Two compressed air systems for glaciating supercooled clouds were studied in the laboratory. The first system used the sudden expansion of compressed air. The second system used a continuous flow of air through nozzles of various designs, of which the supersonic nozzle was found to be the most efficient. The data were obtained at an ambient temperature of -4C, but data for other temperatures and pressures were obtained and are presented in the text.

Series of controlled and free environment tests were conducted to determine the technical feasibility of using the cooling resulting from the adiabatic expansion of compressed air to initiate ice crystal production in a supercooled fog. It was found that approximately 1000 cc of air, when compressed to 60 psig and released through a supersonic nozzle, will produce the same number of ice crystals as does the evaporation of 1 cc of liquid propane. An analysis was made of the Air Force locations in the U.S. and Europe where supercooled fog can be expected to most seriously restrict runway operations. The bases where such restrictions can be expected to be most acute are Elmendorf AFB Fairchild AFB, Hahn AB, Zweibrucken AB, and K.I. Sawyer AFB. The AWS is already conducting operational supercooled fog dispersal programs using liquid propane at the first three of these bases. Various methods of producing compressed air are described and the operating cost advantage of using this technique in lieu of liquid propane are discussed. It is estimated that a compressed air system would consume approximately 1/17 as much fuel as would a system using liquid propane spray. In an average year, the estimated savings at Elmendorf AFB is projected to be over 34,000 gallons (129,000 liters) costing over $16,000. (Author).