Bridge Over Trebled Water: How The Golden Gate Bridge Started To Sing

Throughout the spring, some Bay Area residents from Marin County to the Presidio noticed a sustained, unplaceable high-pitched tone. In early June, the sound reached a new peak volume, and recordings of the eerie noise spread across Twitter and Facebook. Soon after, The Golden Gate Bridge, Highway, & Transportation District, the agency responsible for the iconic suspension bridge’s maintenance, solved the mystery: The sound was due to high winds blowing through the slats of the bridge’s newly-installed sidewalk railing. Though a more specific explanation was not provided, the sound is most likely an Aeolian tone, a noise produced when wind blows over a sharp edge, resulting in tiny harmonic vortices in the air.

The modification of the Golden Gate Bridge railing is the most recent and most audible element of a multi-phase retrofit that has been underway since 1997. Following the magnitude 6.9 Loma Prieta Earthquake in 1989, The Golden Gate Bridge, Highway, & Transportation District (The District) began to prepare the iconic bridge for the wind and earthquake loads that it may encounter in its hopefully long life. Though the bridge had already withstood the beating of the Bay’s strong easterly winds and had been rattled by minor earthquakes, new analysis technology and construction methods could help the span hold strong against any future lateral loading. The first and second phases of the retrofit targeted the Marin Viaduct (the bridge’s north approach) and the Fort Point Arch respectively. The third and current phase addresses the main span.

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Why The Wright Brothers Succeeded

The types of steps and missteps the Wright brothers took in developing the first practical airplane should be familiar to hackers. They started with a simple kite design and painstakingly added only a few features at a time, testing each, and discarding some. The airfoil data they had was wrong and they had to make their own wind tunnel to produce their own data. Unable to find motor manufacturers willing to do a one-off to their specifications, they had to make their own.

Sound familiar? Here’s a trip through the Wright brothers development of the first practical airplane.

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Hackaday Prize Entry: Non-Computational Fluid Dynamics

Computational Fluid Dynamics, or CFD, and is applied to everything from aircraft design to how good of a wing a new skyscraper will be. Of course, the science of building airfoils is much older than CFD, leading to the question of how airfoil design was done before computers.

The answer, of course, is a wind tunnel. Walk around a few very good air museums, and you’ll find wind tunnels ranging from the long wooden boxes built by the Wright brothers to fantastic plywood contraptions that are exceptionally interesting to woodworkers.

[Joel] needed final project as an upcoming aeronautical engineer, but he wanted his project to be something physical, and a tool that could be used again. He decided to build a wind tunnel that’s also his entry for The Hackaday Prize.

This wind tunnel isn’t a gigantic device the size of a building. The very first wind tunnels were simple devices just a few meters long. With a fan at one end, a section to stabilize the wind, a chamber, and a place for the air to go, it’s also a very simple device. Just because something is simple doesn’t mean anyone has built one recently, though: [Joel] couldn’t find anyone who built a wind tunnel with step-by-step instructions. This project is just that – an Open Source wind tunnel.

The design of this wind tunnel is simple enough, built out of fiberglass with relatively simple molds. The design can be adapted to various electric fans, and the most fun part of the build – the smoke machine – is already complete.

Retrotechtacular: The Construction Of Wooden Propellers

During World War I, the United States felt they were lagging behind Europe in terms of airplane technology. Not to be outdone, Congress created the National Advisory Committee for Aeronautics [NACA]. They needed to have some very large propellers built for wind tunnel testing. Well, they had no bids, so they set up shop and trained men to build the propellers themselves in a fantastic display of coordination and teamwork. This week’s film is a silent journey into [NACA]’s all-human assembly line process for creating these propellers.

Each blade starts with edge-grained Sitka spruce boards that are carefully planed to some top-secret exact thickness. Several boards are glued together on their long edges and dried to about 7% moisture content in the span of five or so days. Once dry, the propeller contours are penciled on from a template and cut out with a band saw.

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Wind Tunnel Testing Now Available To The Common Man

DIY Wind Tunnel

If you are in the market for a DIY wind tunnel the folks over at have got you covered. They have done a great job documenting how they built their own wind tunnel. Most of the structure is made of plywood with the test chamber is made of plexi-glass so that the operator can visually observe what is happening during a test. A common gable-mount fan provides the air flow, you may have one installed in your attic to keep it cool. The only non-widely available components are the force sensors that feed data to a computer for logging.

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