 Since the first airplane flight in 1903, flying in winter has been a problem because of dangerous situations created by ice formations on aircraft. During the 1920s and 30s, when aviation was still in its infancy, the limitations of winter flying were very apparent. One example was the attempt to establish transatlantic routes between the United States and Europe over the North Atlantic, which were considered much too dangerous to fly. During the Second World War, more than 100 C-46 aircraft were lost while flying over the Himalayas between India and China. This route was known as the Humph. Responding to this need, the National Advisory Committee for Aeronautics, NACA, directed that an icing research tunnel be constructed at the Aircraft Engine Research Laboratory, which was the former name of the Lewis Research Center. The icing research tunnel was designed and constructed from 1942 to 1944 for $670,000. The first icing test was run on June 9, 1944. The icing research within NACA first started in the 1920s at Langley Research Center in Virginia. Icing research was also conducted at Ames Research Center in California prior to the research at Lewis Research Center in the 1940s. Soon, NACA turned to NASA and their attention from aeronautics to space. The icing technology developed through the 40s and 50s at NACA NASA formed the basis of what the U.S. aircraft industry used to solve various icing problems. Dr. Joe Shaw, Deputy Chief for Applied Dynamics at the NASA Lewis Research Center, explains the icing research program. The icing research program at Lewis was begun in the early 40s. It was felt that an icing research activity, including the construction of a ground icing test facility or the icing research tunnel, was needed to address the wartime icing problems that the military was having. There was expressed a need for an icing test facility, ground test facility that would accurately and adequately duplicate natural icing conditions. And you need to generate a cloud in that tunnel, an icing cloud that simulates the right amount of liquid water content and droplet size distribution to be typical of those you might find in natural icing, as well as you need to control the temperature of the airflow in the tunnel. So again, you would be able to simulate accurate conditions that you would expect to see in flight. It is not the weight of the ice on the various parts of the aircraft that causes the problem, but the altered aerodynamics that change the performance, stability, and control characteristics of the airplane. The ice forms may be small, but they do have a significant effect on the airplane and its actions. When ice accretes or grows on the surfaces of the airplane, wings, tails, fuselage, whatever, the result is a change or degradation in the performance of the airplane as well as a degradation in the stability and control of the airplane. If the ice shapes or ice accretions, as we called them, become severe enough, the stability and control of the aircraft can be completely lost and the aircraft cannot be controlled. The IRT is similar to other subsonic wind tunnels in that a wing or other aircraft component when placed in the test section may be subjected to various air speeds, the airflow being created by a motor-driven fan. The IRT has several unique features to simulate icing conditions, a heat exchanger and a refrigeration plant to achieve the desired temperature and a unique spray system to generate a cloud of microscopic droplets of unfrozen water. This makes the IRT capable of duplicating the icing conditions that an aircraft might encounter. All aircraft, whatever their size, can be susceptible to icing. General aviation aircraft can be more susceptible to icing because they have smaller wing sections. Smaller wing sections tend to accrete ice at a faster rate than larger wing sections. Helicopters also have icing problems because helicopter rotors are small and are spinning at high speeds. They therefore tend to build up ice quickly and it does not take long before you get some severe icing conditions on the helicopter rotor. Now Dr. Shaw will tell us about anti-icing. Anti-icing simply means that you are using some technique which prevents the build up of ice. That is when the water droplets hit the surface of the airplane, of course they're in the liquid state and they remain in the liquid state. De-icing means that you allow the ice to grow, that is you form an ice accretion or an ice growth and then you get rid of or de-ice that ice accretion before. It reaches a size that can significantly impact the aerodynamic performance and stability and control performance of that airplane. In the 1970s the aircraft industry realized that there was a need for additional icing technology and NASA re-instituted an icing research program to meet the new icing technology needs which occur as a result of the ever-changing aircraft design problems. From basically 1950 through 1957 when the NAC or NASA program was concluded, a tremendous icing technology database was developed and the technology being used today on today's aircraft came from largely from that program. Examples of that would be the hot gas anti-icing system that is used by all transports today for ice protection. Today about 90% of the smaller general aviation aircraft certified for flight into forecast icing conditions are using the pneumatic boot system for de-icing. It was developed in the 1930s by the BF Goodrich Company. The pneumatic boot is a rubber boot placed over the leading edge of the wing or tail. When the ice accretes or grows, a pneumatic air source is used to inflate the boot which destroys the ice aircraft surface bond to clean the surface of the craft. The NASA Lewis icing research tunnel was named an international historic mechanical engineering landmark in 1987. It is the oldest and largest refrigerated icing wind tunnel in the world. Two major achievements of this installation are the unique heat exchanger and the spray system that simulates a natural icing cloud of tiny droplets. Icing is no longer a major problem for many of today's aircraft because of the ice protection systems technology largely developed in the NASA Lewis Research Center icing research tunnel. As new aircraft are developed and operating practices are changed, the recently modernized IRT will continue to lead the way in solving the icing problems of the future.