High-Altitude Kite
Aerial Photography

James S. and Susan W. Aber

Air density

The force that holds a kite up is determined by wind speed and air density acting on the lifting surface of the kite. In most situations, wind speed is the deciding factor for choosing an appropriate kite to carry the camera rig. However, at high altitude the lower air density also becomes an important factor. Lower air density means there are fewer or lighter molecules (per air volume) to flow over the kite's lifting surface. Air density is determined by three factors.

  1. Pressure -- The weight or force per area exerted by a column of air. Common pressure units are pounds per square inch (psi), inches of mercury (Hg) or millibars. Standard atmospheric pressure at sealevel = 29.92 inches of Hg.

  2. Temperature -- As air is warmed, it expands and thus has a lower density. Hot air rises, which is what keeps hot-air balloons up, and cold air sinks. Standard atmospheric temperature at sealevel = 59.0°F.

  3. Humidity -- Water vapor molecules (H2O) are lighter than are nitrogen N2 and oxygen O2 molecules that make up most of the atmosphere. Humid air has a higher proportion of light water molecules than does dry air. The result is that wet air is lighter than dry air. This humidty effect is fairly small.

The combination of these three factors determines the air density and thus lifting power for a given wind speed. A good way to understand how air density varies with altitude is with the standard atmosphere, which is an ideal model of atmospheric conditions. The table below gives standard values for pressure, temperature and density (ignoring the slight effect of humidity) at altitudes from sealevel to 16,000 feet (about 4900 m).

Standard Atmospheric Conditions
Altitude
(feet)
Pressure
(in. Hg)
Temp.
(F°)
Density
(%)
sealevel 29.92 59.0 100
2,000 27.82 51.9 94.3
4,000 25.84 44.7 88.8
6,000 23.98 37.6 83.6
8,000 22.22 30.5 78.6
10,000 20.57 23.3 73.8
12,000 19.02 16.2 69.3
14,000 17.57 9.1 65.0
16,000 16.21 1.9 60.9

These values reveal that density decrease is fairly slight up to about one mile (5280 feet) high, the elevation of Denver, Colorado. At altitudes above 8000 feet (2450 m), however, air density declines significantly. For example, at 10,000 feet (3060 m) air density is less than ¾ of sealevel density. However, this assumes the "standard" temperature of 23°F at 10,000 feet altitude. What kite flyer wants to work at that temperature in a brisk wind? At higher temperature, say 60F (15C), air density is even less.

The relationship of pressure, temperature, and humidity can be understood in terms of the density altitude, which is the equivalent "standard altitude" based on actual conditions at a site. Take the following example, in which pressure is 20½ inches of mercury (std. at 10,000 feet), humidity is 50%, and temperature is 60°F. The density altitude is equivalent to about 12,500 feet in the standard atmosphere, which is less than 70% of sealevel air density. To achieve sufficient lift, a very large kite or train of kites would be necessary to hold up the KAP rig.

More information on air density.

Mountain KAP

High-altitude kite flying usually means mountains. Mountain ranges often create strong local weather effects, which include enhanced cloud cover and more precipitation than for adjacent lowlands. Mountain peaks and valleys are well known for rapid weather changes. Swirling winds funnel along valleys and over passes with frequent and abrupt changes in direction. Finding a large enough space for kite flying can be a challenge in forested mountains, and access to alpine areas above timberline can be quite limited. Areas with good access are often sites with other human structures and activities that could prove dangerous for kite flying. Highways, buildings and power lines follow the valleys. Towers, ski lifts and cable cars may occupy the higher slopes and mountain peaks. The combination of cloud cover, fickle wind, and limited access makes for difficult kite aerial photography in many mountain settings.

Culebra Range, Sangre de Cristo Mountains

The Culebra Range of the Sangre de Cristo Mountains forms the "front range" of the Rocky Mountains in south-central Colorado. Mountain peaks exceed 13,000 feet (4000 m). Parts of the Culebra Range and adjacent Spanish Peaks are contained within the San Isabel National Forest--see map. The forest includes dense growth of pine, fir, spruce, and aspen. Timberline is around 11,600 to 12,000 feet in the Culebra Range, although some lower parts have been logged or cleared for development. Wind gusts more than 100 mph (160 km/h) occur often. Major tourist attractions in the vicinity include Cuchara Mountain Resort and Monument Lake.

The following kite aerial photographs were taken in vicinity of Cuchara, Colorado in June 1999. The single-camera, radio-controlled KAP rig was utilized with Kodak Elite 200 color-slide film. All photographs © J.S. Aber.

View over Blue Lakes campground with Trinchera Peak (13,517 feet) in the center background. Dark trees are mainly blue spruce and lighter trees are aspen. Ground elevation of kite flyers about 10,400 feet. Flying the KAP rig in this narrow valley proved to be quite tricky.
View toward the Culebra Range from Cucharas Pass. Blue/Bear Lakes campground is located at extreme left edge of view (up the red-colored valley), and Cuchara Mountain Resort is in the right background. Ground elevation of kite flyers about 10,000 feet.
Cuchara Mountain Resort base area and ski runs. The crest of the Culebra Range can be seen in the right background. Ground elevation of kite flyers about 9200 feet. Large parking area for the ski resort was a good site for flying the KAP rig.
View eastward from Cuchara Mountain Resort. The top of West Spanish Peak (13,626 feet) is visible on the far horizon. The light-colored, rocky ridge in front of West Spanish Peak is granite outcrop of White Peaks. Ground elevation of kite flyers about 9200 feet.

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Last update: Jan. 2005, © J.S. Aber.