Page 16 - Volume 18 Number 2

Figure 3Tilt Management+10° - EW10nm 20nm 30nm12,000 below, but the hazardous top may be only 8,000 or 9,000 below. And the storm may possibly be growing at 4,000, 5,000 or more fpm. You’re four to five minutes away from it. In that time, it could grow right on up through your altitude and--”wham”, scrapes, cuts, broken bones and very irate passengers. So, bottom line, to be certain it’s safe, 30 nm ahead with NAP selected is as close as you should get. A little conservative, yes, but better than a turbulence encounter.That takes care of TIP and NAP. Now the final one of the three TILT selections, TUT, in which the center of the beam is angled up 10o (Tilt Up Ten), as illustrated in figure 3.Finding it is easy. Increase TILT one-half your beam’s diameter from TIP and that’s TUT.What’s your beam’s diameter? Depends on antenna size. It rangesfrom10ofora10-inchantennadown to 3o with a 30-inch one.To simplify it for you, the chart below is for setting TILT to TUT by increasing TILT one-half of a beam diameter.Antenna Diameter (Inches) 10” 12” 15” 18” 24” 28” 30”Tilt Increase from TIP to TUT 5o 6o 6.2o 7.2o 8o 8.25o 8.5oWhy TUT? Because it’s a quick, simple way to estimate the height of a thunderstorm. It just requires another form of the “Rule of 60”.This time — 100 X degrees X nm = height. So, with TUT selected, if an echo is detected at 30 nm its height is running at least 30,000 feet above your current altitude — 100 X 10o X 30 nm = 30,000. At 20 nm, at least 20,000 feet. At 10 nm,14 • TWIN & TURBINEFEBRUARY 2014