NASA’s Ingenuity helicopter has made history by flying on Mars. To celebrate the first flight of a copter on another planet, here’s a simple unpowered helicopter you can build at home!
You will need
- A4 paper
- Pencil or pen
What to do
- With a pencil and ruler, draw a line 4 cm in from one of the short sides of the paper.
- Use scissors to cut along the line.
- Take the strip of paper you’ve cut, and check the length of its sides. It should be 4 cm wide and 21 cm long. Put it on the table so the short sides are top and bottom.
- Measure halfway along the top edge, and rule a line running down to the middle of the paper – it should be about 10 cm long.
- About 2 centimetres below the middle of the paper, rule lines coming in from the two sides. Make these lines about 1.3 cm long.
- Cut along the lines you’ve drawn.
- At the bottom of the paper, fold the two sides into the middle. Put a paperclip or two on the bottom to hold the flaps in place.
- At the top, fold one strip towards you and one away.
- Your copter is now finished! Hold it up above your head, with any paperclips at the bottom, and drop it. The copter will spin gracefully to the ground.
This spinning helicopter is great fun, but how does it work? There are two competing forces involved – gravity and air resistance.
When you let go of the copter, it’s pulled to the ground by gravity. However, the flaps at the top push lots of air out of the way on the way down. At the same time, the air is pushing against the flaps, slowing the copter’s fall.
This air resistance also has other effects. First, it bends the flaps back, making the whole copter more streamlined, and letting it fall faster. It also spins the copter, because the flaps are bent in different directions.
As the copter spins, the flaps are pulled outwards by the spinning. As they spread out, the copter starts falling more slowly, because the flaps are catching more air. Catching more air makes it spin faster too!
If you watch carefully, you can see this entire process unfold in just a second or two.
A thought experiment
You might wonder what would happen if you dropped this spinning helicopter on Mars. The red planet only has one third the gravity of Earth, so the copter would fall slower at first. Then, Mars only has 1% of the density of Earth’s atmosphere. That means there wouldn’t be much air resistance slowing the copter or making it spin!
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