Dyneema®, the world’s strongest fiber™
WORLD ALTITUDE RECORD

 

Measurement

Kite altitude normally is measured by simple triangulation, that is, the length of the line is multiplied by the sine of the kite angle of elevation from horizontal. If the angle is 45 degrees and line out 100 meters then the height of the kite above ground level is 100 x sin45 degrees = 100 x 0.707 or 70.7 meters above ground level.

One of the Pentax Laser theodolites we used in 2005

Of course the weight of the line and wind drag will cause a little line sag but this will usually be minimal on lines under 100 meters and high tension. For instance a line sag of 5 meters will reduce straight line distance by less than 20 cm over 100 meters. In fact the straight line distance will be at least 99.8 meters and the error in height measurement less than 0.2%. At record altitudes the measurement of altitude using line out and kite angle will not be accurate enough because the percentage error is much greater. At 10,000 ft elevation with 15,000 ft of line out the difference  between the altitude calculated from line out and kite angle and the true altitude is still less than 2% at best and 5% at worst but this is not good enough for record verification.The most accurate method of altitude measurement is triangulation using 2 theodolites but this method depends on clear skies. The simpler method is GPS and it is almost as accurate as a theodolite pair triangulation.

Typical kite track showing vertical profile and horizontal track on Garmin proprietry Mapsource program. This data is downloaded from GPS units to a computer after the flight is completed.

Garmin geko (discontinued 2009) is small and light but has plenty of features.

Early model etrex (left) have less memory but later models similar to Geko in that respect.

Above: Pentax laser theodolite used in 2005 to setup reference points. The regular theodolites are optical instruments but still highly accurate. The laser can reach 4.5 km using reflective prisms on the target. More expensive instruments have a range of over 20km, enough to measure the kite’s altitude directly.

Gpsflight Rx3 base station used in conjunction with onboard telemetry module (right) and connected via USB cable to laptop which displays position of the kite in real time via GPSflight software, GPS Team. The software is also able to display many functions including:

* Horizontal position in degrees north and south producing an accuracy of 1 meter or better.

* Altitude above sea level with an accuracy of 2 meters or better.

* Barometric altitude with accuracy >99.9%

* Air temperature

* Vertical speed in mph or kph

* Climb rate in mph or kph.

* Horizontal speed

* Number of satellites acquired

Garmin Mapsource software is used to display GPS data collected by Garmin Geko and etrex. The green graph is the kite altitude track profile and the yellow plot is the horizontal track of the kite. The altitude is above sea level and requires the altitude of the launch point to be subtracted to give altitude above ground level.