipment, consisting of radio beacon receivers, small ear “phonettes” permitting the pilot to hear signals, visual signal indicators, two radio transmitters for voice and Morse transmission, a tall radio mast sprouting from behind the cockpit and a trailing antenna that could stream a thin wire some 60 feet behind the plane. The pilot had a “visual course indicator” with rapidly vibrating reeds that showed if the plane was left or right of the equisignal or flying down it. Thus equipped, the NY-2 could fly to the limits of the Mitchel Field beacon—approximately 125 miles—then make its way back safely.

Much of the testing could be accomplished in good weather, since technicians installed a foldable canvas hood to cover the aft cockpit, simulating blind flight. Thus Doolittle could make “blind” flights while Lieutenant Ben Kelsey, a fellow MIT graduate, rode in the front cockpit as safety pilot, ensuring Doolittle didn’t stray into another flier’s path. Over the summer of 1929, Doolittle made literally hundreds of blind-flying approaches. With practice, he found he could also land blind. He and Harry Guggenheim agreed that the next step was to wait for a truly foggy day and then try out the system for real.

On Tuesday, September 24, 1929, dense fog rolled in from Long Island Sound, producing perfect conditions for testing a blowtorch heater that a gravel pit owner had proposed as a way to disperse fog. But as Doolittle, a mechanic and the pit owner watched, the heater failed to do any good. At that point, almost casually, the pilot ordered the NY-2 warmed up. As excitement spread, technicians manned the radio network and localizer beacon. Doolittle’s wife, Josephine, and young Sperry arrived at the field. Harry Guggenheim and other fund trustees also made their way toward Mitchel.

Doolittle strapped himself into the cockpit. Then the trainer accelerated across the wet grass, lifting into the opaque murk and quickly disappearing from view. Doolittle concentrated on radio navigation. He followed a racecourse pattern at 500 feet, following the localizer beam west for five miles before turning south and continuing around to the east, then flying along the localizer for seven miles. As he passed the field, the little biplane remained invisible to those on the ground, its presence obvious only from the engine’s drone. He turned back two miles east of the field, beginning his descent. Ten minutes after takeoff, the NY-2 dropped out of the fog and landed safely.

Later that same morning Guggenheim had Doolittle make a “for the record” flight, this time with the hood, as the fog was lifting; Ben Kelsey rode as safety pilot. Doolittle flew and landed safely, observed by a small crowd. “Actually,” Doolittle recalled years later, “despite previous practice, the final approach and landing were sloppy.”Well, perhaps—but his two short hops that morning were the most technically influential flights since the Wright Flyer left its monorail at Kitty Hawk.

Over the next decade, engineers in Europe and America would refine many other blind flying techniques and tools, particularly in Germany. Six decades later, with a remarkable aviation career behind him, Doolittle would tell historian Carroll V. Glines that his flights at Mitchel Field constituted “my most significant contribution to aviation.”

The great confluence that made possible the jet age’s mass air transportation—the joining of the aeronautical revolution with the electronic revolution—began with the intensive work of the Guggenheim Fund on airways and blind flight. In the interest of air safety, the fund integrated developments from multiple agencies, organizations and companies, linking many different people in a quest to achieve reliable and routine all-weather air transportation. Certainly it was just a beginning: The radar revolution emerging over the next decade expanded and transformed flight safety and aircraft operations in ways the Guggenheims could hardly have imagined. But the Guggenheim Fund, the inventiveness of Bureau of Standards radio engineers, the creative insight of Elmer Sperry and Paul Kollsman, and the skill and courage of Jimmy Doolittle combined to usher in the age of instrument flight—to the benefit of all passengers and aircrews who have since traversed the world’s skyways.


Former U.S. Air Force historian Richard P. Hallion is the author of numerous books about aviation history, including Legacy of Flight: The Guggenheim Contribution to American Aviation, which he recommends for further reading, along with I Could Never Be So Lucky Again, by General James H. “Jimmy” Doolittle with Carroll V. Glines, and Flight Patterns: Trends of Aeronautical Development in the United States, 1918-1919, by Roger E. Bilstein.

Originally published in the January 2012 issue of Aviation History Magazine. To subscribe, click here.