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<br />Pyrotechnic devices were used for airborne seeding and tested extensively. <br />Two main types were utilized. O'ne was a droppable type containing a charge <br />of 25g of AgI and burning for 20-40 sec. while falling. The calibration for <br />this flare is given in Figure 4. The other pyrotechnic device that was used <br />consists of an aircraft-attached flare which contains an AgI charge of 30g <br />and burns for a nominal period of six minutes. The calibration curve for <br />this device is presented in Figure 5. Both types of unit were the subject of <br />tracer tests, which are reported on in the diffusion section (3. 2). <br /> <br />. <br /> <br />A non-pressurized ground generator system based on the Skyfire Airborne <br />generator was dfyveloped for remote operation. The generator system was <br />developed to successfully ignite or extinguish upon the operation of a single <br />electrical switc"h. The system burns no propane and utilizes a gravity feed <br />system. <br /> <br />~ field technique for g~~erator calibr_aIiQILIi\T9-~9~yel<?Eed. The procedure <br />is depicted schematically in Figure 6. The technique consists of placing a <br />vertical wind tunnel over the generator burner, so that the entire output of <br />the generator is mi.xed with the airflow through the tunnel. An air sample <br />is taken out of the top of the tunnel with a syringe, diluted, and injected into <br />a 100 liter mylar bag. The sample air input into an NCAR nucleus counter <br />is taken from this mylar bag. <br /> <br />The technique requires some skill and practice to obtain reproducible re- <br />sults. First of all, a nuclei counter operated in the vicinity of a high output <br />generator is subject to saturation by exceedingly high nuclei concentrations <br />unless much care is taken. Secondly, very small samples (lcc) and very <br />high dilutions (105) are involved, so that experimental error can easily be <br />in the orders of magnitude range. <br /> <br />~ <br /> <br />! <br /> <br />The air in the mylar bag must be nuclei free and it was found this could best <br />be accomplished by several evacuations and fillings with air filtered through <br />a glass fibre filter. One alteration from the initial tests was the method <br />used to take the sample. In the initial tests, a 100cc syringe was used and <br />a 100cc sample was taken from the top of the wind tunnel. Ninety cc of the <br />sample was then expelled, 90 cc of filtered air drawn into the syringe, 90 <br />cc of this mixture expelled, and the remaining 10 cc injected into the mylar <br />bag -- - giving a net sample of 1 cc of wind tunnel air. More consistently <br />reproducible results were found to be obtained by using smal1er syringes <br />and taking land 1 cc samples and injecting them directly into the mylar bag <br />without a dilution step. The flow through the wind tunnel was checked peri- <br />odically with a precision anemometer. The fan blades were changed on one <br />occasion and a slightly lower flow factor was used subsequently Cfable 1). <br /> <br />The results of a series of tests are listed in Table 2. These generator out- <br />puts are plotted in Figure 7. The values span approximately an order of <br /> <br />~ <br /> <br />10 <br />