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Retrotechtacular: Forces Acting On An Airfoil

floating film title We’ve probably all experimented with a very clear demonstration of the basic principles of lift: if you’re riding in a car and you put your flattened hand out the window at different angles, your hand will rise and fall like an airplane’s wing, or airfoil. This week’s Retrotechtacular explains exactly how flight is possible through the principles of lift and drag. It’s an Army training documentary from 1941 titled “Aerodynamics: Forces Acting on an Air Foil“.

What is an airfoil? Contextually speaking, it’s the shape of an airplane’s wing. In the face of pressure differences acting upon their surfaces, airfoils produce a useful aerodynamic reaction, such as the lift that makes flight possible. As the film explains, the ideas of lift and drag are measured against the yardstick of relative wind. The force of this wind on the airfoil changes according to the acute angle formed between the airfoil and the direction of the air flow acting upon it. As you may already know, lift is measured at right angles to the relative wind, and drag occurs parallel to it. Lift is opposed by the weight of the foil, and drag by tension.

wind tunnel testing

Airfoils come in several types of thicknesses and curvatures, and the film shows how a chord is derived from each shape. These chords are is used to measure and describe the angle of attack in relation to the relative wind.

The forces that act upon an airfoil are measured in wind tunnels which provide straight and predictable airflow. A model airplane is supported by wires that lead to scales. These scales measure drag as well as front and rear lift.

In experimenting with angles of attack, lift and drag increase toward what is known as the stalling angle. After this point, lift decreases abruptly, and drag takes over. Lift and drag are proportional to the area of the wing, the relative wind velocity squared, and the air density. When a plane is in the air, drag is a retarding force that equals the thrust of the craft, or the propelling force.

monometer tubesAirfoil models are also unit tested in wind tunnels. They are built with small tubes running along many points of the foil that sit just under the surface. The tubes leave the model at a single point and are connected to a bank of manometer tubes. These tubes compare the pressures acting on the airfoil model to the reference point of atmospheric pressure. The different liquid levels in the manometer tubes give clear proof of the pressure values along the airfoil. These levels are photographed and mapped to a pressure curve. Now, a diagram can be made to show the positive and negative pressures relative to the angle of attack.

In closing, we are shown the effects of a dive on lift as an aircraft approaches and reaches terminal velocity, and that lift is attained again by pulling slowly out of the dive. Remember that the next time you fly your hand-plane out the window.

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Open Source GPU Released

GPLGPU

Nearly a year ago, an extremely interesting project hit Kickstarter: an open source GPU, written for an FPGA. For reasons that are obvious in retrospect, the GPL-GPU Kickstarter was not funded, but that doesn’t mean these developers don’t believe in what they’re doing. The first version of this open source graphics processor has now been released, giving anyone with an interest a look at what a late-90s era GPU looks like on the inside, If you’re cool enough, there’s also enough supporting documentation to build your own.

A quick note for the PC Master Race: this thing might run Quake eventually. It’s not a powerhouse. That said, [Bunnie] had a hard time finding an open source GPU for the Novena laptop, and the drivers for the VideoCore IV in the Raspi have only recently been open sourced. A completely open GPU simply doesn’t exist, and short of a few very, very limited thesis projects there hasn’t been anything like this before.

Right now, the GPL-GPU has 3D graphics acceleration working with VGA on a PCI bus. The plan is to update this late-90s setup to interfaces that make a little more sense, and add DVI and HDMI output. Not bad for a failed Kickstarter, right?

Developed On Hackaday: Beta Testers And Automated Testing

Mooltipass with Holder

At Hackaday we believe that your encrypted vault containing your credentials shouldn’t be on a device running several (untrusted) applications at the same time. This is why many contributors and beta testers from all over the globe are currently working on an offline password keeper, aka the Mooltipass.

Today we’re more than happy to report that all of our 20 beta testers started actively testing our device as they received the v0.1 hex file from the development team. Some of them had actually already started a few days before, as they didn’t mind compiling our source files located on our github repository and using our graphics generation tools. We are therefore expecting (hopefully not) many bug reports and ways to improve our device. To automatize website compatibility testing, our beta tester [Erik] even developed a java based tool that will automatically report non-working pages found inside a user generated list. You may head here to watch a demonstration video.

The Most Basic BASIC Computer

avr computer

AVR microcontrollers can do pretty much anything nowadays. Blinking LEDs, handling sensor inputs, engine control modules, and now, thanks to [Dan], a small single chip BASIC computer with only ten parts (and four of them are capacitors).

[Dan]‘s homebrew computer has it all. The ATmega 1284P microcontroller outputs a composite video signal and handles inputs from a PS/2 keyboard. The microcontroller runs at 16 MHz, has 7 kB of memory for programs, and can use a separate EEPROM to store data. It also has an array of GPIO pins for interacting with the physical world.

For software, the microcontroller runs a version of BASIC called Tiny BASIC plus, which is a stripped-down language that can fit in 3 kB of memory. This is crucial if you’re in the 1970s or if you’re programming on an AVR microcontroller in the 21st century.

We’ve seen other Arduinos and AVR-type microcontrollers that can run BASIC, but this one has a great form factor and clean look. It’s also a great way to get familiar with homebrew computing and the BASIC programming language!

An Auto-Leveling Gyro Camera For Motorcycle Enthusiasts

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[Saftari] was inspired by the technology used to capture video in the MotoGP World Championship races to create these instructables on how to build an auto-leveling Gyro camera. The setup he developed maintains the camera at a consistent level perpendicular to the earth no matter how much the motorcycle angles against the ground when turning.

The components involved include an Arduino Uno, a Triple Axis Accelerometer, a digital servo, and a Gyro breakout board. A bracket was built to house and secure the camera to the side of the vehicle. 2mm acrylic was used for this and was bent by heating up the material. Once complete, test runs were completed showcasing the capabilities of this type of Do-It-Yourself rig.

The quality of the video after the break is a little bit blurry, but it proves the point that a Gyro camera setup can be built at home:

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Beach Buddy is a Boombox, Phone Charger, and Sunburn Warner

The Beach Buddy

When you venture out onto the beach for a day in the sun, you’re probably not preoccupied with remembering the specifics about your sunscreen’s SPF rating—if you even remembered to apply any. [starwisher] suffered a nasty sunburn after baking in the sunlight beyond her sunscreen’s limits. To prevent future suffering, she developed The Beach Buddy: a portable stereo and phone charger with a handy sunburn calculator to warn you the next time the sun is turning you into barbecue.

After telling the Beach Buddy your skin type and your sunscreen’s SPF rating, a UV sensor takes a reading and an Arduino does a quick calculation that determines how long until you should reapply your sunscreen. Who wants to lug around a boring warning box, though?

[starwisher] went to the trouble of crafting a truly useful all-in-one device by modifying this stereo and this charger to fit together in a sleek custom acrylic enclosure. There’s a switch to activate each function—timer, charger, stereo—a slot on the side to house your phone, and an LCD with some accompanying buttons for setting up the UV timer. You can check out a demo of all the Beach Buddy’s features in a video below.

[Read more...]

The Remaining Hours Are More than Enough to Get in the Game

thp-time-leftWhether you’re just finding out now or are a procrastination ninja, it is not too late to give yourself a shot at winning that trip to space. The Hackaday Prize is really just getting started. At 11:50pm Wednesday night ( that’s PDT on 8/20/14, or 06:50 GMT on Aug 21) we close the entry window and the build phases will begin. That’s right, you don’t actually need to have any hardware done, you only need to document your idea and how you’re going to get there.

Close your eyes and assemble your vision of a connected device. Now open them and start typing. You need to share your overall idea and how you’re going to get there. Draw out a basic system design, and film a video of 2 minutes or less that explains it all. Think this sounds like a lot? You’re wrong… I did it in only a few minutes.

When will you have such a great opportunity to win something awesome and secure the adoration of the hacking masses? Enter now and have no regrets!

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