how far is that aeroplane ?

[funkymoped]

in a costal region, how far away would a jet liner be at first sighting ? i know its as simple as "triangulation". time, height and speed,but was wondering what the maximum distance would be if the view was as far as the horizon, on a crisp winters morning with zero cloud cover.

working with averages of 550mph at 6.5miles altitude.

anyone ?

[JudgeJ]

An easy way to do this without getting too involved in maths is to measure the period that elapses from the time you first sight the aircraft until it is overhead. Jet airliners travelling at full speed cover about 8 miles per minute (about a mile every 8 seconds).

[mibn2cweus]

Ignoring visibility, refraction or terrestrial features (mountains, valleys) at 6.5 miles the horizon would be about 250 miles away. Typically visibility rare exceeds 100 miles so Judge J probably has the right approach for calculating the apparent distance of an observed commercial jetliner.

[funkymoped]

mibn.

i have worked the method JudgeJ mentioned and the best i could manage was about 35 miles. tried that method during the day and night, winter and summer.

was interested to learn how you calculated 250miles at 6.5 miles altitude. if the maths are not too difficult, i wouldnt mind the method for that. 100 miles is still more than i expected.

[mibn2cweus]

Pythagoras said, �Sum of squared sides of right triangle = hypotenuse squared�.

The Earth�s radius (Er ~4000 miles) plus an elevation (H) is the hypotenuse of a right triangle formed by Er and D (the distance to the horizon).

Alternatively Er ^2 + D ^2 = (Er+H) ^2

Example: radius of Earth squared = 4,000^2 = 16,000,000
(radius plus altitude of jet) squared = 4,006.5^2 = 16,052,042
Square root of difference = distance = sqrt(52,042) =
228 miles to horizon

calculator here

[funkymoped]

Erm, thanks for that Mibn !

i thought i was ok at maths, but you just proved me wrong... lol