Colorful parachutes at different levels of expansion

Holy Parachute Out Of Kirigami

If you have a fear of heights and find yourself falling out of an airplane, you probably don’t want to look up to find your parachute full of holes. However, if the designer took inspiration from kirigami in the same way researchers have, you may be in better shape than you would think. This is because properly designed kirigami can function as a simple and effective parachute.

Kirigami, for those unfamiliar, is a cousin of origami where, instead of folding, you cut slits into paper. In this case, the paper effectively folds itself after being dropped, which allows the structure to create drag in ways similar to traditional parachute designs. Importantly, however, the stereotypical designs of parachutes have some more severe drawbacks than they appear. Some major issues include more obvious things, such as having to fold and unpack before and after dropping. What may be less obvious are the large eddies that traditional parachutes create or their ease at being disturbed by the surrounding wind.

The kirigami chutes fix these issues while being easier to manufacture and apply. While these are not likely to be quite as effective for human skydiving, more durable applications may benefit. Quoted applications, including drone delivery or disaster relief, worry more about accuracy and scalability rather than the fragile bones of its passenger.

Clever and simple designs are always fun to try to apply to your own projects, so if you want to have your own hand, make sure to check out the paper itself here. For those more interested in clever drone design to take inspiration from, look no further than this maple seed-inspired drone.

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Too Smooth: Football And The “KnuckleBall” Problem

Picture a football (soccer ball) in your head and you probably see the cartoon ideal—a roughly spherical shape made with polygonal patches that are sewn together, usually in a familiar pattern of black and white. A great many balls were made along these lines for a great many decades.

Eventually, though, technology moved on. Footballs got rounder, smoother, and more colorful. This was seen as a good thing, with each new international competition bringing shiny new designs with ever-greater performance. That was, until things went too far, and the new balls changed the game. Thus was borne the “knuckleball” phenomenon.

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Small Feathers, Big Effects: Reducing Stall Speeds With Strips Of Plastic

Birds have long been our inspiration for flight, and researchers at Princeton University have found a new trick in their arsenal: covert feathers. These small feathers on top of birds’ wings lay flat during normal flight but flare up in turbulence during landing. By attaching flexible plastic strips – “covert flaps” – to the top of a wing, the team has demonstrated impressive gains in aircraft performance at low speeds.

Wind tunnel tests and RC aircraft trials revealed a fascinating two-part mechanism. The front flaps interact with the turbulent shear layer, keeping it close to the wing surface, while the rear flap create a “pressure dam” that prevents high-pressure air from moving forward. The result? Up to 15% increase in lift and 13% reduction in drag at low speeds. Unfortunately the main body of the paper is behind a paywall, but video and abstract is still fascinating.

This innovation could be particularly valuable during takeoff and landing – phases where even a brief stall could spell disaster. The concept shares similarities with leading-edge slats found on STOL aircraft and fighter jets, which help maintain control at high angles of attack. Imitating feathers on aircraft wings can have some interesting applications, like improving control redundancy and efficiency.

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The Dyke Delta: A DIY Flying Wing Fits Four

The world of experimental self-built aircraft is full of oddities, but perhaps the most eye-catching of all is the JD-2 “Dyke Delta” designed and built by [John Dyke] in the 1960s. Built to copy some of the 1950’s era innovations in delta-style jet aircraft, the plane is essentially a flying wing that seats four.

And it’s not just all good looks: people who have flown them say they’re very gentle, they get exceptional gas mileage, and the light wing-loading means that they can land at a mellow 55 miles per hour (88 kph). And did we mention the wings fold up so you can store it in your garage?

Want to build your own? [John] still sells the plans. But don’t jump into this without testing the water first — the frame is entirely hand-welded and he estimates it takes between 4,000 and 5,000 hours to build. It’s a labor of love. Still, the design is time-tested, and over 50 of the planes have been built from the blueprints. Just be sure to adhere to the specs carefully!

It’s really fun to see how far people can push aerodynamics, and how innovative the experimental airplane scene really is. The JD-2 was (and probably still is!) certainly ahead of its time, and if we all end up in flying wings in the future, maybe this plane won’t look so oddball after all.

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Sharkskin Coating Reduces Airliner Fuel Use, Emissions

The aviation industry is always seeking advancements to improve efficiency and reduce carbon emissions. The former is due to the never-ending quest for profit, while the latter helps airlines maintain their social license to operate. Less cynically, more efficient technologies are better for the environment, too.

One of the latest innovations in this space is a new sharkskin-like film applied to airliners to help cut drag. Inspired by nature itself, it’s a surface treatment technology that mimics the unique characteristics of sharkskin to enhance aircraft efficiency. Even better, it’s already in commercial service! Continue reading “Sharkskin Coating Reduces Airliner Fuel Use, Emissions”

Victorian Train Tunnel Turned Test Track

Characterizing the aerodynamic performance of a vehicle usually requires a wind tunnel since it’s difficult to control all variables when actually driving. Unless you had some kind of perfectly straight, environmentally controlled, and precision-graded section of road, anyway. Turns out the Catesby Tunnel in the UK meets those requirements exactly, and [Tom Scott] recently got to take a tour of it.

The 2.7 kilometer (1.7 mile) long tunnel was constructed as a railway tunnel between 1895 and 1897, thanks to the estate owner objecting to the idea of “unsightly trains” crossing his property. The tunnel’s construction was precise even by modern standards, deviating only 3 mm from being perfectly straight along its entire length. It lay abandoned for many years until it was paved and converted into a test facility, opening in 2021.

To measure the speed without the luxury of GPS reception, a high-speed camera mounted inside a vehicle detects reflective tags mounted every 5 m along the tunnel’s wall. This provides accurate speed measurement down to 0.001 km/h. A pair of turntables are installed at the ends of the tunnel to avoid an Austin Powers multi-point turn (apparently that’s the technical term) when turning around inside the confined space.

Due to the overhead soil and sealed ends, the temperature in the tunnel only varies by 1 – 2 °C year round. This controlled environment makes the tunnel perfect for coastdown tests, where a vehicle accelerates to a designated speed and then is put into neutral and allowed to coast. By measuring the loss of speed across multiple runs, it’s possible to calculate the aerodynamic drag and friction on the wheels. Thanks to the repeatable nature of the tests, it was even possible to calculate the aerodynamic losses caused by [Tom]’s cameras mounted to the outside of the vehicle.

The Catesby Tunnel is an excellent example of repurposing old infrastructure for modern use. Some other examples we’ve seen include using coal mines and gold mines for geothermal energy.

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Remote-Controlled Hypercar Slices Through Air

Almost all entry-level physics courses, and even some well into a degree program, will have the student make some assumptions in order to avoid some complex topics later on. Most commonly this is something to the effect of “ignore the effects of wind resistance” which can make an otherwise simple question in math several orders of magnitude more difficult. At some point, though, wind resistance can’t be ignored any more like when building this remote-controlled car designed for extremely high speeds.

[Indeterminate Design] has been working on this project for a while now, and it’s quite a bit beyond the design of most other RC cars we’ve seen before. The design took into account extreme aerodynamics to help the car generate not only the downforce needed to keep the tires in contact with the ground, but to keep the car stable in high-speed turns thanks to its custom 3D printed body. There is a suite of high-speed sensors on board as well which help control the vehicle including four-wheel independent torque vectoring, allowing for precise control of each wheel. During initial tests the car has demonstrated its ability to  corner at 2.6 lateral G, a 250% increase in corning speed over the same car without the aid of aerodynamics.

We’ve linked the playlist to the entire build log above, but be sure to take a look at the video linked after the break which goes into detail about the car’s aerodynamic design specifically. [Indeterminate Design] notes that it’s still very early in the car’s development, but has already exceeded the original expectations for the build. There are also some scaled-up vehicles capable of transporting people which have gone to extremes in aerodynamic design to take a look at as well.

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