SP-4302 Adventures in Research: A History of Ames Research Center 1940-1965

 

Part I : INITIATIONS : 1936-1945

 

9

The Ice Research Story

 

[69] ANY account of important research conducted at the NACA Ames Aeronautical Laboratory must certainly start with the first research program undertaken at the Laboratory. This program had for its objective the development of means for protecting airplanes from the many hazards of having ice form on their surfaces while flying in moisture-laden clouds. Such hazards were many: for example, ice formation on wings would cause loss of lift; on control surfaces, loss of control; on airspeed heads, loss of airspeed indications; on radio antennas, loss of communications; on wind-shields, loss of vision; and, in engine intakes and on propellers, loss of power.

By 1940, the airplane had reached a state of development where its users were unwilling to consider it merely a fair-weather device. Flight reliability was becoming increasingly important to commercial users and even more so to the military. As the war got under way, it was imperative that our B-17 and B-24 bombers not be held up by weather; in fact, the safety of clouds might actually be sought by such aircraft. Later in the war, our Curtiss C-46 cargo planes were flying the Himalayan hump with vital materiel that had to get through to its destination despite weather conditions. By 1940 the all-weather flying reliability of airplanes had been much improved by the development of advanced radio aids and blind-flying equipment. But these were to no avail if an aircraft was forced down by ice. It was essential that an ice-protection system be developed. The urgency of developing such a system was endorsed by the military services, the CAA, the airlines, the aircraft companies, and also by NACA. Some ice protection had in the past been obtained by the use of inflatable rubber shoes mounted externally on the leading edges of the wings and tail surfaces, but this device would not Work for high-speed airplanes and its drag was very high.

Actually, NACA had been working on the problem of heat deicing at Langley since 1930 TR 403 by Theodorsen and Clay on the subject of ice prevention on aircraft by means of engine exhaust heat appeared in 1931. Following the publication of that report, however, the work had progressed for a while at rather low priority. Clay had left NACA, and the task had...

 


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Ice formation on radio antenna and airspeed mast of C-46 airplane.

Ice formation on radio antenna and airspeed mast of C-46 airplane.

 

....been taken over by Lewis A. Rodert. Soon Alun R. Jones joined the effort, and the two of them arranged to make some flight tests in which a test wing panel was mounted on a Martin XPM bomber. The airplane was flown by Langley test pilots William A. McAvoy and Lawrence A. Clousing.

The tests on the XPM bomber were fairly rudimentary, but the results convinced NACA of the desirability of buying a small two-engined Lockheed 12 transport airplane for ice-research work. The wings of the Lockheed 12, it was planned, would be rebuilt to incorporate an ice-protection system utilizing the engine exhaust as the means of deicing. The project was supported by the Army Air Corps and by Lockheed. Kelly Johnson and his staff at Lockheed designed, built, and installed the new wings. Earlier NACA had decided that the ice-research project, as it was called, should be transferred to the new Ames Aeronautical Laboratory. Rodert, McAvoy, and Clousing came out to Ames in the fall of 1940 and, while waiting for the Lockheed 12 to he modified, carried out some minor icing flight-research tests with a North American O-47, which was the first airplane assigned to Ames for research purposes. McAvoy made the first flight test with the O-47 on November 16, 1940. But early in 1941 the Lockheed 12 was ready and, with McAvoy and Clousing at the controls, the initial flight was made on....

 


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Nov. 16, 1940, test pilot W. H. McAvoy returning from an early flight of first test airplane at Ames, a North American 0-47.

Nov. 16, 1940, test pilot W. H. McAvoy returning from an early flight of first test airplane at Ames, a North American 0-47.

 


Lockheed 12A ice-research airplane.

Lockheed 12A ice-research airplane.

 

....January 22. From then on, the deicing flight program proceeded at a good pace.

To protect the wings of the Lockheed 12 against icing, the exhaust pipes of the engines had been run out through the leading edges and exhausted at the wingtips. Fresh air taken through openings in the leading edge circulated around the exhaust pipe, then through a double-skin structure ahead of the spar. Passing through openings in the spar webs, the warm air entered the interior of the wings and was finally exhausted to the atmosphere through louvers located far back on the upper surface.

The problem was to provide enough heat for deicing (ice protection) without reducing the wing strength by overheating. The evidence as to how much heat was required was extremely meager but, based on data obtained at Langley, Lew Rodert felt that, if the wing skin forward of the front spar....

 


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Diagram of the system using exhaust-heated air to prevent icing on the Lockheed 12A wings.

Diagram of the system using exhaust-heated air to prevent icing on the Lockheed 12A wings.

 

....could be maintained at a temperature 100° F above the ambient-air temperature under clear-air conditions, satisfactory ice protection would probably be provided under icing conditions. Although the Lockheed 12 was incompletely protected against icing and despite their limited experience with blind flying, McAvoy and Clousing, together with Lew Rodert and sometimes Ray Braig, flew the little transport plane into some of the worst weather they could find on the West Coast. Ice would sometimes form on the windows so thickly that they could not see whether the wings were ice-free or not, the radio would cut out due to icing, and ice would sometimes form on the tail surfaces which were only partially protected by an inflatable rubber shoe.

 


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Curtiss C-46 ice-research airplane.

Curtiss C-46 ice-research airplane.

 

In the first report written on this program (mentioned in ch. 6), the authors, Rodert, McAvoy, and Clousing, commented, "The severe icing encountered was accompanied by violent turbulence, snow-and-rain static which stopped radio communication, and occasional dangerous electrical discharges...." Describing one flight, they said:

 

The icing rate and violence of the turbulence increased steadily during the flight. About 5 minutes after severe icing conditions were encountered, the tests were terminated because of dangerous flight conditions. The airplane was struck by an electrical charge [lightning] which melted the trailing edge of one propeller blade and the edges of the airplane structure at several points.

 

Such experiences were all in the day's work for the intrepid crew of the Lockheed 12. Their reward was their finding that the use of exhaust heat for protecting the wings of an airplane such as the Lockheed 12 did, indeed, appear to be feasible. This conclusion did not come just from the fact that they and the airplane had survived the repeated ordeal of flying under severe icing conditions but also from a mass of quantitative data obtained from special instruments with which the airplane was equipped.

Although work on improvements in the Lockheed 12 deicing system continued for several years, the year 1941 had not ended before the Army Air Corps had asked NACA to develop a deicing system for the B-24 and the B-17 bombers. While design information was still pitifully scarce, the Ames Flight Engineering Section launched into the project with a spirit and resolve that were immeasurably bolstered by the catastrophe that had recently occurred at Pearl Harbor. The staff of the Section was considerably increased and was joined by Alun Jones early in 1942.

The same basic deicing principle as developed for the Lockheed 12 would work, it was thought, on the B-24 and the B-17. This process would require a hot-air source and a double-walled leading edge, but the airflow system would have to be adapted to the particular wing structures of the two airplanes. Also, protection would have to be extended to the tail surfaces, Windshields, airspeed head, and other points vulnerable to icing. But it would not be feasible to run the exhaust pipe through the leading-edge structure of a military airplane. .Suppose the exhaust pipe were ruptured by a bullet? The hot exhaust gas would pour into the wing and probably [74] destroy the airplane. What was needed, it was thought, was a heat exchanger that would transfer the heat of the exhaust pipe to a flow of fresh air that would be ducted into the leading edge. Then the engine exhaust would not enter the wing at all but would be disposed of in pretty much the normal fashion.

Rodert visited the airplane-accessories companies and encouraged a number of them to develop heat exchangers for this purpose. Further, he enlisted the aid of Prof. L. M. K. Boelter and his mechanical engineering staff at the University of California by arranging for UC to be given a NACA contract to study various aspects of the heat-exchange process. A special laboratory facility was set up at Ames to evaluate the performance of heat exchangers, and the heat exchangers were also checked out in flight on the O-47 airplane.

By the end of 1942, the combined efforts of Ames, the industry, and the military had produced prototype installations of heat deicing systems in both the B-24 and the B-17. Reports describing the systems were later written by Rodert and Jones. The Navy had also made an installation on the Consolidated PBY flying boat along the lines of the Lockheed 12 installation. The Navy noted that the deicing installation so decreased the noise and exhaust flame that the airplane could fly over a carrier at night, at part throttle, at an altitude of as low as 200 feet without being detected.

Rodert and the other men involved in the deicing project felt that a special base should be established in the north-central part of the United States for the purpose of evaluating prototype deicing installations such as those incorporated in the B-24 and the B-17. This idea was approved, and such a base was set up and first used in the winter of 1942-1943. It was located at Minneapolis, near the headquarters of Northwest Airlines. At this time the effort to develop deicing systems for aircraft involved many people and agencies. In the first place, NACA had established a technical subcommittee to provide a general surveillance and coordination of the work on deicing. This subcommittee, headed by Karl Larsen of Northwest Airlines, had a membership derived from industry and the airlines, as well as the military, the Civil Aeronautics Administration, and of course NACA. Next, the new Ice Research Base at Minneapolis was staffed by men from NACA and the Air Corps, but it also received much help from Northwest Airlines and United Air Lines.

In addition to the assistance just mentioned, the U.S. Weather Bureau assigned William Lewis to work directly with the Ames group on important meteorological phases of the icing problem. Similarly, the British Royal Aircraft Establishment assigned a very able research man, J. K. Hardy, to work with the Ames group. The RAE apparently felt that it would be foolish for Britain to attempt to duplicate the work done by NACA in the icing matter and that it would make more sense to provide the services of a good man [75] who would not only contribute to the project but also, quite naturally, acquire know-how that would be useful to Britain. The British, of course, received all of NACA's test reports on deicing work. This arrangement proved very profitable to NACA as Hardy's efforts were exceptionally productive.

The prototype deicing systems in the B-24 and the B-17 passed their winter evaluation tests in good fashion and served as models for the design of production systems for these aircraft types. The work on these installations had been carried out at high pressure. The military services had impressed Dr. Lewis with the importance of the work, and Dr. Lewis had passed the word to DeFrance. Smitty in turn followed the program closely and spurred the icing research effort using tactics which were scarcely subtle. In one case, when it appeared that a test airplane might not be ready to fly before the winter icing season was over, Smitty threatened to wipe out the Flight Engineering Section if that eventuality developed. The Section staff thereupon began a 24-hour-a-day operation and the airplane flew on time.

The Ames staff recognized all too well that the design of their airplane deicing systems had so far been on a very empirical basis. Before any really refined systems could be built, a large amount of rather basic design information would have to be acquired by theoretical and experimental means. The acquisition of this information would take time; it was fortunate that sufficient information had been available to serve the immediate needs of the military. Now, however, the problem must be approached from a more scientific basis. Toward this end, a Curtiss C-46 cargo airplane was acquired and modified to incorporate the most complete ice-protection system yet provided for any airplane. Moreover, the airplane was thoroughly instrumented in itself and carried special newly developed instruments for obtaining basic information on the character of the icing cloud. Bill Lewis of the Weather Bureau made major contributions in this phase of the program.

The C-46, which was considered a flying icing-research laboratory, was operated from the Ice Research Base in Minneapolis and flew far and wide searching for icing conditions. Airport habitues were often astonished to see a C-46 airplane come boring in through the murk when all other planes were grounded. The C-46 was flown by a number of pilots but most often, perhaps, by Captain C. M. Christensen, Senior Pilot of United Air Lines. Chris was one of those calm, competent, unexcitable chaps whose appearance and obvious know-how inspire confidence. His contributions to the project were great.

It was the prime objective of Bill Lewis and certain other icing-project people to amass enough statistical data on icing clouds to serve as a reliable basis for future designs of ice-protection systems. Statistics on liquid-water content, temperature, and drop size were of particular interest, as was the interrelationship between these icing factors. Liquid-water content and temperature were perhaps the most important factors, but drop size was also a [76] significant design parameter. It was known that little drops approaching the wing would be deflected by the local airflow around the wing and fly harmlessly by. Larger drops, on the other hand, would be too massive to be deflected by the local airflow and would thus smash into, and freeze on, the leading edge of the wing. And if the drops were prevented from freezing on the forepart of a heated wing, the rainwater might run back and freeze on the cooler afterpart of the wing.

Meteorological data, however, were not the only requirement for the rational design of an airplane deicing system. More information was needed on the aerothermodynamic processes of transferring heat from the wing surface to the surrounding airstream. The problem was complicated by the free-water content of the surrounding air and also by the question of whether the boundary layer on the wing was laminar or turbulent. The boundary layer acted like an insulator the effectiveness of which increased with thickness hut, for the same thickness, a laminar boundary layer was a much more effective insulator than a turbulent boundary layer.

A number of theoretical studies of heat transfer from a wing to the surrounding airstream had been made over the preceding 10 years and, in 1942, Harvey Allen and Bonne Look of Ames had made another study which was published in TR 764. All of these studies, as applying to the deicing problem, were somewhat idealized and thus their use for deicing designs was limited. However, in the design of the deicing system for the C-46, the Ames group exerted a great deal of effort to develop rational analytical methods for solving the heat-transfer problem. A major contributor in this effort was Hardy, the RAE representative on the icing project. Hardy's report (ref. A-2) is a good example of his work. Another important contributor in this area was Carr Neel of the Ames staff. His report (ref. A-3), the first of a long series on the C-46 project, covers the analytical phases of the design. Authors of the C-46 report series included Alun Jones, James Selna, Richard Jackson, Carr Neel, and others. At the end, a summary report (ref A-4) was written by Alun Jones, who, at that time had replaced Rodert a head of the Flight Engineering Section.

Lewis Rodert resigned in .September 1945. While many people had made contributions to the icing-research project, Rodert had been the driving, coordinating sparkplug. He had lived with the project. It became pat of him. Throughout his waking hours, he appeared to be thinking of little else. The methods he used to achieve his ends were frequently blunt, an sometimes irritated his fellow workers. But they were effective, and the results of his early work were vastly appreciated by both the military and the commercial operators of aircraft.

The icing project, first investigation to be undertaken at Ames, was not at all representative of NACA research projects. Seldom before had NACA research work been carried so far into the hardware stage or so far in achie-

 


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Carr Neel

Carr Neel (above) and Lewis A. Rodert (below).

Lewis A. Rodert

 

-ing a complete and satisfying solution to a major operational problem. The project was unique and NACA management could only be pleased that it had been so successful. Lew Rodert deserved much credit for his important share in this success; his good work was recognized when, at a White House ceremony in 1947, President Truman presented him with the Collier Trophy, regarded as the Nation's highest aeronautical award, "for his pioneering research and guidance in the development of a practical application of a thermal ice prevention system for aircraft."

It should also be mentioned that, in 1943, the Institute of the Aeronautical Sciences had given Ames pilot William H. McAvoy the Octave Chanute Award for "continuous service in the flight testing of experimental planes under hazardous conditions imposed by aeronautical research." Certainly an important part of the motivation for this award came from the hazardous deicing flights of the Lockheed 12 on which McAvoy had served as pilot.


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