One night it "rained ducks" over Thief River, Minnesota. It happened during the year's first sleet storm. All night long the seasonal flight could be heard honking overhead. Then, about 4 a.m., the ducks began dropping in. Thousands of them crashed into the streets and buildings. Ice had coated their wings and forced them down.

Pondering this difficult aeronautical problem, Dr. William C. Geer of Ithaca, New York, experimented with ice adhering to a base of rubber. When the rubber base was stretched, the ice did not stick. With the cooperation of the B.F. Goodrich Company and the able assistance of a young engineer named Russell S. Colley who designed a refrigerated wind tunnel (one of the largest in the United States) in which simulated tests on model airplane wings proved that a small accumulation of ice on the leading edge of wings changed their profile, acted as a spoiler, and resulted in a loss of lift.

A possible solution suggested that a change of base adhesion, combined with a changing shape, would permit the airstream to get under the ice, dislodge it, and in effect serve as a deicer. This brought about the invention of the deicing boot, which consisted of long rubber strips attached to the wing's leading edge. Tubes inside the boot could be inflated and deflated by air pressure in regular pulsation. This flexing action (like bending a rubber tray with ice cubes in it) would crack the ice, which in turn would blow away in the windstream.

The first test of the new device was conducted in a Douglas M-2 Mailplane flown by veteran airmail pilot Wesley L. Smith assisted by Russ Colley sitting on a soap box in the forward mail compartment, both men wearing parachutes. When they found a freezing zone and picked up ice, Colley, working furiously, operated a bicycle hand pump with a two-way valve to alternate the inflation of the three tubes running the length of the boots on each wing. Bracing wires began to sag under the weight of the ice and set up dangerous vibration. The metal propeller picked up ice and threw it off unevenly, making matters rough on the powerful engine. But the pulsating tubes worked successfully, and the ice particles slithered off.

Engineer Russell L. Colley (left) and airmail pilot Wesley L. Smith standing beside their Douglas M-2 after their successful tests conducted over Cleveland municipal airport.

The next step resulted in mechanically operated inflatable tubes. Both men continued to research deicing. Colley developed the rivnut (part rivet and part nut) to fasten the fairing strip to each wing-tip edge of the deicer. His system allowed a single worker to perform a task that had previously required two workers. Geer continued his research, especially in the area of identifying materials which would prevent ice adhesion all together.

An Eastern Airlines DC-3 with wing deicers installed. The black panels were installed along the entire leading edge of the wings.

When biplanes gave way to monoplanes, wires were no longer a problem. And as fabric-covered wings gave way to metal, new deicer boot attachments were devised. On larger transport planes electrically heated surfaces prevented ice accumulation just as effectively.

A review of various methods to prevent ice formation and adhesion to aircraft surfaces is given. It was concluded that the adhesion of ice to a surface may be reduced somewhat by the application of certain waxes and varnishes. In the experiments described, the varnishes containing calcium stearate and calcium oleate gave the best results. In wind tunnel tests, the adhesion was further reduced by the application of these waxes and varnishes to a thin, heat insulating layer of rubber. The adhesion of ice is greatly reduced when the surface consists of a vehicle which carries an oil in sufficient quantity so that the surface of the vehicle is self lubricating. Ice may be removed from wings, struts, wires and other parts of an airplane during flight by the inflation of properly constructed pneumatic rubber members, providing that these members have been previously treated with a suitable low adhesion oil.