Thread: Discussion XC#10 in a series, Giant Icon? View Single Post
Jun 08, 2010, 11:52 PM
Master of the Wind
United States, CA, San Jose
Joined Sep 2008
1,289 Posts
Here is a sketch of the geometry I used to calculate the visibility angle for a given chord. The equation for the angular portion of a cylinder taken up by the chord width as seen from the ground is Angle=2xArctan(0.5xchord/altitude).

Also two graphs of the visible angle vs the altitude using 3 different chords, 12" 13" and 14". Note on the full scale the slope of the lines gets flatter as the altitude increases. If you look at the expanded scale, this means that for a given angle the larger chord is visible farther away not just in a linear fashion, but more. For example, at an angle of .014 degress the altitude difference between the 12 and 14" chord is 200m, while at .012 degrees, the difference is almost 250m. On a super clear day this means the wider chord has an advantage flying in the risky but worthwhile range of 1250-1750m. On a hazy day neither plane is likely to be comfortably visible above 1250 and the advantage may be less. For the purposes of this analysis, it is probably reasonable to assume a linear relationship between chord and max visible altitude.