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David Winters wrote: "Anyway, as I recall, the equation for line of sight horizon is 1.144 * sqr rt (height of eye in feet) = distance to the horizon in nautical miles. (This assumes the horizon is at sea-level...which, of course, it ain't, as a rule.) For radar freqs, substitute a multiplicand of 1.23. How do we get such different numbers?" I know this isn't a big deal to most of the list members, but since I don't do much flying these days, this is one of the ways I can contribute to the list. Deriving the horizon equation is actually pretty simple. Just draw a circle to represent the Earth, then a triangle with one vertex at the center of the Earth, another at your airplane, and another that represents your horizon. Then, just use the Pythagorean Theorem. After all of the simplification is done, the equation works out to: dist = sqrt[height(2*Radius_Earth + height)] Since your height is pretty small compared to that of the Earth, this equation usually gets approximated as: Dist = sqrt[2*height*Radius_Earth] Doesn't matter what units you use, as long as they're consistent. Any other forumulas you find assume a certain unit that you'll be using for height and distance, put in the Earth's radius, and add a conversion factor. For reference, the Earth's radius is somewhere between 3963.2 miles (20,925,639.8 ft) or 3949.9 miles (20,855,479 ft), depending on if you measure it at the equator or at the poles, or somewhere in between. For line of sight, remember that the cell phone tower (or whatever else you're looking at) sticks up above the horizon. So to calculate the maximum line of sight distance, calculate the horizon for you, and the tower, and then add the two together. As far as radio frequencies, I don't know the exact reason why, but at those wavelengths electromagnetic radiation follows the curve of the Earth a little bit. The rule of thumb to calculate line of sight is to use the equations above, assuming everything travels in straight lines, but use 4/3 of the Earth's radius, instead of the actual radius. ============================================================================== To leave this forum go to: http://ercoupers.com/lists.htm
