Chapter 4 - Propellers to Jets: The Impetus of World War II

"Hot Jobs for a Cold Tunnel"


[45] So read a 1977 headline. The text that followed described the 1944 Lewis Icing Research Tunnel, the world's largest. Passengers on today's commercial airliners hear nothing of the terror of icing, which 30 years ago could render a plane uncontrollable in a few minutes, as heavy layers of ice collected on wings and control [46] surfaces. During World War II, over 100 cargo planes enroute over the Hump from India to China were lost, most because of severe icing. Aircraft icing is not as critical today because these problems are solved first on the ground in the Lewis icing research tunnel.

Externally, the Lewis icing research tunnel has the lines of a conventional subsonic wind tunnel. Inside, a 4160-horsepower electric motor generates 300-mph air in a 6 x 9-foot test section. There the similarity ends. The first departure from conventionality is the 2100-ton refrigeration system that can cool the air down to - 40° F. However, cold air by itself cannot produce icing. There must be water vapor and droplets in the air to condense and freeze on the aircraft surfaces. The appropriate atmospheric conditions are created by a battery of atomizers upstream of the test section. The aircraft in the test section is thus forced to fly through a cold, supersaturated cloud of air resulting in rapid ice buildup on the craft. As the deadly layers grow, heating elements in the crucial aircraft components go into action, and the detached ice shards fly off downstream. Cameras record the whole sequence to show engineers where to make improvements in the de-icing system.

The icing wind tunnel shell is insulated by a 3-inch layer of fiberglass to help keep the tunnel cold. In a strange turnabout, some parts of the tunnel must be heated to keep ice from accumulating and thus spoiling the experiment. The observation windows, for example, are electrically de-iced, like the rear windows on some automobiles. Downstream of the test section, internally circulated steam de-ices turning vanes that would otherwise become clogged with ice and block airflow. Through the judicious application of heat and cold, the tunnel works, and modern air travelers need not worry about aircraft icing.


Lewis icing research

Plan of the Lewis icing research tunnel.

Lewis Icing tunnel

[47] Ice sheets adhere to the propeller and nose of a fighter in the Lewis Icing tunnel.