Tag Archives: Aerodynamics

Lift: The Key to Flight

A Boeing 747 weighs around 750,000 pounds, so how does it manage to get off the ground? It’s all thanks to a force called lift and something you may be familiar with from other AstroCamp videos: Bernoulli’s Principle.

Flight Lift

Lift is just the name for the force pushing an object up into the air, but Bernoulli’s Principle is a little more involved. It states that whenever a flowing substance like air increases in speed, the pressure inside the flowing portion decreases. This means that if the air flowing along one side of a surface is moving faster than on the other side, there’s higher pressure on one side, pushing the surface. We can see that with Lin’s sheet of paper; blowing on only the top side causes the now higher pressure below to push up on the paper, generating lift.

Flight Airflow

The same concept applies with the wings of a 747, though with one important difference: there’s airflow along both sides of the wing. However, airplane wings are designed to provide some air resistance along the underside, so the air moving along the top is still flowing faster, generating lift.

 

DIY Tumblewing Glider

To build a tumblewing glider, start with a long, thin rectangle of paper. We experimented with gliders ranging from about three to eight inches in length and had good results with rectangles roughly 4-6 times as long as they were wide. The lighter and thinner the building material you use, the easier your glider will be to fly. Printer paper, craft tissue, and phone book pages all work well.

Screen Shot 2016-05-18 at 12.23.36 PM

First, fold the short ends of the rectangle straight up away from your work surface, forming 90 degree angles with the middle of the glider, as shown in the center picture. The long edges of the glider body, between the two folded-up ends, will need to point in opposite directions, as in the picture on the right. Fold a long, thin flap towards you on one side and away from you on the other (it doesn’t matter which edge points up and which points down).

TumbleGif

Next, check out how your glider moves through the air. Hold it by one of the long, thin folded edges and drop it with a gentle flick of the wrist. It might take a few tries to get a feel for what’s going on… don’t worry if it doesn’t seem to work right away! Ultimately, the tumblewing should rotate smoothly and quickly as it floats to the ground.

Once you’ve mastered dropping your tumblewing into a stable spin, try piloting it with a large, flat object, like a piece of cardboard. When you push a flat object through the air, air molecules move up and over it, creating a swell. The swell pushes the glider along a little bit like the water wave behind a surfer in the ocean!

TumbleWave

Image courtesy of Science World British Columbia

For a more challenging (and portable) piloting experience, try using smaller and smaller surfaces to push the tumblewing through the air. With enough practice, it’s possible to control a phone book paper glider using just your hands.

Our tumblewings were inspired by Science Toy Maker. Check out their site for even more glider ideas!

Written By: Caela Barry

Aerodynamics, Fire, & the Coanda Effect

Imagine a torpedo in a wind tunnel. Incoming air slips around the torpedo’s nose, slides along its surface, and flies off its blunt back end. The air stream can’t navigate sharp corners, but as long as a smooth contour is available, it clings to that curve. This is called flow attachment, or the Coanda effect.

Coanda1

The Coanda effect on an airplane wing.


Image source: http://cdn.theatlantic.com/static/mt/assets/jamesfallows/angleOfAttack.jpg

A fluid is anything that can flow freely– think water or air. Thanks to the Coanda effect, we can get a stream of fluid to go anywhere we want by giving it a smooth surface to follow. Helicopters and other VTOL aircraft use this principle to enhance lift! If a blade contour is smooth everywhere except a single edge, then that edge is where passing air slides off (just like in the image above). If the edge is angled towards the ground, then the air moves downward as it leaves the blade surface. Every action has an equal and opposite reaction; in this case, the downward momentum of the air translates to upward momentum of the aircraft. This isn’t the main way that airplanes gain altitude (that’s the Bernoulli effect), but it’s a useful way to improve performance. The Coanda effect can triple the Bernoulli lift on a blade or wing!

Coanda2

In this experiment, we put a cylindrical container in the path of a breath of air and attempt to blow out a candle on the other side. The air stream splits in two and follows the curved surface. There’s no sharp edge for the two halves to slide off of, so they hug the contour of the obstacle until they run into each other on the far side. The collision redirects the flow, causing a burst of air to continue on past the cylinder– almost as if it wasn’t there.

coanda3

Try it for yourself with a round container and a candle! Please use adult supervision testing experiments using fire.

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