Notes on Kite Aerial Photography: Photo Gallery
For some time I've wanted to take kite aerial photographs of Wurster Hall, home of UC Berkeley's College of Environmental Design. This is where I work and I'd specifically wondered what it would be like to launch a kite from the roof. Last Saturday I decided to find out. This page presents some images from above Wurster Hall and discusses the challenges of flying kites adjacent to large buildings.
My kite launching spot atop Wurster Hall. I'm visible in the upper center of the photo, April 1996 (38K jpg)
An 11th floor balcony served as my flying site for the first Wurster images. The wind was blowing between 15 and 20 mph with occasional gusts. I flew the Sutton Flowform 16 with a long, frilly tail. It was a hard pulling kite in these conditions making me wish I'd had an assistant.
Boundary layers and bluff bodies
In the last issue of the Aerial Eye editor Brooks Leffler asked readers to report on technique. So I thought I would take this opportunity to discuss kite flying near buildings, an inherently entertaining - if somewhat nerve-racking - pursuit. In planning your kite launch it is useful to think about two phenomena that influence urban flying: the boundary layer and air flow around buildings. But before discussing these I should insert some cautionary language urging common sense. It is your decision whether to put your kite at risk by flying in more congested circumstances. But under no conditions should you cause the potential of harm to humans or your subject buildings. Identify and avoid exposed utility lines. Do not fly over or near active roadways. Pay attention to weather trends. Act wisely. Sermonette over.
A boundary layer diagram showing wind velocity profiles above city (left), suburban (center), and open (right) landscapes. The vertical scale of the diagram is height above ground in meters. Wind velocities are expressed on the horizontal scale as percent of the gradient (or upper undisturbed ) wind. (link to larger diagram, illustration by Eleanor Lee, 5K jpg)
The boundary layer is a zone of varying wind speeds ranging from near still air at the earth's surface to the steady winds aloft. Generally speaking wind speeds increase as you get higher above the surface of the earth. Lower winds are slowed and tumbled by the friction of the earth's surface and objects in the landscape. Eventually as altitude increases you reach a "gradient wind" or air flow that is essentially undisturbed by ground friction. Over large open fields it may take 250 meters of altitude to reach totally undisturbed winds. Over urban terrain it can be twice that height. In either case, the greatest gains in advancing toward clean air are achieved the first 100 feet of altitude. The size of turbulent eddies or gusts also changes with altitude. At lower levels the gusts are smaller in scale and they become larger as you rise.
So when flying in urban areas have faith, winds should become stronger as you gain height. The first hundred feet of altitude are often the most difficult. If you can get your kite to the higher winds you are often rewarded with increased lift and stability. Once the kite has reached stable winds at higher altitude you can attach the camera rig. On occasion I'll have 500 feet of kiteline out before attaching the rig. I keep track of the higher level winds by looking for windsign in the tops of trees, from "steam" issued by rooftop mechanical rooms, from flags, etc. If those clues are favorable I get the kite to higher levels by several methods: 1) the time-honored technique of running with the kiteline, 2) launching from higher points like the rooftop of Wurster, or 3) taking advantage of local air flow patterns created by the buildings themselves.
A diagram of air flow patterns around a bluff-body (building). Buildings introduce interesting and distinct patterns of wind flow. Illustration by Eleanor Lee.
Air flow around buildings
can be used to advantage. Having declared that winds increase in
velocity as you get higher above the ground let me contradict
myself. When you are near large buildings the wind can act in
very peculiar ways due to local accelerations, eddies, and
reversals. For instance, winds reverse direction and head
downward in the "upwind roller" that can form before a
large building (see diagram.) Our Building Science Laboratory has
a Boundary Layer Wind Tunnel that allows us to visualize these flows
using scale models and smoke. You can see the same patterns in
the real world by observing vegetation, birds in flight, flags,
etc. near the building. Once the kite is launched, I find a long
tail is also useful for flow visualization. If you plan to fly
near buildings it is well worth your while to seek out and study
The most useful - read stable and smoothly flowing - air tends to be on the windward side of a building while turbulence prevails near the edges and in the leeward zone. On campus it is not unusual for my soft Sutton Flowforms to swing through 90 degrees of the compass as I launch them from quadrangles surrounded by buildings. I've also used the accelerated air between two buildings to gain lift. Sometimes it works and sometimes it doesn't - in any event anticipate shifts in direction and work hard to keep the kite from fouling on obstructions.
My launch from the Wurster Hall rooftop was a dramatic affair. I first checked the upwind edge of the balcony for clean air. There was far too much turbulence there due to the adjacent building mass rising above the balcony. So, the Sutton Flowform 16 and its ten-meter-long frilly tail were dropped over the leeward railing. In this zone the kite thrashed around as though in a blender. My charge was keeping the kiteline from chafing on the concrete rail and coaxing the kite toward the stable air above and to the side of the building's wake. After a couple of minutes the kite did catch stable air and then flew above the leeward zone turbulence for the rest of the session. Great fun.
For further reading on architectural aerodynamics try: Ansley, R. M., Melbourne, W. and Vickery, B. J., Architectural Aerodynamics, Applied Science Publishers, Essex, England, 1977.
Back to the Wurster Hall images:
The south facade of Wurster Hall's studio tower as seen from above, April 1996 (52K jpg)
Wurster Hall is not air conditioned and relies instead on concrete mass, extended surface area, and sunshades to remain cool. In this view you can see the eggcrate sunshades covering the south facade.
A view of Wurster Hall and Hertz Hall, April 1996 (47K jpg)
I took this view during a lull in the wind. You can see that the camera's elevation is not greatly above my flying perch in proportion to the horizontal distance from perch to camera. I worried at times that the kite would lower into the turbulence of the leeward zone but it stayed in clear air. The view shows Wurster Hall's low-rise section covered with skylights. The building's main west entry is in the center of the photo. Hertz Hall, scene of campus concerts, is in the upper left (tile roof.)
This view shows Wurster Hall and the new School of Business building, April 1996 (52K jpg)
This north-facing view from relatively high shows Wurster Hall in the foreground. Beyond Wurster, from left to right, are the Faculty Club, Minor Hall, and the recently-completed Haas School of Business.
Views from high above Wurster Hall toward the University Art Museum and the Campanile, April 1996 (left 58K jpg, right 48K jpg, )
On the left you can see the landscape to the south of Wurster Hall including the southside dorms, Cafe Strada, the University Art Museum, tennis courts, and Kroeber Hall. The street bisecting the scene is Bancroft Way, the campus' southern edge. To the right is a view of the Campanile and central campus. Faculty Glade and Hertz Hall are in the foreground with Albany Knoll on the distant horizon.
A plan view of the Wurster Hall Courtyard, April 1996 (47K jpg)
We use this east-facing courtyard for project reviews. I find this image interesting in that it reveals the asymmetry of the olive trees - in the upper part of the image - due to their placement against the studio tower.
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All rights reserved. Revised: Thursday, July 18, 1996