Beam
Yes, 1.5 up and 1.5 down from the central position of -2 degrees.
Tilt control is the most important factor for proper manual operationof the radar. When outsideair temperature falls below -40 °C, thunderstorm tops are formed entirely of ice crystalsand reflect very little radar energy. Significant down tiltis required to ensure that the radar beam is picking up the more reflective part of the storm that is at lower altitudes. Over land ground clutter can be used to determine proper tilt within 160NM of the aircraft. Within 160 NM, tilting the radar so that some groundclutter appears in the outer most range scale keeps the antenna pointedtowards the reflective portion of the thunderstorms.
A 28-inch flat-plate antenna produces a 3.5°-wide beam. At ranges less than 80 NM, this produces a fairly narrow and well-focused beam. Beyond 80 NM, the beam diameter increases until at 300 NM it is equal to 105,000 feet. To put this into perspective, at this distance, it would take a storm cell over 22 NM tall and wide to fill the beam.
Because the beam remains fairly focused within 80 NM of the aircraft, it is recommended that weather evaluation be done only when the weather is within 80 NM of the aircraft. Beyond 80 NM, the radar should be used primarily for strategic planning and weather avoidance.
The following formula can be used to calculate the approximate beam width at any range:
Beam width (in feet) = (Distance in NM x 3.5)+ “00”
20NM: 7,000’
40NM:14,000’
80NM: 28,000’
100NM: 35,000
160NM: 56,000’
Last edited by stratofactor; 27th Nov 2013 at 16:54.
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