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Paper Helicopters

Primary schoolInterdisciplinarySpinning rotor falls like a parachute of the same disc area: weight = ½ρv²C_d πR², with air drag ∝ v² while it speeds up

About this experiment

Cut a strip of paper, fold two wings and add a paper clip: drop it and it spins slowly to the floor like a sycamore seed. What makes it fall more slowly? Make paper helicopters with longer or shorter wings, more clips or thicker paper, drop them from a measuring pole and time the fall with a stopwatch. Record every drop, repeat your tests, and check that each test is fair by changing only one thing at a time.

Learning goals

  • Plan a fair test by changing one variable and keeping the others the same
  • Measure fall times and record them in a table
  • Repeat measurements and work out an average
  • Describe how wing length and weight change the fall time
  • Explain that air resistance slows falling objects down

How to use it

  1. 1Drop the helicopter with 8 cm wings and 1 clip three times. Are the times exactly the same? Why not?
  2. 2Change only the wing length to 6 cm and drop it three times. Then try 10 cm and 12 cm.
  3. 3Look at the graph. What happens to the fall time as the wings get longer?
  4. 4Keep the wings at 8 cm and try 0, 2 and 3 clips. Predict first, then test.
  5. 5Try card instead of printer paper. Is a heavier helicopter faster or slower?
  6. 6Switch on the prediction line. Do your results follow it?

The model

Average of three repeat measurements
Average speed of the fall
For older pupils: at steady speed the weight is balanced by air resistance on the spinning wings

Assumptions

  • The helicopter is cut from paper: two wings 3 cm wide and a body 3 cm × 8 cm. Each paper clip has a mass of 0.5 g.
  • The spinning wings act like a disc of radius equal to the wing length, with a drag coefficient of 1.3, which gives fall speeds similar to real paper helicopters.
  • Each stopwatch reading includes a small random human timing error, but the same helicopter and drop number always give the same reading.
  • The helicopter starts spinning straight away and the air is still. Real helicopters with no clip can wobble or tumble instead of spinning.

Try this in class

  1. Q1Why should you drop each helicopter more than once?
  2. Q2A pupil changed the wing length and the number of clips at the same time. Why is the test not fair?
  3. Q3A helicopter took 2.4 s, 2.6 s and 2.5 s. What is the average time?
  4. Q4Which helicopter would stay in the air longest: long wings and no clips, or short wings and three clips?
  5. Q5How do sycamore and maple seeds use the same idea?

Frequently asked questions

Why does the helicopter spin?

As it falls, air pushes up under the wings. Because the wings are folded in opposite directions, the push on each wing is slightly sideways, and the two pushes turn the helicopter round. Spinning wings catch more air and slow the fall.

Why do longer wings make it fall more slowly?

Longer wings sweep a bigger circle of air as they spin, so there is more air resistance. They add a little weight too, but the extra air resistance matters more.

Why add a paper clip at all?

The clip keeps the weight low, so the helicopter stays upright and spins instead of tumbling. Too many clips make it heavy, so it falls faster.