**< version française >**

The
satisfaction if determining the altitude of a kite is as great as the
challenge that it represents. Calculating height is not a simple
operation without a theodolite or an electronic rangefinder, but it can
be done.

Referring to the right-angled triangle

Having read the length of the hypotenuse

As will be seen from the diagram, establishing the length of the hypotenuse by measuring the flying line tends to be unsatisfactory because of the catenary in the line.

Assuming that such sophisticated - and expensive - a piece of equipment as a rangefinder is not available, establishing the length of the hypotenuse becomes more difficult, more entertaining, and infinitely more satisfying.

Referring to the main figure

Therefore, in triangle

With the first of the above methods, however, the height of the rangefinder from the ground should be added to the final total: and with the second method, twice the height of the clinometer must be added, that is once for each reading. For maximum accuracy with such a simple measuring system, a second observation should be made simultaneously by a helper; the mean of the two results giving a tolerably accurate result.

Obviously any preferred unit of measurement, such as yards, may be substituted for meters in either system.

*below, a number of enthusiasts use commercial rangefinders to establish the distance between themselves and their kite***ABC***, while others measure the flying line as it is taken off the reel***BA***. This is done in order to establish the length of the hypotenuse***BDA***of the right-angled triangle***BA***. Assuming***ABC****to be horizontal, the angle***BC**is measured (52°) and its logarithmic since (0.7880) is established.***ABC**Having read the length of the hypotenuse

*with the rangefinder as 138 m (represented in the diagram at a scale of 1mm = 1 m), by applying the formula :***BA***, that is 0.7880 x 138 = 108.7 (say 109) the height of the kite is established as being as being 109 m above***sine x hypotenuse opposite****.***C*As will be seen from the diagram, establishing the length of the hypotenuse by measuring the flying line tends to be unsatisfactory because of the catenary in the line.

Assuming that such sophisticated - and expensive - a piece of equipment as a rangefinder is not available, establishing the length of the hypotenuse becomes more difficult, more entertaining, and infinitely more satisfying.

Referring to the main figure

**below, tether the kite at any point,***ABD***. From a suitable point,***E**, angle***C****is measured by means of a clinometer, (71°). Then a distance***ACD***is measured so that***BC**and***B****are in the same horizontal plane as***C***, and the triangle***D***and***ABC***are in the same vertical plane. Then measure angle***AD***, (32°).***ABC*Therefore, in triangle

**,***ABC***is known; angle***BC***is known; and angle***ABC**is known, being the supplement of angle***ACB****. Draw***ACD***onto graph paper (at a scale of, say, 1 mm = 1 m). As angle***BC**and angle***ABC****are known, construct the obtuse-angled triangle***ACB***, extending sides***ABC***and***BA**to their point of convergence at***CA****. Extend***A***to***BC***. By measuring***D***(see caption) the length of the hypotenuse of triangle***CA***is found (115 m). Reading the sine of angle***ACD**(71°) to be 0-9455, by applying the same formula: sine x hypotenuse = opposite, that is 0-9455 x 115 = 108-7 (say 109) it is again established that the kite is 109 m above***ACD****.***D*With the first of the above methods, however, the height of the rangefinder from the ground should be added to the final total: and with the second method, twice the height of the clinometer must be added, that is once for each reading. For maximum accuracy with such a simple measuring system, a second observation should be made simultaneously by a helper; the mean of the two results giving a tolerably accurate result.

Obviously any preferred unit of measurement, such as yards, may be substituted for meters in either system.