Space Shuttle Model In A Hypersonic Wind Tunnel

Mach 20 In A Wind Tunnel: Yes, It’s Rocket Science

November 4, 2021 by Ryan Flowers 5 Comments

Hypersonic speeds are defined by those exceeding Mach 5, and lately there’s been a lot of buzz about unmanned hypersonic vehicles making test flights. Vehicles returning from orbital flight also travel at hypersonic speeds as they do their best to transition back to the terrestrial realm. Before anything leaves ground though, these machines are tested in wind tunnels. [Scott Manley]’s video “How Hypersonic Wind Tunnels Recreate Mach 20” (embedded below) does a wonderful job of explaining the engineering behind wind tunnels for testing hypersonic vehicles.

While the earliest wind tunnels such as that used by the Wright Brothers were powered by simple fans, it is not possible for any propeller to surpass subsonic speeds. This is evidenced by there not being any propeller driven aircraft that can exceed Mach 1. Since an aircraft can’t reach those speeds with a propeller, it follows that a wind tunnel cannot be driven by propellers, fans, or any such device, and exceed Mach 1 wind speed, either. So it begs the question: Just how do they do it?

You might think that the answer lays in Bernoulli’s law – but it does not. You might think it involves compressing the air into smaller and smaller tubes and pipes. It doesn’t. As [Scott Manley] so expertly explains in the video below the break, it has quite a lot in common with actual rocket science.

You may be interested to know that we’ve covered some DIY wind tunnel builds as well as a small desktop wind tunnel in the past. While not hypersonic, they’re exactly what you’d want to have if you’re an aerospace hacker of any kind.

Thanks [Zane Atkins] for the tip!

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Retrotechtacular: Discovering Aerodynamics With The Chrysler Airflow

June 16, 2021 by Dan Maloney 31 Comments

When you think about it, for most of human history we’ve been a pretty slow bunch. At any time before about 150 years ago, if you were moving faster than a horse can run, you were probably falling to your death. And so the need to take aerodynamics into consideration is a pretty new thing.

The relative novelty of aerodynamic design struck us pretty hard when we stumbled across this mid-1930s film about getting better performance from cars. It was produced for the Chrysler Sales Corporation and featured the innovative design of the 1934 Chrysler Airflow. The film’s narration makes it clear why the carmaker would go through the trouble of completely rethinking how cars are made; despite doubling average engine horsepower over the preceding decade, cars had added only about 15% to their top speed. And while to our 21st-century eyes, the Chrysler Airflow might look like a bulked-up Volkswagen Beetle, compared to the standard automotive designs of the day, it was a huge aerodynamic leap forward. This makes sense with what else was going on in the technology world at the time — air travel — the innovations of which, such as wind tunnel testing of models, were spilling over into other areas of design. There’s also the influence of [Orville Wright], who was called in to consult on the Airflow design.

While the Airflow wasn’t exactly a huge hit with the motoring public — not that many were built, and very few remain today; [Jay Leno] is one of the few owners, because of course he is — it set standards that would influence automotive designs for the next 80 years. It’s fascinating too that something seemingly as simple as moving the engine forward and streamlining the body a bit took so long to hit upon, and yet yielded so much bang for the buck.

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jellyandmarshmallows windTunnel close-up

Perfecting Paper Planes Peering Past Perspex Portals

May 19, 2021 by Michael Shaub 11 Comments

This wind tunnel is a pile of junk and we love it! When making science and engineering accessible to kids, it really helps to show that it doesn’t require a fancy research lab. [Jelly & Marshmallows] show kids that it takes little more than cardboard, duct tape, and dumpster-diving to up your paper airplane game to NASA levels of engineering.

[Jelly & Marshmallows] built their wind tunnel for a Maker Faire using the aforementioned cheap and free materials for the straightener, collector, diffuser, and fan sections. We especially love the efficient hack of using stacked ceiling light diffusers rather than hundreds of straws for the straightener.

The most time went into the working section, custom-built from plywood frames and acrylic windows. Many 3D printed parts came together to convert a smoke-ring gun to emit smoke trails and LEDs were employed to make those trails a little easier to see. We think the magnetic clips for quick changes of aircraft and their position along a steel ruler were inspired.

The kids attending the Maker Faire (we miss those!) loved the exhibit, having the best time hitting a big green arcade button to spin up the fan. It’s the little things in life. How would you get the kids even more involved with analyzing aerodynamics and make the smoke trails more visible?

Thanks for the tip [Rómulo Antão]

Desktop Wind Tunnel Brings Aerospace Engineering To The Home Gamer

November 20, 2020 by Mike Szczys 10 Comments

Computer simulation is indispensable in validating design and used in every aspect of engineering from finite element analysis to traffic simulation to fluid dynamics. Simulations do an amazing job and at a fraction of the time and expense of building and testing a scale model. But those visceral ah-ha moments, and some real-world gremlins, can be easier to uncover by the real thing. Now you don’t need a university research or megacorp lab to run aerodynamic study IRL, you can just build a functional desktop wind tunnel for a pittance.

[Mark Waller] shows off this tidy little design that takes up only about two feet of desk space, and includes the core features that make a wind tunnel useful. Air is pulled through the tunnel using a fan mounted at the exhaust side of the tunnel. The intake is the horn-like scoop, and he’s stacked up a matrix of drinking straws there to help ensure laminar flow of the air as it enters the tunnel. (The straw trick is frequently used with laminar flow water fountains). It also passes through a matrix of tubes about the diameter of a finger at the exhaust to prevent the spin of the fan from introducing a vortex into the flow.

For analysis, five tubes pipe in smoke from an vape pen, driven into the chamber by an aquarium pump. There’s a strip of LEDs along the roof of the tunnel, with a baffle to prevent the light shining on the black rear wall of the chamber for the best possible contrast. The slow-motion video after the break shows the effectiveness of the setup.

Whether you’re a Hackaday Editor cutting their own glider wing profiles using foam and hot wire, or just want to wrap your head around how different profiles perform, this will get you there. And it’ll do it at a fraction of the size that we’ve seen in previous wind tunnel builds.

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

July 8, 2020 by Alex Weinberg 28 Comments

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

January 10, 2017 by Steven Dufresne 95 Comments

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

August 9, 2016 by Brian Benchoff 21 Comments

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.