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Ron's Web Site
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Date: 5-13-2008
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Number of Hours: 2.50
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Manual Reference:
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Brief Description: AOA Heat 1
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I wanted to provide a means of heating the AFS angle-of-attack AOA ports, which will be mounted on the wing. I came up with a way to do it using disc-type 25 vdc PTC thermistors. I wanted to make a test unit to figure out the current draw and efficacy of the system. The discs are sandwiched between an .025 aluminum disc and the wing, maintained in place with a phenolic insulator and nylon screws. The aluminum disc is electrically hot and the wing is grounded. I made the test using only 6 of the 8 discs which will ultimately be installed. At room temperature, the 6 discs drew 0.56 amps, at 27 deg they drew 1.504 amps max off of a 12 volt battery (the current draw rapidly goes down as the discs warm up). Using an infrared thermometer and the panel painted black to aid in its use, the temperature before applying power was uniformly 27 deg in the ice box. With the test panel in contact with the ice, the center panel temperature rose to 46 deg with the periphery temperature rising to 37 deg. On the aircraft, all the unit has to do is keep the central AOA ports free of ice, so I believe the unit will be adequate, particularly with an additional 2 more discs on each port. Doing the math on the current draw indicates a peak draw of 2 x 8/6 x1.504 amps = 4.01 amps for both the upper and lower wing units, so a 5 or 7.5 amp circuit should be adequate. I needed the current draw information for making up the fuse box labels.
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Disassembled test unit.
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Top and bottom test unit.
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Refrigerator test.
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